GLERL Publications with Abstracts
Fiscal year 2017

October 2016 - Present

ANDERSON, E.J., and D.J. Schwab. Meteorological influence on summertime baroclinic exchange in the Straits of Mackinac. Journal of Geophysical Research: Oceans 122(3):2171-2182 (DOI:10.1002/2016JC012255) (2017).

Straits flows can impose a complex hydrodynamic environment with high seasonal variability and significant impacts to nearby water bodies. In the Straits of Mackinac, exchange flow between Lake Michigan and Lake Huron influences water quality and ecological processes, as well as the transport of any contaminants released in or near the straits. Although previous work has shown that a Helmholtz mode is responsible for the barotropic flow oscillations in the straits, baroclinic effects impose opposite surface and subsurface flows during the summer months. In this study, we use observations of currents and water temperatures from instruments deployed in the straits to validate a hydrodynamic model of the combined Lake Michigan-Huron system and then use the model results to investigate the baroclinic flow and determine the forcing mechanisms that drive exchange flow in the Straits of Mackinac. Analysis shows that although the Helmholtz mode drives a 3 day oscillation throughout the year, thermal stratification in the summer establishes a bidirectional flow that is governed by a shift from regional-scale to local-scale meteorological conditions. These results detail the seasonal variability in the straits, including the barotropic and baroclinic contributions to exchange flow and the influence of local atmospheric forcing on transport through the Straits of Mackinac.

Bechle, A., C.H. Wu, D.A.R. Kristovich, E.J. ANDERSON, D.J. Schwab, and A.B. Rabinovich. Meteotsunamis in the Laurentian Great Lakes. Scientific Reports (DOI:10.1038/srep37832) (2016).

The generation mechanism of meteotsunamis, which are meteorologically induced water waves with spatial/temporal characteristics and behavior similar to seismic tsunamis, is poorly understood. We quantify meteotsunamis in terms of seasonality, causes, and occurrence frequency through the analysis of long-term water level records in the Laurentian Great Lakes. The majority of the observed meteotsunamis happen from late-spring to mid-summer and are associated primarily with convective storms. Meteotsunami events of potentially dangerous magnitude (height > 0.3 m) occur an average of 106 times per year throughout the region. These results reveal that meteotsunamis are much more frequent than follow from historic anecdotal reports. Future climate scenarios over the United States show a likely increase in the number of days favorable to severe convective storm formation over the Great Lakes, particularly in the spring season. This would suggest that the convectively associated meteotsunamis in these regions may experience an increase in occurrence frequency or a temporal shift in occurrence to earlier in the warm season. To date, meteotsunamis in the area of the Great Lakes have been an overlooked hazard.

BELETSKY, D., R. BELETSKY, E.S. RUTHERFORD, J.L. Sieracki, J.M. Bossenbroek, W.L. Chadderton, M.E. Wittmann, and D.M. Lodge. Predicting spread of aquatic invasive species by lake currents. Journal of Great Lakes Research 43(3):14-32 (DOI:10.1016/j.jglr.2017.02.001) (2017).

Knowledge of aquatic invasive species (AIS) dispersal is important to inform surveillance and management efforts to slow the spread of established invaders. We studied potential dispersal of invasive Eurasian ruffe Gymnocephalus cernua and golden mussel Limnoperna fortunei larvae in Lakes Michigan and Erie using a three-dimensional particle transport model. Ruffe is currently in Lake Superior and northern Lake Michigan, while Limnoperna has not yet invaded the Great Lakes. We predicted larval transport during several spawning seasons (individual years) from several major tributaries and ports that are most prone to invasion because of their significant recreational and commercial usage. Depending on release location, larvae traveled distances ranging from < 1 km to tens of kilometers (in some cases over 100–200 km, depending on species) during 2–3 weeks of drift time. Dispersal distances from nearshore locations (i.e. rivers and ports) were smaller than from offshore deballasting locations near ports. Limnoperna dispersal distances were larger than ruffe due to stronger seasonal currents and longer drift period. Settlement areas resulting from offshore releases were larger than for nearshore releases, and larger for Limnoperna than for ruffe. Model results compared favorably to observed spread of ruffe and Dreissena spp. mussels in Lake Michigan. Our modeling effort suggests that larval advection by lake currents is an important AIS dispersal mechanism in the Great Lakes. It also emphasizes the importance of effective surveillance programs that maximize early detection of new introductions before lake current dispersal obviates containment and prevention of spread and impacts.

Berry, M.A., T.W. DAVIS, R.M. Cory, M.B. Duhaime, T.H. JOHENGEN, C.L. Kling, J.A. Marino, P.A. Den Uyl, D.C. GOSSIAUX, G.J. Dick, and V.J. Denef. Cyanobacterial harmful algal blooms are a biological disturbance to western Lake Erie bacterial communities. Environmental Microbiology 19(Thematic Issue on Environmental Glycerol Metabolism ):1149-1162 (DOI:10.1111/1462-2920.13640) (2017).

Human activities are causing a global proliferation of cyanobacterial harmful algal blooms (CHABs), yet we have limited understanding of how these events affect freshwater bacterial communities. Using weekly data from western Lake Erie in 2014, we investigated how the cyanobacterial community varied over space and time, and whether the bloom affected non-cyanobacterial (nc-bacterial) diversity and composition. Cyanobacterial community composition fluctuated dynamically during the bloom, but was dominated by Microcystis and Synechococcus OTUs. The bloom's progression revealed potential impacts to nc-bacterial diversity. Nc-bacterial evenness displayed linear, unimodal, or no response to algal pigment levels, depending on the taxonomic group. In addition, the bloom coincided with a large shift in nc-bacterial community composition. These shifts could be partitioned into components predicted by pH, chlorophyll a, temperature, and water mass movements. Actinobacteria OTUs showed particularly strong correlations to bloom dynamics. AcI-C OTUs became more abundant, while acI-A and acI-B OTUs declined during the bloom, providing evidence of niche partitioning at the sub-clade level. Thus, our observations in western Lake Erie support a link between CHABs and disturbances to bacterial community diversity and composition. Additionally, the short recovery of many taxa after the bloom indicates that bacterial communities may exhibit resilience to CHABs.

Berry, M.A., J.D. White, T.W. DAVIS, S. Jain, T.H. JOHENGEN, G.J. Dick, O. Sarnelle, and V.J. Denef. Are oligotypes meaningful ecological and phylogenetic units? A case study of Microcystis in freshwater lakes. Frontiers in Microbiology 8:Article 365 (DOI:10.3389/fmicb.2017.00365 ) (2017).

Oligotyping is a computational method used to increase the resolution of marker gene microbiome studies. Although oligotyping can distinguish highly similar sequence variants, the resulting units are not necessarily phylogenetically and ecologically informative due to limitations of the selected marker gene. In this perspective, we examine how oligotyping data is interpreted in recent literature, and we illustrate some of the method’s constraints with a case study of the harmful bloom-forming cyanobacterium Microcystis. We identified three Microcystis oligotypes from a western Lake Erie bacterial community 16S rRNA gene (V4 region) survey that had previously clustered into one OTU. We found the same three oligotypes and two additional sequence variants in 46 Microcystis cultures isolated from Michigan inland lakes spanning a trophic gradient. In Lake Erie, shifts in Microcystis oligotypes corresponded to spatial nutrient gradients and temporal transitions in bloom toxicity. In the cultures, Microcystis oligotypes showed preferential distributions for different trophic states, but genomic data revealed that the oligotypes identified in Lake Erie did not correspond to toxin gene presence. Thus, oligotypes could not be used for inferring toxic ecotypes. Most strikingly, Microcystis oligotypes were not monophyletic. Our study supports the utility of oligotyping for distinguishing sequence types along certain ecological features, while it stresses that 16S rRNA gene sequence types may not reflect ecologically or phylogenetically cohesive populations. Therefore, we recommend that studies employing oligotyping or related tools consider these caveats during data interpretation.

Bertani, I., D.R. Obenour, C.E. Stegera, C.A. STOW, A.D. GRONEWOLD, and D. Scavia. Probabilistically assessing the role of nutrient loading in harmful algal bloom formation in western Lake Erie. Journal of Great Lakes Research 42:1184-1192 (DOI:10.1016/j.jglr.2016.04.002) (2016).

Harmful algal blooms (HABs) have increased in frequency and magnitude in western Lake Erie and spring phosphorus (P) load was shown to be a key driver of bloom intensity. A recently developed Bayesian hierarchical model that predicts peak bloom size as a function of Maumee River phosphorus load suggested an apparent increased susceptibility of the lake to HABs. We applied that model to develop load–response curves to inform revision of Lake Erie phosphorus load targets under the 2012 Great Lakes Water Quality Agreement. In this application, the model was modified to estimate the fraction of the particulate P (PP) load that becomes bioavailable, and it was recalibrated with additional bloom observations. Although the uncertainty surrounding the estimate of the bioavailable PP fraction is large, inclusion in the model improves prediction of bloom variability compared to dissolved reactive P (DRP) alone. The ability to characterize model and measurement uncertainty through hierarchical modeling allowed us to show that inconsistencies in bloom measurement represent a considerable portion of the overall uncertainty associated with load–response curves. The updated calibration also lends support to the system's apparent enhanced susceptibility to blooms. The temporal trend estimated by the model results in an upward shift of the load–response curve over time such that a larger load reduction is required to achieve a target bloom size today compared to earlier years. More research is needed to further test the hypothesis of a shift in the lake's response to stressors over time and, if confirmed, to explore underlying mechanisms.

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) (2017).

The National Oceanic and Atmospheric Administration’s Climate Prediction Center (CPC) provides access to a suite of real-time monthly climate forecasts that compose 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 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 (RSCF–NMME) tool 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 CPC, shows that the tool can provide additional useful information to users and overcome some of the limitations of the 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.

Cable, R.N., D. BELETSKY, R. BELETSKY, B.W. Locke, K. Wigginton, and M.B. Duhaime. Distribution and modeled transport of plastic pollution in the Great Lakes, the world’s largest freshwater resource. Frontiers in Environmental Science (DOI:10.3389/fenvs.2017.00045) (2017).

