GLERL Publication Abstracts: FY 2013


Ahmed, S., C.D. Troy, and N. HAWLEY. Spatial structure of internal Poincare waves in Lake Michigan. Environmental Fluid Mechanics:21 pp. (DOI:10.1007/s10652-013-9294-3) (2013).

In this paper we examine the characteristics of near-inertial internal Poincaré waves in Lake Michigan (USA) as discerned from field experiments and hydrodynamic simulations. The focus is on the determination of the lateral and vertical structure of the waves. Observations of near-inertial internal wave properties are presented from two field experiments in southern Lake Michigan conducted during the years 2009 and 2010 at Michigan City (IN, USA) and Muskegon (MI, USA), respectively. Spectra of thermocline displacements and baroclinic velocities show that kinetic and potential baroclinic energy is dominated by near-inertial internal Poincaré waves. Vertical structure discerned from empirical orthogonal function analysis shows that this energy is predominantly vertical mode 1. Idealized hydrodynamic simulations using stratifications from early summer (June), mid-summer (July) and fall (September) identify the basin-scale internal Poincaré wave structure as a combination of single- and two-basin cells, similar to those identified in Lake Erie by Schwab, with near-surface velocities largest in the center of the northern and southern basins. Near inertial bottom kinetic energy is seen to have roughly constant magnitude over large swathes across the basin, with higher magnitude in the shallower areas like the Mid-lake Plateau, as compared with the deep northern and southern basins. The near-bottom near-inertial kinetic energy when mapped appears similar to the bottom topography map. The wave-induced vertical shear across thermocline is concentrated along the longitudinal axis of the lake basin, and both near-bottom velocities and thermocline shear are reasonably explained by a simple conceptual model of the expected transverse variability.

Allan, J.D., P.B. McIntyre, S.D.P. Smith, B.S. Halpern, G.L. Boyer, A. Buchsbaum, G.A. BURTON, L.M. Campbell, W.L. Chadderton, J.J.H. Ciborowski, P.J. Doran, T. Eder, D.M. Infante, L.B. Johnson, C.A. Joseph, A.L. Marino, A. Prusevich, J.G. Read, J.B. Rose, E.S. RUTHERFORD, S.P. Sowa, and A.D. Steinman. Joint analysis of stressors and ecosystem services to enhance restoration effectiveness. Proceedings of the National Academy of Sciences 110(1):372-377 (DOI:10.1073/pnas.1213841110) (2013).

With increasing pressure placed on natural systems by growing human populations, both scientists and resource managers need a better understanding of the relationships between cumulative stress from human activities and valued ecosystem services. Societies often seek to mitigate threats to these services through largescale, costly restoration projects, such as the over one billion dollar Great Lakes Restoration Initiative currently underway. To help inform these efforts, we merged high-resolution spatial analyses of environmental stressors with mapping of ecosystem services for all five Great Lakes. Cumulative ecosystem stress is highest in nearshore habitats, but also extends offshore in Lakes Erie, Ontario, and Michigan. Variation in cumulative stress is driven largely by spatial concordance among multiple stressors, indicating the importance of considering all stressors when planning restoration activities. In addition, highly stressed areas reflect numerous different combinations of stressors rather than a single suite of problems, suggesting that a detailed understanding of the stressors needing alleviation could improve restoration planning. We also find that many important areas for fisheries and recreation are subject to high stress, indicating that ecosystem degradation could be threatening key services. Current restoration efforts have targeted high-stress sites almost exclusively, but generally without knowledge of the full range of stressors affecting these locations or differences among sites in service provisioning. Our results demonstrate that joint spatial analysis of stressors and ecosystem services can provide a critical foundation for maximizing social and ecological benefits from restoration investments.

ANDERSON, E.J., and D.J. SCHWAB. Contaminant transport and spill reference tables for the St. Clair River. Marine Technology Society Journal 46(5):34-47 (2012).

The goal of this work is to calibrate a real-time hydrodynamic model for spill tracking in the St. Clair River and to provide decision makers with information for response planning and in the event of a spill. In order to provide experimental validation data, three dye releases were carried out to simulate movement of a potential contaminant in the river. Measurements of dye concentration were used to provide estimates of lateral and vertical mixing as well as travel time of the dye cloud. Model simulations were able to recreate the dye movement and concentrations with model-estimated arrival times within 14 min of the observed plume arrival times and concentrations within 0.005 normalized concentration units of the observed concentrations (which ranged from 0.06 to 0.004). Following model calibration, a set of spill scenarios was chosen to encompass the types and locations of spills commonly experienced in the St. Clair River. These spill scenarios were then simulated with the HECWFS model to predict transport characteristics such as plume leading edge travel time, duration, concentration, and cross-channel mixing. Results from the scenarios were compiled into reference tables in which spill characteristics are listed at several downstream transects. These spill reference tables provide water intake operators with information before the event of a spill, enabling decision makers to plan for potential or common spills as well as providing a quick reference library that can be accessed immediately after a spill is detected to aid in mitigating the effects on drinking water supply.

