GLERL Publications with Abstracts

October 2015 - September 2016

Allan, J.D., S.D.P. Smith, P.B. McIntyre, C.A. Joseph, C.E. Dickinson, A.L. Marino, R.G. Biel, J.C. Olson, P.J. Doran, E.S. RUTHERFORD, J.E. Adkins, and A.O. Adeyemo. Using cultural ecosystem services to inform restoration priorities in the Laurentian Great Lakes. Frontiers in Ecology and the Environment 13(8):418-424 (DOI:10.1890/140328) (2015).

Ecological restoration programs often attempt to maintain or enhance ecosystem services (ES), but fine-scale maps of multiple ES are rarely available to support prioritization among potential projects. Here we use agency reports, citizen science, and social media as data sources to quantify the spatial distribution of five recreational elements of cultural ES (CES) – sport fishing, recreational boating, birding, beach use, and park visitation – across North America’s Laurentian Great Lakes, where current restoration investments exceed US$1.5 billion. These recreational CES are widely yet unevenly distributed, and spatial correlations among all except park visitation indicate that many locations support multiple CES benefits. Collectively, these five service metrics correlate with tourism gross domestic product, indicating that local economies benefit from ecosystem conditions that support CES. However, locations of high recreational CES delivery are often severely affected by environmental stressors, suggesting that either ecosystem condition or human enjoyment of these recreational CES is resilient even to substantial levels of stress. Our analyses show that spatial assessments of recreational CES are an informative complement to ecosystem stress assessments for guiding large-scale restoration efforts.

ANDERSON, E.J., Bechle A. J., Wu, C.H., Schwab, D.J. Mann, G.E. and Lombardy, K.A. Reconstruction of a meteotsunami in Lake Erie on 27 May 2012: Roles of atmospheric conditions on hydrodynamic response in enclosed basins. Journal of Geophysical Research: Oceans (DOI:10.1002/2015JC010883) (2015).

On 27 May 2012, atmospheric conditions gave rise to two convective systems that generated a series of waves in the meteotsunami band on Lake Erie. The resulting waves swept three swimmers a 0.5 mi offshore, inundated a marina, and may have led to a capsized boat along the southern shoreline. Analysis of radial velocities from a nearby radar tower in combination with coastal meteorological observation indicates that the convective systems produced a series of outflow bands that were the likely atmospheric cause of the meteotsunami. In order to explain the processes that led to meteotsunami generation, we model the hydrodynamic response to three meteorological forcing scenarios: (i) the reconstructed atmospheric disturbance from radar analysis, (ii) simulated conditions from a high-resolution weather model, and (iii) interpolated meteorological conditions from the NOAA Great Lakes Coastal Forecasting System. The results reveal that the convective systems generated a series of waves incident to the southern shore of the lake that reflected toward the northern shoreline and reflected again to the southern shore, resulting in spatial wave focusing and edge wave formation that combined to impact recreational users near Cleveland, OH. This study illustrates the effects of meteotsunami development in an enclosed basin, including wave reflection, focusing, and edge wave formation as well as temporal lags between the causative atmospheric conditions and arrival of dangerous wave conditions. As a result, the ability to detect these extreme storms and predict the hydrodynamic response is crucial to reducing risk and building resilient coastal communities.

Baskaran, M., T. Novell, S.A. RUBERG, B.A. Biddanda, T.H. JOHENGEN, N. HAWLEY, and J.V. Klump. Seepage of subsurface sinkhole vent waters into Lake Huron using radium and stable isotopes of oxygen and hydrogen. Aquatic Geochemistry 22(4):349-374 (DOI:10.1007/s10498-015-9286-7) (2016).

Exchange of water between groundwater and surface water could alter water quality of the surface waters and thereby impact its ecosystem. Discharges of anoxic groundwater, with high concentrations of sulfate and chloride and low concentrations of nitrate and oxygen, from three sinkhole vents (El Cajon, Middle Island and Isolated) in Lake Huron have been recently documented. In this investigation, we collected and analyzed a suite of water samples from these three sinkhole vents and lake water samples from Lake Huron for Ra, radon-222, stable isotopes of oxygen and hydrogen, and other ancillary parameters. These measurements are among the first of their kind in this unique environment. The activities of Ra are found to be one to two orders of magnitude higher than that of the lake water. Isotopic signatures of some of the bottom lake water samples indicate evidences for micro-seeps at distances farther from these three vents. A plot of δD versus δ18O indicates that there are deviations from the Global Meteoric Line that can be attributed to mixing of different water masses and/or due to some subsurface chemical reactions. Using the Ra isotopic ratios, we estimated the transit times of the vent waters from the bottom to the top of the vent (i.e., sediment–water interface) to be 4–37 days. More systematic studies on the distribution of the radioactive and stable isotope studies are needed to evaluate the prevalence of micro-seeps in Lake Huron and other Great Lakes system.

BOLINGER, R.A., A.D. GRONEWOLD, K.A. Kompoltowicz, and L.M. Fry. Application of the NMME in the Development of a New Regional Seasonal Climate Forecast Tool. Bulletin of the American Meteorological Society (DOI:10.1175/BAMS-D-15-00107.1) (2016). (IN PRESS)

With the use of the North American Multi-Model Ensemble, a web-based tool provides useful information to users who rely on seasonal climate forecasts for their operations and decision making.

The National Oceanic and Atmospheric Administration's Climate Prediction Center (NOAA – CPC) provides access to a suite of real-time monthly climate forecasts that comprise the North American Multi-Model Ensemble (NMME), in an attempt to meet the increasing demands for monthly to seasonal climate prediction. While the North American and global map-based forecasts provided by NOAA – CPC are informative on a broad or continental scale, operational and decision-making institutions need products with a much more specific regional focus. To address this need, we developed a Region-specific Seasonal Climate Forecast tool (RSCF-NMME) by combining NMME forecasts with regional climatological data. The RSCF-NMME automatically downloads and archives data, and is displayed via a dynamic web-based graphical user interface. The tool has been applied to the Great Lakes region and utilized as part of operational water level forecasting procedures by the U.S. Army Corps of Engineers, Detroit District (USACE-Detroit). Evaluation of the tool, compared with seasonal climate forecasts released by NOAA – CPC, shows that the tool can provide additional useful information to users and overcomes some of the limitations of the NOAA – CPC forecasts. The RSCF-NMME delivers details about a specific region’s climate, verification observations, and the ability to view different model forecasts. With its successful implementation within an operational environment, the tool has proven beneficial and thus set a precedent for expansion to other regions where there is a demand for region-specific seasonal climate forecasts.

Bourdeau, P.E., K.L. Pangle, and S.D. PEACOR. Factors affecting the vertical distribution of the zooplankton assemblage in Lake Michigan: The role of the invasive predator Bythotrephes longimanus. Journal of Great Lakes Research 41(Supplement 3):115-124 (DOI:10.1016/j.jglr.2015.09.017) (2015).

We analyze six years of survey data in Lake Michigan, which spanned large ranges in the abundance of the invasive predatory cladoceran Bythotrephes, to quantify the effect of this predator on the daytime vertical distribution of the nine most common species and life stages of Lake Michigan zooplankton. We found that Bythotrephes abundance and hypolimnion depth explained almost 50% of the variation in the vertical distribution of many zooplankton. Bythotrephes abundance was associated with significant and large (approximately 5–11 m) depth increases in cladocerans Daphnia and Bosmina, adult and copepodite stages of cyclopoid copepods, and adult diaptomid copepods Leptodiaptomus minutus, and Leptodiaptomus ashlandi; but did not significantly affect the depth of copepod nauplii, diaptomid copepodites, and adult Leptodiaptomus sicilis.Whereas other environmental factors, such as light attenuation coefficient, epilimnion and hypolimnion temperature, and sampling date significantly influenced the depth of various species and life stages, the inclusion of such environmental factors into linear models did not significantly lower the predicted influence of Bythotrephes. These results suggest that Bythotrephes abundance has a significant and large influence on the vertical distribution of a large component of the zooplankton assemblage in Lake Michigan. We argue that this pattern is driven by a Bythotrephesinduced anti-predator response in zooplankton prey. Such effects could lead to widespread growth costs to the zooplankton assemblage due to the colder water temperatures experienced at greater depths, which could in turn affect the rapidly changing Lake Michigan food web.

Bullerjahn, G.S., R.M. McKay, T.W. DAVIS, D.B. Baker, G.L. Boyer, L.V. D'Anglada, G.J. Doucette, J.C. Ho, E.G. Irwin, C.L. Kling, R.M. Kudela, R. Kurmayer, A.M. Michalak, J.D. Ortiz, T.G. Otten, H.W. Paerl, B. Qin, B. Sohngen, R.P. Stumpf, P.M. Visser, and R.W. Wilhelm. Global solutions to regional problems: Collecting global expertise to address the problem of harmful cyanobacterial blooms. Harmful Algae 54:223-238 (DOI:10.1016/j.hal.2016.01.003) (2016).

In early August 2014, the municipality of Toledo, OH (USA) issued a ‘do not drink’ advisory on their water supply directly affecting over 400,000 residential customers and hundreds of businesses (Wilson, 2014).

This order was attributable to levels of microcystin, a potent liver toxin, which rose to 2.5 mg L1 in finished drinking water. The Toledo crisis afforded an opportunity to bring together scientists from around the world to share ideas regarding factors that contribute to bloom formation and toxigenicity, bloom and toxin detection as well as prevention and remediation of bloom events. These discussions took place at an NSF- and NOAA-sponsored workshop at Bowling Green State University on April 13 and 14, 2015. In all, more than 100 attendees from six countries and 15 US states gathered together to share their perspectives. The purpose of this review is to present the consensus summary of these issues that emerged from discussions at the Workshop. As additional reports in this special issue provide detailed reviews on many major CHAB species, this paper focuses on the general themes common to all blooms, such as bloom detection, modeling, nutrient loading, and strategies to reduce nutrients.

Carrick, H.J., E. Butts, D. Daniels, M. Fehringer, C. Frazier, G.L. Fahnenstiel, S.A. POTHOVEN, and H.A. VANDERPLOEG. Variation in the abundance of pico, nano, and microplankton in Lake Michigan: Historic and basin-wide comparisons. Journal of Great Lakes Research 41(Supplement 3):63-74 (DOI:1016/j.jglr.2015.09.009) (2015).

