GLERL Publications with Abstracts

January 2014 - December 2014

Capitalized names represent GLERL authors.

To request hard copies of any of these publications, contact:

ANDERSON, E.J., and D.J. SCHWAB. Spill reference tables for the St. Clair River. NOAA Technical Memorandum GLERL-162. NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 16 pp. (2014).

Serving as the international border between the United States and Canada, the St. Clair River provides a source for public drinking water as well as a hub for petrochemical refineries and commercial shipping (Fig. 1). This dichotomy creates the potential threat to public health via drinking water contamination in the event of a toxic spill from commercial freighters or refineries within the waterway. Due to the high flow rates experienced in the river (average discharge of 5,200 m3/s; Holtschlag and Koschik 2002), once released, contaminants can travel to downstream public water intakes within minutes (Anderson and Schwab, 2012; Tsanis et al., 1996; Derecki 1983; Sun et al., 2013). As a result, water intake managers may need to react immediately in order to mitigate contaminant uptake. However, the common approach for spill response is to use real-time operational hydrodynamic models to predict currents in the system and then simulate spill transport forecasts via Lagrangian particle transport simulations, a process that may not provide decision makers with the necessary spill information in time.

Arhonditsis, G.B., C.A. STOW, Y.R. Rao, and G. Perhar. What has been accomplished twenty years after the Oreskes et al. (1994) critique? Current state and future perspectives of environmental modeling in the Great Lakes. Journal of Great Lakes Research 40(Supplement 3):1-7 (DOI:10.1016/j.jglr.2014.11.002) (2014).

With well over 1000 citations, the Oreskes et al. (1994) paper stands out as one of the classical critiques of the veracity of the scientific methodology of models in earth sciences, arguing that the validation of models that deal with natural systems is inherently impossible. Going beyond the controversy of the “technical versus philosophical” meaning of validation, this viewpoint reflects the important notion that model outputs should be viewed through the prism of the underlying assumptions and that good model performance in one or more settings is not evidence for general applicability, but rather the start of a perpetual race for predictive confirmation. While the Oreskes et al.'s (1994) critique has been a defining moment of the broader appreciation of the challenges surrounding a model validation exercise the documented inadequacy of many models to address important societal issues reflects the fact that the field has advanced without the healthy dose of introspection required to obtain good science. An evidence of the latter assertion is the inconsistency that still characterizes the environmental modeling practice with respect to the methodological steps typically followed (Arhonditsis and Brett, 2004; Arhonditsis et al., 2006; Stow et al., 2009; Robson, 2014; Wellen et al., submitted for publication). After more than four decades of active modeling in the context of environmental management and policy analysis, many of the published aquatic ecosystem and watershed modeling studies still fail to report the results of predictive confirmation, goodness of fit statistics, and uncertainty analysis in the broader sense.

BAI, X., J. WANG, J. Austin, D.J. SCHWAB, R.A. ASSEL, A.H. CLITES, J.F. BRATTON, M.C. COLTON, J. Lenters, B.M. LOFGREN, T. Wohlleben, S. Helfrich, H.A. VANDERPLOEG, L. LUO, and G.A. LESHKEVICH. A record-breaking low ice cover over the Great Lakes during winter 2011/2012: Combined effects of a strong positive NAO and La Nina. Climate Dynamics:27 pp. (DOI:10.1007/s00382-014-2225-2) (2014).

A record-breaking low ice cover occurred in the North American Great Lakes during winter 2011/2012, in conjunction with a strong positive Arctic Oscillation/ North Atlantic Oscillation (AO/NAO) and a La Nina event. Large-scale atmosphere circulation in the Pacific/ North America (PNA) region reflected a combined signal of La Nina and NAO. Surface heat flux analysis shows that sensible heat flux contributed most to the net surface heat flux anomaly. Surface air temperature is the dominant factor governing the interannual variability of Great Lakes ice cover. Neither La Nina nor NAO alone can be responsible for the extreme warmth; the typical midlatitude response to La Nina events is a negative PNA pattern, which does not have a significant impact on Great Lakes winter climate; the positive phase of NAO is usually associated with moderate warming. When the two occurred simultaneously, the combined effects of La Nina and NAO resulted in a negative East Pacific pattern with a negative center over Alaska/Western Canada, a positive center in the eastern North Pacific (north of Hawaii), and an enhanced positive center over the eastern and southern United States. The overall pattern prohibited the movement of the Arctic air mass into mid-latitudes and enhanced southerly flow and warm advection from the Gulf of Mexico over the eastern United States and Great Lakes region, leading to the record-breaking low ice cover. It is another climatic pattern that can induce extreme warming in the Great Lakes region in addition to strong El Nino events. A very similar event occurred in the winter of 1999/2000. This extreme warm winter and spring in 2012 had significant impacts on the physical environment, as well as counterintuitive effects on phytoplankton abundance.

BELETSKY, D., H. HU, J. WANG, and N. HAWLEY. Modeling thermal structure, circulation, and ice in Lake Erie. Proceedings, 22nd IAHR International Symposium on Ice 2014, Singapore, August 11-15, 2014. International Association of Hydro-Environment Engineering and Research, 449-451 pp. (2014).

Winter circulation and thermal structure in Lake Erie is studied with a three-dimensional coupled Great Lakes Ice-circulation Model (GLIM) during 1979-1980 and 2010-2011. The hydrodynamic model has 20 vertical levels and a uniform horizontal grid size of 2 km. The model uses time-dependent wind stress and heat flux forcing at the surface which are calculated from the hourly meteorological observations obtained from National Weather Service land stations and NOAA buoys. The model reproduces several month long ice periods in both winters with maximum ice thicknesses up to 45 cm in 1979-1980. The model is validated with hourly temperature and current measurements at several moorings that were deployed in central basin of Lake Erie during both winters and additionally with ice concentration and thickness measurements in 2010-2011.

BELETSKY, R., D. BELETSKY, N. HAWLEY, and J. WANG. Interannual variability of winter circulation and ice in Lake Erie. Proceedings, 22nd IAHR International Symposium on Ice 2014, Singapore, August 11-15, 2014. International Association of Hydro-Environment Engineering and Research, 905-907 pp. (2014).

Winter circulation in the Laurentian Great Lakes is less known than summer circulation and impacts of ice on lake circulation are poorly understood. Lake Erie is at least partially covered with ice from December until April, and its normal peak ice cover is about 90%. To study thermal structure, circulation, and ice thickness, 7 current profilers, 4 ice profilers and 37 temperature sensors were deployed in Lake Erie in October 2010 - May 2011, and again in September 2011 - May 2012. Wind speed observations were obtained from National Weather Service and Environment Canada meteorological stations. Significant interannual variability in the extent of ice cover was observed during the two field years, and that allowed us to study the impact of ice on thermal structure and circulation in Lake Erie.

CHA, Y.K., S.S. Park, K. Kim, M. Byeon, and C.A. STOW. Probabilistic prediction of cyanobacteria abundance in a Korean reservoir using a Bayesian Poisson model. Water Resources Research 50:2518-2532 (DOI:10.1002/2013WR014372) (2014).

There have been increasing reports of harmful algal blooms (HABs) worldwide. However, the factors that influence cyanobacteria dominance and HAB formation can be site-specific and idiosyncratic, making prediction challenging. The drivers of cyanobacteria blooms in Lake Paldang, South Korea, the summer climate of which is strongly affected by the East Asian monsoon, may differ from those in well studied North American lakes. Using the observational data sampled during the growing season in 2007– 2011, a Bayesian hurdle Poisson model was developed to predict cyanobacteria abundance in the lake. The model allowed cyanobacteria absence (zero count) and nonzero cyanobacteria counts to be modeled as functions of different environmental factors. The model predictions demonstrated that the principal factor that determines the success of cyanobacteria was temperature. Combined with high temperature, increased residence time indicated by low outflow rates appeared to increase the probability of cyanobacteria occurrence. A stable water column, represented by low suspended solids, and high temperature were the requirements for high abundance of cyanobacteria. Our model results had management implications; the model can be used to forecast cyanobacteria watch or alert levels probabilistically and develop mitigation strategies of cyanobacteria blooms.

CHA, Y.K., and C.A. STOW. A Bayesian network incorporating observation error to predict phosphorus and chlorophyll a in Saginaw Bay. Environmental Modelling and Software:11 pp. (DOI:10.1016/j.envsoft.2014.02.010) (2014).

Empirical relationships between lake chlorophyll a and total phosphorus concentrations are widely used to develop predictive models. These models are often estimated using sample averages as implicit surrogates for unknown lake-wide means, a practice than can result in biased parameter estimation and inaccurate predictive uncertainty. We develop a Bayesian network model based on empirical chlorophyll-phosphorus relationships for Saginaw Bay, an embayment on Lake Huron. The model treats the means as unknown parameters, and includes structure to accommodate the observation error associated with estimating those means. Compared with results from an analogous simple model using sample averages, the observation error model has a lower predictive uncertainty and predicts lower chlorophyll and phosphorus concentrations under contemporary lake conditions. These models will be useful to guide pending decision-making pursuant to the 2012 Great Lakes Water Quality Agreement.

CLITES, A.H., J.P. SMITH, T.S. HUNTER, and A.D. GRONEWOLD. Visualizing relationships between hydrology, climate, and water level fluctuations on Earth's largest system of lakes. Journal of Great Lakes Research 40(3):807-811 (DOI:10.1016/j.jglr.2014.05.014) (2014).

Understanding drivers behind monthly, annual, and decadal water level fluctuations on the North American Great Lakes is a high priority for regional research and water resource management planning. The need for improved understanding of these relationships is underscored by a series of recent unprecedented extreme water level patterns, including (but not limited to) record low water levels on Lakes Michigan and Huron in December 2012 and January 2013. To address this need, we developed the Great Lakes Hydro-Climate Dashboard (GLHCD), a dynamic flash-based web interface that builds upon the previously-released Great Lakes Water Level Dashboard (GLWLD). In addition to including water level data and projections from the GLWLD, the GLHCD presents a range of hydrological and climatological data through an improved graphical user interface specifically designed to manage, and display simultaneously, a variety of data time series from different sources. By serving as a common portal to critical regional hydro-climate and water level data, the GLHCD helps visualize and explain lake level phenomena including water level declines across all of the Great Lakes in the early 1960s and their relationship to changes in regional precipitation, as well as the abrupt water level declines in the late 1990s and their relationship to remarkable changes in over-lake evaporation. By providing insight into these, and other important regional hydro-climate events, the GLHCD helps practitioners, researchers, and the general public improve their understanding of the drivers behind Great Lakes water levels, and to employ that understanding in prudent water resource management planning.

CLITES, A.H., J. WANG, K.B. CAMPBELL, A.D. GRONEWOLD, R.A. ASSEL, X. BAI, and G.A. LESHKEVICH. Cold water and high ice cover on Great Lakes in spring 2014. EOS 95(34):305-306 (DOI:10.1002/2014EO340001) (2014).

Very cold temperatures across much of North America caused by the recent anomalous meridional upper air flow—commonly referred to in the public media as a polar vortex (for details, see Blackmon et al. [1977] and National Climatic Data Center, State of the climate: Synoptic discussion for January 2014, https://—have contributed to extreme hydrologic conditions on the Great Lakes. The Great Lakes are the largest system of lakes and the largest surface of freshwater on Earth—Lake Superior alone is the single largest lake by surface area.

Cooke, R.M., M.E. Wittmann, D.M. Lodge, J.D. Rothlisberger, E.S. RUTHERFORD, H. ZHANG, and D.M. MASON. Out-of-sample validation for structured expert judgment of Asian Carp establishment in Lake Erie. Integrated Environmental Assessment and Management 10(4):522-528 (2014).

Structured expert judgment (SEJ) is used to quantify the uncertainty of nonindigenous fish (bighead carp [Hypophthalmichthys nobilis] and silver carp [H. molitrix]) establishment in Lake Erie. The classical model for structured expert judgment model is applied. Forming a weighted combination (called a decision maker) of experts' distributions, with weights derived from performance on a set of calibration variables from the experts' field, exhibits greater statistical accuracy and greater informativeness than simple averaging with equal weights. New methods of cross validation are applied and suggest that performance characteristics relative to equal weighting could be predicted with a small number (1–2) of calibration variables. The performance-based decision maker is somewhat degraded on out-of-sample prediction, but remained superior to the equal weight decision maker in terms of statistical accuracy and informativeness.

Cosens, B., and C.A. STOW. Chapter 5: Resilience and water governance: Addressing fragmentation and uncertainty in water allocation and water quality law. In Social-Ecological Resilience and Law. A.S. Garmestani and C.R. Allen (Eds.). Columbia University Press, New York, NY, 142-175 pp. (2014).