ASSEL, R.A., J. WANG, A.H. CLITES, and X. BAI. Analysis of Great Lakes ice cover climatology: Winters 2006-2011. NOAA Technical Memorandum GLERL-157. NOAA Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 26 pp. (2013).

A 33-winter ice concentration climatology (Assel 2003a, Assel 2005a) was recently updated for winters 2006-2011 (Wang et al. 2012a). This report provides an analysis of the 2006-2011 ice cycles within the context of: dates of first (last) ice, ice duration, ice cover distribution, ice cover anomalies, and seasonal progression of lake-averaged ice cover. Analysis data are available as ASCII and graphic files.

BAI, X., and J. WANG. Atmospheric teleconnection patterns associated with severe and mild ice cover on the Great Lakes, 1963-2011. Water Quality Research Journal of Canada, Special Issue on Physical Processes in Natural Waters 47(3-4):421-435 (DOI:10.2166/wqrjc.2012.009) (2012).

Atmospheric teleconnection circulation patterns associated with severe and mild ice cover over the Great Lakes are investigated using the composite analysis of lake ice data and National Center of Environmental Prediction (NCEP) reanalysis data for the period 1963–2011. The teleconnection pattern associated with the severe ice cover is the combination of a negative North Atlantic Oscillation (NAO) or Arctic Oscillation (AO) and negative phase of Pacific/North America (PNA) pattern, while the pattern associated with the mild ice cover is the combination of a positive PNA (or an El Niño) and a positive phase of the NAO/AO. These two extreme ice conditions are associated with the North American ridge–trough variations. The intensified ridge–trough system produces a strong northwest-to-southeast tilted ridge and trough and increases the anomalous northwesterly wind, advecting cold, dry Arctic air to the Great Lakes. The weakened ridge–trough system produces a flattened ridge and trough, and promotes a climatological westerly wind, advecting warm, dry air from western North America to the Great Lakes. Although ice cover for all the individual lakes responds roughly linearly and symmetrically to both phases of the NAO/AO, and roughly nonlinearly and asymmetrically to El Niño and La Niña events, the overall ice cover response to individual NAO/AO or Niño3.4 index is not statistically significant. The combined NAO/AO and Niño3.4 indices can be used to reliably project severe ice cover during the simultaneous –NAO/AO and La Niña events, and mild ice cover during the simultaneous þNAO/AO and El Niño events.

BAI, X., J. WANG, D.J. SCHWAB, Y. Yang, L. LUO, G.A. LESHKEVICH, and S. LIU. Modeling 1993-2008 climatology of seasonal general circulation and thermal structure in the Great Lakes using FVCOM. Ocean Modeling 65:40-63 (DOI:10.1016/j.ocemod.2013.02.003) (2013).

An unstructured Finite Volume Coastal Ocean Model was applied to all five Great Lakes simultaneously to simulate circulation and thermal structure from 1993 to 2008. Model results are compared to available observations of currents and temperature and previous modeling work. Maps of climatological circulation for all five Great lakes are presented. Winter currents show a two-gyre type circulation in Lakes Ontario and Erie and one large-scale cyclonic circulation in Lakes Michigan, Huron, and Superior. During the summer, a cyclonic circulation remains in Lakes Superior; a primarily cyclonic circulation dominates upper and central Lake Huron; Lake Ontario has a single cyclonic circulation, while circulation in the central basin of Lake Erie remains two-gyre type; Lake Michigan has a cyclonic gyre in the north and an anticyclonic one in the south. The temperature profile during the summer is well simulated when a surface wind-wave mixing scheme is included in the model. Main features of the seasonal evolution of water temperature, such as inverse temperature stratification during the winter, the spring and autumn overturn, the thermal bar, and the stratification during summer are well reproduced. The lakes exhibit significant annual and interannual variations in current speed and temperature.

Baskaran, M., and J.F. BRATTON. Investigating human-induced changes of elemental cycles in the Great Lakes. EOS 94(28):248 (DOI:10.1002/eost.v94.28/issuetoc) (2013).