The Lake Michigan ecosystem has undergone numerous, systemic changes (reduced nutrient, changing climate, invasive mussels) that have altered portions of the food web and thus, appear to have changed the lake's trophic state. That said, little is known about the components of the microbial food web (MFW, heterotrophic and phototrophic pico, nano, and micro-plankton), which we hypothesized have compensated as a food source for crustacean zooplankton given the recent declines in the biomass of large phytoplankton (mainly diatoms). Therefore, we measured the abundance of the entire MFW using complementary microscopic techniques, flow cytometry, and size fractionated chlorophyll concentrations at sites in northern and southern Lake Michigan, and one site in Lake Superior; the latter site served as a benchmark for oligotrophic conditions. In addition, a historic comparison was made between 1987 and 2013 for the southern Lake Michigan site. Ppico numbers (i.e., picocyanobacteria) in 2013 were lower compared with those in the 1980s; however, the percent contribution of the b2 μm fraction increased 2-fold (N50% of total chlorophyll). The abundance of small, pigmented chrysomonads and cryptomonads (Pnano size category) was not significantly different between 1987 and 2013 at the same time Pmicro did decline; this shift towards Ppico and Pnano dominance may be related to the recent oligotrophication of Lake Michigan. The abundance of ciliated protists (Hmicro size class) was 3-fold lower in 2013 compared with levels in 1987, while the abundance of both Hpico (eubacteria, range 0.24– 1.36 × 106 cells mL−1) and Hnano (mainly colorless chrysomonads; range 0.11–6.4 × 103 cells mL−1) remained stable and reflected the resilience of bacteria–flagellate trophic linkage.

Cha, Y.K., S.S. Park, H.W. Lee, and C.A. STOW. A Bayesian hierarchical approach to model seasonal algal variability along an upstream to downstream river gradient. Water Resources Research 52(1):348-357 (DOI:10.1002/2015WR017327) (2016).

Modeling to accurately predict river phytoplankton distribution and abundance is important in water quality and resource management. Nevertheless, the complex nature of eutrophication processes in highly connected river systems makes the task challenging. To model dynamics of river phytoplankton, represented by chlorophyll a (Chl a) concentration, we propose a Bayesian hierarchical model that explicitly accommodates seasonality and upstream-downstream spatial gradient in the structure. The utility of our model is demonstrated with an application to the Nakdong River (South Korea), which is a eutrophic, intensively regulated river, but functions as an irreplaceable water source for more than 13 million people. Chl a is modeled with two manageable factors, river flow, and total phosphorus (TP) concentration. Our model results highlight the importance of taking seasonal and spatial context into account when describing flow regimes and phosphorus delivery in rivers. A contrasting positive Chl a-flow relationship across stations versus negative Chl a-flow slopes that arose when Chl a was modeled on a station-month basis is an illustration of Simpson's paradox, which necessitates modeling Chl a-flow relationships decomposed into seasonal and spatial components. Similar Chl a-TP slopes among stations and months suggest that, with the flow effect removed, positive TP effects on Chl a are uniform regardless of the season and station in the river. Our model prediction successfully captured the shift in the spatial and monthly patterns of Chl a.

Chaffin, B.C., A.S. Garmestani, D.G. Angeler, D.L. Hermann, C.A. STOW, M. Nystrom, J. Sendzimir, M.E. Hopton, J. Kolasa, and C.R. Allen. Biological invasions, ecological resilience and adaptive governance. Journal of Environmental Management 183, Part 2:399-407 (DOI:10.1016/j.jenvman.2016.04.040) (2016). (IN PRESS)

In a world of increasing interconnections in global trade as well as rapid change in climate and land cover, the accelerating introduction and spread of invasive species is a critical concern due to associated negative social and ecological impacts, both real and perceived. Much of the societal response to invasive species to date has been associated with negative economic consequences of invasions. This response has shaped a war-like approach to addressing invasions, one with an agenda of eradications and intense ecological restoration efforts towards prior or more desirable ecological regimes. This trajectory often ignores the concept of ecological resilience and associated approaches of resilience-based governance. We argue that the relationship between ecological resilience and invasive species has been understudied to the detriment of attempts to govern invasions, and that most management actions fail, primarily because they do not incorporate adaptive, learning-based approaches. Invasive species can decrease resilience by reducing the biodiversity that underpins ecological functions and processes, making ecosystems more prone to regime shifts. However, invasions do not always result in a shift to an alternative regime; invasions can also increase resilience by introducing novelty, replacing lost ecological functions or adding redundancy that strengthens already existing structures and processes in an ecosystem. This paper examines the potential impacts of species invasions on the resilience of ecosystems and suggests that resilience-based approaches can inform policy by linking the governance of biological invasions to the negotiation of tradeoffs between ecosystem services.

Choi, J., C.D. Troy, and N. HAWLEY. Shear dispersion from near-inertial internal Poincare waves in large lakes. Limnology and Oceanography 60:2222-2235 (DOI:10.1002/lno.10163) (2015).

In this work, we study mixed layer lateral dispersion that is enhanced by near-inertial internal Poincarewaves in the offshore region of a large stratified lake, Lake Michigan. We examine the hypothesis that thevertical shear created by near-inertial internal Poincare waves is not only an energy source for vertical mixingin the thermocline and mixed layer, but also enhances horizontal dispersion via an unsteady shear flow dispersionmechanism. Complex empirical orthogonal function analysis reveals that the dominant shear structure is observed to mirror the thermal structure, with the location of maximum shear gradually lowered asthe mixed layer deepens. This changing structure of shear and vertical mixing produces different characteristicsin shear flow dispersion between the early and later stratified periods. The estimated depth-averaged surfacelayer vertical turbulent diffusivity grows from 1025 m2s21 to 1023 m2s21 over the stratified period, and the associated lateral dispersion coefficients are estimated as 0.1–40 m2s21. The Poincare waves are found toenhance greatly lateral dispersion for times less than the inertial period following release. In contrast, subinertial shear is the dominant mechanism responsible for shear dispersion for times greater than the inertial period. A simple approximation of the dispersion coefficient for lateral dispersion is developed, which scales as the product of surface current velocity (or wind friction velocity) and mixed layer depth. The calculated dispersion coefficients agree well with Okubo’s diffusion diagram for times up to a week, which suggests that unsteady shear dispersion is a plausible mechanism to explain observed dispersion rates in the mixed layer for early times after release.

CLITES, A.H., J. WANG, and Z. Yang. Great Lakes Ice Cover Database Update: 1973 – 2015. Proceedings of the 23rd IAHR International Symposium on Ice (2016).

Cory, R., T.W. DAVIS, G.J. Dick, T.H. JOHENGEN, V.J. DENEF, M.A. Berry, S.E. Page, S.B. Watson, K. Yuhas, and G.W. Kling. Seasonal Dynamics in Dissolved Organic Matter, Hydrogen Peroxide, and Cyanobacterial Blooms in Lake Erie. Frontiers in Marine Science 3(00054)(DOI:10.3389/fmars.2016.00054 ) (2016).

Hydrogen peroxide (h1O2) has been suggested to influence cyanobacterial community structure and toxicity. However, no study has investigated h1O2 concentrations in freshwaters relative to cyanobacterial blooms when sources and sinks of h1O2 may be highly variable. For example, photochemical production of h1O2 from chromophoric dissolved organic matter (CDOM) may vary over the course of the bloom with changing CDOM and UV light in the water column, while microbial sources and sinks of h1O2 may change with community biomass and composition. To assess relationships between h1O2 and harmful algal blooms dominated by toxic cyanobacteria in the western basin of Lake Erie, we measured h1O2 weekly at six stations from June to November, 2014 and 2015, with supporting physical, chemical, and biological water quality data. Nine additional stations across the western, eastern, and central basins of Lake Erie were sampled during August and October, 2015. CDOM sources were quantified from the fluorescence fraction of CDOM using parallel factor analysis (PARAFAC). CDOM concentration and source were significantly correlated with specific conductivity, demonstrating that discharge of terrestrially-derived CDOM from rivers can be tracked in the lake. Autochthonous sources of CDOM in the lake increased over the course of the blooms. Concentrations of h1O2 in Lake Erie ranged from 47 ± 16 nM to 1570 ± 16 nM (average of 371 ± 17 nM; n = 225), and were not correlated to CDOM concentration or source, UV light, or estimates of photochemical production of h1O2 by CDOM. Temporal patterns in h1O2 were more closely aligned with bloom dynamics in the lake. In 2014 and 2015, maximum concentrations of h1O2 were observed prior to peak water column respiration and chlorophyll a, coinciding with the onset of the widespread Microcystis blooms in late July. The spatial and temporal patterns in h1O2 concentrations suggested that production and decay of h1O2 from aquatic microorganisms can be greater than photochemical production of h1O2 from CDOM and abiotic decay pathways. Our study measured h1O2 concentrations in the range where physiological impacts on cyanobacteria have been reported, suggesting that h1O2 could influence the structure and function of cyanobacterial communities in Lake Erie.

Daigle, R.M., C.J. Monaco, and A.K. BALDRIDGE. An adaptable toolkit to assess commercial fishery costs and benefits related to marine protected area network design [version 1; referees: 1 approved, 1 approved with reservations]. F1000Research 4(1234)(DOI:10.12688/f1000research.7312.1)) (2015).

Around the world, governments are establishing Marine Protected Area (MPA) networks to meet their commitments to the United Nations Convention on Biological Diversity. MPAs are often used in an effort to conserve biodiversity and manage fisheries stocks. However, their efficacy and effect on fisheries yields remain unclear. We conducted a case-study on the economic impact of different MPA network design strategies on the Atlantic cod (Gadus morhua) fisheries in Canada. The open-source R toolbox that we developed to analyze this case study can be customized to conduct similar analyses for other systems. We used a spatially-explicit individual-based model of population growth and dispersal coupled with a fisheries management and harvesting component. We found that MPA networks that both protect the target species’ habitat (particularly the spawning grounds), and were spatially optimized to improve population connectivity had the highest net present value (i.e., were most profitable for the fishing industry). These higher profits were achieved primarily by reducing the distance travelled for fishing and reducing the probability of a moratorium event. These findings add to a growing body of knowledge demonstrating the importance of incorporating population connectivity in the MPA planning process, as well as the ability of this R toolbox to explore ecological and economic consequences of alternative MPA network designs.

DAVIS, T.W., and C.J. Gobler. Preface for Special Issue on “Global expansion of harmful cyanobacterial blooms: Diversity, ecology, causes, and controls”. Harmful Algae 54:1-3 (DOI:10.1016/j.hal.2016.02.003) (2016).

Denef, V.J., R.S. Mueller, E. Chiang, J.R. Liebig, and H.A. VANDERPLOEG. Chloroflexi CL500-11 populations that predominate deep lake hypolimnion bacterioplankton rely on nitrogen-rich DOM metabolism and C1 compound oxidation. Applied and Environmental Microbiology 82(5):1423-1432 (DOI:10.1128/AEM.03014-15) (2016).