The U.S. EPA reports that almost half of the nation's rivers and two thirds of its lakes are use-impaired due to poor water quality (U.S. EPA 1998, 2002, 2010; Houck 2002). The Western Water Policy Review Advisory Commission identified both poor water quality and unhealthy aquatic systems among the water challenges facing the West (Western Water Policy Review Advisory Commission 1998). The water quality impairment is caused both by chemical pollution and physical alteration of streams. Nutrients and excess sediment impair water quality in 30 percent of the nation's streams (U.S. EPA 2011). In the Great Basin nearly two-thirds of the native fish are either listed under the Endangered Species Act (ESA) or considered of concern by the U.S. Fish and Wildlife Service (USFWS). Water development is considered second only to the introduction of nonnative fish in causing these problems (Doremus 2001).

Cross, V.A., J.F. BRATTON, H.A. Michael, K.D. Kroeger, A. Green, and E. Bergeron. Continuous resistivity profiling and seismic-reflection data collected in April 2010 from Indian River Bay, Delaware. Open File Report 2011-1039. U.S. Geological Survey, Reston, VA, 32 pp. (2014).

A geophysical survey to delineate the fresh-saline groundwater interface and associated sub-bottom sedimentary structures beneath Indian River Bay, Delaware, was carried out in April 2010. This included surveying at higher spatial resolution in the vicinity of a study site at Holts Landing, where intensive onshore and offshore studies were subsequently completed. The total length of continuous resistivity profiling (CRP) survey lines was 145 kilometers (km), with 36 km of chirp seismic lines surveyed around the perimeter of the bay. Medium-resolution CRP surveying was performed using a 50-meter streamer in a baywide grid. Results of the surveying and data inversion showed the presence of many buried paleochannels beneath Indian River Bay that generally extended perpendicular from the shoreline in areas of modern tributaries, tidal creeks, and marshes. An especially wide and deep paleochannel system was imaged in the southeastern part of the bay near White Creek. Many paleochannels also had high-resistivity anomalies corresponding to low-salinity groundwater plumes associated with them, likely due to the presence of fine-grained estuarine mud and peats in the channel fills that act as submarine confining units. Where present, these units allow plumes of low-salinity groundwater that was recharged onshore to move beyond the shoreline, creating a complex fresh-saline groundwater interface in the subsurface. The properties of this interface are important considerations in construction of accurate coastal groundwater flow models. These models are required to help predict how nutrient-rich groundwater, recharged in agricultural watersheds such as this one, makes its way into coastal bays and impacts surface-water quality and estuarine ecosystems.

DAVIS, T.W., S.B. Watson, M.J. Rozmarynowycz, J.J.H. Ciborowski, R.M. McKay, and G.S. Bullerjahn. Phylogenies of microcystin-producing cyanobacteria in the lower Laurentian Great Lakes suggest extensive genetic connectivity. PLOS One 9(9):9 pp. (DOI:10.1371/journal.pone.0106093) (2014).

Lake St. Clair is the smallest lake in the Laurentian Great Lakes system. MODIS satellite imagery suggests that high algal biomass events have occurred annually along the southern shore during late summer. In this study, we evaluated these events and tested the hypothesis that summer bloom material derived from Lake St. Clair may enter Lake Erie via the Detroit River and represent an overlooked source of potentially toxic Microcystis biomass to the western basin of Lake Erie. We conducted a seasonally and spatially resolved study carried out in the summer of 2013. Our goals were to: 1) track the development of the 2013 summer south-east shore bloom 2) conduct a spatial survey to characterize the extent of toxicity, taxonomic diversity of the total phytoplankton population and the phylogenetic diversity of potential MC-producing cyanobacteria (Microcystis, Planktothrix and Anabaena) during a high biomass event, and 3) compare the strains of potential MC-producers in Lake St. Clair with strains from Lake Erie and Lake Ontario. Our results demonstrated a clear predominance of cyanobacteria during a late August bloom event, primarily dominated by Microcystis, which we traced along the Lake St. Clair coastline downstream to the Detroit River’s outflow at Lake Erie. Microcystin levels exceeded the Province of Ontario Drinking Water Quality Standard (1.5 mg L21) for safe drinking water at most sites, reaching up to five times this level in some areas. Microcystis was the predominant microcystin producer, and all toxic Microcystis strains found in Lake St. Clair were genetically similar to toxic Microcystis strains found in lakes Erie and Ontario. These findings suggest extensive genetic connectivity among the three systems.

Deal, C.J., N. Steiner, J. Christian, J. Clement Kinney, K. Denman, S. Elliott, G. Gibson, M. Jin, D. Lavoie, S. Lee, W. Lee, W. Maslowski, J. WANG, and E. Watanabe. Chapter 12. Progress and challenges in biogeochemical modeling of the Pacific Arctic region. In The Pacific Arctic Region: Ecosystem Status and Trends in a Rapidly Changing Environment. J.M. Grebmeier and W. Maslowski (Eds.). Springer Science+Business Media, Dordrecht, 393-445 pp. (DOI:10.1007/978-94-017-8863-2_12) (2014).

At this early stage of modeling marine ecosystems and biogeochemical cycles in the Pacific Arctic Region (PAR), numerous challenges lie ahead. Observational data used for model development and validation remain sparse, especially across seasons and under a variety of environmental conditions. Field data are becoming more available, but at the same time PAR is rapidly changing. Biogeochemical models can provide the means to capture some of these changes. This study introduces and synthesizes ecosystem modelling in PAR by discussing differences in complexity and application of one-dimensional, regional, and global earth system models. Topics include the general structure of ecosystem models and specifics of the combined benthic, pelagic, and ice PAR ecosystems, the importance of model validation, model responses to climate influences (e.g. diminishing sea ice, ocean acidification), and the impacts of circulation and stratification changes on PAR ecosystems and biogeochemical cycling. Examples of modeling studies that help place the region within the context of the Pan-Arctic System are also discussed. We synthesize past and ongoing PAR biogeochemical modelling efforts and briefly touch on decision makers’ use of ecosystem models and on necessary future developments.

Dufour, M.R., J.J. Pritt, C.M. Mayer, C.A. STOW, and S.S. Qian. Bayesian hierarchical modeling of larval walleye (Sander vitreus) abundance and mortality: Accounting for spatial and temporal variability on a large river. Journal of Great Lakes Research 40(Supplement 3):29-40 (DOI:10.1016/j.jglr.2014.08.001) (2014).

Larval fish are extremely variable in space and time while sampling of populations is generally restricted and incomplete. However, estimates of abundance and mortality are important for understanding population dynamics, habitat quality, and anthropogenic impacts. Acknowledging and addressing variability during sampling and data analysis are imperative to producing informative estimates. A combination of spatially and temporally distributed ichthyoplankton sampling and Bayesian hierarchical and state-space modeling was used to partition variance and estimate abundance and mortality of larval walleye (Sander vitreus) in the Maumee River during 2010 and 2011. System variability and degree of sampling coverage have a direct impact on the quality of abundance estimates. Small scale factors (i.e., within site and day-to-day) accounted for the most variation in larval walleye densities, therefore sampling should concentrate on capturing these sources. Bayesian state-space modeling can improve estimates by sharing information through time, properly accounting for uncertainty, and producing probability distribution based estimates. Larval fish are highly variable and difficult to sample; however, the application of Bayesian methods during the data analysis process can lead to improved estimates of abundance and informed management actions.

Filstrup, C.T., T. Wagner, P.A. Soranno, E.H. Stanley, C.A. STOW, K.E. Webster, and E.J. Downing. Regional variability among nonlinear chlorophyll-phosphorus relationships in lakes. Limnology and Oceanography 59(5):1691-1703 (DOI:10.4319/lo.2014.59.5.1691) (2014).

The relationship between chlorophyll a (Chl a) and total phosphorus (TP) is a fundamental relationship in lakes that reflects multiple aspects of ecosystem function and is also used in the regulation and management of inland waters. The exact form of this relationship has substantial implications on its meaning and its use. We assembled a spatially extensive data set to examine whether nonlinear models are a better fit for Chl a–TP relationships than traditional log-linear models, whether there were regional differences in the form of the relationships, and, if so, which regional factors were related to these differences. We analyzed a data set from 2105 temperate lakes across 35 ecoregions by fitting and comparing two different nonlinear models and one log-linear model. The two nonlinear models fit the data better than the log-linear model. In addition, the parameters for the best-fitting model varied among regions: the maximum and lower Chl a asymptotes were positively and negatively related to percent regional pasture land use, respectively, and the rate at which chlorophyll increased with TP was negatively related to percent regional wetland cover. Lakes in regions with more pasture fields had higher maximum chlorophyll concentrations at high TP concentrations but lower minimum chlorophyll concentrations at low TP concentrations. Lakes in regions with less wetland cover showed a steeper Chl a–TP relationship than wetland-rich regions. Interpretation of Chl a–TP relationships depends on regional differences, and theory and management based on a monolithic relationship may be inaccurate.

Foley, C.J., G.J. Bowen, T.F. NALEPA, M.S. Sepulveda, and T.O. Hook. Stable isotope patterns of benthic organisms from the Great Lakes region indicate variable dietary overlap of Diporeia spp. and dreissenid mussels. Canadian Journal of Fisheries and Aquatic Sciences 71:12 pp. (DOI:10.1139/cjfas-2013-0620) (2014).

Competition between native and invasive species may bring about a suite of ecological and evolutionary outcomes, including local extirpations. In the Laurentian Great Lakes, competition for food may explain the dramatic decline of Diporeia spp. amphipods following the introduction of dreissenid mussels. This hypothesis has not been confirmed, in part because dreissenids and Diporeia appear to co-exist and flourish in other systems, including the Finger Lakes of New York. We used carbon, nitrogen, hydrogen, and oxygen stable isotope ratios to examine resource use by Diporeia from three spatially distinct populations (Lake Michigan, Lake Superior, and Cayuga Lake), dreissenids from areas where they co-occur with Diporeia (Lake Michigan and Cayuga Lake), and Diporeia from Lake Michigan collected before and after dreissenid invasion (1986–2009). Our results suggest that dreissenids may affect resource use by Diporeia in areas of co-occurrence, but the extent to which those effects are positive or negative is unclear. Terrestrial inputs may provide an important subsidy for Diporeia populations in small systems but may not be substantial enough in the Great Lakes to ensure that both taxa thrive.

Francoeur, S.N., K.A. Peters-Winslow, D. Miller, C.A. STOW, Y.K. CHA, and S.D. Peacor. Spatial and temporal patterns in macroscopic benthic primary producers in Saginaw Bay, Lake Huron. Journal of Great Lakes Research 40(Supplement 1):53-63 (DOI:10.1016/j.jglr.2014.01.011) (2014).

We investigated spatial and temporal patterns in macroscopic benthic primary producer biomass, production, and composition in inner Saginaw Bay in 2009 and 2010. Charophytes and filamentous algae (FA) were relatively abundant, and vascular macrophytes were less common. The probability of benthic primary producer presence increased with the proportion of benthic substrate composed of rock. Most benthic primary producer biomass occurred at depths of 2–4 m, with very little biomass observed beyond 4 m deep. Charophyte and vascular macrophyte abundances displayed consistent patterns related to distance from the mouth of the Saginaw River. FA abundance also displayed such patterns, but they reversed between 2009 and 2010. Macrophytic benthic primary producer communities were generally dominated by charophytes. Three genera of vascular macrophytes, including Myriophyllum, were also observed. Filamentous algal communities were composed of a mixture of FA taxa. Ten FA genera were observed, including the red alga Compsopogon. Dominance of Compsopogon was related to low water clarity and low TP. Biomass-based benthic production estimates indicated that charophytes and FA strongly dominated macroscopic benthic production; production of vascular macrophytes was relatively low. The observed relationships of abundance and environmental conditions suggested regulation of benthic producer biomass by a shifting mosaic of substratum, nutrient, and light availabilities. The diverse nature of the benthic producer community could complicate understanding and management of excess benthic biomass and beach fouling in Saginaw Bay.

FRY, L.M., A.D. GRONEWOLD, V. Fortin, S. Buan, A.H. CLITES, C. Luukkonen, D. Hotsschlag, D. L., T.S. HUNTER, F. Seglenieks, D. Durnford, M. Dimitrijevic, C. Subich, E. Klyszejko, K. KEA, and P. Restrepo. The Great Lakes Runoff Intercomparison Project, Phase 1: Lake Michigan (GRIP-M). Journal of Hydrology 519(Part D):3448-3465 (DOI:10.1016/j.jhydrol.2014.07.021) (2014).