Food webs and associated elemental cycles in the Laurentian Great Lakes have been considerably altered over the past 30 years due to factors such as phosphorus abatement, introduction of zebra and quagga mussels, and climate change. These perturbations provide a unique opportunity to document how this natural system has responded and possibly to predict future changes in biogeochemical cycling. To identify the most important scientific questions associated with these changes, a workshop was held at Wayne State University, hosted with funding from the U.S. National Science Foundation (NSF), the National Oceanic and Atmospheric Administration (NOAA), NASA, and eight universities. The workshop brought together 60 participants, mostly from across the Great Lakes states, representing research expertise in nutrient and carbon cycling, trace elements and stable isotopes, radiochemistry, ecology, hydrogeology, physical oceanography, remote sensing, and climate change. Presentations included plenary, invited, and advocacy talks, along with poster presentations during the 3-day workshop. Funding and research agencies (NSF, NOAA, NASA, U.S. Geological Survey, and U.S. Environmental Protection Agency) presented their perspectives on the topics, along with overviews of their related regional and national research programs, facilities, data sets, models, and vessels.

Blouzdis, C.E., L.N. IVAN, S.A. POTHOVEN, C.R. Roswell, C.J. Foley, and T.O. Hook. A trophic bottleneck?: The ecological role of trout-perch Percopsis omiscomaycus in Saginaw Bay, Lake Huron. Journal of Applied Ichthyology 29(2):416-424 (DOI:10.1111/jai.12023) (2013).

Trout-perch are abundant in many North American aquatic systems, but the ecological roles of trout-perch as predators, competitors and prey remain relatively understudied. To elucidate the ecological role of trout-perch in Saginaw Bay (Lake Huron, North America), the spatial and temporal diet composition was quantified and the frequency of occurrence of trout-perch in diets of piscivorous walleye and yellow perch was evaluated. From May through November 2009–2010, trout-perch and their potential predators and prey were collected. Trout-perch were abundant components of the Saginaw Bay fish community, and in 2009, represented 13.5% of fish collected in trawls, with only yellow perch (38%) and rainbow smelt (19.1%) being more common. Trout-perch primarily consumed Chironomidae (84.0% of diet biomass) and exhibited strong, positive selection for Chironomidae and Amphipoda, suggesting that their diet preferences overlap with the economically important yellow perch and juvenile walleye. Energy content of trout-perch averaged 4795 J g _1 wet and was similar to yellow perch (4662 J g _1 wet) and round goby (3740 J g _1 wet). Thus, they may provide a comparable food source for larger piscivorous fish. However, despite their high energy density, abundance, and spatial overlap with other fish prey species, trout-perch were very rare in diets of piscivorous walleye and yellow perch in Saginaw Bay, indicating that trout-perch are a weak conduit of energy transfer to higher trophic levels.

Bourdeau, P.E., K.L. Pangle, E.M. Reed, and S.D. PEACOR. Finely tuned response of native prey to an invasive predator in a freshwater system. Ecology 94(7):1449-1455 (2013).

Lack of shared evolutionary history reduces the expectation that native prey will detect and respond to invasive predators. Four mechanisms may explain the adaptive response that is nevertheless seen in various systems: prey may perceive the invasive predator through cue similarity with preexisting predators, cues of conspecifics eaten by the invasive predator, a learned response based on experience with the invasive predator (e.g., cue association), and cues from the invasive predator that are specific to it. We performed laboratory experiments in which zooplankton (Daphnia mendotae) responded adaptively to the zooplanktivore Bythotrephes longimanus (migrating downward), showed no response to taxonomically similar predatory cladocerans, and responded adaptively to more taxonomically distant native fish (migrating downward) and native shrimp (migrating upward). Conspecific cues associated with Bythotrephes predation actually reduced the response of D. mendotae to Bythotrephes. Combined with previous experiments that rule out learning, our experiments rule out the first three mechanisms above, demonstrating that D. mendotae respond to cues specific to and produced directly by Bythotrephes. This finely tuned response may be retained from an ancestral species that coevolved with Bythotrephes in its native range, or may have rapidly evolved due to strong selection by the invasive predator.

CHA, Y.K., C.A. STOW, and E.S. Bernhardt. Impacts of dreissenid mussel invasions on chlorophyll and total phosphorus in 25 lakes in the USA. Freshwater Biology:1-15 (DOI:10.1111/fwb.12050) (2012).