The Chloroflexi CL500-11 clade predominates bacterial biomass in oxygenated hypolimnia of deep lakes worldwide, including the world's largest freshwater system, the Laurentian Great Lakes. Trains that allow CL500-11 to thrive and its biochemical role in these environments are currently unknown. Here, we found that a CL500-11 population was mostly present in off-shore waters along a transect in ultra-oligotrophic Lake Michigan (a Laurentian Great Lake). It occurred throughout the water column in spring, and only in the hypolimnion during summer stratification, contributing up to 18.1% of all cells. Genome reconstruction from metagenomic data suggested an aerobic, motile, heterotrophic lifestyle with additional energy gained through carboxidovory and methylovory. Comparisons to other available streamlined freshwater genomes revealed that CL500-11 contains disproportionate number of cell wall/capsule biosynthesis genes and the most diverse DOM substrate uptake spectrum, particularly for peptides. In situ expression patterns indicate the importance of DOM uptake and protein/peptide turnover, as well as Type I and Type II carbon monoxide dehydrogenase and flagellar motility. Location in the water column influenced expression patterns most, marked by increased bacteriorhodospin expression and a response to oxidative stress in surface compared to deep waters. While carrying multiple adaptations to an oligotrophic and mesotrophic lakes indicate the ability to thrive under conditions where resources are more plentiful. Our data indicate that CL500-11 plays an important role in nitrogen-rich DOM mineralization in the extensive deep lake hypolimnion habitat.

Eason, T., A.S. Garmestani, C.A. STOW, C. Rojo, M. Alvarez-Coelas, and H. Cabezas. Managing for resilience: an information theory-based approach to assessing ecosystems. Journal of Applied Ecology 53(3):656-665 (DOI:10.1111/1365-2664.12597) (2016).

Summary: 1. Ecosystems are complex and multivariate; hence, methods to assess the dynamics ofecosystems should have the capacity to evaluate multiple indica tors simultaneously. 2. Most research on identifying leading indicators of regime shifts has focused on univariatemethods and simple models which have limited utility when evaluating real ecosystems, par-ticularly because drivers are often unknown. 3. We discuss some common univariate and multivariate approaches for detecting criticaltransitions in ecosystems and demonstrate their capabilities via case studies. 4. Synthesis and applications. We illustrate the utility of an information theory-based indexfor assessing ecosystem dynamics. Trends in this index also provide a sentinel of both abruptand gradual transitions in ecosystems.

FAHNENSTIEL, G.L., M.J. Sayers, R.A. Shuchman, F. Yousef, and S.A. POTHOVEN. Lake-wide phytoplankton production and abundance in the upper Great Lakes: 2010-2013. Journal of Great Lakes Research 42(3):619-629 (DOI:10.1016/j.jglr.2016.02.004) (2016).

Lake-wide phytoplankton chlorophyll a concentrations and primary production were determined for lakes Huron, Michigan, and Superior in 2010–2013. Chlorophyll a concentrations were determined using MODIS imagery with a color-producing agent algorithm and primary production with the Great Lakes Production Model using remotely sensed and empirically derived input from the Upper Great Lakes. The new chlorophyll a and primary production estimates agreed well with field measurements. Lake-wide mean chlorophyll a concentrations determined from observations in all 12 months were highest in Lake Superior (mean = 0.99 mg/m3), intermediate in Lake Michigan (mean = 0.88 mg/m3), and lowest in Lake Huron (mean = 0.77 mg/m3). In Lake Superior, a gradient in chlorophyll a concentrations was noted from the shallow zone (0–30 m, mean = 1.57 mg/m3) to the deep-water zone (> 150 m, mean = 0.94 mg/m3). However, in Lake Michigan, no differences in mean chlorophyll a concentrations were noted in shallow-, mid-, or deep-water zones (means, 0.83, 0.86, 0.90 mg/m3, respectively). Lake-wide areal integrated primary production rates in lakes Huron, Michigan, and Superior were not significantly different for the 2010–2013 period (means, 216, 259, and 228 mg C/m2/d, respectively). Also, primary production in all depth zones (shallow, mid, and deep) were similar across lakes. Annual whole-lake phytoplankton carbon fixation values for 2010–2013 ranged from 4.4 to 5.7 Tg/y for Lake Huron, 5.0–7.2 Tg/y for Lake Michigan, and 6.4–9.5 Tg/y for Lake Superior.

Feiner, Z.S., H.-Y. Wang, D.W. Einhouse, J.R. Jackson, E.S. RUTHERFORD, C.S. Schelb, C.S. Vandergoot, T.G. Zorn, and T.O. Hook. Thermal environment and maternal effects shape egg size in a freshwater fish. Ecosphere 7(5)(DOI:10.1002/ecs2.1304) (2016).

Offspring size determines offspring survival rates; thus, understanding factors influencing offspring size variability could elucidate variation in population dynamics. Offspring size variation is influenced through multigenerational adaptation to local environments and within-lifetime plastic responses to environmental variability and maternal effects among individuals. Moreover, offspring size variation may represent trade-offs in energy allocation within individuals that influence lifetime reproductive success. However, the mechanisms whereby environmental conditions influence offspring size, e.g., via inducing adaptive and plastic variation in population-scale maternal effects, remain poorly understood. We evaluated intra-specific variation in maternal effects, egg size, and intra-individual egg size variation in six populations of walleye (Sander vitreus) and related among- and within-population patterns to thermal conditions. Egg size was conserved within populations and negatively related to long-term thermal conditions among populations, while maternal effect strengths were positively related to thermal conditions, suggesting that populations inhabiting warmer environments adapted to produce smaller eggs but stronger maternal effects. Within a population, egg size was positively related to colder winters, suggesting cold winters may alter egg size through effects on maternal condition or as an adaptive maternal effect to improve offspring survival. Intra-individual egg size variation varied little among populations or with female size, but declined with increasing summer and decreasing winter temperatures. Our result suggests that environmental conditions could impact not only short-term offspring production but also spur adaptive changes in offspring phenotypes. Thus, it is necessary to account for adaptive responses to predict population dynamics under environmental changes.

Fortin, D., D.S. Kaufman, M. Arnold, E. Schiefer, and N. HAWLEY. Late-summer peak in sediment accumulation in two lakes with contrasting watersheds. Geografiska Analler A. 97(4):709-719 (DOI:10.1111/geoa.12110) (2015).

The timing of clastic sedimentation in two glacial-fed lakes with contrasting watersheds was monitored using sequencing sediment traps for two consecutive years at Allison Lake (Chugach Range, Alaska) and four months at Shainin Lake (Brooks Range, Alaska). Shainin Lake is a weakly stratified lake fed by distant glaciers, whereas Allison Lake is more strongly stratified and fed predominantly by proximal glaciers. At Shainin Lake, sediment accumulation started in late June and reached its maximum in mid-August, just before lake mixing and during a period of low river discharge. The grain size of the sediment reaching the sediment trap in Shainin Lake was homogenous throughout the summer. At Allison Lake, pulsed sedimentation of coarse particles during late summer and early fall storms were superimposed on the fine-grained sedimentation pattern similar to that observed at Shainin Lake. These storms triggered underflows that were observed in the thermal structure of the lake and deposited abundant sediment. The sequencing sediment traps reveal a lag between fluvial discharge and sediment deposition at both lakes, implying limitations to interpreting intra-annual sedimentary features in terms of inflow discharge.

Gobler, C.J., J.M. Burkholder, T.W. DAVIS, M.J. Harke, T.H. JOHENGEN, C.A. STOW, and D.B. VandeWaal. The dual role of nitrogen supply in controlling the growth and toxicity of cyanobacterial blooms. Harmful Algae 54:87-97 (DOI:10.1016/j.hal.2016.01.010) (2016).

Using satellite imagery to quantify the spatial patterns of cyanobacterial toxins has several challenges. These challenges include the need for surrogate pigments – since cyanotoxins cannot be directly detected by remote sensing, the variability in the relationship between the pigments and cyanotoxins – especially microcystins (MC), and the lack of standardization of the various measurement methods. A dual-model strategy can provide an approach to address these challenges. One model uses either chlorophyll-a (Chl-a) or phycocyanin (PC) collected in situ as a surrogate to estimate the MC concentration. The other uses a remote sensing algorithm to estimate the concentration of the surrogate pigment. Where blooms are mixtures of cyanobacteria and eukaryotic algae, PC should be the preferred surrogate to Chl-a. Where cyanobacteria dominate, Chl-a is a better surrogate than PC for remote sensing. Phycocyanin is less sensitive to detection by optical remote sensing, it is less frequently measured, PC laboratory methods are still not standardized, and PC has greater intracellular variability. Either pigment should not be presumed to have a fixed relationship with MC for any water body. The MCpigment relationship can be valid over weeks, but have considerable intra- and inter-annual variability due to changes in the amount of MC produced relative to cyanobacterial biomass. To detect pigments by satellite, three classes of algorithms (analytic, semi-analytic, and derivative) have been used. Analytical and semi-analytical algorithms are more sensitive but less robust than derivatives because they depend on accurate atmospheric correction; as a result derivatives are more commonly used. Derivatives can estimate Chl-a concentration, and research suggests they can detect and possibly quantify PC. Derivative algorithms, however, need to be standardized in order to evaluate the reproducibility of parameteriza- tions between lakes. A strategy for producing useful estimates of microcystins from cyanobacterial biomass is described, provided cyanotoxin variability is addressed.

GRONEWOLD, A.D., J. Bruzer, D. Durnford, A.H. CLITES, J.P. SMITH, F. Segleniecks, S.S. Qian, T.S. HUNTER, and V. Fortin. Hydrological drivers of record-setting water level rise on Earth's largest lake system. Water Resources Research 52(DOI:10.1002/2015WR018209) (2016).

Abstract Between January 2013 and December 2014, water levels on Lake Superior and Lake Michigan-Huron, the two largest lakes on Earth by surface area, rose at the highest rate ever recorded for a 2 yearperiod beginning in January and ending in December of the following year. This historic event coincidedwith below-average air temperatures and extensive winter ice cover across the Great Lakes. It also broughtan end to a 15 year period of persistently below-average water levels on Lakes Superior and Michigan-Huron that included several months of record-low water levels. To differentiate hydrological drivers behindthe recent water level rise, we developed a Bayesian Markov chain Monte Carlo (MCMC) routine for inferringhistorical estimates of the major components of each lake’s water budget. Our results indicate that, in 2013,the water level rise on Lake Superior was driven by increased spring runoff and over-lake precipitation. In2014, reduced over-lake evaporation played a more significant role in Lake Superior’s water level rise. Thewater level rise on Lake Michigan-Huron in 2013 was also due to above-average spring runoff and persistentover-lake precipitation, while in 2014, it was due to a rare combination of below-average evaporation,above-average runoff and precipitation, and very high inflow rates from Lake Superior through the St. MarysRiver. We expect, in future research, to apply our new framework across the other Laurentian Great Lakes,and to Earth’s other large freshwater basins as well.

Harke, M.J., T.W. DAVIS, S.B. Watson, and C.J. Gobler. Nutrient-controlled niche differentiation of western Lake Erie cyanobacterial populations revealed via metatranscriptomic surveys. Environmental Science & Technology (DOI:10.1021/acs.est.5b03931) (2016).