Most plastic pollution originates on land. As such, freshwater bodies serve as conduits for the transport of plastic litter to the ocean. Understanding the concentrations and fluxes of plastic litter in freshwater ecosystems is critical to our understanding of the global plastic litter budget and underpins the success of future management strategies. We conducted a replicated field survey of surface plastic concentrations in four lakes in the North American Great Lakes system, the largest contiguous freshwater system on the planet. We then modeled plastic transport to resolve spatial and temporal variability of plastic distribution in one of the Great Lakes, Lake Erie. Triplicate surface samples were collected at 38 stations in mid-summer of 2014. Plastic particles >106 µm in size were quantified. Concentrations were highest near populated urban areas and their water infrastructure. In the highest concentration trawl, nearly 2 million fragments km-2 were found in the Detroit River—dwarfing previous reports of Great Lakes plastic abundances by over 4-fold. Yet, the accuracy of single trawl counts was challenged: within-station plastic abundances varied 0- to 3-fold between replicate trawls. In the smallest size class (106-1000 µm), false positive rates of 12-24% were determined analytically for plastic versus non-plastic, while false negative rates averaged ~18%. Though predicted to form in summer by the existing Lake Erie circulation model, our transport model did not predict a permanent surface “Lake Erie Garbage Patch” in its central basin—a trend supported by field survey data. Rather, general eastward transport with recirculation in the major basins was predicted. Further, modeled plastic residence times were drastically influenced by plastic buoyancy. Neutrally buoyant plastics—those with the same density as the ambient water—were flushed several times slower than plastics floating at the water’s surface and exceeded the hydraulic residence time of the lake. It is likely that the ecosystem impacts of plastic litter persist in the Great Lakes longer than assumed based on lake flushing rates. This study furthers our understanding of plastic pollution in the Great Lakes, a model freshwater system to study the movement of plastic from anthropogenic sources to environmental sinks.

Collingsworth, P.D., D.B. Bunnell, M.W. Murray, Y.C. Kao, Z.S. Feiner, R.M. Claramunt, B.M. LOFGREN, T.O. Hook, and S.A. Ludsin. Climate change as a long-term stressor for the fisheries of the Laurentian Great Lakes of North America. Reviews in Fish Biology and Fisheries:1-29 (DOI:10.1007/s11160-017-9480-3) (2017).

The Laurentian Great Lakes of North America provide valuable ecosystem services, including fisheries, to the surrounding population. Given the prevalence of other anthropogenic stressors that have historically affected the fisheries of the Great Lakes (e.g., eutrophication, invasive species, overfishing), climate change is often viewed as a long-term stressor and, subsequently, may not always be prioritized by managers and researchers. However, climate change has the potential to negatively affect fish and fisheries in the Great Lakes through its influence on habitat. In this paper, we (1) summarize projected changes in climate and fish habitat in the Great Lakes; (2) summarize fish responses to climate change in the Great Lakes; (3) describe key interactions between climate change and other stressors relevant to Great Lakes fish, and (4) summarize how climate change can be incorporated into fisheries management. In general, fish habitat is projected to be characterized by warmer temperatures throughout the water column, less ice cover, longer periods of stratification, and more frequent and widespread periods of bottom hypoxia in productive areas of the Great Lakes. Based solely on thermal habitat, fish populations theoretically could experience prolonged optimal growth environment within a changing climate, however, models that assess physical habitat influences at specific life stages convey a more complex picture. Looking at specific interactions with other stressors, climate change may exacerbate the negative impacts of both eutrophication and invasive species for fish habitat in the Great Lakes. Although expanding monitoring and research to consider climate change interactions with currently studied stressors, may offer managers the best opportunity to keep the valuable Great Lakes fisheries sustainable, this expansion is globally applicable for large lake ecosystem dealing with multiple stressors in the face of continued human-driven changes.

Davidson, A., A. Fusaro, R.A. STURTEVANT, and D.R. Kashian. Development of a risk assessment framework to predict invasive species establishment for multiple taxonomic groups and vectors of introduction. Management of Biological Invasions 8(1):25-36 (2016).

A thorough assessment of aquatic nonindigenous species’ risk facilitates successful monitoring and prevention activities. However, species- and vector-specific information is often limited and difficult to synthesize across a single risk framework. To address this need, we developed an assessment framework capable of estimating the potential for introduction, establishment, and impact by aquatic nonindigenous species from diverse spatial origins and taxonomic classification, in novel environments. Our model builds on previous approaches, while taking on a new perspective for evaluation across species, vectors and stages to overcome the limitations imposed by single species and single vector assessments. We applied this globally-relevant framework to the Laurentian Great Lakes to determine its ability to evaluate risk across multiple taxa and vectors. This case study included 67 aquatic species, identified as “watchlist species” in NOAA’s Great Lakes Aquatic Nonindigenous Species Information System (GLANSIS). Vectors included shipping, hitchhiking/fouling, unauthorized intentional release, escape from recreational or commercial culture, and natural dispersal. We identified potential invaders from every continent but Africa and Antarctica. Of the 67 species, more than a fifth (21%) had a high potential for introduction and greater than 60% had a moderate potential for introduction. Shipping (72%) was the most common potential vector of introduction, followed by unauthorized intentional release (25%), hitchhiking/fouling (21%), dispersal (19%), stocking/planting/escape from recreational culture (13%), and escape from commercial culture. The ability to assess a variety of aquatic nonindigenous species from an array of potential vectors using a consistent methodology is essential for comparing likelihoods of introduction, establishment, and impact. The straightforward design of this framework will allow its application and modification according to policy priorities by natural resource managers. The ability to use a variety of information sources facilitates completion of assessments despite the paucity of data that often plagues aquatic nonindigenous species management.

Denef, V.J., H.J. Carrick, J.F. CAVALETTO, E. Chiang, T.H. JOHENGEN, and H.A. VANDERPLOEG. Lake Bacterial Assemblage Composition Is Sensitive to Biological Disturbance Caused by an Invasive Filter Feeder. mSphere 2(3)(DOI:10.1128/mSphere.00189-17) (2017).

One approach to improve forecasts of how global change will affect ecosystem processes is to better understand how anthropogenic disturbances alter bacterial assemblages that drive biogeochemical cycles. Species invasions are important contributors to global change, but their impacts on bacterial community ecology are rarely investigated. Here, we studied direct impacts of invasive dreissenid mussels (IDMs), one of many invasive filter feeders, on freshwater lake bacterioplankton. We demonstrated that direct effects of IDMs reduced bacterial abundance and altered assemblage composition by preferentially removing larger and particle-associated bacteria. While this increased the relative abundances of many free-living bacterial taxa, some were susceptible to filter feeding, in line with efficient removal of phytoplankton cells of <2 μm. This selective removal of particle-associated and larger bacteria by IDMs altered inferred bacterial functional group representation, defined by carbon and energy source utilization. Specifically, we inferred an increased relative abundance of chemoorganoheterotrophs predicted to be capable of rhodopsin-dependent energy generation. In contrast to the few previous studies that have focused on the longer-term combined direct and indirect effects of IDMs on bacterioplankton, our study showed that IDMs act directly as a biological disturbance to which freshwater bacterial assemblages are sensitive. The negative impacts on particle-associated bacteria, which have been shown to be more active than free-living bacteria, and the inferred shifts in functional group representation raise the possibility that IDMs may directly alter bacterially mediated ecosystem functions.

Dias, J.P., (and 44 others), and S.A. POTHOVEN. Establishment of a taxonomic and molecular reference collection to support the identification of species regulated by the Western Australian Prevention List for Introduced Marine Pests. Management of Biological Invasions 8(2):215-225 (DOI:10.3391/mbi.2017.8.2.09) (2017).

Introduced Marine Pests (IMP, = non-indigenous marine species) prevention, early detection and risk-based management strategies have become the priority for biosecurity operations worldwide, in recognition of the fact that, once established, the effective management of marine pests can rapidly become cost prohibitive or impractical. In Western Australia (WA), biosecurity management is guided by the " Western Australian Prevention List for Introduced Marine Pests " which is a policy tool that details species or genera as being of high risk to the region. This list forms the basis of management efforts to prevent introduction of these species, monitoring efforts to detect them at an early stage, and rapid response should they be detected. It is therefore essential that the species listed can be rapid and confidently identified and discriminated from native species by a range of government and industry stakeholders. Recognising that identification of these species requires very specialist expertise which may be in short supply and not readily accessible in a regulatory environment, and the fact that much publicly available data is not verifiable or suitable for regulatory enforcement, the WA government commissioned the current project to collate a reference collection of these marine pest specimens. In this work, we thus established collaboration with researchers worldwide in order to source representative specimens of the species listed. Our main objective was to build a reference collection of taxonomically vouchered specimens and subsequently to generate species-specific DNA barcodes suited to supporting their future identification. To date, we were able to obtain specimens of 75 species (representative of all but four of the pests listed) which have been identified by experts and placed with the WA Government Department of Fisheries and, where possible, in accessible museums and institutions in Australasia. The reference collection supports the fast and reliable taxonomic and molecular identification of marine pests in WA and constitutes a valuable resource for training of stakeholders with interest in IMP recognition in Australia. The reference collection is also useful in supporting the development of a variety of DNA-based detection strategies such as real-time PCR and metabarcoding of complex environmental samples (e.g. biofouling communities). The Prevention List is under regular review to ensure its continued relevance and that it remains evidence and risk-based. Similarly, its associated reference collection also remains to some extent a work in progress. In recognition of this fact, this report seeks to provide details of this continually evolving information repository publicly available to the biosecurity management community worldwide.

Foley, C.J., S.R. Andree, S.A. POTHOVEN, T.F. NALEPA, and T.O. Hook. Quantifying the predatory effect of round goby on Saginaw Bay dreissenids. Journal of Great Lakes Research 43(1):121-131 (DOI:10.1016/j.jglr.2016.10.018) (2017).