1. Invasions of zebra and quagga mussels have had long-term, large-scale impacts on lake ecosystems in the USA as characterised by high abundance, broad-scale spread and effective adaption to new environmental conditions. Due to their high filtering capacity, decreases in chlorophyll a (Chl) and total phosphorus (TP) concentrations have been reported in many affected lakes. 2. In 25 US lakes, we analysed the effects of dreissenid invasions on changes in Chl and TP concentrations, measured as the probability of a concentration decrease in the post-invasion period and changes in Chl–TP relationships using Bayesian hierarchical regressions. We also examined whether changes in Chl and TP concentrations and in the Chl–TP relationship differed according to lake hydromorphology, such as mean depth or mixing status (mixed versus stratified lakes). 3. Our results showed that dreissenid invasions were often, but not always, associated with subsequent TP and Chl declines. Dreissenid effects on Chl and TP may be influenced by lake thermal structure. Decreases in Chl and TP were consistently found in mixed lakes where benthic–pelagic coupling is tight, while the effects were less predictable in stratified lakes. Within stratified lakes, Chl and TP reductions were more clearly discernible in deeper lakes with long water residence times. 4. Regression results demonstrated that a joint increase in slope and decrease in intercept and a tighter correlation of the Chl–TP relationship were likely to occur in dreissenid-invaded lakes; this does not support the idea of a shift from bottom-up to top-down control of primary production. These results have important implications for management, suggesting that a relaxation of TP standards would be unwarranted. 5. Across lakes, the slope of the Chl–TP relationship for mixed lakes was substantially higher than that for stratified lakes before mussel invasion, indicating an important role of light in limiting primary production. The slope differences between mixed and stratified lakes decreased in the post-invasion period, possibly because mussel filtration results in a relaxation of light limitation that is more pronounced in deeper, stratified lakes.

COLTON, M.C. Developing a Great Lakes remote sensing community. Journal of Great Lakes Research 39(Supplement 1):6-7 (DOI:10.1016/j.jglr.2013.07.002) (2013).

Observational data collection of the Laurentian Great Lakes has advanced during the past decade to such a level as to allow real-time analysis from moorings and near real-time from satellite data. Ocean color satellite-based remote sensing provides a rich data set that when properly analyzed allows for the generation of geospatial maps of chlorophyll, dissolved organic carbon, suspended minerals, harmful algae blooms (HABs), surface plumes, benthic vegetation communities, primary productivity (pp) and optical water properties (extinction coefficient (kd), photosynthetically active radiation (PAR) and photic zone depth) on a 2 m to 1 km grid dating back in some cases to the early 1970s. Microwave satellite sensors such as synthetic aperture radar (SAR) and scatterometers provide near real-time information on lake ice cover, winds and waves. Multi-temporal Landsat and ALOS PALSAR satellite data are also being used in the Great Lakes to map wetlands and invasive plants within these coastal areas. Airborne LiDARs also provide useful nearshore water depth and bottom type mapping in Great Lakes waters. Making the most of such improvements in the historical Great Lakes dataset will require diligence and a comprehensive strategy, with recognition of the importance of open collaboration in developing a regional working strategy for remote sensing technologies, sensor data applications, and the data management methods that will integrate the technologies within regional and global observation systems.

Cross, V.A., J.F. BRATTON, K.D. Kroeger, J. Crusius, and C.W. Worley. Continuous resistivity profiling data from Great South Bay, Long Island, New York. Open File Report 2011-1040. U.S. Geological Survey, Woods Hole, MA (2013).

An investigation of submarine aquifers adjacent to the Fire Island National Seashore and Long Island, New York was conducted to assess the importance of submarine groundwater discharge as a potential nonpoint source of nitrogen delivery to Great South Bay. Over 200 kilometers of continuous resistivity profiling data were collected to image the fresh-saline groundwater interface in sediments beneath the bay. In addition, groundwater sampling was performed at sites (1) along the north shore of Great South Bay, particularly in Patchogue Bay, that were representative of the developed Long Island shoreline, and (2) at sites on and adjacent to Fire Island, a 50-kilometer-long barrier island on the south side of Great South Bay. Other field activities included sediment coring, stationary electrical resistivity profiling, and surveys of in situ pore water conductivity. Results of continuous resistivity profiling surveys are described in this report. The onshore and offshore shallow hydrostratigraphy of the Great South Bay shorelines, particularly the presence and nature of submarine confining units, appears to exert primary control on the dimensions and chemistry of the submarine groundwater flow and discharge zones. Sediment coring has shown that the confining units commonly consist of drowned and buried peat layers likely deposited in salt marshes. Low-salinity groundwater extends from 10 to 100 meters offshore along much of the north and south shores of Great South Bay based on continuous resistivity profiling data, especially off the mouths of tidal creeks and beneath shallow flats to the north of Fire Island adjacent to modern salt marshes. Human modifications of much of the shoreline and nearshore areas along the north shore of the bay, including filling of salt marshes, construction of bulkheads and piers, and dredging of navigation channels, has substantially altered the natural hydrogeology of the bay's shorelines by truncating confining units and increasing recharge near the shore in filled areas. Better understanding of the nature of submarine groundwater discharge along developed and undeveloped shorelines of embayments such as this could lead to improved models and mitigation strategies for nutrient overenrichment of estuaries.