While toxic cyanobacterial blooms in western Lake Erie threaten drinking water supplies and are promoted by nutrient loading, the precise nutrient regime that selects specific cyanobacteria populations is poorly understood. Here, we assess shifts in cyanobacterial abundances and global gene expression patterns in response to natural and manipulated gradients in nitrogen and phosphorus to identify gene pathways that facilitate dominance by different cyanobacteria. Gradients in soluble reactive phosphorus shaped cyanobacterial communities and elicited the largest transcriptomic responses. Under high P conditions (closest to the mouth of the Maumee River), Anabaena and Planktothrix were the dominant cyanobacterial populations and experimental P and ammonium enrichment promoted nitrogen fixation gene (nifH) expression in Anabaena. For Microcystis, experimental additions of P upregulated genes involved in phage defense, genomic rearrangement, and nitrogen acquisition, but led to lower abundances. Within offshore, low P regions of the western basin of Lake Erie, Microcystis upregulated genes associated with P scavenging (pstSCAB, phoX) and dominated cyanobacterial communities. Experimental additions of ammonium and urea did not alter Microcystis abundances but did upregulate protease inhibitors (aer, mcn gene sets) and microcystin synthetase genes (mcy) with urea enrichment yielding significant increases in microcystin concentrations. Our findings suggest that management plans that reduce P loads alone may not significantly reduce the risk of cyanobacterial blooms in western Lake Erie, but rather may promote a shift among cyanobacterial populations (Microcystis, Anabaena, and Planktothrix) towards a greater dominance by toxic strains of Microcystis.

HU, H., J. WANG, H. Liu, and J. Goes. Simulation of phytoplankton distribution and variation in the Bering-Chukchi Sea using a 3-D physical-biological model. Journal of Geophysical Research: Oceans 121(6):4041-4055 (DOI:10.1002/2016JC011692) (2016).

A three-dimensional physical-biological model has been used to simulate seasonal phytoplankton variations in the Bering and Chukchi Seas with a focus on understanding the physical and biogeochemical mechanisms involved in the formation of the Bering Sea Green Belt (GB) and the Subsurface Chlorophyll Maxima (SCM). Model results suggest that the horizontal distribution of the GB is controlled by a combination of light, temperature, and nutrients. Model results indicated that the SCM, frequently seen below the thermocline, exists because of a rich supply of nutrients and sufficient light. The seasonal onset of phytoplankton blooms is controlled by different factors at different locations in the Bering-Chukchi Sea. In the off-shelf central region of the Bering Sea, phytoplankton blooms are regulated by available light. On the Bering Sea shelf, sea ice through its influence on light and temperature plays a key role in the formation of blooms, whereas in the Chukchi Sea, bloom formation is largely controlled by ambient seawater temperatures. A numerical experiment conducted as part of this study revealed that plankton sinking is important for simulating the vertical distribution of phytoplankton and the seasonal formation of the SCM. An additional numerical experiment revealed that sea ice algae account for 14.3–36.9% of total phytoplankton production during the melting season, and it cannot be ignored when evaluating primary productivity in the Arctic Ocean.

Kao, Y.C., S.A. Adlerstein, and E.S. RUTHERFORD. Assessment of top-down and bottom-up controls on the collapse of alewives (Alosa pseudoharengus) in Lake Huron. Ecosystems:1-29 (DOI:10.​1007/​s10021-016-9969-y) (2016).

Food web models are powerful tools to inform management of lake ecosystems, where top-down (predation) and bottom-up (resource) controls likely propagate through multiple trophic levels because of strong predator–prey links. We used the Ecopath with Ecosim modeling approach to assess these controls on the Lake Huron main basin food web and the 2003 collapse of an invasive pelagic prey fish, alewife (Alosa pseudoharengus). We parameterized two Ecopath models to characterize food web changes occurring between two study periods of 1981–1985 and 1998–2002. We also built an Ecosim model and simulated food web time-dynamics under scenarios representing different levels of top-down control by Chinook salmon (Oncorhynchus tshawytscha) and of bottom-up control by quagga mussels (Dreissena rostriformis bugensis) and nutrients. Ecopath results showed an increase in the relative importance of bottom-up controls between the two periods, as production decreased across all trophic levels. The production of non-dreissenid benthos decreased most, which could cause decreases in production of pelagic prey fishes feeding on them. Ecosim simulation results indicated that the alewife collapse was caused by a combination of top-down and bottom-up controls. Results showed that while controls by Chinook salmon were relatively constant before alewife collapse, controls by quagga mussels and nutrients increased jointly to unsustainable levels. Under current conditions of low nutrients and high quagga mussel biomass, simulation results showed that recovery of alewives is unlikely regardless of Chinook salmon biomass in Lake Huron, which implies that the shrinking prey base cannot support the same level of salmonine predators as that prevailed during the 1980s.

Krueger, D.M., E.S. RUTHERFORD, and D.M. MASON. Foraging ecology of walleye and brown trout in a Great Lakes tributary. Journal of Great Lakes Research:8 pp. (DOI:DOI:10.1016/j.jglr.2015.10.016) (2015).

The role of alternative prey on predator diet selection and survival of juvenile (parr) Chinook salmon (Oncorhynchus tshawytscha) is not well understood in the Laurentian Great Lakes. Therefore, measures of predator foraging ecology (prey species and size selection), prey densities, and functional response relationships were determined for adult walleye (Sander vitreus) and brown trout (Salmo trutta) (hatchery-reared) feeding on parr and alternate prey in the Muskegon River, a tributary of Lake Michigan, USA, from 2004 to 2007. Walleye selected for smaller than average brown trout and rainbow trout (hatchery-reared) butwalleye prey size (within-prey) was independent of predator size. In general, walleye showed neutral selection for all prey species but, in some years, showed positive selection for rainbow trout and negative selection for parr. Hatchery-reared brown trout selected the smallest parr in the environment although prey size was independent of predator size. Parr were positively selected by brown trout only in April. Functional response curves were fit to describe the consumption of parr and other prey types by walleye (type II) and brown trout (type I). Interactions among rainbow trout, walleye, and brown trout favored parr survival, i.e. the presence of alternate prey (rainbow trout) significantly influenced walleye predation on parr,while brown trout appeared to become quickly limited by size or escape ability of parr. Our results should enhance understanding of food web dynamics in Great Lakes tributary habitats.

Lei, R., P. Heil, J. WANG, Z. Zhang, Q. Li, and N. Li. Characterization of sea-ice kinematic in the Arctic outflow region using buoy data. Polar Research 35(22658):1-15 (DOI:10.3402/polar.v35.22658) (2016).

A four-buoy array was deployed in August 2010 to measure differential ice motion and to assess ice kinematics in light of environmental conditions from the central Arctic Ocean into the Fram Strait. The dynamic setting of the Transpolar Drift Stream (TDS) and the Fram Strait shaped the ice motion and deformation. On a synoptic scale, the ice drift was largely forced by surface winds, with atmospheric forcing accounting for 33-71% of ice-drift variability. Ice drift was closely aligned with the surface winds, except during quiescent conditions, or at times when the wind direction reversed from the dominant direction, i.e., anomalous winds blow against the TDS under the negative Arctic atmospheric Diplole Anomaly (DA). The inertially-induced ice motion weakened gradually from the zone of compacted ice to the marginal ice zone. As ice drifted south of the Fram Strait, its concentration dropped quite dramatically, the ice speed increased, and ice trajectories became more straightforward. As sea ice drifted through the Fram Strait, the acceleration and convergence of the ice was responsible for further substantial ice-field deformation. From a comparison between our updated ice kinematic data and the historic data from 1990, we find that the ice-drift time from the central Arctic Ocean into the Fram Strait was at a low level after 2007, and the ice-drift time can be explained by a monthly mean DA index at the 99% significance level. The DA-derived wind anomalies more effectively influence the ice-drift time via accelerating meridional ice velocity and reducing the curvature of ice-drift trajectory, compared to zonal sea ice divergence (convergence) caused by the positive (negative) phase of Arctic Oscillation (AO).

Li, Y., X. Li, J. WANG, and S. Peng. Dynamical analysis of a satellite-observed anticyclonic eddy in the northern Bering Sea. Journal of Geophysical Research: Oceans 121(5):3517-3531 (DOI:10.1002/2015JC011586) (2016).

The characteristics and evolution of a satellite-observed anticyclonic eddy in the northern Bering Sea during March and April 1999 are investigated using a three-dimensional Princeton Ocean Model (POM). The anticyclonic-like current pattern and asymmetric feature of the eddy were clearly seen in the synthetic aperture radar (SAR), sea surface temperature, and ocean color images in April 1999. The results from model simulation reveal the three-dimensional structure of the anticyclonic eddy, its movement, and dissipation. Energy analysis indicates that the barotropic instability (BTI) is the main energy source for the growth of the anticyclonic eddy. The momentum analysis further reveals that the larger magnitude of the barotropic pressure gradient in the meridional direction causes the asymmetry of the anticyclonic eddy in the zonal and meridional directions, while the different magnitudes of the meridional baroclinic pressure gradient are responsible for the different intensity of currents between the northern and southern parts of the anticyclonic eddy.

LOFGREN, B.M., and J. Rouhana. Physically plausible methods for projecting changes in Great Lakes water levels under climate change scenarios. Journal of Hydrometeorology 17:2209-2223 (DOI:10.1175/JHM-D-15-0220.1) (2016).

A method for projecting the water levels of the Laurentian Great Lakes under scenarios of human-caused climate change, used almost to the exclusion of other methods in the past, relies very heavily on the large basin runoff model (LBRM) as a component for determining the water budget for the lake system. This model uses near-surface air temperature as a primary predictor of evapotranspiration (ET); as in previous published work, it is shown here that the model’s very high sensitivity to temperature causes it to overestimate ET in a way that is greatly at variance with the fundamental principle of conservation of energy at the land surface. The traditional formulation is characterized here as being equivalent to having several suns in the virtual sky created by LBRM. More physically based methods show, relative to the traditional method, often astoundingly less potential ET and less ET, more runoff from the land and net basin supply for the lake basins, and higher lake water levels in the future. Using various methods of estimating the statistical significance, it is found that, at minimum, these discrepancies in results are significant at the 99.998% level. The lesson for the larger climate impact community is to use caution about whether an impact is forced directly by air temperature itself or is significantly forced by season or latitude independently of temperature. The results here apply only to the water levels of the Great Lakes and the hydrology of its basin and do not affect larger questions of climate change.

Madenjian, C.P., O.P. Jensen, R.R. Rediske, J.P. O'Keefe, A.R. Vastano, and S.A. POTHOVEN. Differences in energy expenditures and growth dilution explain higher PCB concentrations in male summer flounder. PLoS ONE 11(1)(DOI:10.1371/journal.pone.0147223) (2016).