Invasive dreissenid mussels (D. polymorpha and D. r. bugensis) have fundamentally altered Laurentian Great Lake ecosystems, however in many areas their abundances have declined since the mid-1990s. Another invader, the benthic fish round goby (Neogobius melanostomus), is morphologically adapted to feed on dreissenids and likely affects dreissenid populations; however, the degree of this predatory effect is variable. In 2009 and 2010, we examined round goby abundances, size distributions, diet contents, and diet selectivity in Saginaw Bay, Lake Huron; a shallow bay that has been subjected to numerous anthropogenic stressors. We further used a consumption model to estimate dreissenid consumption by three different size classes of round goby. Round gobies were found throughout the bay and most were smaller than 80 mm total length. Round gobies of all sizes consumed dreissenids (including fish as small as 30 mm total length), though dreissenids were rarely preferred. The relative proportion of dreissenids (by biomass) present in diets of round gobies increased with fish size, but also throughout the year for all size classes. Despite this, overall consumptive effects of round gobies on dreissenids in Saginaw Bay were low. Many dreissenids present in the bay were larger than those consumed by round gobies. Bioenergetics-based model estimates suggest that the smallest round gobies are responsible for the majority of dreissenid consumption. While our findings are limited to soft substrates and influenced by sampling restrictions, our study design allowed us to put bounds on our estimates based upon these multiple sources of uncertainty.

Fujimoto, M., J.F. CAVALETTO, J.R. LIEBIG, A. McCarthy, H.A. VANDERPLOEG, and V.J. Denef. Spatiotemporal distribution of bacterioplankton functional groups along a freshwater estuary to pelagic gradient in Lake Michigan. Journal of Great Lakes Research 42(5):1036-1048 (DOI:10.1016/j.jglr.2016.07.029) (2016).

Freshwater bacteria play key roles in biogeochemical cycling and contribute significantly to biomass and energy fluxes. However, studies of Great Lakes ecosystem dynamics often omit bacteria. Here, we used high throughput sequencing to analyze how bacterial diversity and community composition (BCC) vary seasonally along the long-term Muskegon estuary to pelagic research transect. Diversity was higher in the estuary than Lake Michigan, in spring compared to summer, and for particle-associated (PA) relative to free-living (FL) fractions. PA communities were distinct from and more variable than FL communities. For both fractions, spring BCC was more similar between estuary and nearshore Lake Michigan compared to offshore waters. In summer and fall, nearshore and offshore BCC were more similar compared to estuary BCC. Most abundant taxa were inferred to be chemoorganoheterotrophs. While, as a whole, this functional group only showed habitat preference for the PA fraction, we observed phylum- and class-level seasonal and spatial preferences. Chemoorganoheterotrophs that also perform bacteriorhodopsin-mediated phototrophy, such as acI Actinobacteria and LD12, strongly preferred FL fractions. Photoautotrophs (Cyanobacteria) were least abundant in spring, when mixotrophic methylotrophs were more abundant, particularly in the estuary. Organisms with chemolithotrophic capabilities, including a mixotrophic, highly abundant Limnohabitans (Lhab-A1) OTU, showed limited spatiotemporal patterns. One exception was Nitrosospira, an autotrophic ammonium oxidizer, which peaked in deep offshore waters in fall. Nitrosospira co-occurred with Chloroflexi CL500-11, which likely mineralizes nitrogen-rich organic matter in deep waters. These spatiotemporal BCC shifts suggest differences in bacterially mediated elemental cycling along estuary to pelagic gradients in Lake Michigan.

Fusaro, A., E. Baker, W. Conard, A. Davidson, K. Dettloff, J. Li, G. Nunez-Mir, R.A. STURTEVANT, and E.S. RUTHERFORD. A risk assessment of Great Lakes aquatic invaders. NOAA Technical Memorandum GLERL-169. NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 1638 pp. (2016).

Introduced species have the potential for both ecological and socioeconomic effects. Once established, these species can be nearly impossible to eradicate (Hobbs & Humphries 1995). In the few successful eradication efforts, the cost has been substantial (Simberloff 2003). Managing spread and controlling for impact are also costly (Leung et al. 2002). At least 31% nonindigenous species established in the Great Lakes have significant impacts (Sturtevant et al. 2014). The most economically and practically effective strategy is therefore to prevent species introduction in the first place (Lodge et al. 2006). As a means of prioritizing management efforts, risk assessment tools that consider vectors and pathways of introduction, species life history traits, habitat suitability, historical patterns of invasion, impacts realized in other invaded regions have become commonly implemented (Gordon et al. 2012, Keller et al. 2009). In order to accurately predict risk, a thorough understanding of these potentially introduced species is needed (Keller et al. 2007b, Springborn et al. 2011—but see Simberloff 2003). However, species and pathway information can also be scarce or diffuse (e.g., 95/156 species assessed as “not enough known” in USEPA 2008).

Gaborit, E., V. Fortin, B. Tolson, L.M. FRY, T.S. HUNTER, and A.D. GRONEWOLD. Great Lakes Runoff Inter-comparison Project, phase 2: Lake Ontario (GRIP-O). Journal of Great Lakes Research 43(2):217-227 (DOI:10.1016/j.jglr.2016.10.004) (2017).

The Great Lakes Runoff Inter-comparison Project for Lake Ontario (GRIP-O) aims to compare different hydrologic models, using the same settings, in their ability to estimate runoff for the Lake Ontario watershed. The watershed is challenging because many of its tributaries have a regulated flow regime and a significant part remains ungauged. GRIP-O follows the GRIP-M project which focused on Lake Michigan. It involves a comparison between two different sources of precipitation data (CaPA - Canadian Precipitation Analysis and the GHCND - Global Historical Climatology Network - Daily), and focuses here on two lumped models, GR4J (modèle du Génie Rural à 4 paramètres Journalier) and LBRM (Large Basin Runoff Model).

Results indicate that both models perform very well, with GR4J performing slightly better than LBRM and the GHCND precipitation dataset resulting in better simulations than CaPA, for this area. Performances are, however, always very satisfactory whatever the combination of model/precipitation data used, even for regulated catchments, and do not show any clear correlation to any of the catchments' properties studied here. Results also tend to confirm that the Area-Ratio Method is appropriate for extrapolating flows from the gauged part of a catchment to the whole catchment including its ungauged parts, as demonstrated in GRIP-M.

Gaborit, E., V. Fortin, A. Xu, F. Seglenieks, B. Tolson, L.M. Fry, T.S. HUNTER, F. Anctil, and A.D. GRONEWOLD. A Hydrological Prediction System Based on the SVS Land–Surface Scheme: Implementation and Evaluation of the GEM-Hydro platform on the watershed of Lake Ontario. Hydrology and Earth System Sciences (DOI:10.5194/hess-2016-508) (2017).

This work describes the implementation of the distributed GEM-Hydro runoff modeling platform, developed at Environment and Climate Change Canada (ECCC) over the last decade. The latest version of GEM-Hydro combines the SVS (Soil, Vegetation and Snow) land-surface scheme and the WATROUTE routing scheme in order to provide streamflow predictions on a gridded river network. SVS is designed to be two-way coupled to the GEM (Global Environmental Multi-scale) atmospheric model exploited by ECCC for operational weather and environmental forecasting. Although SVS has been shown to accurately track soil moisture during the warm season, it has never been evaluated before for hydrological prediction. This paper presents a first evaluation of its ability to simulate streamflow for all major rivers flowing into Lake Ontario. The skill level of GEM-Hydro is assessed by comparing the quality of simulated flows to that of two established hydrological models, MESH and WATFLOOD, which share the same routing scheme (WATROUTE) but rely on different land–surface schemes. All models are calibrated using the same meteorological forcings, objective function, calibration algorithm, and watershed delineation. Results show that GEM-Hydro performs well and is competitive with MESH and WATFLOOD. A computationally efficient strategy is proposed to calibrate the land-surface model of GEM-Hydro: a simple unit hydrograph is used for routing instead of its standard distributed routing component. The distributed routing part of the model can then be run in a second step to estimate streamflow everywhere inside the domain. Global and local calibration strategies are compared in order to estimate runoff for ungauged portions of the Lake Ontario watershed. Overall, streamflow predictions obtained using a global calibration strategy, in which a single parameter set is identified for the whole watershed of Lake Ontario, show skills comparable to the predictions based on local calibration. Hence, global calibration provides spatially consistent parameter values, robust performance at gauged locations, and reduces the complexity and computational burden of the calibration procedure. This work contributes to the Great Lakes Runoff Inter-comparison Project for Lake Ontario (GRIP-O) which aims at improving Lake Ontario basin runoff simulations by comparing different models using the same input forcings.

Goto, D., J.J. Roberts, S.A. POTHOVEN, S.A. Ludsin, H.A. VANDERPLOEG, S.B. Brandt, and T.O. Höök. Size-mediated control of perch–midge coupling in Lake Erie transient dead zones. Environmental Biology of Fishes (DOI:10.1007/s10641-017-0667-1) (2017).

Transient ecosystem-level disturbances such as oxygen depletion (hypoxia) in aquatic systems modulate species distributions and interactions. In highly eutrophic systems, hypoxic areas (“dead zones”) have expanded around the world, temporarily preventing many demersal predators from accessing their food resources. Here, we investigate how yellow perch (Perca flavescens), an exploited, cool-water mesopredator, interact with their dominant invertebrate prey in benthic habitat–non-biting midge (chironomid) larvae–as bottom-water hypoxia develops in central Lake Erie (United States–Canada) during summer. We apply linear mixed-effects models to individual-level data from basin-wide field surveys on size-based interactions between perch and midge larvae under varying habitat conditions and resource attributes. We test if 1) midge populations (larval body size and density) differ among habitat states (unstratified normoxia, stratified normoxia, and stratified hypoxia); and 2) size-based perch–midge interactions (predator–prey mass ratio or PPMR) differ among habitat states with varying temperature and midge density. Midge populations remained highly abundant after bottom-water oxygen depletion. Despite their high densities, midge larvae also maintained their body size in hypoxic water. In contrast, perch on average consumed relatively smaller (by up to ~64%) midges (higher PPMR) in warmer and hypoxic water, while prey size ingested by perch shrunk less in areas with higher midge density. Our analysis shows that hypoxia-tolerant midges largely allow perch to maintain their consumer–resource relationships in contracted habitats through modified size-mediated interactions in dead zones during summer, revealing plasticity of their trophic coupling in the chronically perturbed ecosystem.

GRONEWOLD, A.D. The Great Lakes System. In Handbook of Applied Hydrology, Second Edition. Vijay P. Singh. McGraw Hill, (2016).