We assembled and applied five models (one of which included three different configurations) to the Lake Michigan basin to improve our understanding of how differences in model skill at simulating total runoff to Lake Michigan relate to model structure, calibration protocol, model complexity, and assimilation (i.e. replacement of simulated discharge with discharge observations into historical simulations), and evaluate historical changes in runoff to Lake Michigan. We found that the performance among these models when simulating total runoff to the lake varied relatively little, despite variability in model structure, spatial representation, input data, and calibration protocol. Relatively simple empirical, assimilative models, including the National Oceanic and Atmospheric Administration (NOAA) Great Lakes Environmental Research Laboratory (GLERL) area ratio-based model (ARM) and the United States Geological Survey (USGS) Analysis of Flows in Networks of CHannels (AFINCH) model, represent efficient and effective approaches to propagating discharge observations into basin-wide (including gaged and ungaged areas) runoff estimates, and may offer an opportunity to improve predictive models for simulating runoff to the Great Lakes. Additionally, the intercomparison revealed that the median of the simulations from non-assimilative models agrees well with assimilative models, suggesting that using a combination of different methodologies may be an appropriate approach for estimating runoff into the Great Lakes. We then applied one assimilative model (ARM) to the Lake Michigan basin and found that there was persistent reduction in the amount of precipitation that becomes runoff following 1998, corresponding to a period of persistent low Lake Michigan water levels. The study was conducted as a first phase of the Great Lakes Runoff Intercomparison Project, a regional binational collaboration that aims to systematically and rigorously assess a variety of models currently used (or that could readily be adapted) to simulate basin-scale runoff to the North American Laurentian Great Lakes.

FUJISAKI, A., H. Mitsudera, J. WANG, and M. Wakatsuchi. How does the Amur River discharge flow over the northwestern continental shelf in the Sea of Okhotsk? Progress in Oceanography 126:8-20 (DOI:10.1016/j.pocean.2014.04.028) (2014).

The paths of the Amur River discharge on the continental shelf in the Sea of Okhotsk are still unknown despite their significance in transporting dissolved and particulate iron. In this study, we conduct a coupled ice-ocean simulation for the northern Sea of Okhotsk from June 1998 to September 2000 to answer the question: Does the Amur River discharge deposit materials to the pathway of the dense shelf water? In a series of numerical experiments, we identified two routes (the western and eastern routes) that could transport the river water more than 100 km offshore over the northwestern continental shelf. The two routes share the clockwise gyre in the Sakhalin Gulf and the northeastward flow on the northwestern continental shelf. These features are connected through the westward jet along the slope from the Sakhalin Gulf (the western route) and the northward transport over the shelf break canyon (the eastern route). The river water, the dense shelf water, and the easterly wind are in a fine geophysical balance for those features, and all are required for the formation of the two routes. The model results show that these unique joint effects in the Sea of Okhotsk allow the Amur River discharge to be effectively transported over the northwestern continental shelf, unlike a general river discharge that flows along the coast, and deposit materials into the pathway of the dense shelf water.

GRONEWOLD, A.D., and C.A. STOW. Unprecedented seasonal water level dynamics on one of the Earth's largest lakes. Bulletin of the American Meteorological Society 95:15-17 (DOI:10.1175/BAMS-D-12-00194.1) (2014).

The North American Great Lakes (Fig. 1) contain roughly 20% of the Earth’s unfrozen fresh surface water and cover a massive area (Lake Superior alone is the largest unfrozen freshwater surface on the planet). Water levels on the Great Lakes have been recorded continuously for more than 150 years, representing one of the longest sets of direct hydroclimate measurements. This dataset, synthesized by Quinn (1981) and Lenters (2001), among many others, indicates that water levels on each of the Great Lakes follow a strong seasonal pattern closely linked with the timing and magnitude of the major components of the regional water budget, with relatively low water levels in the winter months, rising water levels in the spring, and decreasing water levels in the late summer and early fall. Water-level measurements on Lake Erie during the 2011 and 2012 water years (October 2010 through September 2011, and October 2011 through September 2012, respectively), however, reflect dramatic and unexpected changes in the seasonal water level cycle and in the Great Lakes regional water budget.

GRONEWOLD, A.D., and C.A. STOW. Water loss from the Great Lakes. Science 343:1084-1085 (DOI:10.1126/science.1249978) (2014).

As marine coastal populations experience and plan for rising ocean levels, residents along the coasts of Earth’s largest lake system are encountering the opposite problem: persistent low water levels and a receding shoreline. In January 2013, federal agencies from the United States and Canada documented the lowest water levels ever recorded on lakes Michigan and Huron. Only 6 years earlier, historically low water levels were recorded on Lake Superior, which feeds into the Lake Michigan-Huron system. These low water levels are symptoms of an imbalance in the water budget of the Great Lakes. Adapting to, and potentially mitigating, low water level conditions requires improved quantification of the factors that drive the imbalance.

HAWLEY, N., T. Redder, R. BELETSKY, E. Verhamme, D. BELETSKY, and J.V. DePinto. Sediment resuspension in Saginaw Bay. Journal of Great Lakes Research 40(Supplement 1):18-27 (DOI:10.1016/j.jglr.2013.11.010) (2014).

An integrated hydrodynamic and sediment transport model was applied to Saginaw Bay for the ice-free portions of 2009 and 2010. Observations of surface waves and suspended sediment concentration made during the spring of both years were used to constrain the model and to validate the model output. The results show that sediment resuspension in both the inner and outer bay is due almost entirely to surface wave action, and that the bulk of the resuspension events occur during the fall of each year. Although the model accurately predicted the occurrence of resuspension events, it did not always accurately simulate the amount of material resuspended. Because resuspension mixes bottom sediment into the water column and makes it and associated nutrients available to the biota, the effects of sediment resuspension need to be accounted for in any water quality model of the bay. Better specification of both the surface waves and the initial specification of the bottom sediment would probably improve the performance of the model.

He, C., L. Zhang, C. DeMarchi, and T.E. CROLEY II. Estimating point and nonpoint sources pollution loadings in the Saginaw Bay watersheds. Journal of Great Lakes Research 40(Supplement 1):11-17 (DOI:10.1016/j.jglr.2014.01.013) (2014).

Databases of point sources including combined sewer overflows (CSOs) were acquired from the governmental agencies to map the occurrences and magnitude of the CSOs. Multiple databases of land use, topography, hydrography, soils, and agricultural statistics were used to estimate nonpoint source loading potential in the Saginaw Bay Basin, Michigan. Animal manure production was computed from tabulations of animals by 5-digit zip code area for the census years of 1987, 1992, 1997, and 2002. Fertilizer applications for both urban and agricultural land uses were calculated from county fertilizer estimates for the same periods. Results indicate that point sources from municipalities, industrial sectors and business entities contribute approximately 25% of the total phosphorus load to Saginaw Bay, with the remainder being accounted for by nonpoint source contributions. While the total amount of nutrients (N and P) from animal manure and fertilizer applications and atmospheric deposition declined in the Saginaw Bay Basin, fertilizer applications in non-farmland increased significantly. Estimation of nutrient loading potential at 5-digit zip code level reveals more detailed spatial variation and critical areas of nutrient loading than county level data for implementation of targeted water quality programs.

Hefferman, J.B., P.A. Soranno, M.J. Angilletta, L.B. Buckley, D.S. Gruner, T.H. Keitt, J.R. Kellner, J.S. Kominoski, A.V. Rocha, J. Xiao, T. Harms, S.J. Goring, L.E. Koenig, W.H. McDowell, H. Powell, A.D. Richardson, C.A. STOW, R. Vargas, and K.C. Weathers. Macrosystems ecology: Understanding ecological patterns and processes at continental scales. Frontiers in Ecology and the Environment 12(1):5-14 (DOI:10.1890/130017) (2014).

Macrosystems ecology is the study of diverse ecological phenomena at the scale of regions to continents and their interactions with phenomena at other scales. This emerging subdiscipline addresses ecological questions and environmental problems at these broad scales. Here, we describe this new field, show how it relates to modern ecological study, and highlight opportunities that stem from taking a macrosystems perspective. We present a hierarchical framework for investigating macrosystems at any level of ecological organization and in relation to broader and finer scales. Building on well-established theory and concepts from other subdisciplines of ecology, we identify feedbacks, linkages among distant regions, and interactions that cross scales of space and time as the most likely sources of unexpected and novel behaviors in macrosystems. We present three examples that highlight the importance of this multiscaled systems perspective for understanding the ecology of regions to continents.

IVAN, L.N., D.G. Fielder, M.V. Thomas, and T.O. Hook. Changes in the Saginaw Bay, Lake Huron, fish community from 1970-2011. Journal of Great Lakes Research 40:922-933 (DOI:10.1016/j.jglr.2014.09.002) (2014).

Many aquatic ecosystems experience concurrent anthropogenic stressors that can have complex impacts on fish communities. Limited data and temporal associations among environmental stressors may confound the ability to attribute community-level impacts to single or multiple stressors. Instead, quantitative description of temporal changes in fish communities may shed light on the cumulative and individual impacts of diverse stressors. Saginaw Bay, Lake Huron, has experienced diverse anthropogenic stressors that have been inconsistently quantified over time. We used resampling and multivariate approaches to analyze long-term trawl data to describe how fish community patterns changed in Saginaw Bay from1970–2011. Total, native, and moderately tolerant fish species richness generally increased from 1970–2011. Dynamic factor analysis and nonmetric multidimensional scaling revealed that fish community structure changed from 1970–2011 and that relative abundances of many fish species increased. In general, increases in richness and CPUE were correlated with decreases in total phosphorus, chl a, and water levels. In addition, breakpoint analyses revealed shifts in species richness in the mid-1980s and 1999. Temporal patterns are consistent with the hypothesis that the Saginaw Bay fish community has changed from one dominated by species tolerant of eutrophy to one withmore sensitive species, likely a response to decreased phosphorous loading and resulting changes in water quality. More recently (1999–2011), richness and relative abundance of many fish species in Saginaw Bay declined, a pattern potentially reflective of larger food-web transitions in both Saginaw Bay and open Lake Huron.

Kao, Y.C., S.A. Alderstein, and E.S. RUTHERFORD. The relative impacts of nutrient loads and invasive species on a Great Lakes food web: An Ecopath with Ecosim analysis. Journal of Great Lakes Research 40(Supplement 1):35-52 (DOI:10.1016/j.jglr.2013.11.012) (2014).

Excessive nutrient loads and species invasions pose significant threats to productivity and function of Great Lakes aquatic ecosystems. We used an Ecopath and Ecosim model to analyze impacts of changes in phosphorus loads, and dreissenid mussels and alewife biomass on the Saginaw Bay food web, Lake Huron. We configured the food web model in Ecopath with pre-dreissenids (1990) data on organism biomass, production, consumption, and diet from federal and state agency surveys and other sources. We conducted 70-year simulations in Ecosim of single factors (nutrients, alewives, and dreissenids) and their combinations. Phosphorus load scenarios were run under high (1970s), average (current), and low (target) levels; alewife scenarios were run under 2-fold the 1990?2003 average biomass, 1990?2003 average biomass, and alewife absence; dreissenid scenarios were run under the 1990?1996 average biomass, current (2009?2010) biomass, and dreissenid absence. Results indicated phosphorus loads were positively correlated with simulated biomass of most food web groups, alewife biomass were negatively correlated with biomass of most fish groups and macrozooplankton, while dreissenids impacts were most severe on lower trophic levels, but were relatively minor for fish groups compared with nutrient and alewife scenarios. Dreissenids had little effect on fish because Chironomids, the main component of fish diets that fed mostly on detritus, were not affected by dreissenids. Our results suggest that under current conditions of absence of alewives and reduced dreissenid biomass, obtaining target nutrient loads established in 1978 would not sustain current fishery harvests in Saginaw Bay given food web changes caused by invasive species.

Kao, Y.C., C.P. Madenjian, D.B. Bunnell, B.M. LOFGREN, and M. PERROUD. Temperature effects induced by climate change on the growth and consumption by salmonines in Lakes Michigan and Huron. Environmental Biology of Fishes:16 pp. (DOI:10.1007/s10641-014-0352-6) (2014).