Comparison of polychlorinated biphenyl (PCB) concentrations between the sexes of mature fish may reveal important behavioral and physiological differences between the sexes. We determined whole-fish PCB concentrations in 23 female summer flounder Paralichthys dentatus and 27 male summer flounder from New Jersey coastal waters. To investigate the potential for differences in diet or habitat utilization between the sexes, carbon and nitrogen stable isotope ratios were also determined. In 5 of the 23 female summer flounder, PCB concentrations in the somatic tissue and ovaries were determined. In addition, we used bioenergetics modeling to assess the contribution of the growth dilution effect to the observed difference in PCB concentrations between the sexes. Whole-fish PCB concentrations for females and males averaged 87 and 124 ng/g, respectively; thus males were 43% higher in PCB concentration compared with females. Carbon and nitrogen stable isotope ratios did not significantly differ between the sexes, suggesting that diet composition and habitat utilization did not vary between the sexes. Based on PCB determinations in the somatic tissue and ovaries, we predicted that PCB concentration of females would increase by 0.6%, on average, immediately after spawning due to release of eggs. Thus, the change in PCB concentration due to release of eggs did not explain the higher PCB concentrations observed in males. Bioenergetics modeling results indicated that the growth dilution effect could account for males being 19% higher in PCB concentration compared with females. Thus, the bulk of the observed difference in PCB concentrations between the sexes was not explained by growth dilution. We concluded that a higher rate of energy expenditure in males, stemming from greater activity and a greater resting metabolic rate, was most likely the primary driver for the observed difference in PCB concentrations between the sexes.

MANOME, A.F., and J. WANG. Simulating hydrodynamics and ice cover in Lake Erie using an unstructured grid model. Proceedings of 23th IAHR International Symposium on Ice (2016).

MANOME, A.F., and J. WANG. Simulating sea ice in the Arctic Ocean and Eastern Siberian Sea. Proceedings of the 23rd IAHR International Symposium on Ice (2016).

This study conducts ice-ocean coupled simulations for the Arctic Ocean, with the nested region of the Eastern Siberian Sea with 4km horizontal resolution. The ocean model is based on the Princeton Ocean Model. The ice dynamic model is based on the elastic-viscous-plastic rheology and the ice thermodynamics is based on the one-dimensional 0-layer model. These models are fully parallelized using the Message-Passing Interface. Initial conditions for ocean and sea ice, as well as atmospheric forcing, are provided by NCEP Climate Forecast System Reanalysis. The simulation will ultimately incorporate data assimilation of hydrographic data from the Russian-American Long-term Census of the Arctic (RUSALCA) cruises. The study will present an initial hindcast simulation from 2000 to 2015 with basic model validation based on comparison with satellite observations.

Mason, L.A., C.M. Riseng, A.D. GRONEWOLD, E.S. RUTHERFORD, J. WANG, A.H. CLITES, S.D.P. Smith, and P.B. McIntyre. Fine-scale spatial variation in ice cover and surface temperature trends across the surface of the Laurentian Great Lakes. Climatic Change 138(1):71-83 (DOI:10.1007/s10584-016-1721-2) (2016).

The effects of climate change on north temperate freshwater ecosystems include increasing water temperatures and decreasing ice cover. Here we compare those trends in the Laurentian Great Lakes at three spatial scales to evaluate how warming varies across the surface of these massive inland water bodies. We compiled seasonal ice cover duration (1973–2013) and lake summer surface water temperatures (LSSWT; 1994–2013), and analyzed spatial patterns and trends at lake-wide, lake sub-basin, and fine spatial scales and compared those to reported lake- and basin-wide trends. At the lake-wide scale we found declining ice duration and warming LSSWT patterns consistent with previous studies. At the lake sub-basin scale, our statistical models identified distinct warming trends within each lake that included significant breakpoints in ice duration for 13 sub-basins, consistent linear declines in 11 sub-basins, and no trends in 4 sub-basins. At the finest scale, we found that the northern- and eastern-most portions of each Great Lake, especially in nearshore areas, have experienced faster rates of LSSWT warming and shortening ice duration than those previously reported from trends at the lake scale. We conclude that lake-level analyses mask significant spatial and temporal variation in warming patterns within the Laurentian Great Lakes. Recognizing spatial variability in rates of change can inform both mechanistic modeling of ecosystem responses and planning for long-term management of these large freshwater ecosystems.

O’Reilly, C.M., and G.A. LESHKEVICH (among 56 others). Rapid and highly variable warming of lake surface waters around the globe. Geophysical Research Letters 42(DOI:10.1002/2015GL066235) (2015).

In this first worldwide synthesis of in situ and satellite-derived lake data, we find that lake summer surface water temperatures rose rapidly (global mean= 0.34 deg C decade-1) between 1985-2009. Our analyses show that surface water warming rates are dependent on combinations of climate and local characteristics, rather than just lake location, leading to the counterintuitive result that regional consistency in lake warming is the exception, rather than the rule. The most rapidly warming lakes are widely geographically distributed, and their warming is associated with interactions among different climatic factors- from seasonally ice-covered lakes in areas where temperature and solar radiation are increasing while cloud cover is diminishing (0.72 deg C decade-1) to ice-free lakes experiencing increases in air temperature and solar radiation (0.53 deg C decade-1). The pervasive and rapid warming observed here signals the urgent need to incorporate climate impacts into vulnerability assessments and adaptation efforts for lakes.

Pisareva, M.N., R.S. Packart, K. Iken, E.A. Ershova, J.M. Grebmeier, L.W. Cooper, B.A. Bluhm, C. Nobre, R.R. Hopcroft, H. HU, J. WANG, C.J. Ashjian, K.N. Kosobokova, and T.E. Whiteledge. The relationship between patterns of benthic fauna and zooplankton in the chukchi sea and physical forcing. Oceanography 28(3):68-83 (DOI:10.5670/oceanog.2015.58) (2015).

Using data from a number of summer surveys of the Chukchi Sea over the past decade, we investigate aspects in which the benthic fauna, sediment structure, and zooplankton there are related to circulation patterns and shelf hydrographic conditions. A flow speed map is constructed that reveals the major pathways on the shelf. Regions of enhanced flow speed are dictated by lateral constrictions—in particular, Bering Strait and Barrow and Herald Canyons—and by sloping topography near coastlines. For the most part, benthic epifaunal and macrofaunal suspension feeders are found in high flow regimes, while deposit feeders are located in regions of weaker flow. The major exceptions are in Bering Strait, where benthic sampling was underrepresented, and in Herald Canyon where the pattern is inexplicably reversed. Sediment grain size is also largely consistent with variations in flow speed on the shelf. Data from three biophysical surveys of the Chukchi Sea, carried out as part of the Russian-American Long-term Census of the Arctic program, reveal close relationships between the water masses and the zooplankton communities on the shelf. Variations in atmospheric forcing, particularly wind, during the three sampling periods caused significant changes in the lateral and vertical distributions of the summer and winter water masses. These water mass changes, in turn, were reflected in the amounts and species of zooplankton observed throughout the shelf in each survey. Our study highlights the close relationship between physical drivers (wind forcing, water masses, circulation, and sediment type) in the Chukchi Sea and the biological signals in the benthos and the plankton on a variety of time scales.

POTHOVEN, S.A., and D.B. Bunnell. Shifts in bloater consumption in Lake Michigan between 193 and 2011 and its effects on Diporeia and Mysis prey. Transactions of the American Fisheries Society 145(1):59-68 (DOI:10.1080/00028487.2015.1094130) (2016).

Bioenergetics modeling was used to determine individual and population consumption by Bloater Coregonus hoyi in Lake Michigan during three time periods with variable Bloater density: 1993–1996 (high), 1998–2002 (intermediate), and 2009–2011 (low). Despite declines in Bloater abundance between 1993 and 2011, our results did not show any density-dependent compensatory response in annual individual consumption, specific consumption, or proportion of maximum consumption consumed. Diporeia spp. accounted for a steadily decreasing fraction of annual consumption, and Bloater were apparently unable to eat enough Mysis diluviana or other prey to account for the loss of Diporeia in the environment. The fraction of production of both Diporeia and Mysis that was consumed by the Bloater population decreased over time so that the consumption-to-production ratio for Diporeia C Mysis was 0.74, 0.26, and 0.14 in 1993–1996, 1998–2002, and 2009–2011, respectively. Although high Bloater numbers in the 1980s to 1990s may have had an influence on populations of Diporeia, Bloater were not the main factor driving Diporeia to a nearly complete disappearance because Diporeia continued to decline when Bloater predation demands were lessening. Thus, there appears to be a decoupling in the inverse relationship between predator and prey abundance in Lake Michigan. Compared with Alewife Alosa pseudoharengus, the other dominant planktivorein the lake, Bloater have a lower specific consumption and higher gross conversion efficiency (GCE), indicating that the lake can support a higher biomass of Bloater than Alewife. However, declines in Bloater GCE since the 1970s and the absence of positive responses in consumption variables following declines in abundance suggest that productivity in Lake Michigan might not be able to support the same biomass of Bloater as in the past.

POTHOVEN, S.A., G.L. Fahnenstiel, H.A. VANDERPLOEG, and T.F. NALEPA. Changes in water quality variables at a mid-depth site after proliferation of dreissenid mussels in southeastern Lake Michigan. Fundamental and Applied Limnology 188(3):233-244 (DOI:10.1127/fal/2016/0883) (2016).

Studies evaluating the impacts of dreissenid mussels in Lake Michigan have largely focused on changes in phytoplankton dynamics in the offshore region (i. e., > 100 m depth) even though mussel biomass is actually highest in mid-depth coastal regions of Lake Michigan (i. e., 30–50 m). Here we report on changes at the base of the food web during 1995–2014 at a mid-depth site located in southeastern Lake Michigan. Specifically, we evalu - ated trends in Secchi depth, surface mixed layer chlorophyll- a and total phosphorus (TP), sub-epilimnetic deep chlorophyll layer concentrations, and near bottom chlorophyll- a concentrations and whether there have been shifts in the seasonal patterns of these variables. Median chlorophyll- a concentrations declined over 63 % during the spring isothermal period following the sharp increase in mussel abundance between 1996–2002 and 2007–2014. Chlorophyll- a concentrations in the spring were generally between 2 and 3 mg m –3 in 1996–2002, but almost never exceeded 1 mg m –3 in 2007–2014. Secchi depths increased in all months between 1996–2002 and 2007–2014, with the greatest changes being observed in the spring. Total phosphorus in the surface mixed layer declined over the study period, but not at as fast a rate as chlorophyll- a, a change consistent with mussel invasions. There was a 90% decline in the median depth integrated deep chlorophyll- a concentration between 1995–2000 and 2007–2014 in June when this feature was at its peak. Chlorophyll- a concentrations in the near bottom zone also decreased over time, likely due to their constant contact with dreissenid mussels. The declines in chlorophyll- a and changes in nutrient dynamics at the mid-depth site are consistent with dreissenid induced impacts that have also been documented at deeper, offshore sites in Lake Michigan.