Introduction to the Great Lakes hydrological system. The North American Great Lakes system is commonly defined, as shown in figure 121-1, as the international waters of the Great Lakes themselves (i.e. Lakes Superior, Michigan, Huron, Erie, and Ontario), the rivers that connect them (commonly referred to as `interconnecting channels’), and their surrounding drainage areas. Generally, water flows through the system from Lake Superior through the St. Marys River, as shown in figure 121-2, to Lake Michigan-Huron (Lake Michigan and Lake Huron are often considered one lake because of their connection at the Straits of Mackinac). From Lake Huron, water flows through the St. Clair River, through Lake St. Clair, and through the Detroit River into Lake Erie. Water then flows out of Lake Erie through the Niagara River and over Niagara Falls into Lake Ontario. The downstream boundary of the Great Lakes is often defined as the outlet of Lake Ontario, as reflected in figure 121-1. However, the downstream boundary of the Great Lakes system is also sometimes defined by the Moses-Saunders dam (the point at which outflows from Lake Ontario are regulated), located along the St. Lawrence River at Cornwall, Ontario (Canada) and Massena, NY (USA). For further reading on the St. Lawrence River system downstream of the Great Lakes, see Chapter 113. The Great Lakes constitute the largest (both by volume and surface area) system of lakes on Earth (Herdendorf, 1990; Quinn, 1992). Lake Michigan-Huron alone has the largest continuous surface area (117,250 km2) of any freshwater surface body on Earth, while Lake Superior has the second largest surface area (82,100 km2). The total volume of the Great Lakes (roughly 22,800 km3) is very close to the volume of Lake Baikal, Earth’s largest lake by volume (roughly 23,000 km3), and is slightly larger than that of Lake Tanganyika (18,900 km3). Together, these three systems (the Great Lakes, Lake Tanganyika, and Lake Baikal) comprise about half of all of the fresh surface water on Earth.

GRONEWOLD, A.D., M.D. Sobsey, and K. McMahan. The compartment bag test (CBT) for enumerating fecal indicator bacteria: Basis for design and interpretation of results. Science of the Total Environment 587-588(1):102-107 (DOI:10.1016/j.scitotenv.2017.02.055) (2017).

For the past several years, the compartment bag test (CBT) has been employed in water quality monitoring and public health protection around the world. To date, however, the statistical basis for the design and recommended procedures for enumerating fecal indicator bacteria (FIB) concentrations from CBT results have not been formally documented. Here, we provide that documentation following protocols for communicating the evolution of similar water quality testing procedures. We begin with an overview of the statistical theory behind the CBT, followed by a description of how that theory was applied to determine an optimal CBT design. We then provide recommendations for interpreting CBT results, including procedures for estimating quantiles of the FIB concentration probability distribution, and the confidence of compliance with recognized water quality guidelines. We synthesize these values in custom user-oriented ‘look-up’ tables similar to those developed for other FIB water quality testing methods. Modified versions of our tables are currently distributed commercially as part of the CBT testing kit.

Hundey, E.J., J.H. Olker, C. Carreira, R.M. Daigle, A.K. ELGIN, M. Finiguerra, N.J. Gownaris, N. Hayes, L. Heffner, N.R. Razavi, P.D. Shirey, B.B. Tolar, and E.M. Wood-Charlson. A shifting tide: Recommendations for incorporating science communication into graduate training. Limnology and Oceanography: Bulletin 25(4):109-116 (DOI:10.1002/lob.10151) (2016).

Scientists who are skilled in communication reap professional and personal rewards. Unfortunately, gaps exist in fostering curricular and extracurricular training in science communication. We focus our article on opportunities for university- and department-level leadership to train new scientists to communicate effectively. Our motivation is threefold: (1) communication training is key to being competitive in the increasingly diverse job market, (2) training early career scientists in communication “jump-starts” personal and societal benefits, and (3) the authors represent a group of early career aquatic scientists with unique insights on the state of and need for training. We surveyed early career aquatic scientists about their science communication training experiences. In summary, survey respondents indicated that (1) science communication training is important; (2) graduate students are interested in training that is not currently available to them; (3) departments and advisors are moderately supportive of students participating in science communication, but less enthusiastic about providing training support; and (4) graduate students lack opportunities to put science communication training into practice. We recommend departments and institutions recognize the benefits of science communication training, develop a strategy to support such training, and facilitate individualized approaches to science communication.

Kramer, A.M., G. Annis, M.E. Wittmann, W.L. Chadderton, E.S. RUTHERFORD, D.M. Lodge, L.A. Mason, D. BELETSKY, C. Riseng, and J.M. Drake. Suitability of Great Lakes for aquatic invasive species basedon global species distribution models and local aquatic habitat. Ecosphere (DOI:10.1002/ecs2.1883) (2017).

Efficient management and prevention of species invasions requires accurate prediction of where species of concern can arrive and persist. Species distribution models provide one way to identify potentially suitable habitat by developing the relationship between climate variables and species occurrence data. However, these models when applied to freshwater invasions are complicated by two factors. The first is that the range expansions that typically occur as part of the invasion process violate standard species distribution model assumptions of data stationarity. Second, predicting potential range of freshwater aquatic species is complicated by the reliance on terrestrial climate measurements to develop occurrence relationships for species that occur in aquatic environments. To overcome these obstacles, we combined a recently developed algorithm for species distribution modeling—range bagging—with newly available aquatic habitat-specific information from the North American Great Lakes region to predict suitable habitat for three potential invasive species: golden mussel, killer shrimp, and northern snakehead. Range bagging may more accurately predict relative suitability than other methods because it focuses on the limits of the species environmental tolerances rather than central tendency or “typical” cases. Overlaying the species distribution model output with aquatic habitat-specific data then allowed for more specific predictions of areas with high suitability. Our results indicate there is suitable habitat for northern snakehead in the Great Lakes, particularly shallow coastal habitats in the lower four Great Lakes where literature suggests they will favor areas of wetland and submerged aquatic vegetation. These coastal areas also offer the highest suitability for golden mussel, but our models suggest they are marginal habitats. Globally, the Great Lakes provide the closest match to the currently invaded range of killer shrimp, but they appear to pose an intermediate risk to the region. Range bagging provided reliable predictions when assessed either by a standard test set or by tests for spatial transferability, with golden mussel being the most difficult to accurately predict. Our approach illustrates the strength of combining multiple sources of data, while reiterating the need for increased measurement of freshwater habitat at high spatial resolutions to improve the ability to predict potential invasive species.

Lauber, T.B., R.C. Stedman, N.A. Connelly, L.G. Rudstam, R.C. Ready, G.L. Poe, D.B. Bunnell, T.O. Hook, M.A. Koops, S.A. Lusdsin, and E.S. RUTHERFORD. Using Scenarios to Assess Possible Future Impacts of Invasive Species in the Laurentian Great Lakes. North American Journal of Fisheries Management 36(6)(DOI:10.1080/02755947.2016.1214647) (2016).

The expected impacts of invasive species are key considerations in selecting policy responses to potential invasions. But predicting the impacts of invasive species is daunting, particularly in large systems threatened by multiple invasive species, such as North America’s Laurentian Great Lakes. We developed and evaluated a scenario-building process that relied on an expert panel to assess possible future impacts of aquatic invasive species on recreational fishing in the Great Lakes. To maximize its usefulness to policy makers, this process was designed to be implemented relatively rapidly and considered a range of species. The expert panel developed plausible, internally consistent invasion scenarios for five aquatic invasive species, along with subjective probabilities of those scenarios. We describe these scenarios and evaluate this approach for assessing future invasive species impacts. The panel held diverse opinions about the likelihood of the scenarios, and only one scenario with impacts on sport fish species was considered likely by most of the experts. These outcomes are consistent with the literature on scenario building, which advocates for developing a range of plausible scenarios in decision-making because the uncertainty of future conditions makes the likelihood of any particular scenario low. We believe that this scenario-building approach could contribute to policy decisions about whether and how to address the possible impacts of invasive species. In this case, scenarios could allow policy makers to narrow the range of possible impacts on Great Lakes fisheries they consider and help set a research agenda for further refining invasive species predictions.

Lei, R., X. Tian-Kunze, B. Li, P. Heil, J. WANG, J. Zeng, and Z. Tian. Characterization of summer Arctic sea ice morphology in the 135°–175°W sector using multi-scale methods. Cold Regions Science and Technology 133:108-120 (DOI:10.1016/j.coldregions.2016.10.009) (2017).

In summer 2014, sea ice morphological characteristics were investigated in the 135°–175°W sector of the Arctic Ocean using in situ, shipborne, and remote sensing measurements. Sea ice in this sector was deformed and compact compared to previous observations. The average ice area in the region (70°–82.5°N, 135°–175°W) was 7.6 × 105 km2 for 29 July through 6 September 2014, the fourth largest record between 2003 and 2014. This can be attributed to the enhanced multiyear sea ice inflow from north of the Canadian Arctic Archipelago from September 2013 to August 2014. Multiyear ice coverage in the study region on 30 April 2014 was 55%, which was larger than the values in 2005–2013. During the melt season of 2014, the Arctic Dipole had a positive anomaly, associated with enhanced southerly wind. In summer 2014 the marginal ice zone exhibited a distinct ice retreat, whereas the pack ice zone (PIZ) showed strong persistence due to the large coverage of multiyear ice. The northward retreat of the PIZ boundary was < 100 km from late July through early September 2014. In the PIZ of 76–80.5°N, average ice thickness weighted by ice concentration, obtained by shipborne measurements in August 2014 was 0.54 m thicker than that obtained in August 2010 due to enhanced ice deformation and less open waters in 2014. At 81°N, sea ice with modal thickness of 1.48 m reached thermodynamic balance by late August 2014, which was much earlier than that in 2010.

Lekki, J., G. LESHKEVICH, S.A. RUBERG, D. STUART, and A. VANDER WOUDE. et al. Airborne Hyperspectral Sensing of Harmful Algal Blooms in the Great Lakes Region: System Calibration and Validation, From Photons to Algae Information: The Processes In-Between. NASA -Technical Memorandum NASA/TM—2017-219071. NASA, (2017).