We used bioenergetics models to investigate temperature effects induced by climate change on the growth and consumption by Chinook salmon Oncorhynchus tshawytscha, lake trout Salvelinus namaycush, and steelhead O. mykiss in Lakes Michigan and Huron. We updated biological inputs to account for recent changes in the food webs and used temperature inputs in response to regional climate observed in the baseline period (1964–1993) and projected in the future period (2043–2070). Bioenergetics simulations were run across multiple age-classes and across all four seasons in different scenarios of prey availability. Due to the increased capacity of prey consumption, future growth and consumption by these salmonines were projected to increase substantially when prey availability was not limited. When prey consumption remained constant, future growth of these salmonines was projected to decrease in most cases but increase in some cases where the increase in metabolic cost can be compensated by the decrease in waste (egestion and excretion) loss. Consumption by these salmonines was projected to increase the most during spring and fall when prey energy densities are relatively high. Such seasonality benefits their future growth through increasing annual gross energy intake. Our results indicated that lake trout and steelhead would be better adapted to the warming climate than Chinook salmon. To maintain baseline growth into the future, an increase of 10 % in baseline prey consumption was required for Chinook salmon but considerably smaller increases, or no increases, in prey consumption were needed by lake trout and steelhead.

Kult, J.M., L.M. FRY, A.D. GRONEWOLD, and W. Choi. Regionalization of hydrologic response in the Great Lakes basin: Considerations of temporal scales of analysis. Journal of Hydrology 519:2224-2237 (DOI:10.1016/j.jhydrol.2014.09.083) (2014).

Methods for predicting streamflow in areas with limited or nonexistent measures of hydrologic response commonly rely on regionalization techniques, where knowledge pertaining to gauged watersheds is transferred to ungauged watersheds. Hydrologic response indices have frequently been employed in contemporary regionalization research related to predictions in ungauged basins. In this study, we developed regionalization models using multiple linear regression and regression tree analysis to derive relationships between hydrologic response and watershed physical characteristics for 163 watersheds in the Great Lakes basin. These models provide an empirical means for simulating runoff in ungauged basins at a monthly time step without implementation of a rainfall–runoff model. For the dependent variable in these regression models, we used monthly runoff ratio as the indicator of hydrologic response and defined it at two temporal scales: (1) treating all monthly runoff ratios as individual observations, and (2) using the mean of these monthly runoff ratios for each watershed as a representative observation. Application of the models to 62 validation watersheds throughout the Great Lakes basin indicated that model simulations were far more sensitive to the temporal characterization of hydrologic response than to the type of regression technique employed, and that models conditioned on individual monthly runoff ratios (rather than long term mean values) performed better. This finding is important in light of the increased usage of hydrologic response indices in recent regionalization studies. Models using individual observations for the dependent variable generally simulated monthly runoff with reasonable skill in the validation watersheds (median Nash–Sutcliffe efficiency = 0.53, median R2 = 0.66, median magnitude of the deviation of runoff volume = 13%). These results suggest the viability of empirical approaches to simulate runoff in ungauged basins. This finding is significant given the many regions of the world with sparse gauging networks and limited resources for gathering the field data required to calibrate rainfall– runoff models.

Lavrentyev, P.J., H.A. VANDERPLOEG, G. Franze, D.H. Chacin, J.R. LIEBIG, and T.H. JOHENGEN. Microzooplankton distribution, dynamics, and trophic interactions relative to phytoplankton and quagga mussels in Saginaw Bay, Lake Huron. Journal of Great Lakes Research 40(Supplement 1):95-105 (DOI:10.1016/j.jglr.2013.11.012) (2014).

Invasive quagga mussels have recently replaced zebra mussels as the dominant filter-feeding bivalves in the Great Lakes. This study examined microzooplankton (i.e., grazers b200 μm) and their trophic interactions with phytoplankton, bacteria, and bivalve mussels in Saginaw Bay, Lake Huron, following the zebra to quagga mussel shift. Microzooplankton distribution displayed strong spatial and temporal variability (1.73–28.5 μg C/L) relative to phytoplankton distribution. Ciliates were the dominant component, especially in the spring and early summer. Rotifers and dinoflagellates increased toward late summer/fall in the inner and outer parts of the bay, respectively. Microzooplankton grazing matched bacterial growth rates and removed ca. 30% of the phytoplankton standing stock in the b100 μm size fraction per day. The greatest herbivory occurred at the site dominated by colonial cyanobacteria. Microzooplankton, which comprised b4% of the quagga mussels prey field (i.e. available prey), contributed 77% and 34% to the quagga carbon-based diet during Microcystis and diatom blooms, respectively. Feeding on microzooplankton could buffer mussels during lean periods, or supplement other consumed resources, particularly during noxious cyanobacterial blooms. The results of this study demonstrate that microzooplankton are a resilient and critical component of the Saginaw Bay ecosystem.

Li, J., Y. Qi, Z. Jing, and J. WANG. Enhancement of eddy-Ekman pumping inside anticyclonic eddies with wind-parallel extension: Satellite observations and numerical studies in the South China Sea. Journal of Marine Systems 132:150-161 (DOI:10.1016/j.jmarsys.2014.02.002) (2014).

Eddy-Ekman pumping was recently proposed as a potential mechanism to explain the high chlorophyll (Chl) concentrations inside anticyclonic eddies (AEs). In this paper, the influence of eddy-shape changes on the strength of eddy-Ekman pumping is investigated for AEs in the South China Sea (SCS) through multi-satellite data and numerical experiments. The results mainly indicate that wind-parallel (-perpendicular) extensions may enhance (reduce) eddy-Ekman pumping inside AEs. First, an AE detected in northern SCS winter shows significant Chl-wind relation and uplifted near-surface isopycnals when its shape extension becomes parallel with the wind direction. In addition, satellite observations indicate significant eddy-Ekman-pumping signals appear in the central-northern SCS during the winter monsoon and in the central-eastern SCS during the winter and summer monsoons, whenever and wherever AEs' shapes show wind-parallel extensions. This regional–seasonal characteristic is further confirmed by the numerical experiments, which display a positive linear relationship between wind-parallel projective length and the strength of eddy-Ekman pumping. This study may contribute to extend the theory of eddy-Ekman pumping with emphasizing the importance of eddy shapes and wind directions, especially in the situations that high spatial-temporal variability appears in eddies and/or the wind field.

Li, Y., S. Peng, J. WANG, and J. Yan. Impacts of non-breaking wave-stirring-induced mixing on the upper ocean thermal structure and typhoon intensity in the South China Sea. Journal of Geophysical Research: Oceans 119(8):5052-5070 (DOI:10.1002/2014JC009956) (2014).

To investigate the effect of nonbreaking wave-induced mixing caused by surface wave stirring on the upper ocean thermal structure (UOTS) and the typhoon intensity, a simple nonbreaking wave stirring- induced mixing parameterization (WMP) scheme is incorporated into a regional coupled atmosphere-ocean model for the South China Sea (SCS), which couples the Princeton Ocean Model (POM) to the Weather Research and Forecasting (WRF) model using the OASIS3 coupler. The results of simulating two selected typhoon cases indicate that the nonbreaking wave-stirring-induced mixing has significant impacts on UOTS and the typhoon intensity, and the incorporation of the simple WMP scheme in the coupled model helps to improve the simulation of UOTS and thus the typhoon intensity. In the case that the typhoon intensity is underestimated by the atmosphere model alone, the improvement of initial UOTS by the ocean model with the WMP included can deepen the initial thermocline depth, reduce the effect of SST cooling, and prevent the typhoon intensity from undesired weakening. In the case that the typhoon intensity is overestimated (with strong winds), including the WMP in the ocean model significantly enhances the total vertical mixing rate in the upper ocean, which in turn enhances the SST cooling and thus reduces the typhoon intensity as desired. The results obtained in this study make a contribution to the ongoing efforts of improving the typhoon intensity forecast using a regional atmosphere-ocean coupled model by worldwide researchers and forecasters, especially for the typhoons in the SCS regions.

LIU, P.C. Freaque wave occurrences in 2013. Natural Hazards and Earth System Sciences 2:7017-7025 (DOI:10.5194/nhessd-2-7017-2014) (2014).

Documenting freaque waves when they occured around the globe in 2013 is based here on news reports on the internet. It was found that there were a total 22 cases of freaque waves in 2013, based on those reported in clearly-defined physically specific environments. There were three cases in the deep ocean, six in nearshore areas, seven on sandy beaches, and seven on rocky shore areas. Note that most of the academic research has been on freaque waves in the deep ocean, which accounts for 13% of all occurrences. The majority of reported occurrences, 87%, are in the nearshore areas or along the beach area. Geographically, these cases are also fairly evenly spread around the globe. As of now, there is no general knowledge regarding the frequency of occurrence of these freaque waves, so that one may assume that 2013 was a customary year for freaque wave occurrences.

LIU, P.C., J.C. Nieto Borge, G. Rodriquez, K.R. MacHutchon, and H.S. Chen. From single point gauge to spatio-temporal measurement of ocean waves - prospects and perspectives. Proceedings of the ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering, San Francisco, California, June 8-13, 2014. OMAE2014, 6 pp. (2014).

With the recent advancement of spatial measurements of ocean waves, we are clearly facing new challenges regarding how to handle an expanded new data system when it becomes widely available. In this paper we wish to present a preliminary attempt at confronting these prospects. Because the data is still very limited at present and also conceptually new, it’s a new, unfamiliar, and unrelenting world to pursue. We need a paradigm shift away from our familiar single-point conceptualization in order to effective approach the new world of truly spatial ocean waves.

LOFGREN, B.M. Simulation of atmospheric and lake conditions in the Laurentian Great Lakes region using the Coupled Hydrosphere-Atmosphere Research Model (CHARM). NOAA Technical Memorandum GLERL-165. NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 23 pp. (2014).

Greenhouse gas-induced climate change will have notable effects on the Great Lakes region, in the atmosphere, land surfaces, and lakes themselves. Simulations of these effects were carried out using the Coupled Hydrosphere-Atmosphere Research Model (CHARM), driven by output from the Canadian General Circulation Model version 3 (CRCM3) for past and future time periods. This results in increased downward longwave radiation and near-surface air temperature. The air temperature increases during summer have strong spatial minima directly over the lakes that are limited to the lowest model layer and seem to be associated with frequent fog depicted by CHARM. Precipitation is also generally increased, with the most spatially coherent, and among the strongest, increases occurring in the near-shore lake effect zones during winter. Evapotranspiration is generally increased, although only weakly over land, but very strongly over the lakes during winter. Water temperatures are increased and the summer stratification pattern (warmer water overlying colder) is established earlier in the year. Ice cover is diminished and limited to shallow parts of the lakes. Several bugs and shortcomings in CHARM are identified for correction in future development and use

LOFGREN, B.M., and A.D. GRONEWOLD. Chapter 12: Water resources. In Climate Change in the Midwest: A Synthesis Report for the National Climate Assessment. J.A. Winkler, J.A. Andresen, J.L. Hatfield, D. Bidwell, and D. Brown (Eds.). Island Press, 224-237 pp. (2014).

The water resources of the Midwest, and how they are managed under a future climate, have a significant collective impact on multiple economic sectors in the U.S., North America, and the world. The North American Laurentian Great Lakes, for example, hold nearly 20% of the earth’s accessible surface fresh water supply and have a coastline, and a coastal population, on the same order of magnitude as frequently-studied ocean coasts around the world (Fuller et al. 1995). In light of growing demands for clean water, access to coastal resources, and an improved understanding of climate dynamics in the Midwest region, a significant amount of research has recently been focused on understanding climate impacts on the lakes (both large and small), rivers, and streams in this region.

Lottig, N.R., T. Wagner, E.N. Henry, K.S. Cheruvelil, K.E. Webster, E.J. Downing, and C.A. STOW. Long-term citizen-collected data reveal geographical patterns and temporal trends in lake water clarity. PLOS One 9(4):1-8 (DOI:10.1371/journal.pone.0095769) (2014).

We compiled a lake-water clarity database using publically available, citizen volunteer observations made between 1938 and 2012 across eight states in the Upper Midwest, USA. Our objectives were to determine (1) whether temporal trends in lake-water clarity existed across this large geographic area and (2) whether trends were related to the lake-specific characteristics of latitude, lake size, or time period the lake was monitored. Our database consisted of .140,000 individual Secchi observations from 3,251 lakes that we summarized per lake-year, resulting in 21,020 summer averages. Using Bayesian hierarchical modeling, we found approximately a 1% per year increase in water clarity (quantified as Secchi depth) for the entire population of lakes. On an individual lake basis, 7% of lakes showed increased water clarity and 4% showed decreased clarity. Trend direction and strength were related to latitude and median sample date. Lakes in the southern part of our study-region had lower average annual summer water clarity, more negative long-term trends, and greater interannual variability in water clarity compared to northern lakes. Increasing trends were strongest for lakes with median sample dates earlier in the period of record (1938–2012). Our ability to identify specific mechanisms for these trends is currently hampered by the lack of a large, multi-thematic database of variables that drive water clarity (e.g., climate, land use/cover). Our results demonstrate, however, that citizen science can provide the critical monitoring data needed to address environmental questions at large spatial and long temporal scales. Collaborations among citizens, research scientists, and government agencies may be important for developing the data sources and analytical tools necessary to move toward an understanding of the factors influencing macro-scale patterns such as those shown here for lake water clarity.