Dekker, T.J., J.V. DePinto, S.A. RUBERG, M.C. COLTON, J. Read, D.J. SCHWAB, and N. Booth. Design of the Great Lakes Observing System enterprise architecture. Proceedings, Integrated Ocean Observing System (IOOS) Summit 2012: A New Decade for an Integrated and Sustained Ocean Observing System, Herndon, VA, November 13-16, 2012. Interagency Ocean Observation Committee (IOOC), 9 pp. (2012).

A comprehensive, collaborative, and consensus-based enterprise architecture design process was conducted under the direction of NOAA-Great Lakes Environmental Research Laboratory (GLERL). The project brought together multi-disciplinary experts to identify and recommend specific actions and investments for the next five years that will achieve an integrated, comprehensive, and sustainable observing system enterprise for the Great Lakes. The enterprise system—a highly-leveraged evolution of existing resources—will provide ready access to vital real-time and historical information to support decision-making by managers and users of this unique and invaluable resource.

FRY, L.M., T.S. HUNTER, M.S. Phanikumar, V. Fortin, and A.D. GRONEWOLD. Identifying streamgage networks for maximizing the effectiveness of regional water balance modeling. Water Resources Research 49:1-12 (DOI:10.1002/wrcr.20233) (2013).

[1] One approach to regional water balance modeling is to constrain rainfall-runoff models with a synthetic regionalized hydrologic response. For example, the Large Basin Runoff Model (LBRM), a cornerstone of hydrologic forecasting in the Laurentian Great Lakes basin, was calibrated to a synthetic discharge record resulting from a drainage area ratio method (ARM) for extrapolating beyond gaged areas. A challenge of such approaches is the declining availability of observations for development of synthetic records. To advance efficient use of the declining gage network in the context of regional water balance modeling, we present results from an assessment of ARM. All possible combinations of ‘‘most-downstream’’ gages were used to simulate runoff at the gaged outlet of Michigan’s Clinton River watershed in order to determine the influence of gages’ drainage area and other physical characteristics on model skill. For nearly all gage combinations, ARM simulations resulted in good model skill. However, the gages’ catchment area relative to that of the outlet’s catchment is not an unquestionable predictor of model performance. Results indicate that combinations representing less than 30% of the total catchment area (less than 10% in some cases) can provide very good discharge simulations, but that similarity of the gaged catchments’ developed and cultivated area, stream density, and permeability relative to the outlet’s catchment is also important for successful simulations. Recognition of thresholds on the relationship between the number of gages and their relative value in simulating flow over large area provides an opportunity for improving historical records for regional hydrologic modeling.

FUJISAKI, A., J. WANG, X. BAI, G. LESHKEVICH, and B. LOFGREN. Model-simulated interannual variability of Lake Erie ice cover, circulation, and thermal structure in response to atmospheric forcing 2003-2013. Journal of Geophysical Research: Oceans 118:19 pp. (2013).

Interannual variability of ice cover, circulation, and thermal structure in Lake Erie for 2003–2012 was investigated using a three-dimensional hydrodynamic model coupled with ice processes. The model reproduced minima of ice extent in the winters of 2006 and 2012 (mild winters), as well as maxima in 2009 and 2011 (severe winters) in agreement with the observational analysis. The model reasonably captured ice thicknesses, seasonal variation of the mean surface temperature, and lake circulation. The model results showed early onset of stratification in March after the almost ice-free winter of 2012. In the mild winters, the
coastal current speed was significantly higher than the 9 year mean, since the larger open water region due to less ice cover allowed the more effective wind driven circulation. In the severe winters, the lake circulation was slowed because the packed ice reduced wind stress on the water surface. Seasonal means of coastal current speed ranged from 3.9 cm/s in the severe winter (January to March mean) of 2009 to 7.2 cm/s in the mild winter of 2012. The variation was much larger than in the other seasons (60.6 cm/s). The results imply that decreasing ice cover could lead to a more energetic coastal circulation in winter, which could influence lake turbidity, material transport, and nearshore waves. Finally, the interannual variation of ice cover is discussed in relation to teleconnection patterns. The ice minimum (maximum) in the winter of 2006 (2009) can be explained by the intermittent positive (negative) North Atlantic Oscillation that occurred in January (December to January).

FUJISAKI, A., J. WANG, H. HU, D.J. SCHWAB, N. HAWLEY, and Y.R. Rao. A modeling study of ice-water processes for Lake Erie applying coupled ice-circulation models. Journal of Great Lakes Research 38(4):585-599 (DOI:10.1016/j.jglr.2012.09.021) (2012).