Lodge, D.M., et. al, (Including RUTHERFORD, E.S.; BELETSKY, D.; MASON, D.; MARTINEZ, F.; ZHANG, H. Risk Analysis and Bioeconomics of Invasive Species to Inform Policy and Management. Annual Review of Environment and Resources 41:453-488 (DOI:10.1146/annurev-environ-110615-085532) (2016).

Risk analysis of species invasions links biology and economics, is increasingly mandated by international and national policies, and enables improved management of invasive species. Biological invasions proceed through a series of transition probabilities (i.e., introduction, establishment, spread, and impact), and each of these presents opportunities for management. Recent research advances have improved estimates of probability and associated uncertainty. Improvements have come from species-specific trait-based risk assessments (of estimates of introduction, establishment, spread, and impact probabilities, especially from pathways of commerce in living organisms), spatially explicit dispersal models (introduction and spread, especially from transportation pathways), and species distribution models (establishment, spread, and impact). Results of these forecasting models combined with improved and cheaper surveillance technologies and practices [e.g., environmental DNA (eDNA), drones, citizen science] enable more efficient management by focusing surveillance, prevention, eradication, and control efforts on the highest-risk species and locations. Bioeconomic models account for the interacting dynamics within and between ecological and economic systems, and allow decision makers to better understand the financial consequences of alternative management strategies. In general, recent research advances demonstrate that prevention is the policy with the greatest long-term net benefit.

LOFGREN, B.M. Comment on Hicham Bahi, et al. Effects of Urbanization and Seasonal Cycle on the Surface Urban Heat Island Patterns in the Coastal Growing Cities: A Case Study of Casablanca, Morocco. Remote Sens. 2016, 8, 829. Remote Sensing 9(1):91 (DOI:10.3390/rs9010091) (2017).

A statement in this recently published paper makes a point that is largely at odds with the main point of the paper that is cited. Stating that higher air temperatures lead to greater evapotranspiration is an oversimplification; the true story is more complex. Although this is by no means central to the conclusions of the paper being commented on, we have demonstrated the danger in taking too literally the idea that air temperature determines potential evapotranspiration.

Lottig, N.R., P.-N. Tan, T. Wagner, K.S. Cheruvelil, P.A. Soranno, E.H. Stanley, C.E. Scott, C.A. STOW, and S. Yuan. Macroscale patterns of synchrony identify complex relationships among spatial and temporal ecosystem. Ecology (2017). (In Press)

Luo, L., J. WANG, T.S. HUNTER, D. Wang, and H.A. VANDERPLOEG. Modeling spring-summer phytoplankton bloom in Lake Michigan with and without riverine nutrient loading. Ocean Dynamics:1-14 (DOI:10.1007/s1023) (2017).

There were two phytoplankton blooms captured by remote sensing in Lake Michigan in 1998, one from March to May, and one during June. In this paper, those phytoplankton blooms were simulated by a coupled physical–biological model, driven by observed meteorological forcing in 1998. The model reasonably reproduced the lake currents. The biological model results, with and without riverine nutrient loading, were compared with the remote sensing data. A 3-month-long donut-like phytoplankton bloom that appeared in southern Lake Michigan was reasonably well simulated only when riverine input was included, indicating the importance of riverine nutrient input for supporting the growth of phytoplankton in Lake Michigan. The model with riverine input also captured a second event-driven phytoplankton bloom during June with weaker magnitude that occurred in mid-south Lake Michigan, which lasted for about 20 days. The major reason for the weaker bloom in June was that vertical mixing in the hydrodynamic model was too weak (leading to a mixed-layer depth of 20 m) to bring the bottom nutrient-rich water up to the epilimnion. High chlorophyll concentration that persisted in Green Bay for almost a year was simulated with less intensity.

Marcus, D.N., A. Pinto, K. Anantharaman, S.A. RUBERG, E.L. Kramer, L. Raskin, and G.L. Dick. Diverse manganese(II)-oxidizing bacteria are prevalent in drinking water systems. Environmental Microbiology Reports 9(2)(DOI:10.1111/1758-2229.12508) (2017).

Manganese (Mn) oxides are highly reactive minerals that influence the speciation, mobility, bioavailability and toxicity of a wide variety of organic and inorganic compounds. Although Mn(II)-oxidizing bacteria are known to catalyze the formation of Mn oxides, little is known about the organisms responsible for Mn oxidation in situ, especially in engineered environments. Mn(II)-oxidizing bacteria are important in drinking water systems, including in biofiltration and water distribution systems. Here, we used cultivation dependent and independent approaches to investigate Mn(II)-oxidizing bacteria in drinking water sources, a treatment plant and associated distribution system. We isolated 29 strains of Mn(II)-oxidizing bacteria and found that highly similar 16S rRNA gene sequences were present in all culture-independent datasets and dominant in the studied drinking water treatment plant. These results highlight a potentially important role for Mn(II)-oxidizing bacteria in drinking water systems, where biogenic Mn oxides may affect water quality in terms of aesthetic appearance, speciation of metals and oxidation of organic and inorganic compounds. Deciphering the ecology of these organisms and the factors that regulate their Mn(II)-oxidizing activity could yield important insights into how microbial communities influence the quality of drinking water.

McArthur, S., K.E. Bailey, T. Murphy, J. Newton, C. Janzen, R. Morrison, S.A. RUBERG, U. Send, and H. Worthington. A National Strategy for a Sustained Network of Coastal Moorings. NOAA IOOS, (2017).

Moore, T.S., C.B. Mouw, J.M. Sullivan, M.S. Twardowski, A. BURTNER, A.B. Ciochetto, M.N. McFarland, A.R. Nayak, D. PALADINO, N. Stockley, T.H. JOHENGEN, A.W. Yu, S.A. RUBERG, and A. Weidemann. Bio-optical Properties of Cyanobacteria Blooms in Western Lake Erie. Frontiers in Marine Science (DOI:10.3389/fmars.2017.00300) (2017).

There is a growing use of bio-optical products for quantifying freshwater cyanobacteria blooms, yet their measurements of their inherent optical properties in natural settings are sparse and not well known. Towards improving this knowledge gap in the context of bio-optical algorithms for remote sensing applications, we measured a compliment of inherent optical properties in western Lake Erie during cyanobacteria blooms in the summers of 2013 and 2014. Western Lake Erie is an interesting test bed for optical data collections and bio-optical algorithms, as there are different hydrographic regimes present across a small area that is amenable to remote sensing across a variety of platforms. It is also a region that experiences regular cyanobacteria blooms comprising a variety of toxic and non-toxic species. Sampling included measurements for a suite of environmental and optical parameters, including the volume scattering function, covering a variety of water types inside and outside of cyanobacteria blooms. Large variability of optical properties was observed across the area, with over a two-orders of magnitude range in chlorophyll a concentration. Based on the regional hydrography and the distributions our measurements of biological and optical properties, we partitioned the data into three different sub-regions. The Maumee Bay region, bounded by the southwest corner to Peelee and Kelleys islands 18 towards the east, is shallow and impacted by the Maumee River and contained the highest amount of cyanobacteria dominated by gas-vacuolate Microcystis. This region was characterized by high scattering and absorption coefficients, and a high mean backscatter ratio at 443nm, greater than 0.03. The Detroit River plume region, in the northwest corner, was characterized by low scattering and absorption with particles dominated by inorganic minerals and backscatter ratios closer to 0.023. The third region, east of the islands in the central basin, had moderate absorption and scattering properties and was dominated by Planktothrix, also a gas-vacuolate cyanobacteria with mean backscatter ratios of 0.026. These particle fields in cases were of mixed assemblages of inorganic and organic particles. From a remote sensing perspective, this present a challenge for algorithms because of the optical complexity and diversity of conditions present at the same time over a small region. The measurements focus attention on the optical uniqueness of cyanobacteria blooms, which are extreme compared to non-bloom conditions. These results contribute to establishing baseline values for optical properties specific to freshwater cyanobacteria blooms and applicable to other systems.

Nguyen, T.D., N. HAWLEY, and M.S. Phanikumar. Ice cover, winter circulation, and exchange in Saginaw Bay and Lake Huron. Limnology and Oceanography 62(1):375-393 (DOI:10.1002/lno.10431) (2016).

Winter circulation exerts a strong control on the release and timing of nutrients and contaminants from bays into the adjoining lakes. To estimate winter residence times of solutes in the presence of ice cover, we used an ice model coupled to hydrodynamic, thermal and solute transport models of Saginaw Bay and Lake Huron for two low (2010 and 2013) and two high (2009 and 2014) ice years. The models were tested using temperature data from thermistor chains and current data from ADCP moorings deployed during the wintertime. Simulated water temperatures compared favorably to lake-wide average surface temperatures derived from NOAA's AVHRR satellite imagery. Simulated results of ice cover are in agreement with observed data from the Great Lakes Ice Atlas. Our results indicate that ice cover significantly dampens water movement producing almost stagnant conditions around February. Estimates of residence times for Saginaw Bay (defined as the e-folding flushing time based on vertically integrated dye concentrations) show that the mean residence times in a low ice year (2013) are 2.2 months for the inner bay, and 3.5 months for the entire bay. The corresponding numbers for a high ice year (2014) are 4.9 and 5.3 months, respectively. Considering the entire bay, solutes stored in the bay can be expected to be released into the lake between March (low ice year) and April (high ice year). These results are expected to aid in understanding the behavior of contaminants in the Great Lakes during the winter months and in early spring.

Nojavan, F.A., S.S. Qian, and C.A. STOW. Comparative analysis of discretization methods in Bayesian networks. Environmental Modeling & Software 87:64-71 (DOI:10.1016/j.envsoft.2016.10.007) (2017).

A key step in implementing Bayesian networks (BNs) is the discretization of continuous variables. There are several mathematical methods for constructing discrete distributions, the implications of which on the resulting model has not been discussed in literature. Discretization invariably results in loss of information, and both the discretization method and the number of intervals determines the level of such loss. We designed an experiment to evaluate the impact of commonly used discretization methods and number of intervals on the developed BNs. The conditional probability tables, model predictions, and management recommendations were compared and shown to be different among models. However, none of the models did uniformly well in all comparison criteria. As we cannot justify using one discretization method against others, we recommend caution when discretization is used, and a verification process that includes evaluating alternative methods to ensure that the conclusions are not an artifact of the discretization approach.