Lu, Y., P.A. Meyers, J.A. ROBBINS, B.J. EADIE, N. HAWLEY, and K.H. Ji. Sensitivity of sediment geochemical proxies to coring location and corer type in a large lake: Implications for paleolimnological reconstruction. Geochemistry, Geophysics, Geosystems 15:17 pp. (DOI:10.1002/2013GC004989) (2014).

We compared a suite of geochemical proxies in sediment cores collected in 1982, 1988, 1991, and 2003 from sites near the depocenter of Lake Erie to evaluate the reliability of paleoenvironmental reconstructions derived from lacustrine sediments. Our proxies included the concentrations and carbon isotopic compositions of organic and inorganic carbon (TOC, CaCO3, d13Corg, and d13CCaCO3), augmented by organic C to total N ratios (Corg:Ntot), d15N, and carbonate d18O values (d18OCaCO3). The three coring sites were clustered within 12 km; two types of corers—a Box corer and a Benthos gravity corer—were used for the 1991 sampling campaign. The variance of most proxies was accounted for not only by temporal environmental changes but also by coring locations and corer type, indicating that sediment spatial heterogeneity and differences in sediment recovery due to the use of different corers also played a part in determining the geochemical compositions of these cores. The TOC, d13Corg, and d13CCaCO3 values showed decadal temporal patterns that were consistent between the multiple sampling campaigns. In contrast, the d15N, Corg:Ntot, CaCO3, and d18OCaCO3 exhibited across-core differences in their temporal variations, making it difficult to extract consistent environment information from different cores. Our findings suggest that in addition to temporal environmental changes, high-resolution paleolimnological reconstruction is sensitive to many factors that could include spatial sediment heterogeneity, discontinuous sedimentation processes, bioturbation, sediment dating uncertainty, and artifacts associated with analytical and coring procedures. Therefore, multiple-core sampling and analysis are important in reliably reconstructing environmental changes, particularly for large, heterogeneous lacustrine basins.

Ma, J., Y. Du, H. Zhan, H. Liu, and J. WANG. Influence of oceanic Rossby waves on phytoplankton production in the southern tropical Indian Ocean. Journal of Marine Science 134:12-19 (DOI:10.1016/j.jmarsys.2014.02.003) (2014).

Using Sea-viewing Wide Field-of-view Sensor (SeaWiFS) ocean color data, we investigated the biological responses to oceanic Rossby waves in the southern tropical Indian Ocean (TIO) during 1997–2007. The findings indicate that, during the developing phase of El Niño/La Niña events, usually in boreal fall, and triggered by anomalous anticyclonic/cyclonic wind circulations in the southeast TIO, downwelling/upwelling Rossby waves form and then propagate westward. After a few months, downwelling/upwelling Rossby waves interface with the thermocline dome in the southern TIO, and suppress/enhance the upwelling. Correspondingly, less/more nutrient-rich waters enter the mixed layer and result in lower/higher chlorophyll concentrations. Due to the asymmetric effects on the thermocline dome between downwelling and upwelling Rossby waves, higher chlorophyll concentrations appear earlier and in the eastern part of the dome, whereas lower chlorophyll concentrations appear later and in the central part of the dome. Moreover, when El Niño/La Niña–Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) events coincide, the biological responses are stronger.

MIEHLS, A.L.J., S.D. Peacor, and A.G. McAdam. Gape-limited predators as agents of selection on the defensive morphology of an invasive invertebrate. Evolution 68(9):2633-2643 (DOI:10.1111/evo.12472) (2014).

Invasive species have widespread and pronounced effects on ecosystems and adaptive evolution of invaders is often considered responsible for their success. Despite the potential importance of adaptation to invasion, we still have limited knowledge of the agents of natural selection on invasive species. Bythotrephes longimanus, a cladoceran zooplankton, invaded multiple Canadian Shield lakes over the past several decades. Bythotrephes have a conspicuous caudal process (tail spine) that provides a morphological defense against fish predation. We measured viability selection on the longest component of the Bythotrephes spine, the distal spine segment, through a comparison of the lengths of first and second instar Bythotrephes collected from lakes differing in the dominance of gape-limited predation (GLP) and nongape-limited predation (NGLP) by fish. We found that natural selection varied by predator gape-limitation, with strong selection (selection intensity: 0.20–0.79) for increased distal spine length in lakes dominated by GLP, and no significant selection in lakes dominated by NGLP. Further, distal spine length was 17% longer in lakes dominated by GLP, suggesting the possibility of local adaptation. As all study lakes were invaded less than 20 years prior to our collections, our results suggest rapid divergence in defensive morphology in response to selection from fish predators.

NALEPA, T.F., D.L. FANSLOW, G.A. LANG, K. MABREY, and M. ROWE. Lake-wide benthic surveys in Lake Michigan in 1994-95, 2000, 2005, and 2010: Abundances of the amphipod Diporeia spp. and abundances and biomass of the mussels Dreissena polymorpha and Dreissena rostriformis bugensis. NOAA Technical Memorandum GLERL-164. NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 21 pp. (2014).

This technical report provides basic results of lake-wide, benthic surveys conducted in Lake Michigan in 1994-1995, 2000, 2005, and 2010 to assess temporal trends in the native amphipod Diporeia spp., the zebra mussel (Dreissena polymorpha), and the quagga mussel (Dreissena rostriformis bugensis). These surveys are an expansion of a continuing, monitoring program in the southern basin of the lake conducted by the Great Lakes Environmental Research Laboratory (GLERL) that examines trends in the abundance and composition of the entire macroinvertebrate community (Nalepa 1987, Nalepa et al. 1998). The GLERL program was initiated in 1980 with the original intent of assessing the response of the benthic community to phosphorus abatement efforts in the mid-1970s (Nalepa 1987). However, after D. polymorpha became established in the southwestern portion of the lake in 1989 (Marsden et al. 1993), the monitoring program detected several dramatic changes in the benthic community in the early 1990s. Diporeia began to systematically disappear, and D. polymorpha rapidly expanded and soon became dominant in the nearshore region (Nalepa et al. 1998). To determine if changes in the southern basin were also occurring throughout the lake, the monitoring program was greatly expanded in 1994-1995. Benthic sampling in these two years was conducted jointly with several other sampling programs in Lake Michigan: Environmental Monitoring and Assessment (EMAP) and Lake Michigan Mass Balance (LMMB). After 1994-1995, lakewide monitoring of Diporeia and Dreissena populations continued at 5-year intervals (i.e., 2000, 2005, and 2010) as part of a regular monitoring program at GLERL that supplemented the continued effort in the southern basin.

Nash, K.L., C.R. Allen, D.G. Angeler, C. Barichievy, T. Eason, A.S. Garmestani, N.A.J. Graham, D. Granholm, M. Knutson, R.J. Nelson, M. Nystrom, C.A. STOW, and S.M. Sundstrom. Discontinuities, cross-scale patterns, and the organization of ecosystems. Ecology 95(3):654-667 (DOI:10.1890/13-1315.1) (2014).

Ecological structures and processes occur at specific spatiotemporal scales, and interactions that occur across multiple scales mediate scale-specific (e.g., individual, community, local, or regional) responses to disturbance. Despite the importance of scale, explicitly incorporating a multi-scale perspective into research and management actions remains a challenge. The discontinuity hypothesis provides a fertile avenue for addressing this problem by linking measureable proxies to inherent scales of structure within ecosystems. Here we outline the conceptual framework underlying discontinuities and review the evidence supporting the discontinuity hypothesis in ecological systems. Next we explore the utility of this approach for understanding cross-scale patterns and the organization of ecosystems by describing recent advances for examining nonlinear responses to disturbance and phenomena such as extinctions, invasions, and resilience. To stimulate new research, we present methods for performing discontinuity analysis, detail outstanding knowledge gaps, and discuss potential approaches for addressing these gaps.

Nguyen, T.D., P. Thupaki, E.J. ANDERSON, and M.S. Phanikumar. Summer circulation and exchange in the Saginaw Bay-Lake Huron system. Journal of Geophysical Research: Oceans 119:2713-2734 (DOI:10.1002/2014JC009828.) (2014).

We use a three-dimensional, unstructured grid hydrodynamic model to examine circulation and exchange in the Saginaw Bay-Lake Huron system during the summer months for three consecutive years (2009–2011). The model was tested against ADCP observations of currents, data from a Lagrangian drifter experiment in the Saginaw Bay, and temperature data from the National Data Buoy Center stations. Mean circulation was predominantly cyclonic in the main basin of Lake Huron with current speeds in the surface layer being highest in August. Circulation in the Saginaw Bay was characterized by the presence of an anticyclonic gyre at the mouth of the outer bay and two recirculating cells within the inner bay. New estimates are provided for the mean flushing times (computed as the volume of the bay divided by the rate of inflow) and residence times (computed as e-folding flushing times based on dye concentration modeling treating the bay as a continuously stirred tank reactor) for Saginaw Bay. The average flushing time (over the 3 months of summer and for all 3 years) was 23.0 days for the inner bay and 9.9 days for the entire bay. The mean e-folding flushing time was 62 days (2 months) for the inner bay and 115 days (3.7 months) for the entire bay for the summer conditions examined in this work. To characterize the behavior of river plumes in the inner Saginaw Bay, trajectory data from GPS-enabled Lagrangian drifters were used to compute the absolute diffusivity values in the alongshore and cross-shore directions.

OBENOUR, D.R., A.D. GRONEWOLD, C.A. STOW, and D. Scavia. Using a Bayesian hierarchical model to improve Lake Erie cyanobacterial bloom forecasts. Water Resources Research 50:14 pp. (DOI:10.1002/2014WR015616) (2014).

The last decade has seen a dramatic increase in the size of western Lake Erie cyanobacteria blooms, renewing concerns over phosphorus loading, a common driver of freshwater productivity. However, there is considerable uncertainty in the phosphorus load-bloom relationship, because of other biophysical factors that influence bloom size, and because the observed bloom size is not necessarily the true bloom size, owing to measurement error. In this study, we address these uncertainties by relating late summer bloom observations to spring phosphorus load within a Bayesian modeling framework. This flexible framework allows us to evaluate three different forms of the load-bloom relationship, each with a particular combination of statistical error distribution and response transformation. We find that a novel implementation of a gamma error distribution, along with an untransformed response, results in a model with relatively high predictive skill and realistic uncertainty characterization, when compared to models based on more common statistical formulations. Our results also underscore the benefits of a hierarchical approach that enables assimilation of multiple sets of bloom observations within the calibration processes, allowing for more thorough uncertainty quantification and explicit differentiation between measurement and model error. Finally, in addition to phosphorus loading, the model includes a temporal trend component indicating that Lake Erie has become increasingly susceptible to large cyanobacteria blooms over the study period (2002–2013). Results suggest that current phosphorus loading targets will be insufficient for reducing the intensity of cyanobacteria blooms to desired levels, so long as the lake remains in a heightened state of bloom susceptibility

Overland, J.E., J. WANG, R.S. Pickart, and M. Wang. Chapter 2. Recent and future changes in the meteorology of the Pacific Arctic. In The Pacific Arctic Region: Ecosystem Status and Trends in a Rapidly Changing Environment. J.M. Grebmeier and W. Maslowski (Eds.). Springer Science+Business Media, Dordrecht, 17-30 pp. (DOI:10.1007/978-94-017-8863-2_2) (2014).

The meteorology of the Pacific Arctic (the Bering Sea through the Chukchi and southern Beaufort Seas) represents the transition zone between the moist and relatively warm maritime air mass of the Pacific Ocean to the cold and relatively dry air mass of the Arctic. The annual cycle is the dominant feature shifting from near total darkness with extensive sea ice cover in winter to solar heating in summer that is equal to that of sub-tropic latitudes. Strong north-south gradients in air temperatures and sea level pressure are typical over the Pacific Arctic giving rise to climatological polar easterly winds (blowing from the east) throughout the year. Localized storms (regions of low sea level pressure) can propagate into the region from the south but high pressure regions are typical, connected to either northeastern Siberia or the southern Beaufort Sea. The northern portion of the Pacific Arctic has participated in the general Arctic-wide warming in all seasons over the last decade while the southern Bering Sea turned to near record cold temperatures after 2006. Future climate changes in the Pacific Arctic will come from shifts in the timing and extent of seasonal sea ice. Based on climate model projections, cold and dark conditions will still dominate over a climate warming scenario of +2° C by 2050. The northern Bering Sea will continue to have extensive sea ice through April, while the southern shelf will have on average less sea ice than currently observed but with large interannual variability. The largest change has the southern Chukchi Sea shifting from being sea ice free in September and October to becoming sea ice free from July through November within a decade or two, impacting shipping, oil exploration, and ecosystems.