POTHOVEN, S.A., C.P. Madenjian, and T.O. Hook. Feeding ecology of the walleye (Percidae, Sander vitreus), a resurgent piscivore in Lake Huron (Laurentian Great Lakes) after shifts in the prey community. Ecology of Freshwater Fish (DOI:10.1111/eff.12315) (2016).

Recovering populations of piscivores can challenge understanding of ecosystem function due to impacts on prey and to potentially altered food webs supporting their production. Stocks of walleye (Percidae, Sander vitreus), an apex predator in the Laurentian Great Lakes, crashed in the mid-1900s. Management efforts led to recovery by 2009, but recovery coincided with environmental and fish community changes that also had implications for the feeding ecology of walleye. To evaluate potential changes in feeding ecology for this apex predator, we assessed diets in the main basin of Lake Huron and in Saginaw Bay, a large embayment of Lake Huron, during 2009–2011. Walleye switched their diets differently in the main basin and Saginaw Bay, with non-native round goby (Gobiidae, Neogobius melanostomus) and rainbow smelt (Osmeridae, Osmerus mordax) more prevalent in diets in the main basin, and invertebrates, yellow perch (Percidae, Perca flavescens) and gizzard shad (Clupeidae, Dorosoma cepedianum) more prevalent in diets in the bay. Feeding strategy plots indicated that there was a high degree of individual specialisation by walleye in the bay and the main basin. Bioenergetic simulations indicated that walleye in Saginaw Bay need to consume 10%–18% more food than a walleye that spends part or all of the year in the main basin, respectively, in order to achieve the same growth rate. The differences in diets between the bay and main basin highlight the flexibility of this apex predator in the face of environmental changes, but changes in diet can alter energy pathways supporting piscivore production.

Ptachnikova, R., H.A. VANDERPLOEG, and J.F. CAVALETTO. Big versus small: Does Bythotrephes longimanus predatiaon regulate spatial distribution of another invasive predatory cladoceran, Cercopagis pengoi? Journal of Great Lakes Research 41(Supplement 3):143-149 (DOI:10.1016/j.jglr.2015.10.006) (2015).

Offshore–onshore spatial distribution and abundance of Cercopagis pengoi, a small non-indigenous predatory cercopagid, in Lake Michigan have been hypothesized to be regulated by the larger non-indigenous predatory cercopagid, Bythotrephes longimanus, through predation and/or competition. However, temperature and prey abundance are other factors that could be affecting Cercopagis. First, we examined all these factors on Cercopagis population abundance, life history traits and spatio-temporal distribution. In addition, we examined vertical spatial overlap between these species and determined predation rate of Bythotrephes on Cercopagis. Linear mixed effects analysis of spatial–temporal data showed that biomass of B. longimanus had the strongest effect which was significantly negative on biomass, proportion of fecund females and mean clutch size of Cercopagis. Fecundity increased significantly with density of potential prey zooplankton, whereas Cercopagis total biomass increased significantly with the mean epilimnion temperature. Cercopagis and Bythotrephes overlapped vertically in the epi- and metalimnion, and neither of them showed any appreciable diel vertical migration. In predation experiments, Bythotrephes consumed Cercopagis at the same rate as Daphnia mendotae, a known preferred prey, when offered at equal concentrations. Overall, this observation, togetherwith vertical overlap of Cercopagis with Bythotrephes implies that Bythotrephes predation has a strong influence on Cercopagis distribution; however, prey availability, temperature, and competition may be important secondary factors. These results imply tha invasion success of Cercopagis may be limited by prior invasion by Bythotrephes.

Reavie, E.D., M. Cai, M.R. Twiss, H.J. Carrick, T.W. DAVIS, T.H. JOHENGEN, D.C. GOSSIAUX, D.E. Smith, D. PALLADINO, A. BURTNER, and G.V. Sgro. Winter–spring diatom production in Lake Erie is an important driver of summer hypoxia. Journal of Great Lakes Research 42(3):608-618 (DOI:10.1016/j.jglr.2016.02.013) (2016).

Re-eutrophication and harmful algal blooms in Lake Erie have resulted in a renewed call for remedial measures such as reductions of phosphorus loads to the lake's western basin. The action of further nutrient reductions may also reduce the intensity of seasonal central basin hypolimnetic anoxia by reducing algal biomass. However, winter–spring blooms of diatoms have not been fully recognized as a source of algal biomass that might contribute significantly to summer hypoxia. We compared spring and summer phytoplankton abundance in central and western Lake Erie based on monitoring data to show that spring phytoplankton biovolume was 1.5- to 6-fold greater than summer biovolume and that most spring biovolume was composed of filamentous diatoms, primarily Aulacoseira islandica, that is likely supported by an increasing silica load from Lake Huron. The rise of silica export was attributed to the dreissenid mussel invasion and establishment that reduced diatom abundance in Lake Huron and thereby increased silica availability in the receiving water body of Lake Erie. The relationship between phosphorus and winter–spring diatom blooms was unclear, but diatoms probably contributed the majority of the algal biomass that accumulated annually in the hypolimnion of the central basin of Lake Erie. Remedial measures aimed at reducing hypoxia must consider the winter–spring phytoplankton bloom in Lake Erie as an important and reoccurring feature of the lake that delivers a considerable quantity of algal biomass to the profundal zone of the lake.

ROWE, M.D., E.J. ANDERSON, T.T. Wynne, R.P. Stumpf, D.L. FANSLOW, K. Kijanka, H.A. VANDERPLOEG, J.R. Strickler, and T.W. DAVIS. Vertical distribution of buoyant Microcystis blooms in a Lagrangian particle tracking model for short-term forecasts in Lake Erie. Journal of Geophysical Research 121(7):5296-5314 (DOI:10.1002/2016JC011720) (2016).

Cyanobacterial harmful algal blooms (CHABs) are a problem in western Lake Erie, and in eutrophic fresh waters worldwide. Western Lake Erie is a large (3000 km2), shallow (8 m mean depth), freshwater system. CHABs occur from July to October, when stratification is intermittent in response to wind and surface heating or cooling (polymictic). Existing forecast models give the present location and extent of CHABs from satellite imagery, then predict two-dimensional (surface) CHAB movement in response to meteorology. In this study, we simulated vertical distribution of buoyant Microcystis colonies, and 3-D advection, using a Lagrangian particle model forced by currents and turbulent diffusivity from the Finite Volume Community Ocean Model (FVCOM). We estimated the frequency distribution of Microcystis colony buoyant velocity from measured size distributions and buoyant velocities. We evaluated several random-walk numerical schemes to efficiently minimize particle accumulation artifacts. We selected the Milstein scheme, with linear interpolation of the diffusivity profile in place of cubic splines, and varied the time step at each particle and step based on the curvature of the local diffusivity profile to ensure that the Visser time step criterion was satisfied. Inclusion of vertical mixing with buoyancy significantly improved model skill statistics compared to an advection-only model, and showed greater skill than a persistence forecast through simulation day 6, in a series of 26 hindcast simulations from 2011. The simulations and in situ observations show the importance of subtle thermal structure, typical of a polymictic lake, along with buoyancy in determining vertical and horizontal distribution of Microcystis.

Rucinski, D.K., J.V. DePinto, D. BELETSKY, and D. Scavia. Modeling hypoxia in the central basin of Lake Erie under potential phosphorus load reduction scenarios. Journal of Great Lakes Research (DOI:10.1016/j.jglr.2016.07.001) (2016). (IN PRESS)

A 1-dimensional (vertical), linked hydrodynamic and eutrophication model that was previously calibrated and corroborated with 19 years (1987–2005) of observations in the central basin of Lake Erie, was applied as part of a group of models capable of forecasting ecosystem responses to altered phosphorus loads to Lake Erie. The results were part of the effort guiding the setting of new phosphorus loading targets in accordance with the Great Lakes Water Quality Agreement. Our analysis demonstrated that while reductions in total phosphorus loads can be expected to reduce hypoxia and chlorophyll-a impairments on average, climate and meteorological variability will result in significant year to year variability. We provide examples for achieving hypothetical water quality goals and relate the required reductions to recent nutrient sources.

RUTHERFORD, E.S., J. Allison, C.R. Ruetz, III, J.R. ELLIOTT, J.K. Nohner, M.R. DuFour, R.P. O'Neal, D.J. Jude, and S.R. Hensler. Density and survival of Walleye (Sander vitreus) eggs and larvae in a Great Lakes tributary. Transactions of the American Fisheries Society 145(3):567-577 (DOI:10.1080/00028487.2016.1145135) (2016).

The Walleye Sander vitreus is an important sport fish that has experienced low reproductive success in some Great Lakes tributaries since severe population declines began in the late 1940s. In the Muskegon River, a Lake Michigan tributary, natural reproduction of Walleyes remains low and is largely supplemented by stocking. We evaluated the influence of abiotic factors on Walleye reproductive success in the Muskegon River during April and May 2009 and 2010 by (1) estimating Walleye egg density and survival; (2) estimating the size, density, abundance, and survival of Walleye larvae; and (3) relating our estimates to physical habitat conditions. Egg densities were 70-fold higher in 2009 than in 2010, but eggs experienced colder water temperatures, higher river discharge rates, and lower survival in 2009 relative to 2010. Egg survival in incubators was positively related to temperature and negatively related to flow at most sites. In both years, Walleye larvae that hatched during periods of cooler temperature were smaller than larvae that hatched later during periods of warmer temperature. Walleye larval densities were highest near spawning grounds and decreased downstream. Bayesian estimates of variability in larval densities indicated that temporal variability was twice as high as spatial variability in the Muskegon River. Larval survival was much lower in 2009 than in 2010, resulting in an approximately sevenfold higher production of larvae in 2010 than in 2009. Survival was highest for smaller larvae that hatched early in April 2010, when temperatures were warm and discharges were low and stable; in contrast, survival was much lower for larger larvae hatching later in 2010 or for large and small larvae in 2009, when water temperatures were colder and discharges were higher and more variable. Our results suggest that abiotic factors, primarily temperature and river flow, likely control the early survival of Walleyes in the Muskegon River.

RUTHERFORD, E.S., and K.A. Rose. Individual-Based Model Analysis of Walleye and Yellow Perch Population Dynamics in Response to Changing Ecosystem Conditions. . In Oneida Lake: Long-term Dynamics of a Managed Ecosystem and Its Fishery. Edward L. Mills Lars G. Rudstam, James R. Jackson, and Donald J. Stewart. Published by the American Fisheries Society, Bethesda, MD, (2016).

RUTHERFORD, E.S., R.A. STURTEVANT, N. Mandrak, A. Thompason, A.M. Kramer, M.T. Wittman, O. Kocovsky, H. Embke, C.M. Mayer, S.S. Qian, T. Brendan, C. Krueger, C.K. Harris, and C.S. Vandergoot. Grass Carp Habitat Suitability, Establishment and Movement in the Detroit – St. Clair River Corridor. In Great Lakes Institute for Environmental Research, Occasional Publication No. 9. S. Francoeur, J. Ciborowski, J. Gannon, D. Kashian, and K. Kahl. University of Windsor, Windsor, ON, Canada, 74-76 pp. (2016).