Nowicki, C.J., D.B. Bunnell, P.M. Armenia, D.M. Warner, H.A. VANDERPLOEG, J.F. CAVALETTO, C.M. Mayer, and J.V. Adams. Biotic and abiotic factors influencing zooplankton vertical distribution in Lake Huron. Journal of Great Lakes Research (DOI:10.1016/j.jglr.2017.08.004) (2017). (IN PRESS)

The vertical distribution of zooplankton can have substantial influence on trophic structure in freshwater systems, particularly by determining spatial overlap for predator/prey dynamics and influencing energy transfer. The zooplankton community in some of the Laurentian Great Lakes has undergone changes in composition and declines in total biomass, especially after 2003. Mechanisms underlying these zooplankton changes remain poorly understood, in part, because few studies have described their vertical distributions during daytime and nighttime conditions or evaluated the extent to which predation, resources, or environmental conditions could explain their distribution patterns. Within multiple 24-h periods during July through October 2012 in Lake Huron, we conducted daytime and nighttime sampling of zooplankton, and measured food (chlorophyll-a), temperature, light (Secchi disk depth), and planktivory (biomass of Bythotrephes longimanus and Mysis diluviana). We used linear mixed models to determine whether the densities for 22 zooplankton taxa varied between day and night in the epi-, meta-, and hypolimnion. For eight taxa, higher epilimnetic densities were observed at night than during the day; general linear models revealed these patterns were best explained by Mysis diluviana (four taxa), Secchi disk depth (three taxa), epilimnetic water temperature (three taxa), chlorophyll (one taxon), and biomass of Bythotrephes longimanus (one taxon). By investigating the potential effects of both biotic and abiotic variables on the vertical distribution of crustacean zooplankton and rotifers, we provide descriptions of the Lake Huron zooplankton community and discuss how future changes in food web dynamics or climate change may alter zooplankton distribution in freshwater environments.

Oliver, S.K., S.M. Collins, P.A. Soranno, T. Wagner, E.H. Stanley, J.R. Jones, C.A. STOW, and N.R. Lottig. Unexpected stasis in a changing world: Lake nutrient and chlorophyll trends since 1990. Global Change Biology (DOI:10.1111/gcb.13810) (2017). (In Press)

The United States (U.S.) has faced major environmental changes in recent decades, including agricultural intensification and urban expansion, as well as changes in atmospheric deposition and climate-all of which may influence eutrophication of freshwaters. However, it is unclear whether or how water quality in lakes across diverse ecological settings has responded to environmental change. We quantified water quality trends in 2913 lakes using nutrient and chlorophyll (Chl) observations from the Lake Multi-Scaled Geospatial and Temporal Database of the Northeast U.S. (LAGOS-NE), a collection of preexisting lake data mostly from state agencies. LAGOS-NE was used to quantify whether lake water quality has changed from 1990 to 2013, and whether lake-specific or regional geophysical factors were related to the observed changes. We modeled change through time using hierarchical linear models for total nitrogen (TN), total phosphorus (TP), stoichiometry (TN:TP), and Chl. Both the slopes (percent change per year) and intercepts (value in 1990) were allowed to vary by lake and region. Across all lakes, TN declined at a rate of 1.1% year-1 , while TP, TN:TP, and Chl did not change. A minority (7%-16%) of individual lakes had changing nutrients, stoichiometry, or Chl. Of those lakes that changed, we found differences in the geospatial variables that were most related to the observed change in the response variables. For example, TN and TN:TP trends were related to region-level drivers associated with atmospheric deposition of N; TP trends were related to both lake and region-level drivers associated with climate and land use; and Chl trends were found in regions with high air temperature at the beginning of the study period. We conclude that despite large environmental change and management efforts over recent decades, water quality of lakes in the Midwest and Northeast U.S. has not overwhelmingly degraded or improved.

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.

POTHOVEN, S.A., and H.A. VANDERPLOEG. Changes in Mysis diluviana abundance and life history patterns following a shift toward oligotrophy in Lake Michigan. Fundamental and Applied Limnology (DOI:10.1127/fal/2017/1039) (2017).

The abundance, biomass, and life history characteristics of Mysis diluviana were evaluated at a 110-m (offshore) and 45-m (nearshore) deep station in southeast Lake Michigan during two time periods, 1995 – 2002 and 2007– 2015. Rapid changes in the lake’s productivity were noted between the two time periods, including declines in chlorophyll, the spring phytoplankton bloom, the size of the deep chlorophyll layer, spring/summer zooplankton biomass, and the benthic amphipod, Diporeia spp., which historically served as a major source of food for fish along with Mysis. Mysis were more abundant during 1995 – 2002 than 2007– 2015, with average declines of 82 % at the nearshore station and 54 % at the offshore station. One factor that may have led to declines in M. diluviana between the two time periods was altered reproductive characteristics due to decreases in food availability. Changes in reproductive characteristics included a shorter period of brood release during the spring and early summer and declines in brood sizes. Other characteristics such as growth rate and generation time did not appear to change between periods, however. Predation from fish appears to be focused on newly emerged juveniles and small adults based on the size of mysids found in stomachs of the predominant planktivorous fish in the lake. Despite declining planktivorous fish abundance during the 2007– 2015 time period, M. diluviana populations have not rebounded as in the past, indicating that there has been a decoupling between predator-prey in the lake following declines in system productivity and the loss of the alternative prey for fish, Diporeia spp.

Reavie, E.D., G.V. Sgro, L.R. Estepp, A.J. Bramburger, V.L. Shaw Chraibi, R.W. Pillsbury, M. Cai, C.A. STOW, and A. Dove. Climate warming and changes in Cyclotella sensu lato in the Laurentian Great Lakes. Limnology and Oceanography 62(2):768-783 (DOI:10.1002/lno.10459) (2017).

We present the first evidence of biological change in all of the pelagic Laurentian Great Lakes associated with recent climatic warming. We hypothesized that measured changes in lake temperature, and the resulting physical changes to water columns, were affecting diatom communities in the Great Lakes. A paleolimnological analysis of 10 sediment cores collected from deep locations throughout the Great Lakes basin indicates a recent (30–50 yr) reorganization of the diatom community to one characterized by elevated abundances of several species from the group Cyclotella sensu lato, coinciding with rising atmospheric and water temperatures. These Cyclotella increases are a probable mechanistic result of new physical regimes such as changing stratification depths and longer ice-free periods, and possibly water quality shifts. Efforts to understand the mechanisms of these changes are ongoing, but this compositional reorganization in primary producers could have important implications to Great Lakes food webs.

Reisinger, L.S., A.K. ELGIN, K.M. Towle, D.J. Chan, and D.M. Lodge. The influence of evolution and plasticity on the behavior of an invasive crayfish. Biological Invasions 19(3):815-830 (DOI:10.1007/s10530-016-1346-4) (2017).

Invasion success can be enhanced by evolution and behavioral plasticity, but the importance of these processes for most invasions is not well understood. Previous research suggests there is a genetic basis for differences in growth rate between native and invaded range rusty crayfish (Orconectes rusticus). We hypothesized that invaded range O. rusticus achieve faster growth by allocating more time to foraging and less to defense. We conducted a laboratory experiment to test the effects of range (native or invaded) and plasticity (as induced by exposure to predators) on crayfish behavior. We collected O. rusticus adults and eggs from both ranges, hatched eggs in the lab, and reared juveniles in common conditions either with or without predatory fish. We then quantified adult and juvenile crayfish activity in an experiment with and without predatory fish. In support of our hypothesis, invaded range adults displayed reduced antipredator behavior compared to native range adults. Further, invaded range juveniles were more active than native range juveniles without predators, but all juveniles were inactive with predators. In addition, invaded range juveniles had greater plasticity in behavior than native range juveniles. These results suggest that activity level in the absence of predators has diverged in the invaded range. Because active crayfish consume more prey, this change in behavior may be responsible for rapid growth in the invaded range of O. rusticus, a trait that contributes to the strong ecological impacts of this invasive crayfish.

ROWE, M.D., E.J. ANDERSON, H.A. VANDERPLOEG, S.A. POTHOVEN, A.K. ELGIN, J. WANG, and F. Yousef. Influence of invasive quagga mussels, phosphorus loads, and climate on spatial and temporal patterns of productivity in Lake Michigan: A biophysical modeling study. Limnology and Oceanography (DOI:10.1002/lno.10595) (2017).

We applied a three-dimensional biophysical model to Lake Michigan for the years 2000, 2005, and 2010 to consider the mechanisms controlling spatial and temporal patterns of phytoplankton abundance (chlorophyll a) and lake-wide productivity. Model skill was assessed by comparison to satellite-derived Chl a and field-measured water quality variables. We evaluated model sensitivity to scenarios of varying mussel filter feeding intensity, tributary phosphorus loads, and warm vs. cool winter-spring climate scenarios. During the winter-spring phytoplankton bloom, spatial patterns of Chl a were controlled by variables that influenced surface mixed layer depth: deep mixing reduced net phytoplankton growth through light limitation and by exposing the full water column to mussel filter feeding. Onset of summer and winter stratification promoted higher surface Chl a initially by increasing mean light exposure and by separating the euphotic zone from mussels. During the summer stratified period, areas of relatively high Chl a were associated with coastal plumes influenced by tributary-derived nutrients and coastal upwelling-downwelling. While mussels influenced spatial and temporal distribution of Chl a, lake-wide, annual mean primary production was more sensitive to phosphorus and warm/cool meteorology scenarios than to mussel filter feeding scenarios. Although Chl a and primary production declined over the quagga mussel invasion, our results suggest that increased nutrient loads would increase lake-wide productivity even in the presence of mussels; however, altered spatial and temporal patterns of productivity caused by mussel filter feeding would likely persist.

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 42(6):1306-1211 (DOI:10.1016/j.jglr.2016.07.001) (2016).

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.