POTHOVEN, S.A., and G.L. Fahnenstiel. Declines in the energy content of yearling non-native alewife associated with lower food web changes in Lake Michigan. Fisheries Management and Ecology 21:439-447 (DOI:10.1111/fme.12092) (2014).

Juveniles of non-native alewife, Alosa pseudoharengus (Wilson), were collected in Lake Michigan in 1998, 1999, 2010, 2011 and 2013 to evaluate changes in energy content during a period of major ecosystem changes. Consistent with historical data, energy content of yearling alewife declined from late winter into late spring and was at its lowest point in June. Energy density and length-adjusted, entire-body energy were lower in 2010, 2011 and 2013 than in 1998 and 1999. Energy losses over the first winter in the lake were more severe for the 2010 year class (56% decrease) than for the 1998 year class (28% decrease). Alewife diets in late spring of 2010–2013 reflected the loss of major prey such as Diporeia spp. and a shift towards lower energy prey. The recent decline in energy content of yearling alewife can be linked to recent changes in productivity and abundance of key components of the lower food web of Lake Michigan following the dreissenid invasion.

POTHOVEN, S.A., and T.O. Hook. Predatory demands of Bythotrephes and Leptodora in Saginaw Bay, Lake Huron. Journal of Great Lakes Research 40(Supplement 1):106-112 (DOI:10.1016/j.jglr.2013.07.005) (2014).

Predatory invertebrates can be amajor factor in structuring zooplankton communities.We collected zooplankton and the predatory cladocerans Bythotrephes longimanus and Leptodora kindtii at 4 stations in inner Saginaw Bay, Lake Huron during May–October 2009 and April–November 2010. Production of zooplankton prey was estimated using temperature and biomass based empirical models. Population consumption rates of Bythotrephes and Leptodora were estimated using a combination of conversion efficiency, bioenergetics and experimental based models. Bythotrephes biomass peaked in July of 2009 and 2010, and in 2010, the biomass rebounded in the fall after a late summer decline. Leptodora biomass was generally lower than that of Bythotrephes except in June 2009 and August 2010. Zooplankton biomass, production and composition showed strong seasonal patterns, with biomass more than tripling between May and June each year, largely due to an increase in biomass of Daphnia in June. By contrast, total zooplankton biomass declined by over 70% between June and July owing to declines in Daphnia biomass. Population consumption by predatory cladocerans was a large percentage or even exceeded prey production during July and August in Saginaw Bay regardless of which consumption models were used. This short term (b2 months) but pronounced predation capacity of predatory cladocerans in Saginaw Bay was mainly due to consumption by Bythotrephes rather than Leptodora. Bythotrephes likely play an important role in food web function and should be accounted for when evaluating the flow of energy within the Laurentian Great Lakes systems.

POTHOVEN, S.A., T.O. Hook, and C.R. Roswell. Feeding ecology of age-0 lake whitefish in Saginaw Bay, Lake Huron. Journal of Great Lakes Research 40(Supplement 1):148-155 (DOI:10.1016/j.jglr.2013.09.016) (2014).

Age-0 lake whitefish Coregonus clupeaformis (11–160 mm total length) were collected from Saginaw Bay, Lake Huron during April–November 2009 and 2010 for diet analysis and for the evaluation of ontogenetic changes in feeding ecology. Lake whitefish ≤ 50 mm ate mainly zooplankton, after which their diets switched mainly to benthic macroinvertebrates. Cyclopoida were the dominant prey consumed by very small lake whitefish (b17 mm) and the most frequently selected zooplankton type for individual small fish. Once lake whitefish reached 18–19 mm, Cyclopoida in the diet declined and cladocerans emerged as an important diet item. Daphnia were the most common cladoceran in the diets, but for fish 31–50 mm Bosminidae were also relatively important. Although the shift to Daphnia could represent an ontogenetic point when lake whitefish were large enough to effectively handle this prey, it also took place when the relative availability of Daphnia increased. Once lake  whitefish were N50 mm, Chironomidae larvae became a dominant prey item and this shift to benthivory coincided with a 55% increase in length-adjusted energy content between June and July. However, as fish grew (around 110–120 mm), Sphaeriidae and the benthic zooplankton Chydoridae became increasingly important in the diet. As these less energetically rich prey were incorporated into the diet, there were corresponding 21 and 15% decreases in length-adjusted energy content from July to August and September, respectively.

POTHOVEN, S.A., T.O. Hook, and C.R. Roswell. Energy content of young yellow perch and walleye in Saginaw Bay, Lake Huron. Journal of Great Lakes Research 40(Supplement 1):133-138 (DOI:10.1016/j.jglr.2013.10.002) (2014).

We evaluated seasonal energy content of age-0 yellow perch Perca flavescens and walleye Sander vitreus in Saginaw Bay, Lake Huron in 2009 and 2010. We also determined the energy content of age-1 fish from the 2009 and 2010 cohorts the following spring (i.e., for fish that had survived one winter) to evaluate overwinter energy losses. As expected, larger fish within each species had disproportionately higher energy content (i.e., slope relating length and energy N3.0) than smaller conspecifics. By contrast to expectations, allometric slopes were N3.0 in nearly all months, not just the fall, and were higher for age-0 yellow perch than for walleye, even though increased allocation to growth would have seemingly been beneficial to even the largest yellow perch during summer. Seasonal energy allocation patterns differed between years. In 2009, length specific energy content increased from late summer to fall for both species. However, for the 2010 cohorts of fish, length specific energy content decreased between late summer and fall for yellow perch and did not change for walleye. There were 13–17% overwinter declines in length specific energy content between the fall (October or November) and the spring (May) with no major differences between cohorts within a species or between species for a given year. Because young yellow perch and walleye are similar physiologically but differ in size (i.e., yellow perch are smaller), it is possible that overwinter energy losses are more important for yellow perch than for walleye.

ROCKWELL, D.C., S.J. JOSHI, and H. Wirick. Beach health information needs assessment: 9 years later -- results from follow-up survey. NOAA Technical Memorandum GLERL-163. NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI (2014).

The Beach Health Interagency Coordination Team (BHICT) representing NOAA, USGS, USEPA, and the Centers for Disease Control (CDC) developed a survey for distribution to determine issues important to beach managers. The survey was distributed during Fall 2013 (August 28 to November 8). Responses were obtained when it was believed that federal funding from the BEACH Act would no longer be available. This survey is a follow-up to the Beach Health Research Needs Workshop held during the fall of 2005 at the Great Lakes Beach Association Conference in Green Bay (GLBA et. al. 2006, NOAA Technical Memorandum GLERL-138). The purpose of the survey is to assist BHICT member agencies in prioritizing their beach program based on input from the respondents on information, data, and tools they need to more effectively manage recreational water quality and beach health issues.

Roswell, C.R., S.A. POTHOVEN, and T.O. Hook. Patterns of age-0 yellow perch growth, diets, and mortality in Saginaw Bay, Lake Huron. Journal of Great Lakes Research 40(Supplement 1):123-132 (DOI:10.1016/j.jglr.2014.01.008) (2014).

Identifying mechanisms influencing early-life survival may elucidate recruitment variability of fish populations. Yellow perch (Perca flavescens), are economically and ecologically important in Saginaw Bay, Lake Huron, but have recently experienced low recruitment despite strong production of age-0 fish. Recent year classes have been characterized by slow first-year growth, as indexed by fall size of age-0 yellow perch; however, seasonal growth patterns and accompanying diet and survivorship patterns have not been documented for age-0 yellow perch in Saginaw Bay. To this end, we collected age-0 yellow perch weekly (larvae) and monthly (juveniles) throughout the first year of life during 2009 and 2010 to track changes in growth and diet composition. We also evaluated predation and over-winter energy-loss as potential mechanisms of size-selective mortality. Yellow perch growth, energy accumulation and size-specific condition decreased during late summer and fall. During larval and juvenile stages, predominant components of yellow perch diets transitioned from copepods to Daphnia and other zooplankton; however, we observed only weak ontogenetic shifts toward benthic prey. Smaller yellow perch a) were preferentially preyed upon by walleye (the bay's main piscivore) and b) displayed lower mass-specific energy content, potentially increasing overwinter starvation risk, suggesting that slow growth increases mortality risk. Our results are consistent with the hypothesis that recruitment dynamics are influenced by an interplay of size-selective mortality and diet-induced reductions in growth.

Rucinski, D.K., J.V. DePinto, D. Scavia, and D. BELETSKY. Modeling Lake Erie's hypoxia response to nutrient loads and physical variability. Journal of Great Lakes Research 40:11 pp. (DOI:10.1016/j.jglr.2014.02.003) (2014).

A 1-dimensional, linked hydrodynamic and eutrophication model was developed and calibrated with 19 years of observations (1987–2005) for the summer stratification period in the central basin of Lake Erie, corroborated by comparison with observed process rates and areal hypoxic extents, and confirmed with observations from the 1960s and 1970s. The model effectively captures observations of both vertical and temporal trends in dissolved oxygen, as well as temporal trends in chlorophyll-a, phosphorus, zooplankton biomass, and several key processes. The model was used to develop a relationship between external phosphorus load and hypolimnion oxygen conditions, and then to establish load–response envelopes that account for inter-annual variability in physical conditions driven by variation in meteorological drivers. The curves provide a valuable tool for reassessing phosphorus loading targets with respect to reducing hypoxia in Lake Erie.

Scavia, D., J.D. Allan, K.K. Arend, S. Bartell, D. BELETSKY, N.S. Bosch, S.B. Brandt, R.D. Briland, I. Daloglu, J.V. DePinto, D.M. Dolan, M.A. Evans, T.M. Farmer, D. Goto, H. Han, T.O. Hook, R. Knight, S.A. Ludsin, D.M. MASON, A.M. Michalak, R.P. Richards, J.J. Roberts, D.K. Rucinski, E.S. RUTHERFORD, D.J. SCHWAB, T. Sesterhenn, H. ZHANG, and Y. Zhou. Assessing and addressing the re-eutrophication of Lake Erie: Central basin hypoxia. Journal of Great Lakes Research 40:226-246 (DOI:10.1016/j.jglr.2014.02.004) (2014).

Relieving phosphorus loading is a key management tool for controlling Lake Erie eutrophication. During the 1960s and 1970s, increased phosphorus inputs degraded water quality and reduced central basin hypolimnetic oxygen levels which, in turn, eliminated thermal habitat vital to cold-water organisms and contributed to the extirpation of important benthic macroinvertebrate prey species for fishes. In response to load reductions initiated in 1972, Lake Erie responded quickly with reduced water-column phosphorus concentrations, phytoplankton biomass, and bottom-water hypoxia (dissolved oxygen b2 mg/l). Since the mid-1990s, cyanobacteria blooms increased and extensive hypoxia and benthic algae returned. We synthesize recent research leading to guidance for addressing this re-eutrophication, with particular emphasis on central basin hypoxia. We document recent trends in key eutrophication-related properties, assess their likely ecological impacts, and develop load response curves to guide revised hypoxia-based loading targets called for in the 2012 Great Lakes Water Quality Agreement. Reducing central basin hypoxic area to levels observed in the early 1990s (ca. 2000 km2) requires cutting total phosphorus loads by 46% from the 2003–2011 average or reducing dissolved reactive phosphorus loads by 78% from the 2005–2011 average. Reductions to these levels are also protective of fish habitat. We provide potential approaches for achieving those new loading targets, and suggest that recent load reduction recommendations focused on western basin cyanobacteria blooms may not be sufficient to reduce central basin hypoxia to 2000 km2.

Schloesser, D.W., J.A. ROBBINS, G.A. Matisoff, T.F. NALEPA, and N. MOREHEAD. A 200-year chronology of burrowing mayflies (Hexagenia spp.) in Saginaw Bay. Journal of Great Lakes Research 40(1):80-91 (DOI:10.1016/j.jglr.2013.12.016) (2014).