A hydrodynamic model that includes ice processes and is optimized for parallel processing was configured for Lake Erie in order to study the ice–water coupling processes in the lake. A hindcast from April 2003 to December 2004 with hourly atmospheric forcing was conducted. The model reproduced the seasonal variation of ice cover, but the development of ice extent in January and its decay in March somewhat preceded the observations. Modeled lake circulation in ice-free seasons is consistent with previous studies for Lake Erie. Thermal structure of the lake was reasonably comparable to both satellite-derived observations and in-situ measurements, with mean differences ranging from−2 °C to 4 °C, depending on the season. The impacts of ice–water stress coupling and basal melting of ice were examined based on numerical experiments. The results show that: 1) ice–water stress coupling significantly dampens the subjacent lake circulation in winter due to packed ice cover that slows down the surface water, and 2) basal melting of ice contributes to widespread ice cover in the lake. The demonstrated model validity could lead to further studies of ice–water processes in the lake, including interannual variation and impacts on ecosystems.

Greene, C.H., E. Meyer-Gutbrod, B.C. Monger, L.P. McGarry, A.J. Pershing, I.M. Belkin, P.S. Fratantoni, D.G. Mountain, R.S. Pickart, A. Proshutinsky, R. Ji, J.J. Bisagni, S. Hakkinen, D.B. Haidvogel, J. WANG, E. Head, P. Smith, P.C. Reid, and A. Conversi. Remote climate forcing of decadal-scale regime shifts in Northwest Atlantic shelf ecosystems. Limnology and Oceanography 58(3):803-816 (DOI:10.4319/lo.2013.58.3.0803) (2013).

Decadal-scale regime shifts in Northwest Atlantic shelf ecosystems can be remotely forced by climate associated atmosphere–ocean interactions in the North Atlantic and Arctic Ocean Basins. This remote climate forcing is mediated primarily by basin- and hemispheric-scale changes in ocean circulation. We review and synthesize results from process-oriented field studies and retrospective analyses of time-series data to document the linkages between climate, ocean circulation, and ecosystem dynamics. Bottom-up forcing associated with climate plays a prominent role in the dynamics of these ecosystems, comparable in importance to that of top down forcing associated with commercial fishing. A broad perspective, one encompassing the effects of basin- and hemispheric-scale climate processes on marine ecosystems, will be critical to the sustainable management of marine living resources in the Northwest Atlantic.

GRONEWOLD, A.D., A.H. CLITES, J.P. SMITH, and T.S. HUNTER. A dynamic graphical interface for visualizing projected, measured, and reconstructed surface water elevations on the earth's largest lakes. Environmental Modelling and Software 49:34-39 (DOI:10.1016/j.envsoft.2013.07.003) (2013).

There is a growing need within the international water research and water resources management community, and the general public, for easy access to time-series of projected, measured, and reconstructed marine and freshwater coastal surface water elevations. There is also a need for effectively communicating variability among different surface water elevation data sets, as well as the intrinsic uncertainties in surface water elevation forecasts. Here, we introduce an interactive web-based interface, the Great Lakes Water Level Dashboard (GLWLD), designed to address this need for the North American Laurentian Great Lakes, the largest assemblage of unfrozen fresh surface water bodies on planet Earth, and one with a coastline of over 16,000 km (roughly 10,000 miles). The GLWLD is a Flash-based tool that can simultaneously display time-series of measured monthly and annual water level data and seasonal forecasts for each of the Great Lakes, reconstructed lake levels from paleoclimate research, and decadal lake level projections under alternative climate scenarios. By employing a suite of novel data transfer, processing, and visualization tools, the GLWLD allows users to seamlessly transition not only between alternate displays of Great Lakes water levels over different temporal scales, but between different data sets and forecasts as well. Furthermore, the unique GLWLD interface can help users understand the extent to which decisions regarding the use of the lakes depend on an appreciation of uncertainty and variability within, and between, different sources of Great Lakes water level information.

GRONEWOLD, A.D., and V. Fortin. Advancing Great Lakes hydrological science through targeted binational collaborative research. Bulletin of the American Meteorological Society 93(12):1921-1925 (DOI:10.1175/BAMS-D-12-00006.1) (2012).

As one of the Earth’s largest surface freshwater resources, the North American Laurentian Great Lakes are an ideal test bed for understanding water balance dynamics of large hydrologic systems and for establishing effective protocols for collaborative binational water resources and ecosystem services research. To leverage ongoing and future federal government research efforts in the Great Lakes region, representatives from the National Oceanic and Atmospheric Administration (NOAA), the Cooperative Institute for Limnology and Ecosystems Research (CILER), and Environment Canada (EC) convened a workshop on Great Lakes hydrological modeling with an emphasis on improving regional hydrological and hydrodynamic science.