Sharrar, A.M., B.E. Flood, J.V. Bailey, D.S. Jones, B.A. Biddanda, S.A. RUBERG, D.N. Marcus, and G.J. Dick. Novel Large Sulfur Bacteria in the Metagenomes of Groundwater-Fed Chemosynthetic Microbial Mats in the Lake Huron Basin. Frontiers in Microbiology (DOI: (2017).

Little is known about large sulfur bacteria (LSB) that inhabit sulfidic groundwater seeps in large lakes. To examine how geochemically relevant microbial metabolisms are partitioned among community members, we conducted metagenomic analysis of a chemosynthetic microbial mat in the Isolated Sinkhole, which is in a deep, aphotic environment of Lake Huron. For comparison, we also analyzed a white mat in an artesian fountain that is fed by groundwater similar to Isolated Sinkhole, but that sits in shallow water and is exposed to sunlight. De novo assembly and binning of metagenomic data from these two communities yielded near complete genomes and revealed representatives of two families of LSB. The Isolated Sinkhole community was dominated by novel members of the Beggiatoaceae that are phylogenetically intermediate between known freshwater and marine groups. Several of these Beggiatoaceae had 16S rRNA genes that contained introns previously observed only in marine taxa. The Alpena fountain was dominated by populations closely related to Thiothrix lacustris and an SM1 euryarchaeon known to live symbiotically with Thiothrix spp. The SM1 genomic bin contained evidence of h1-based lithoautotrophy. Genomic bins of both the Thiothrix and Beggiatoaceae contained genes for sulfur oxidation via the rDsr pathway, h1 oxidation via Ni-Fe hydrogenases, and the use of O2 and nitrate as electron acceptors. Mats at both sites also contained Deltaproteobacteria with genes for dissimilatory sulfate reduction (sat, apr, and dsr) and hydrogen oxidation (Ni-Fe hydrogenases). Overall, the microbial mats at the two sites held low-diversity microbial communities, displayed evidence of coupled sulfur cycling, and did not differ largely in their metabolic potentials, despite the environmental differences. These results show that groundwater-fed communities in an artesian fountain and in submerged sinkholes of Lake Huron are a rich source of novel LSB, associated heterotrophic and sulfate-reducing bacteria, and archaea.

Simpson, N.T., A. Honsey, E.S. RUTHERFORD, and T.O. Hook. Spatial shifts in salmonine harvest, harvest rate, and effort by charter boat anglers in Lake Michigan, 1992–2012. Journal of Great Lakes Research 42(5):1109-1117 (DOI:10.1016/j.jglr.2016.07.030) (2016).

Stocked and naturally reproducing salmonids in Lake Michigan support an economically important charter boat fishery which operates from multiple locations around the lake. Charter boat operators depend on the sustainability and spatial availability of salmonid species. We analyzed the spatial distributions of charter boat harvest of brown trout, Chinook salmon, coho salmon, lake trout, and rainbow trout from 1992 to 2012. We found that during this 21 year period fishing effort shifted closer to shore, to the west, and to the north. Harvest of some species, namely lake trout and rainbow trout, shifted towards shallower bottom depths and closer to shore. In contrast, harvests of Chinook and coho salmon have not shifted closer to shore in a consistent manner. We suggest that a variety of factors may have contributed to these trends in harvest patterns, including recent ecosystem shifts in Lake Michigan. While we acknowledge that spatial harvest patterns are unlikely to precisely mirror salmonid distribution patterns, we believe that reporting coarse shifts in harvest has implications for future management options including, but not limited to, stocking decisions and harvest regulations.

Soranno, P.A., (among 23 others), and C.A. STOW. A multi-scaled geospatial and temporal database of lake ecological context and water quality for thousands of U.S. lakes. GigaScience (DOI:10.1093/gigascience/gix101) (2017). (In Press)

Steffen, M.M., T.W. DAVIS, R.M. McKay, G.S. Bullerjahn, L.E. Krausfeldt, J.M.A. Stough, M.L. Neitzey, N.E. Gilbert, G.L. Boyer, T.H. JOHENGEN, D.C. GOSSIAUX, A.M. BURTNER, D. PALLADINO, M.D. ROWE, G.J. Dick, K.A. Meyer, S. Levy, B.E. Boone, R.P. Stumpf, T.T. Wynne, P.V. Zimba, D. Gutierrez, and S.W. Wilhelm. Ecophysiological Examination of the Lake Erie Microcystis Bloom in 2014: Linkages between Biology and the Water Supply Shutdown of Toledo, OH. Environmental Science & Technology (DOI:0.1021/acs.est.7b00856) (2017).

Annual cyanobacterial blooms dominated by Microcystis have occurred in western Lake Erie (U.S./Canada) during summer months since 1995. The production of toxins by bloom-forming cyanobacteria can lead to drinking water crises, such as the one experienced by the city of Toledo in August of 2014, when the city was rendered without drinking water for >2 days. It is important to understand the conditions and environmental cues that were driving this specific bloom to provide a scientific framework for management of future bloom events. To this end, samples were collected and metatranscriptomes generated coincident with the collection of environmental metrics for eight sites located in the western basin of Lake Erie, including a station proximal to the water intake for the city of Toledo. These data were used to generate a basin-wide ecophysiological fingerprint of Lake Erie Microcystis populations in August 2014 for comparison to previous bloom communities. Our observations and analyses indicate that, at the time of sample collection, Microcystis populations were under dual nitrogen (N) and phosphorus (P) stress, as genes involved in scavenging of these nutrients were being actively transcribed. Targeted analysis of urea transport and hydrolysis suggests a potentially important role for exogenous urea as a nitrogen source during the 2014 event. Finally, simulation data suggest a wind event caused microcystin-rich water from Maumee Bay to be transported east along the southern shoreline past the Toledo water intake. Coupled with a significant cyanophage infection, these results reveal that a combination of biological and environmental factors led to the disruption of the Toledo water supply. This scenario was not atypical of reoccurring Lake Erie blooms and thus may reoccur in the future.

Stein, S.R., C.R. Roswell, S.A. POTHOVEN, and T.O. Hook. Diets and growth of age-0 walleye in a recently recovered population. Journal of Great Lakes Research 43(2):100-107 (DOI:10.1016/j.jglr.2017.03.019) (2017).

Most fishes undergo ontogenetic diet shifts, progressing from small to larger prey as they grow. The availability of suitable prey throughout early ontogeny can influence growth, survival and ultimately, year-class strength. Simultaneously, due to their numeric abundance and high mass-specific consumption rates, young fish can serve as influential consumers and thereby affect abundance of various prey. The walleye Sander vitreus population in Saginaw Bay, Lake Huron, recently recovered and is now entirely supported by natural reproduction. Recovery coincided with a dramatic decline of alewife Alosa pseudoharengus, a preferred prey of walleye. Thus, we are uncertain what primary prey now support production of young life stages of this recovered walleye population. To this end, we collected young (larval and later-stage young of year) walleye in Saginaw Bay and characterized their growth, diets and cumulative consumption using bioenergetics models. Young walleye progressed from feeding entirely on zooplankton as larvae in April to feeding almost entirely on fish by September. Based on bioenergetics analyses, fish were the most important prey for young walleye cohorts. Shiners Notropis spp., along with invasive rainbow smelt Osmerus mordax and round goby Neogobius melanostomus, were the primary fish prey. In contrast, yellow perch Perca flavescens, an important prey for adult walleye in Saginaw Bay, were largely absent in young walleye diets. Young walleye growth rates were similar to rates observed in other systems, but lower than growth rates previously observed in Saginaw Bay when alewife were abundant and the density of walleye was low.

Sundstrom, S.M., T. Eason, R.J. Nelson, D.G. Angeler, C. Barichievy, A.S. Garmestani, N.A.J. Graham, D. Granholm, L. Gunderson, M. Knutson, K.L. Nash, T. Spanbauer, C.A. STOW, and C.R. Allen. Detecting spatial regimes in ecosystems. Ecology Letters 20(1):19-32 (DOI:10.1111/ele.12709) (2017).

Research on early warning indicators has generally focused on assessing temporal transitions with limited application of these methods to detecting spatial regimes. Traditional spatial boundary detection procedures that result in ecoregion maps are typically based on ecological potential (i.e. potential vegetation), and often fail to account for ongoing changes due to stressors such as land use change and climate change and their effects on plant and animal communities. We use Fisher information, an information theory-based method, on both terrestrial and aquatic animal data (U.S. Breeding Bird Survey and marine zooplankton) to identify ecological boundaries, and compare our results to traditional early warning indicators, conventional ecoregion maps and multivariate analyses such as nMDS and cluster analysis. We successfully detected spatial regimes and transitions in both terrestrial and aquatic systems using Fisher information. Furthermore, Fisher information provided explicit spatial information about community change that is absent from other multivariate approaches. Our results suggest that defining spatial regimes based on animal communities may better reflect ecological reality than do traditional ecoregion maps, especially in our current era of rapid and unpredictable ecological change.

VANDERPLOEG, H.A., O. Sarnelle, J.R. LIEBIG, N.R. MOREHEAD, S.D. Robinson, T.H. JOHENGEN, and G.P. Horst. Seston quality drives feeding, stoichiometry and excretion of zebra mussels. Freshwater Biology 62:664-680 (DOI:10.1111/fwb.12892) (2017).


1. Seston availability and quality can affect the condition, nutrient stoichiometry and nutrient excretion of dreissenid mussels and other aquatic consumers. Nutrient excretion by dreissenid mussels may affect phytoplankton community composition by altering nitrogen:phosphorus (N:P) ratios of the water and may be an important accessory factor leading to increased Cladophora and toxic Microcystis blooms in mussel-invaded lakes.

2. We manipulated phosphorus enrichment levels [no (L), moderate (M) and high (H)] and zebra mussel concentrations (1, 2 and 4 g dry mass m−2) to produce a total of nine treatment combinations, each one held in a 31 m3 enclosure in an oligotrophic lake. We measured zebra mussel condition, carbon:nitrogen:phosphorus (C:N:P) tissue stoichiometry, feeding rate and nutrient excretion and egestion as related to varying conditions of chlorophyll a (Chl), particulate phosphorus (PP), particulate organic nitrogen (PON) and seston C:N:P ratios at three time periods: 5–7, 18–20 and 32–34 days subsequent of adding mussels to the enclosures.