After an absence of 50 years, burrowing mayflies (Hexagenia spp.) colonized western Lake Erie which led to interest in whether this fauna can be used to measure recovery in nearshore waters throughout the Great Lakes. However, in many areas we do not know if mayflies were native/endemic and thus, whether recovery is a logical measure to assess progress of recovery. In the present study, we construct a chronologic record of relative abundance of burrowing mayflies in Saginaw Bay by the use of mayfly tusks and radionuclides in sediments (i.e., a paleoecologic record) and historic records of mayfly nymphs in the bay. These records reveal that mayflies: (1) were few before 1799, which indicates that nymphs were probably native/endemic in the bay, (2) increased between 1799 and 1807 and remained at relatively high levels between 1807 and 1965, probably in response to increased nutrient run-off from the watershed, (3) declined dramatically between 1965 and 1973, probably as a result of excessive eutrophication in the mid-1950s; and, (4) were few and highly variable between 1973 and 2001, probably as a result of low and unstable abundances of mayfly nymphs. Historic records verify that nymphs disappeared in the bay in the late-1950s to early-1960s which is in agreement with the paleoecologic record. Reoccurrence of low abundances of nymphs in the bay between 1991 and 2008 and comparison of chronologic records of nymphs in Saginaw Bay and western Lake Erie suggest that mayflies may return to Saginaw Bay in the early-21st century. Undoubtedly, watershed conservation and three decades of pollution abatement have set the stage for a recovery of burrowing mayflies in Saginaw Bay, and possibly in other areas of the Great Lakes.

Sesterhenn, T.M., C.R. Roswell, S.R. Stein, P. Klaver, E. Verhamme, S.A. POTHOVEN, and T.O. Hook. Modeling the implications of multiple hatching sites for larval dynamics in the resurgent Saginaw Bay walleye population. Journal of Great Lakes Research 40(Supplement 1):113-122 (DOI:10.1016/j.jglr.2013.09.022) (2014).

The early life environment experienced by most larval fish is largely dependent on a combination of hatch site and water currents. Until larvae are able to swim fast enough to overcome currents, they are largely passively transported and have limited control over ambient environmental conditions, including temperature and prey availability. These factors strongly influence growth and survival of larvae, with direct consequences for subsequent recruitment. Early life survival of Saginaw Bay walleye was formerly limited by alewife predation on larvae; but following the collapse of Lake Huron alewives, the walleye population has rebounded and recruitment success may now be influenced by other factors including spawning habitat. We sought to assess the implications of successful hatching at multiple locations in Saginaw Bay, using a hydrodynamics model, particle transport model, and an individual-based bioenergetics model in series. Model results were compared to locations of young larvae collected in Saginaw Bay during 2009–2010. Results suggest that larval growth is strongly influenced by hatch date, driven by seasonal variation in temperature between sites. Larvae hatched at any location could be transported extensively within inner Saginaw Bay before reaching a sufficient size to swim independently of currents, and retention within the productive inner bay varied among years and sites. Our results indicate multiple larval walleye origins in the field, augmenting the continued production from the Saginaw River system. Successful hatching at more locations would serve to buffer walleye recruitment variation through portfolio effects, supporting arguments for more emphasis on diverse spawning habitat management and restoration.

Soranno, P.A., K.S. Cheruvelil, E. Bissell, M.T. Bremigan, J.A. Downing, C.E. Fergus, C. Filstrup, E.N. Henry, N.R. Lottig, E.H. Stanley, C.A. STOW, P.-N. Tan, T. Wagner, and K.E. Webster. Cross-scale interactions: Quantifying multi-scaled cause-effect relationships in macrosystems. Frontiers in Ecology and the Environment 12(1):65-73 (DOI:10.1890/120366) (2014).

Ecologists are increasingly discovering that ecological processes are made up of components that are multiscaled in space and time. Some of the most complex of these processes are cross-scale interactions (CSIs), which occur when components interact across scales. When undetected, such interactions may cause errors in extrapolation from one region to another. CSIs, particularly those that include a regional scaled component, have not been systematically investigated or even reported because of the challenges of acquiring data at sufficiently broad spatial extents. We present an approach for quantifying CSIs and apply it to a case study investigating one such interaction, between local and regional scaled land-use drivers of lake phosphorus. Ultimately, our approach for investigating CSIs can serve as a basis for efforts to understand a wide variety of multi-scaled problems such as climate change, land-use/land-cover change, and invasive species.

Staton, J.M., C.R. Roswell, D.G. Fielder, M.V. Thomas, S.A. POTHOVEN, and T.O. Hook. Condition and diet of yellow perch in Saginaw Bay, Lake Huron (1970-2011). Journal of Great Lakes Research 40(Supplement 1):139-147 (DOI:10.1016/j.jglr.2014.02.021) (2014).

In Saginaw Bay, Lake Huron, yellow perch (Perca flavescens) constitute an ecologically important component of the ecosystem and support both recreational and commercial fisheries. Over the past 40 years, Saginaw Bay has experienced multiple ecosystem-level changes (e.g., non-indigenous species introductions, reduced nutrient loading and variable temperatures). In turn, abundances and growth rates of yellow perch and their predators and prey have fluctuated. Recent changes to Saginaw Bay and Lake Huron foodwebs have potential to influence prey composition and subsequently, growth and condition for yellow perch; but a complete description of yellow perch diet composition across seasons has not been undertaken in recent years. We calculated mean relative weight (Wr), an index of condition, of age-1 and older yellow perch in Saginaw Bay annually for 1970–2011. We found high interannual variation in condition and documented low meanWr during 1978–1991.We developed regression models to explain this variation using phosphorus load, temperature, forage fish density, and yellow perch density as potential explanatory factors. Patterns of Wr were associated with changes in yellow perch densities, although interannual variation was not significantly associated with any of the available explanatory variables. Diet analysis of yellow perch collected in 2009 and 2010 demonstrated that age-1 and older yellow perch consumed a fundamentally different diet from a previous study (1986–1988), exhibiting a greater reliance on non-indigenous prey (e.g. Bythotrephes longimanus).

STOW, C.A. The news from Saginaw Bay: Where the mussels are strong, the walleye are good-looking, and all the phosphorus is above average. Journal of Great Lakes Research 40(Supplement 1):1-3 (DOI:10.1016/j.jglr.2014.04.006) (2014).

Saginaw Bay has experienced some ups and downs since “Saginaw Michigan” was a hit song for Lefty Frizzell in 1964. By the 1960s the cumulative impact of years of anthropogenic stressors had taken its toll on the fishery and the ecosystem supporting it. The Bay was suffering from numerous water quality impairments including eutrophication, nuisance beach deposits (aka “muck”), and taste and odor problems at the drinking water intakes. A growing recognition of the loss of Saginaw Bay's ecosystem services, as they have since come to be called, helped catalyze a series of mitigation actions. In 1972 the US Congress passed the Clean Water Act which established defined water quality goals and began the process of regulating point and non-point discharges. The 1978 Great Lakes Water Quality Agreement set target total phosphorus loads for the Great Lakes, including a 440 MT/year target specific to Saginaw Bay, and a goal that the Bay should attain a mesotrophic state. Modeling efforts to support these developments established a template for subsequent efforts under the Clean Water Act, and the target loads became the prototype for what we now call TMDLs (Total Maximum Daily Loads). Initial assessments in the 1980s documented improvements in eutrophication-related water quality symptoms (Bierman et al., 1984); but then, attention was diverted to issues associated with toxic contaminants and nutrient monitoring lapsed.

STOW, C.A., Y.K. CHA, and S.S. Qian. A Bayesian hierarchical model to guide development and evaluation of substance objectives under the 2012 Great Lakes Water Quality Agreement. Journal of Great Lakes Research 40(Supplement 3)):49-55d (DOI:10.1016/j.jglr.2014.07.005) (2014).

Under the 2012 Great Lakes Water Quality Agreement Canada and the United States are obliged to develop target concentrations for water quality constituents of particular concern. These “substance objectives” are closely analogous to numerical criteria under the US Clean Water Act. To develop effective substance objectives, it is important to consider how compliance with these objectives will be evaluated. Total phosphorus concentrations, for example, vary temporally and spatially, thus sample-based statistics will always be uncertain measures of the “true” underlying population characteristic. Using data from Saginaw Bay in Lake Huron, we develop a Bayesian hierarchical model that can be used to evaluate compliance with target concentrations on a temporally and spatially explicit basis. The “confidence of compliance” with targets can be assessed from the variance of the model parameter posterior distributions. This approach allows data to be grouped to represent spatial and temporal domains of particular interest, such as spring mean conditions in a certain area, and facilitates “partial pooling” of information so that regions with sparse data and high uncertainty can “borrow information” from more data-rich areas.

STOW, C.A., J. DYBLE, D.R. Kashian, T.H. JOHENGEN, K.P. Winslow, S.D. Peacor, S.N. Francoeur, A.M. BURTNER, D. PALLADINO, N. MOREHEAD, D.C. GOSSIAUX, Y.K. CHA, S.S. Qian, and D. Miller. Phosphorus targets and eutrophication objectives in Saginaw Bay: A 35-year assessment. Journal of Great Lakes Research 40(Supplement 1):4-10 (DOI:10.1016/j.jglr.2013.10.003) (2014).

An aggregated view of total phosphorus and chlorophyll a in Saginaw Bay indicates that concentrations of both constituents declined approximately in concert with declining total phosphorus (P) loads stabilizing by the late 1980s. A more spatially focused view reveals that total phosphorus declines outside of the Saginaw River plume, accompanied by more subtle chlorophyll a decreases. In contrast, soluble reactive phosphorus and ammonia have recently declined throughout the bay, while nitrate has remained relatively stable. Concentration data from nearshore transects do not exhibit large differences from open-water sample sites. The 440 tonne P/year target phosphorus load established in the 1978 amendments to the Great Lakes Water Quality Agreement has almost never been met, and total phosphorus concentrations regularly exceed the 15 μg/L concentration objective proposed in documentation supporting the 1978 amendments. Seasonal patterns in both total phosphorus and chlorophyll a are more pronounced in the most recent data, with peaks occurring in September–October. This apparently evolving seasonal pattern may result from seasonal changes in Saginaw River flow inputs, or seasonal variation in dreissenid mussel feeding and filtration rates. The adaptive management framework stipulated in the 2012 Great Lakes Water Quality Protocol should promote better monitoring of Saginaw Bay water quality into the future, with enhanced opportunities to better understand the factors that have maintained ongoing eutrophication symptoms.

STURTEVANT, R.A., J. LARSON, L. BERENT, M. McCARTHY, A. BOGDANOFF, A. Fusaro, and E.S. RUTHERFORD. An impact assessment of Great Lakes aquatic nonindigenous species. NOAA Technical Memorandum GLERL-161. NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 1022 pp. (2014).

This purpose of this study is to provide a baseline assessment of realized, potential, and unknown impacts for established nonindigenous species in the Great Lakes. An organism impact assessment (OIA) tool was developed in order to analyze the extent of each species’ impact in a standardized manner. Following a thorough literature review, the OIA was used to rank the environmental impact, socio-economic impact, and beneficial effect of each species as high, moderate, low, or unknown. Importantly, this ranking system provides a method of identifying and comparing impacts across taxa and type of impact.

TANG, H., H.A. VANDERPLOEG, T.H. JOHENGEN, and J.R. LIEBIG. Quagga mussel (Dreissena rostriformis bugensis) selective feeding of phytoplankton in Saginaw Bay. Journal of Great Lakes Research 40(Supplement 1):83-94 (DOI:10.1016/j.jglr.2013.11.011) (2014).

Experiments from May to December measuring selective grazing and egestion of different phytoplankton taxa in natural Saginaw Bay (Lake Huron) seston by shallow-water morph quagga mussels (Dreissena bugensis rostriformis) showed that the mussels were highly selective filter feeders and that their net clearance rates on different species ranged widely, resulting in food consumption that was strongly driven by seasonal phytoplankton dynamics. Overall, net clearance rates by quagga mussels on the entire phytoplankton assemblage were similar to those observed for zebra mussels (Dreissena polymorpha) during the 1990s. Phytoplankton taxon, rather than size, was more important to food selection since quagga mussels cleared similar sized but different species of algae at very different rates. In contrast to many studies with zebra mussels, larger-sized algae such as Dinobryon divergens, Aulacoseira italica, Fragilaria crotonensis, and Anabaena were cleared at high rates and rejected at lower rates than many smaller species within the same broad taxonomic group. We suspect that these differences between dreissenid species do not stem from species differences but methodological factors and phytoplankton composition of systems studied. Small-sized diatoms, green algae with thick cell walls (Scenedesmus and Oocystis), and colonial cyanobacteria with gelatinous sheaths (Aphanocapsa, Chroococcus, and Microcystis) were cleared at low rates and rejected in high proportion in pseudofeces or feces during all seasons. We describe the likely mechanisms of pre- and post-ingestive behavior that explain these differences, which relate to phytoplankton size, morphology, cell wall characteristics, and chemical composition. Changes in the Great Lakes phytoplankton communities are consistent with mussel grazing preferences.