GRONEWOLD, A.D., V. Fortin, B.M. LOFGREN, A.H. CLITES, C.A. STOW, and F.H. QUINN. Coasts, water levels, and climate change: A Great Lakes perspective. Climatic Change 120:697-711 (DOI:10.1007/s10584-013-0840-2) (2013).

The North American Laurentian Great Lakes hold nearly 20% of the earth’s unfrozen fresh surface water and have a length of coastline, and a coastal population, comparable to frequently-studied marine coasts. The surface water elevations of the Great Lakes, in particular, are an ideal metric for understanding impacts of climate change on large hydrologic systems, and for assessing adaption measures for absorbing those impacts. In light of the importance of the Great Lakes to the North American and global economies, the Great Lakes and the surrounding region also serve as an important benchmark for hydroclimate research, and offer an example of successful adaptive management under changing climate conditions. Here, we communicate some of the important lessons to be learned from the Great Lakes by examining how the coastline, water level, and water budget dynamics of the Great Lakes relate to other large coastal systems, along with implications for water resource management strategies and climate scenario-derived projections of future conditions. This improved understanding fills a critical gap in freshwater and marine global coastal research.

GRONEWOLD, A.D., C.A. STOW, K. Vijayavel, M.A. Moynihan, and D.R. Kashian. Differentiating Enterococcus concentration spatial, temporal, and analytical variability in recreational waters. Water Research 47(7):2141-2152 (DOI:10.1016/j.watres.2012.12.030) (2013).

Monitoring recreational waters for fecal contamination is an important responsibility of water resource management agencies throughout the world, yet fecal indicator bacteria (FIB)-based recreational water quality assessments rarely distinguish between analytical, spatial, and temporal variability. To address this gap in water resources research and management protocol, we compare two methods for quantifying FIB concentration variability at a frequently-used beach on Lake Huron (Michigan, USA). The first method calculates differences between most probable number (MPN) and colony-forming unit (CFU) values derived from conventional analysis procedures. The second method uses the “raw data” from these analysis procedures in a Bayesian hierarchical model to explicitly acknowledge analytical variability and subsequently infer the relative significance of the effect of sampling location and time on in situ FIB concentrations. Results of the Bayesian analysis indicate that in situ FIB concentrations do not vary significantly over small spatial and temporal scales, and that observed differences in MPN and CFU values over these same spatial and temporal scales are due almost entirely to intrinsic variability introduced by laboratory analysis procedures. Our findings underscore potential opportunities for incorporating Bayesian statistical models directly into routine recreational water quality assessments and for advancing the state of the art in methods for protecting humans from waterborne disease.

KRUEGER, D.M., E.S. RUTHERFORD, and D.M. MASON. Modeling the influence of parr predation by walleyes and brown trout on the long-term population dynamics of chinook salmon in Lake Michigan: A stage matrix approach. Transactions of the American Fisheries Society 142(4):1101-1113 (DOI:10.1080/00028487.2013.797496) (2013).

Predation events during ontogeny may have long-term consequences for fish population abundance and variability. We used a stage-based matrix model to evaluate Walleye Sander vitreus and BrownTrout Salmo trutta predation on Chinook Salmon Oncorhynchus tshawytscha parr of the Muskegon River stock and the relative influence of parr predation on the long-term population dynamics and recruitment of Chinook Salmon in Lake Michigan. The model predicted the number of Chinook Salmon individuals in each stage (fry, smolts, and lake age 0 [recruits] through lake age 4) and forecasted population trajectories based on demographic data (e.g., survival, growth, and fecundity). The relative influence of parr predation was compared with influences of environmental stochasticity in the egg stage and Alewife Alosa pseudoharengus abundance (prey for lake-stage salmon) on Chinook Salmon fecundity, recruitment, and population growth. To simulate environmental stochasticity and the influence of Alewife abundance, we varied Chinook Salmon stage-specific survival rates, growth rates, maturity schedule, and carrying capacity. Relative to a baseline recruitment scenario, removal of stocked Brown Trout resulted in a significant increase in parr survival and long-term Chinook Salmon abundance. Walleye predation on parr had little apparent influence on Chinook Salmon population dynamics. Predation on parr during out-migration was positively correlated with variation in Chinook Salmon population stability and was negatively correlated with population growth, suggesting that Brown Trout have a significant negative effect on Chinook Salmon recruitment and long-term population stability. The negative effects of variation in egg survival rates and Alewife abundance on Chinook Salmon recruitment and population growth rates were similar to the negative effects from parr predation scenarios. Our study suggests that management decisions to promote Great Lakes Chinook Salmon populations may require evaluation of trout stocking practices in nursery habitats.