SMITH, J.P., A.H. CLITES, C.A. STOW, T.S. HUNTER, A.D. GRONEWOLD, T. Slawecki, and G. MUHR. An expandable world wide web based platform for visually analyzing multiple data series related to the Laurentian Great Lakes. Environmental Modelling and Software 78:97 - 105 (DOI:0.1016/j.envsoft.2015.12.005) (2016).

Growing demand from the general public for centralized points of data access and analytics tools coincides with similar, well-documented needs of regional and international hydrology research and resource management communities. To address this need within the Laurentian Great Lakes region, we introduce the Great Lakes Dashboard (GLD), a dynamic web data visualization platform that brings multiple time series data sets together for visual analysis and download. The platform's adaptable, robust, and expandable Time Series Core Object Model (GLD-TSCOM) separates the growing complexity and size of Great Lakes data sets from the web application interface. Although the GLD-TSCOM is currently applied exclusively to Great Lakes data sets, the concepts and methods discussed here can be applied in other geographical and topical areas of interest.

Spanbauer, T., C.R. Allen, D.G. Angeler, T. Eason, S.C. Fritz, A.S. Garmestani, K.L. Nash, J.R. Stone, C.A. STOW, and S.M. Sundstrom. Body size distributions signal a regime shift in a lake ecosystem. Proceedings of the Royal Society B 283(1833)(DOI:10.1098/rspb.2016.0249) (2016).

Communities of organisms, from mammals to microorganisms, have discontinuous distributions of body size. This pattern of size structuring is a conservative trait of community organization and is a product of processes that occur at multiple spatial and temporal scales. In this study, we assessed whether body size patterns serve as an indicator of a threshold between alternative regimes. Over the past 7000 years, the biological communities of Foy Lake (Montana, USA) have undergone a major regime shift owing to climate change. We used a palaeoecological record of diatom communities to estimate diatom sizes, and then analysed the discontinuous distribution of organism sizes over time. We used Bayesian classification and regression tree models to determine that all time intervals exhibited aggregations of sizes separated by gaps in the distribution and found a significant change in diatom body size distributions approximately 150 years before the identified ecosystem regime shift. We suggest that discontinuity analysis is a useful addition to the suite of tools for the detection of early warning signals of regime shifts.

Stumpf, R.P., T.W. DAVIS, T.T. Wynne, J.L. Graham, K.A. Loftin, T.H. JOHENGEN, D.C. GOSSIAUX, D. PALLADINO, and A. BURTNER. Challenges for mapping cyanotoxin patterns from remote sensing of cyanobacteria. Harmful Algae 54:160-173 (DOI:10.1016/j.hal.2016.01.005) (2016).

Using satellite imagery to quantify the spatial patterns of cyanobacterial toxins has several challenges. These challenges include the need for surrogate pigments – since cyanotoxins cannot be directly detected by remote sensing, the variability in the relationship between the pigments and cyanotoxins – especially microcystins (MC), and the lack of standardization of the various measurement methods. A dual-model strategy can provide an approach to address these challenges. One model uses either chlorophyll-a (Chl-a) or phycocyanin (PC) collected in situ as a surrogate to estimate the MC concentration. The other uses a remote sensing algorithm to estimate the concentration of the surrogate pigment. Where blooms are mixtures of cyanobacteria and eukaryotic algae, PC should be the preferred surrogate to Chl-a. Where cyanobacteria dominate, Chl-a is a better surrogate than PC for remote sensing. Phycocyanin is less sensitive to detection by optical remote sensing, it is less frequently measured, PC laboratory methods are still not standardized, and PC has greater intracellular variability. Either pigment should not be presumed to have a fixed relationship with MC for any water body. The MCpigment relationship can be valid over weeks, but have considerable intra- and inter-annual variability due to changes in the amount of MC produced relative to cyanobacterial biomass. To detect pigments by satellite, three classes of algorithms (analytic, semi-analytic, and derivative) have been used. Analytical and semi-analytical algorithms are more sensitive but less robust than derivatives because they depend on accurate atmospheric correction; as a result derivatives are more commonly used. Derivatives can estimate Chl-a concentration, and research suggests they can detect and possibly quantify PC. Derivative algorithms, however, need to be standardized in order to evaluate the reproducibility of parameteriza- tions between lakes. A strategy for producing useful estimates of microcystins from cyanobacterial biomass is described, provided cyanotoxin variability is addressed.

STURTEVANT, R.A., L. BERENT, T. MAKLED, w. CONARD, A. Fusaro, and E.S. RUTHERFORD. An overview of the management of established nonindigenous species in the Great Lakes. NOAA Technical Memorandum GLERL-168. NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 273 pp. (2016).

The Great Lakes are host to thousands of native fishes, invertebrates, plants, and other species that not only provide recreational and economic value to the region, but also hold important ecological value. However, with over 180 documented aquatic nonindigenous species1 (ANS) and an apparent introduction rate estimated at 1.3-1.8 species·year-1 through 2006, the Great Lakes basin is considered one of the most heavily invaded aquatic systems in the world (Mills et al. 1993, Ricciardi 2006, GLRI Task Force 2010). Some of these nonindigenous species may become invasive (i.e. “species whose introduction does or is likely to cause economic or environmental harm or harm to human health” (Executive Order 13112, 1999)) and threaten the ecological and/or socio-economic value of the Great Lakes. In contrast, other nonindigenous species are capable of contributing value to the Great Lakes. Pacific salmonids, for instance, are stocked annually by the millions to help support the Great Lakes’ multi-billion dollar fishery (Kocik and Jones 1999, USFWS/GLFC 2010, USACE 2012a).

This study provides a snapshot of management of established nonindigenous species in the Great Lakes region as a benchmark for improving management practices. We review the relevant state and federal regulations that impact AIS management as well as management alternatives in a format that allows cross-jurisdictional and cross-taxa analysis. This effort is part of a larger project funded by the Great Lakes Restoration Initiative to enhance the Great Lakes Aquatic Nonindigenous Species Information System (GLANSIS1), an online database containing information on the identification, distribution, ecology, impact, and management of all established ANS in the Great Lakes. Previously, we assessed the relative ecological and socioeconomic impacts of nonindigenous species (NOAA Technical Memorandum 161 – An Impact Assessment of Great Lakes Aquatic Nonindigenous Species; Sturtevant et al. 2014).

Tucker, A.J., W.L. Chadderton, C.L. Jerde, M.A. Renshaw, K. Uy, C. Gantz, A.R. Mahon, A. Bowen, T. Strakosh, J.M. Bossenbroek, J.L. Sieracki, D. BELETSKY, J. Bergner, and D.M. Lodge. A sensitive environmental DNA (eDNA) assay leads to new insights on Ruffe (Gymnocephalus cernua) spread in North America. Biological Invasions:1-18 (DOI:10.1007/s10530-016-1209-z) (2016).

Detection of invasive species before or soon after they establish in novel environments is critical to prevent widespread ecological and economic impacts. Environmental DNA (eDNA) surveillance and monitoring is an approach to improve early detection efforts. Here we describe a large-scale conservation application of a quantitative polymerase chain reaction assay with a case study for surveillance of a federally listed nuisance species (Ruffe, Gymnocephalus cernua) in the Laurentian Great Lakes. Using current Ruffe distribution data and predictions of future Ruffe spread derived from a recently developed model of ballast-mediated dispersal in US waters of the Great Lakes, we designed an eDNA surveillance study to target Ruffe at the putative leading edge of the invasion. We report a much more advanced invasion front for Ruffe than has been indicated by conventional surveillance methods and we quantify rates of false negative detections (i.e. failure to detect DNA when it is present in a sample). Our results highlight the important role of eDNA surveillance as a sensitive tool to improve early detection efforts for aquatic invasive species and draw attention to the need for an improved understanding of detection errors. Based on axes that reflect the weight of eDNA evidence of species presence and the likelihood of secondary spread, we suggest a two-dimensional conceptual model that management agencies might find useful in considering responses to eDNA detections.

VANDERPLOEG, H.A., D.B. Bunnell, H.J. Carrick, and T.O. Hook. Complex interactions in Lake Michigan's rapidly changing ecosystem. Journal of Great Lakes Research 41 (Supplement 3):1-6 (DOI:10.1016/j.jglr.2015.11.001) (2015).

Over the past 30 years, Lake Michigan's food web has been in a constant state of transition (Vanderploeg et al., 2002, 2012; Madenjian et al., 2002; in this issue), and it is likely that this emerging system has not yet reached a steady state. The proliferation of invasive species at multiple trophic levels (zooplankton, mussels, fish), coupled with the success of a nutrient abatement program that has delivered long-term reductions in nutrient inputs, have together contributed to a series of systemic changes to the Lake Michigan ecosystem (e.g., novel trophic interactions, reengineered nutrient cycling, altered physical habitat, shift from pelagic productivity to enhanced benthic production, and nuisance algal blooms nearshore). Our current understanding and potential future forecasting of ecosystem-wide consequences of such transitions are dependent on describing and understanding changes in the food web in time and space (i.e., horizontal and vertical), variation of key food web components and linkages with physical habitat, and nutrient cycling. Given that other Laurentian Great Lakes share key members of the Lake Michigan food web as well as changing nutrient and climate dynamics, understanding gleaned from this special issue is highly relevant across the basin, especially in Lakes Huron and Ontario.

VANDERPLOEG, H.A., S.A. POTHOVEN, D.M. Krueger, D.M. MASON, J.R. LIEBIG, J.F. CAVALETTO, S.A. RUBERG, G.A. LANG, and R. Ptacnikova. Spatial and predatory interactions of visually preying nonindigenous zooplankton and fish in Lake Michigan during midsummer. Journal of Great Lakes Research 41(Supplement 3):125-142 (DOI:10.1016/j.jglr.2015.10.005) (2015).

A plankton survey system, fisheries acoustics, and opening/closing nets were used to define fine-scale diel vertical spatial interactions among non-indigenous alewives and visually preying cercopagids (Bythotrephes longimanus and Cercopagis pengoi) and indigenous zooplankton in nearshore and offshore Lake Michigan during August 2004. Because of increased water clarity associated with dreissenid mussel expansion and radically different thermal structure between cruises, we were able to observe the effects of thermal structure on diel vertical migration under high light conditions favorable especially to visual predation by cercopagids. Vertical position and overlap between alewives, Bythotrephes, and Daphnia mendotae at a 60-m site were strongly driven by thermal structure. Daphnia showed the strongest diel vertical migration of zooplankton that included migration between the epilimnion at night and the metalimnion–hypolimnion boundary during the day, whereas its major predator, Bythotrephes, was confined at all times to the epilimnion–metalimnion. Some alewives migrated from the hypolimnion to the metalimnion and epilimnion at night. As a result, most spatial overlap of Daphnia, Bythotrephes, and alewives occurred at night. Simple bioenergetics models were used to contrast predatory interactions between alewives and cercopagids at nearshore and offshore sites. Bythotrephes was the preferred prey of alewives, and at the 10-m site, alewives were themajor controller of zooplankton because of its elimination of Bythotrephes. In contrast, Bythotrephes offshore likely escaped predation because of low spatial overlap with a low concentration of alewives and was the major predator and shaper of zooplankton community structure.