VanCleave, K., J. Lenters, J. WANG, and E. Verhamme. A regime shift in Lake Superior ice cover, evaporation, and water temperature following the warm El Nino winter of 1997-98. Limnology and Oceanography 59(6):1889-1898 (DOI:10.4319/lo.2014.59.6.1889) (2014).

Significant trends in Lake Superior water temperature and ice cover have been observed in recent decades, and these trends have typically been analyzed using standard linear regression techniques. Although the linear trends are statistically significant and contribute to an understanding of environmental change, a careful examination of the trends shows important nonlinearities. We identify a pronounced step change that occurred in Lake Superior following the warm El Nin˜o winter of 1997–1998, resulting in a ‘‘regime shift’’ in summer evaporation rate, water temperature, and numerous metrics of winter ice cover. This statistically significant step change accounts for most of the long-term trends in ice cover, water temperature, and evaporation during the period 1973–2010, and it was preceded (and followed) by insignificant linear trends in nearly all of the metrics examined. The 1998 step change is associated with a decrease in winter ice duration of 39 d (a 34% decline), an increase of , 2–3uC in mean surface water temperature (July–September averages), and a 91% increase in July–August evaporation rates, reflecting an earlier start to the summer evaporation season. Maximum wintertime ice extent decreased by nearly a factor of two, from an average of 69% of the lake surface area (before 1997–1998) to 36% after the step change. This reassessment of long-term trends highlights the importance of nonlinear regime shifts such as the 1997–1998 break point—an event that may be related to a similar shift in the Pacific Decadal Oscillation that occurred around the same time. These pronounced changes in Lake Superior physical characteristics are likely to have important implications for the broader lake ecosystem.

WANG, J., X. BAI, J.F. BRATTON, B. Wu, and C.H. Greene. Accelerating Arctic summer sea ice decline driven by the dipole anomaly. Proceedings, 22nd IAHR International Symposium on Ice 2014, Singapore, August 11-15, 2014. International Association of Hydro-Environment Engineering and Research, 745-742 pp. (2014).

Since the beginning of the satellite era (1979), record lows and highs of Arctic summer sea ice extent are found to be caused not only by dynamically-forced meridional wind advection, but also by the intensified ice/ocean albedo feedback, both of which are triggered by the Arctic atmospheric Dipole Anomaly (DA) pattern. This local, secondary mode of anomalous sea-level pressure (SLP) in the Arctic produces a strong anomalous meridional wind, which was responsible for driving more sea ice out of the Arctic Ocean from the western to the eastern Arctic into the northern Atlantic during the summers of 1995, 1999, 2002, 2005, and 2007-2012 during its positive phase. In September of 2012, a new record minimum in Arctic sea ice extent was caused by the combined dynamic wind forcing of +DA and thermodynamic forcing, accelerating melting, and advective loss of Arctic sea ice. Sea ice extent in August 2012 exceeded the previous record low of September 2007, occurring one month earlier in the summer season. In addition, high summer sea ice extent was associated with the –DA dynamic wind forcing and +AO’s divergence effect. A new feedback mechanism for the Pacific Arctic region’s atmosphere-ice-ocean climate system is hypothesized to be responsible for the accelerating decline of Arctic summer sea ice. In this hypothesis, the DA provides an intermittent, pulse-like forcing to the system, directly driving sea ice loss by wind forcing and enhancing northward transport of warm Pacific water, and indirectly driving its loss through thermal melting associated with positive ice/ocean albedo feedback and negative ice/cloud feedback. These processes contributed to a series of summer ice minima, particularly occurring since 1995, in which the +DA was associated with accelerating the Transpolar Drift Stream and sea ice export, and amplifying the melting of sea ice.

WANG, J., X. BAI, A. FUJISAKI-MANOME, H. HU, and D. BELETSKY. Great Lakes ice and climate research and forecast. Proceedings, 22nd IAHR International Symposium on Ice 2014, Singapore, August 11-15, 2014. International Association of Hydro-Environment Engineering and Research, 48-55 pp. (2014).

This paper describes recent progress made by a team from the NOAA Great Lakes Environmental Research Laboratory (GLERL) and the University of Michigan (UMich) Cooperative Institute for Limnology and Ecosystems Research (CILER). Over the past six years (since 2007), this team has studied Great Lakes ice and regional climate in response to global climate changes and how to transfer scientific research results into predictions of lake ice on the scales of several days to several months. The Great Lakes are located at the edge of the action centers of the North Atlantic Oscillation (NAO) and the nodal points of the action centers of the Pacific-North America (PNA) pattern. Aloft, there exists a strong highly-fluctuating annual south-north displacement of the westerly jet. Great Lakes ice responds linearly to the NAO and nonlinearly (quadratically) to the El Niño and South Oscillation (ENSO or Nino3.4). As a result, both NAO and ENSO have impacts on lake ice, but neither of them solely dominates the Great Lakes regional climate and lake ice cover. The combined effects of both NAO and ENSO on lake ice provide high predictability skills using statistical regression models. For the first time, fully-coupled Great Lakes Ice-circulation Models (GLIM) with both dynamics and thermodynamics have been developed at GLERL/CILER to simulate and investigate the lake ice variations on the synoptic, seasonal, interannual, and decadal time scales. The hindcast results were validated using in situ, airborne, and satellite measurements for various periods. The validated GLIM has been used since the 2010-2011 ice season to forecast Great Lakes ice cover concentration, thickness, velocity, and associated air-ice-sea variables for up to five days in advance.

WANG, J., H. Eicken, Y. Yu, X. BAI, J. Zhang, H. HU, D.R. Wang, M. Ikeda, K. Mizobata, and J. Overland. Chapter 4. Abrupt climate changes and emerging ice-ocean processes in the Pacific Arctic region and the Bering Sea. In The Pacific Arctic Region: Ecosystem Status and Trends in a Rapidly Changing Environment. J.M. Grebmeier and W. Maslowski (Eds.). Springer Science+Business Media, Dordrecht, 65-99 pp. (DOI:10.1007/978-94-017-8863-2_4) (2014).

The purpose of this chapter is to reveal several emerging physical ice-ocean processes associated with the unprecedented sea ice retreat in the Pacific Arctic region (PAR). These processes are closely interconnected under the scenario of diminishing sea ice, resulting in many detectable changes from physical environment to ecosystems. Some of these changes are unprecedented and have drawn the attention of both scientific and societal communities. More importantly, some mechanisms responsible for the diminishing sea ice cannot be explained by the leading Arctic Oscillation (AO), which has been used to interpret most of the changes in the Arctic for the last several decades. The new challenging questions are: (1) What is the major forcing? (2) Is the AO, the DA, or their combination, contributing to the sea ice minima in recent years? How do we use models to investigate the recent changes in the PAR. Is the heat transport through the Bering Strait associated with the DA? What processes accelerate sea ice melting in the PAR?

WANG, J., K. Mizobata, X. BAI, H. HU, M. Jin, Y. Yu, M. Ikeda, W. Johnson, W. Perie, and A. FUJISAKI. A modeling study of coastal circulation and landfast ice in the nearshore Beaufort and Chukchi Seas using CIOM. Journal of Geophysical Research: Oceans 19(6):3285-3312 (DOI:10.1002/2013JC009258) (2014).

This study investigates sea ice and ocean circulation using a 3-D, 3.8 km CIOM (Coupled Ice- Ocean Model) under daily atmospheric forcing for the period 1990–2008. The CIOM was validated using both in situ observations and satellite measurements. The CIOM successfully reproduces some observed dynamical processes in the region, including the Bering-inflow-originated coastal current that splits into three branches: Alaska Coastal Water (ACW), Central Channel branch, and Herald Valley branch. In addition, the Beaufort Slope Current (BSC), the Beaufort Gyre, the East Siberian Current (ESC), mesoscale eddies, and seasonal landfast ice are well simulated. The CIOM also reproduces reasonable interannual variability in sea ice, such as landfast ice, and anomalous open water (less sea ice) during the positive Dipole Anomaly (DA) years, vice versa during the negative DA years. Sensitivity experiments were conducted with regard to the impacts of the Bering Strait inflow (heat transport), onshore wind stress, and sea ice advection on sea ice change, in particular on the landfast ice. It is found that coastal landfast ice is controlled by the following processes: wind forcing, Bering Strait inflow, and sea ice dynamics.

Wittmann, M., R. Cooke, J. Rothlisberger, E.S. RUTHERFORD, H. ZHANG, D.M. MASON, and D. Lodge. Use of structured expert judgment to forecast invasions by Bighead and Silver carp in Lake Erie. Conservation Biology:10 pp. (DOI:10.1111/cobi.12369) (2014).

Identifying which nonindigenous species will become invasive, and forecasting their damages is difficult and presents a significant problem for natural resource management. Often, the data or resources necessary for ecological risk assessment are incomplete or absent, leaving environmental decision-makers ill-equipped to effectively manage valuable natural resources. Structured expert judgment (SEJ) is a mathematical and performance-based method of eliciting, weighting and aggregating expert judgments. In contrast to other methods of expert combination where equal weights are assigned to experts, SEJ weights each expert on the basis of his or her statistical accuracy and informativeness, and can be used when the information required for decision-making is sparse or debated. We used SEJ to forecast impacts of nonindigenous Asian carp in Lake Erie, where it is believed not to be established. Experts quantified Asian carp biomass, production, consumption and the impact to four fish species if Asian carp were to become established. According to experts, Asian carp can establish in Lake Erie with the potential to achieve biomass levels that are similar to the sum of biomasses for several fishes that are harvested commercially or recreationally. However, the impact of Asian carp on the biomass of these fishes is estimated by experts to be small, with little uncertainty. Impacts in tributaries and to recreational activities, water quality or other species were not addressed. SEJ can be used to quantify key uncertainties of invasion biology and also provide a decision support tool when the necessary information for natural resource management and policy is not available.

Wu, J., A.D. GRONEWOLD, R. Rodriquez, J.R. Stewart, and M.D. Sobsey. Integrating quantitative PCR and Bayesian statistics in quantifying human adenoviruses in small volumes of source water. Science of the Total Environment 470-471:255-262 (DOI:10.1016/j.scitotenv.2013.09.026) (2014).

Rapid quantification of viral pathogens in drinking and recreational water can help reduce waterborne disease risks. For this purpose, samples in small volume (e.g. 1 L) are favored because of the convenience of collection, transportation and processing. However, the results of viral analysis are often subject to uncertainty. To overcome this limitation, we propose an approach that integrates Bayesian statistics, efficient concentration methods, and quantitative PCR (qPCR) to quantify viral pathogens in water. Using this approach, we quantified human adenoviruses (HAdVs) in eighteen samples of source water collected from six drinking water treatment plants. HAdVs were found in seven samples. In the other eleven samples, HAdVs were not detected by qPCR, but might have existed based on Bayesian inference. Our integrated approach that quantifies uncertainty provides a better understanding than conventional assessments of potential risks to public health, particularly in cases when pathogens may present a threat but cannot be detected by traditional methods.

ZHANG, H., D.M. MASON, C.A. STOW, A.T. ADAMACK, S.B. Brandt, X. Zhang, D.G. Kimmel, M.R. Roman, W.C. Boicourt, and S.A. Ludsin. Effects of hypoxia on habitat quality of pelagic planktivorous fishes in the northern Gulf of Mexico. Marine Ecology Progress Series 505:209-226 (DOI:10.3354/meps10768) (2014).

To evaluate the impact of hypoxia (<2 mg O2 l−1) on habitat quality of pelagic prey fishes in the northern Gulf of Mexico, we used a spatially explicit, bioenergetics-based growth rate potential (GRP) model to develop indices of habitat quality. Our focus was on the pelagic bay anchovy Anchoa mitchilli and Gulf menhaden Brevoortia patronus. Positive GRP was considered high-quality habitat (HQH) and negative GRP was considered low-quality habitat (LQH). Models used water temperature, dissolved oxygen (DO), zooplankton biomass, and phytoplankton concentration collected during the peak periods of hypoxia in 2003, 2004, and 2006 to estimate fish GRP. Results showed that hypoxic areas were always LQH. However, with respect to the entire water column, hypoxia had only a minor impact on overall habitat quality, with habitat quality being driven primarily by prey availability followed by water temperature. These results are in contrast to other ecosystems, such as the Chesapeake Bay, where hypoxia affects a larger fraction of the water column than in the Gulf of Mexico and has a significant impact on overall habitat quality. Differences in the effect of hypoxia on habitat quality between these 2 ecosystems suggest that the vertical extent of hypoxia relative to water column depth (i.e. hypoxic volume) is a fundamental consideration when evaluating the impacts of hypoxia on pelagic fish production.


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