3. Consistent with approximate homeostatic control of N and P, there were only modest differences in C:N:P ratios in mussel soft tissue despite greatly different seston C:N:P ratios among enrichment treatments. Mussel condition (mass per unit length) decreased with increased seston N:P, C:P and C:N ratios and percent composition of Cyanobacteria, and increased with percentage composition of cryptophytes and other flagellates.

4. Assimilation rates of Chl and calculated potential assimilation rates of N and P linearly increased (P < 0.05) with increasing seston Chl, PON and PP concentrations.

5. P excretion measured as soluble reactive phosphorus (SRP) significantly decreased in exponential fashion by two orders of magnitude as C:P (R2 = 0.71) and N:P ratios (R2 = 0.66) increased by a factor of 4. P excretion was significantly correlated with seston PP concentration, which varied over a 19-fold range; however, there was much scatter in the relationship (R2 = 0.29). In contrast, NH4-N excretion significantly decreased (R2 = 0.31) with N:P ratio by a factor of 2 over this same N:P range, and was not significantly correlated with PON concentration. Soluble P excretion was significantly correlated with potential P assimilation, whereas NH4 excretion was not significantly correlated with potential N assimilation. The ratio of N:P excreted showed a significant exponential increase with seston N:P ratio.

6. P and N egestion rates were higher than corresponding P and N excretion rates from the same trials; however, the fate of this egested material – whether recycled by resuspension or remaining in the benthos – is not known.

7. Mussel excretion and its impacts are highly context dependent, varying with algal composition, seston stoichiometry, and mussel abundance and feeding rate. The low P excretion but high N excretion observed when mussel feeding stops implies that under poor feeding conditions typical of summer seston, mussels excrete little P but continue excreting N, which would slow production rate of producers such as Cladophora and Microcystis in low-P systems. In contrast, NH4 excretion by mussels may prolong Microcystis blooms as nitrate is used up by the bloom in moderate-P systems.

Wittman, M.T., G. Annis, A.M. Kramer, L.A. Mason, C.M. Riseng, E.S. RUTHERFORD, W.L. Chadderton, D. BELETSKY, J.M. Drake, and D.M. Lodge. Refining species distribution model outputs using landscape-scale habitat data: Forecasting grass carp and Hydrilla establishment in the Great Lakes region. Journal of Great Lakes Research 4(2):298-301 (DOI:10.1016/j.jglr.2016.09.008) (2017).

Forecasts of the locations of species invasions can improve by integrating species-specific climate and habitat variables and the effects of other invaders into predictive models of species distribution. We developed two species distribution models (SDMs) using a new algorithm to predict the global distributions of two nonindigenous species, grass carp (Ctenopharyngodon idella) and Hydrilla (Hydrilla verticillata), with special attention to the North American Great Lakes. We restricted the projected suitable habitat for these species using relevant habitat data layers including accumulated Growing Degree Days (GDD), submersed aquatic vegetation (SAV), wetlands, and photic zone. In addition, we restricted the grass carp niche by the projected Hydrilla niche to explore the potential spatial extent for grass carp given a joint invasion scenario. SDMs showed that climate conditions in the Great Lakes basin were often suitable for both species, with a high overlap between the areas predicted to be climatologically suitable to both species. Restricting Hydrilla regions by GDD and photic zone depth showed that the nearshore zones are primary regions for its establishment. The area of predicted habitat for grass carp increased greatly when including Hydrilla niche as a potential habitat for this species. Integrated risk maps can provide a means for the scientifically informed prioritization of management resources toward particular species and geographic regions.

Wu, L., J. WANG, S. Gao, X. Zheng, and R.X. Huang. An analysis of dynamical factors influencing 2013 giant jellyfish bloom near Qinhuangdao in the Bohai Sea, China*. Estuarine, Coastal and Shelf Science 185:141-151 (DOI:10.1016/j.ecss.2016.12.010) (2016).

The explosive growth of Nemopilema nomurai occurred near the coastal waters of Qinhuangdao in July 2013. However, it did not take place in 2012. In this paper, the dynamical factors of wind, ocean current and sea temperature on giant jellyfish bloom in 2013 is analyzed by a comprehensive investigation. The numerical experiments are based on a numerical trajectory model of the jellyfish particles, which are released into the waters from Feiyan Shoal to New Yellow River Mouth, where is speculated as the most likely remote source of Qinhuangdao jellyfish bloom. The results show that in surface layer the jellyfish drift is jointly driven by the surface wind and surface current. For example, in northeastern Bohai Bay, the giant jellyfish moved northwestward in surface layer with influence of the westward wind and current anomalies during the second half of May in 2013, then approached the south of Jingtang Port by early June, and accumulated near Qinhuangdao in early July. The 2012 scenario during the same period was quite different. The jellyfish particles influencing waters near Qinhuangdao decreased with depth and there was few (no) particles influencing Qinhuangdao in middle (bottom) layer because the anticyclonic residual circulation weakened with depth in Bohai Bay. Besides, in the potential source waters of jellyfish, sea temperature in 2012 was more suitable for jellyfish bloom than that in 2013 if there was adequate bait. Hence, the specified direction of wind and current pattern in the Bohai Sea in surface layer (especially in the northeastern Bohai Bay during the second half of May) was more important for jellyfish bloom near Qinhuangdao than the sea temperature in the potential source.

XIAO, C., B.M. LOFGREN, J. WANG, and P.Y. CHU. Improving the lake scheme within a coupled WRF-lake model in the Laurentian Great Lakes. Journal of Advances in Modeling Earth Systems (DOI:10.1002/2016MS000717) (2016).

In this study, a one-dimensional (1-D) thermal diffusion lake model within the Weather Research and Forecasting (WRF) model was investigated for the Laurentian Great Lakes. In the default 10-layer lake model, the albedos of water and ice are specified with constant values, 0.08 and 0.6, respectively, ignoring shortwave partitioning and zenith angle, ice melting, and snow effect. Some modifications, including a dynamic lake surface albedo, tuned vertical diffusivities, and a sophisticated treatment of snow cover over lake ice, have been added to the lake model. A set of comparison experiments have been carried out to evaluate the performances of different lake schemes in the coupled WRF-lake modeling system. Results show that the 1-D lake model is able to capture the seasonal variability of lake surface temperature (LST) and lake ice coverage (LIC). However, it produces an early warming and quick cooling of LST in deep lakes, and excessive and early persistent LIC in all lakes. Increasing vertical diffusivity can reduce the bias in the 1-D lake but only in a limited way. After incorporating a sophisticated treatment of lake surface albedo, the new lake model produces a more reasonable LST and LIC than the default lake model, indicating that the processes of ice melting and snow accumulation are important to simulate lake ice in the Great Lakes. Even though substantial efforts have been devoted to improving the 1-D lake model, it still remains considerably challenging to adequately capture the full dynamics and thermodynamics in deep lakes.

Xue, P., J.S. Pal, X. Ye, J.D. Lenters, C. Huang, and P.Y. CHU. Improving the Simulation of Large Lakes in Regional Climate Modeling: Two-way Lake-atmosphere Coupling with a 3-D Hydrodynamic Model of the Great Lakes. Journal of Climate 30:1605-1627 (DOI:10.1175/JCLI-D-16-0225.1) (2017).

Accurate representations of lake-ice-atmosphere interactions in regional climate modeling remain one of the most critical and unresolved issues for understanding large-lake ecosystems and their watersheds. To date, the representation of the Great Lakes two-way interactions in regional climate models is achieved with 1-D lake models applied at the atmospheric model lake grid points distributed spatially across a 2-D domain. While some progress has been made in refining 1-D lake model processes, such models are fundamentally incapable of realistically resolving a number of physical processes in the Great Lakes. In this study we develop a two-way coupled 3-D climate-lake-ice modeling system (named TC-3D-GLARM) aimed at improving the simulation of large lakes in regional climate models and accurately resolving the hydroclimatic interactions. Model results are compared to a wide variety of observational data and demonstrate the unique skill of the coupled 3-D modeling system in reproducing trends and variability in the Great Lakes regional climate, as well as in capturing the physical characteristics of the Great Lakes by fully resolving the lake hydrodynamics. Simulations of the climatology and spatiotemporal variability of lake thermal structure and ice are significantly improved over previous coupled, 1-D simulations. At seasonal and annual time scales, differences in model results are primarily observed for variables that are directly affected by lake surface temperature (e.g., evaporation, precipitation, and sensible heat flux) while no significant differences are found in other atmospheric variables (e.g., solar radiation, cloud cover). Underlying physical mechanisms for the simulation improvements using TC-3D-GLARM are also discussed.

ZHANG, H., L. Boegman, D. Scavia, and D.A. Culver. Spatial distributions of external and internal phosphorus loads in Lake Erie and their impacts on phytoplankton and water quality. Journal of Great Lakes Research 42(6):1212-1227 (DOI:10.1016/j.jglr.2016.09.005) (2016).

Re-eutrophication in Lake Erie has led to new programs to reduce external phosphorus loads, and it is important to understand the interrelated dynamics of external and internal phosphorus loads. In addition to developing phosphorus load response curves for algal biomass in the western basin and hypoxia in the central basin, we used a two-dimensional (vertical-longitudinal) hydrodynamic and ecological model to show that both external and internal phosphorus loads were distributed homogeneously in the water column in Lake Erie's western basin. In the stratified central and eastern basins phosphorus released by organic matter decay and crustacean zooplankton excretion was concentrated in the upper water column, contributing 100–119% of the phytoplankton phosphorus demand, while phosphorus released by dreissenids and from anoxic sediments was distributed primarily in the hypolimnion during the growing season. Simulated reductions in external phosphorus loads decreased individual phytoplankton groups most at times when they were normally most abundant, e.g., Microcystis decreased the most during September. Phosphorus was limiting over the simulation periods, but water temperature and light conditions also played critical roles in phytoplankton succession. While water column phosphorus responded quickly to external phosphorus reduction, pulses of phosphorus (riverine input or sediment resuspension) occurring immediately before the Microcystis bloom period could allow it to bloom despite long-term external phosphorus load reduction. Studies are warranted to assess the contribution of seasonal dynamics in phosphorus loading (including sediment resuspension) to Microcystis bloom development.


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