Visser, P.M., J.M.H. Verspagen, G. Sandrini, L.J. Stal, H.C.P. Matthijs, T.W. DAVIS, H.W. Paerl, and J. Huisman. How rising CO2 and global warming may stimulate harmful cyanobacterial blooms. Harmful Algae 54:145-159 (DOI:10.1016/j.hal.2015.12.006) (2016).

Climate change is likely to stimulate the development of harmful cyanobacterial blooms in eutrophic waters, with negative consequences for water quality of many lakes, reservoirs and brackish ecosystems across the globe. In addition to effects of temperature and eutrophication, recent research has shed new light on the possible implications of rising atmospheric CO2 concentrations. Depletion of dissolved CO2 by dense cyanobacterial blooms creates a concentration gradient across the air–water interface. A steeper gradient at elevated atmospheric CO2 concentrations will lead to a greater influx of CO2, which can be intercepted by surface-dwelling blooms, thus intensifying cyanobacterial blooms in eutrophic waters. Bloom-forming cyanobacteria display an unexpected diversity in CO2 responses, because different strains combine their uptake systems for CO2 and bicarbonate in different ways. The genetic composition of cyanobacterial blooms may therefore shift. In particular, strains with high-flux carbon uptake systems may benefit from the anticipated rise in inorganic carbon availability. Increasing temperatures also stimulate cyanobacterial growth. Many bloom-forming cyanobacteria and also green algae have temperature optima above 25 8C, often exceeding the temperature optima of diatoms and dinoflagellates. Analysis of published data suggests that the temperature dependence of the growth rate of cyanobacteria exceeds that of green algae. Indirect effects of elevated temperature, like an earlier onset and longer duration of thermal stratification, may also shift the competitive balance in favor of buoyant cyanobacteria while eukaryotic algae are impaired by higher sedimentation losses. Furthermore, cyanobacteria differ from eukaryotic algae in that they can fix dinitrogen, and new insights show that the nitrogen-fixation activity of heterocystous cyanobacteria can be strongly stimulated at elevated temperatures. Models and lake studies indicate that the response of cyanobacterial growth to rising CO2 concentrations and elevated temperatures can be suppressed by nutrient limitation. The greatest response of cyanobacterial blooms to climate change is therefore expected to occur in eutrophic and hypertrophic lakes.

Wagner, T., C.E. Fergus, C.A. STOW, K.S. Cheruvelil, and P.A. Soranno. The statistical power to detect cross-scale interactions at macroscales. Ecosphere 7(7)(DOI:10.1002/ecs2.1417) (2016).

Macroscale studies of ecological phenomena are increasingly common because stressors such as climate and land-use change operate at large spatial and temporal scales. Cross-scale interactions (CSIs), where ecological processes operating at one spatial or temporal scale interact with processes operating at another scale, have been documented in a variety of ecosystems and contribute to complex system dynamics. However, studies investigating CSIs are often dependent on compiling multiple data sets from different sources to create multithematic, multiscaled data sets, which results in structurally complex, and sometimes incomplete data sets. The statistical power to detect CSIs needs to be evaluated because of their importance and the challenge of quantifying CSIs using data sets with complex structures and missing observations. We studied this problem using a spatially hierarchical model that measures CSIs between regional agriculture and its effects on the relationship between lake nutrients and lake productivity. We used an existing large multithematic, multiscaled database, LAke multiscaled GeOSpatial, and temporal database (LAGOS), to parameterize the power analysis simulations. We found that the power to detect CSIs was more strongly related to the number of regions in the study rather than the number of lakes nested within each region. CSI power analyses will not only help ecologists design large-scale studies aimed at detecting CSIs, but will also focus attention on CSI effect sizes and the degree to which they are ecologically relevant and detectable with large data sets.

WANG, J., X. BAI, Z. Yang, A.H. CLITES, and H. HU. Projection of Great Lakes seasonal ice cover using multi-variable regression models. Proceedings of the 23rd IAHR International Symposium on Ice (2016).

In this study, temporal variability of ice cover in the Great Lakes is investigated using historical satellite measurements undated from 1973 to 2015. With high ice cover in the last two winters (2013/14 and 2014/15), the trend was significantly reduced, compared to the period 1973-2013. The decadal variability in lake ice attributed to the decreased trend. It was found that 1) Great Lakes ice cover has a linear relationship with Atlantic Multidecadal Oscillation (AMO), similar to the relationship of lake ice cover with the North Atlantic Oscillation (NAO), and 2) a weak quadratic relation with the Pacific Decadal Oscillation (PDO), similar to the relationship of lake ice cover with the Niño3.4. Based on these dynamic relationships, the original multiple variable regression models established using the indices of NAO and Niño3.4 is updated by adding both AMO and PDO, as well their competing mechanism. With the AMO and PDO added, the correlation between the model and observation increases to 0.68, compared to 0.44 using NAO and Niño3.4 only. The new model was used to project the annual maximum ice coverage using projected indices of Niño3.4, NAO, PDO, and AMO. On November 30, 2015, the AMIC of 2015/16 winter was projected to be 31%.

Wang, L., Y. Qian, Y. Zhang, C. Zhoa, L.R. Leung, A. Huang, and C. XIAO. Observed variability of summer precipitation pattern and extreme events in East China associated with variations of the East Asian summer monsoon. International Journal of Climatology 36(8):2942-2957 (DOI:10.1002/joc.4530) (2016).

This article presents a comprehensive analysis of interannual and interdecadal variations of summer precipitation and precipitation-related extreme events in East China associated with variations of the East Asian summer monsoon (EASM) from 1979 to 2012. A high-quality daily precipitation data set covering 2076 observational stations in China is analysed. Based on the precipitation pattern analysis using empirical orthogonal functions and the regime shift detection method, three sub-periods of 1979–1992 (period I), 1993–1999 (period II) and 2000–2012 (period III) are identified to be representative of the precipitation variability. Similar significant variability of the extreme precipitation indices is found across four sub-regions in eastern China. The spatial patterns of summer mean precipitation, the number of days with daily rainfall exceeding 95th percentile precipitation (R95p) and the maximum number of consecutive wet days (CWD) anomalies are consistent, but opposite to that of maximum consecutive dry days (CDD) anomalies to some extent during the three sub-periods. However, the spatial patterns of hydroclimatic intensity (HY-INT) are notably different from that of the other three extreme indices, but highly correlated to the dry events. The changes of precipitation anomaly patterns are accompanied by the change of the EASM regime and the abrupt shift of the position of the west Pacific subtropical high around 1992/1993 and 1999/2000, respectively, which influence the moisture transport and contributes to the precipitation anomalies. In addition, the EASM intensity is linked to sea surface temperature anomaly over the tropical Indian and Pacific Ocean through its effects on convective activity over the west Pacific that induces the cyclonic or anticyclonic anomaly over the South China and northwest Pacific.

XIAO, C., Y. Zhang, B.M. LOFGREN, and Y. Nie. The concurrent variability of East Asian subtropical and polar-front jets and its implication for the winter climate anomaly in China. Journal of Geophysical Research: Atmosphere 121(12):6787-6801 (DOI:10.1002/2016JD025038) (2016).

The variability of East Asian upper level westerly jets in winter is studied with regard to the concurrent existence of subtropical jet (East Asian subtropical jet (EASJ)) and polar-front jet (East Asian polar-front jet (EAPJ)) using the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis. In the distribution of jet occurrence revealed in 6-hourly data, two jet branches along 30°N and 55°N, corresponding to locations of EASJ and EAPJ, respectively, are separated over the Tibetan Plateau. The leading two modes of zonal-mean zonal wind in East Asia extracted from a mass-weighted empirical orthogonal function analysis are characterized by the intensity changes and location displacements of two jets. The key regions for EASJ and EAPJ are then defined to represent variabilities of these two jets. Correlation analysis indicates that the subseasonal variation of EAPJ precedes EASJ by around 5 days, which can be interpreted as wave-mean flow interactions via synoptic-scale transient eddy activities. Based on the pentad intensity indices of two jets, the concurrent variabilities of EASJ and EAPJ are investigated with typical temperature and precipitation anomalies in China. The results suggest that by taking account of the two jets, we are able to get a more comprehensive understanding of the winter climate.

ZHANG, H., E.S. RUTHERFORD, D.M. MASON, J.T. Breck, M.T. Wittman, R.M. Cooke, D.M. Lodge, J.D. Rothlisberger, X. Zhu, and T.B. Johnson. Forecasting the impacts of silver and bighead carp on the Lake Erie food web. Transactions of the American Fisheries Society 145(1):136-162 (DOI:10.1080/00028487.2015.1069211) (2016).

Nonindigenous bigheaded carps (Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix; hereafter, “Asian carps” [AC]) threaten to invade and disrupt food webs and fisheries in the Laurentian Great Lakes through their high consumption of plankton. To quantify the potential effects of AC on the food web in LakeErie, we developed an Ecopath with Ecosim (EwE) food web model and simulated four AC diet composition scenarios (high, low, and no detritus and low detritus with Walleye Sander vitreus and Yellow Perch Perca flavescens larvae) and two nutrient load scenarios (the 1999 baseline load and 2£ the baseline [HP]). We quantified the uncertainty of the potential AC effects by coupling the EwE model with estimates of parameter uncertainty in AC production, consumption, and predator diets obtained using structured expert judgment. Our model projected mean § SD AC equilibrium biomass ranging from 52 § 34 to 104 § 75 kg/ha under the different scenarios. Relative to baseline simulations without AC, AC invasion under all detrital diet scenarios decreased the biomass of most fish and zooplankton groups. The effects of AC in the HP scenario were similar to those in the detrital diet scenarios except that the biomasses of most Walleye and Yellow Perch groups were greater under HP because these fishes were buffered from competition with AC by increased productivity at lower trophic levels. Asian carp predation on Walleye and Yellow Perch larvae caused biomass declines among all Walleye and Yellow Perch groups. Large food web impacts of AC occurred in only 2% of the simulations, where AC biomass exceeded 200 kg/ha, resulting in biomass declines of zooplankton and planktivorous fish near the levels observed in the Illinois River. Our findings suggest that AC would affect Lake Erie’s food web by competing with other planktivorous fishes and by providing additional prey for piscivores. Our methods provide a novel approach for including uncertainty into forecasts of invasive species’ impacts on aquatic food webs.


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