LESHKEVICH, G.A., and S.V. Nghiem. Great Lakes ice classification using satellite C-band SAR multi-polarization data. Journal of Great Lakes Research 39(Supplement 1):55-64 (DOI:10.1016/j.jglr.2013.05.003) (2013).

The objective of this study is to advance development of algorithms to classify and map ice cover on the Laurentian Great Lakes using satellite C-band synthetic aperture radar (SAR) multi-polarization data. During the 1997 winter season, shipborne polarimetric backscatter measurements of Great Lakes ice types, using the Jet Propulsion Laboratory C-band scatterometer, were acquired together with surface-based ice physical characterization measurements and environmental parameters, concurrently with European Remote Sensing Satellite 2 (ERS-2) and RADARSAT-1 SAR data. This fully polarimetric dataset, composed of over 20 variations of different ice types measured at incidence angles from 0° to 60° for all polarizations, was processed and fully calibrated to obtain radar backscatter, establishing a library of signatures for different ice types. Computer analyses of calibrated ERS-2 and RADARSAT ScanSAR images of Great Lakes ice cover using the library in a supervised classification technique indicate that different ice types in the ice cover can be identified and mapped, but that wind speed and direction can cause misclassification of open water as ice based on single frequency, single polarization data. Using RADARSAT-2 quad-pol and ENVISAT ASAR dual-pol data obtained for Lake Superior during the 2009 and 2011 winter seasons, algorithms were developed for small incidence angle (b35°) and large incidence angle (>35°) SAR images and applied to map ice and open water. Ice types were subsequently classified using the library of backscatter signatures. Ice-type maps provide important input for environmental management, ice-breaking operations, ice forecasting and modeling, and climate change studies.

LESHKEVICH, G.A., and S.V. Nghiem. Great Lakes ice cover mapping with RADARSAT-2 SAR data. Science and Operational Applications Research (SOAR) RADARSAT-2 Data Use and Benefits Report. Canadian Space Agency, Saint-Hubert, Quebec, Canada, 3 pp. (2013).

The objective of this project is to use RADARSAT-2 data to continue the development of advanced algorithms to classify and map ice cover on the Laurentian Great Lakes started using synthetic aperture radar (SAR) data from ERS-1, ERS-2, and RADARSAT-1. NASA JPL and NOAA GLERL together with support from the US Coast Guard have carried out field experiments on the upper Great Lakes, which have resulted in a comprehensive C-band fully-polarimetric backscatter signature data set up to 60o incidence angles for various ice types and calm open water (Nghiem and Leshkevich, Part 1, 2007) together with “ground truth” data. This unique data set is directly applicable to RADARSAT-2 data (same frequency, all polarizations, and incidence angles) using the dual polarimetric and fully polarimetric (Quad-Pol) capabilities. Providing greater discrimination and less ambiguity than single band, single polarization data, dual polarization and Quad-Pol data at large incidence angles can improve ice type discrimination and mapping that are robust over a wide range of wind speed and direction. At small incidence angles and with a single polarization, RADARSAT-2 results over Lake Superior show that ice and water can be discriminated after which the ice-backscatter library can be applied to classify ice types.

LESHKEVICH, G.A., R.A. Shuchman, and M.J. Sayers. An operational algorithm to retrieve chlorophyll, DOC, and suspended minerals from satellite data of the Great Lakes. Proceedings, European Space Agency (ESA) 3rd MERIS/Sentinel-3 Symposium, Franscati, Italy, October 15-19, 2012. ESA-ESRIN, 4 pp. (2012).

A set of algorithms have been developed for the five North American Great Lakes that utilized MERIS, MODIS, or SeaWIFS satellite data to estimate chlorophyll (chl), dissolved organic carbon (doc), and suspended minerals (sm), the three primary Color Producing Agents (CPAs). The algorithms utilize a specific hydro-optical (HO) model for each lake. The HO models provide absorption functions for all three CPA components as well as backscatter relationships for the chl, and sm and were generated using in situ inherent/apparent optical (IOP/AOP) data collected with coincident water chemistry (concentration) measurements. These new algorithms provide more accurate chl values than those obtained using the standard OC3 NASA MODIS retrieval when compared to in situ cruise observations, as well as providing the additional information on doc and sm. The suite of atmospheric correction algorithms for MODIS, was also evaluated. In general, the standard NASA algorithm does an adequate correction all of the time.

LIU, P.C. Contemplating ocean wave measurements. International Journal of Geosciences 4:229-233 (DOI:10.4236/ijg.2013.41A019) (2013).

This is a personal contemplation on the state of ocean wave measurement, historically, and with an eye toward the future. The conceptual basis which leads to the conventional wave measuring instruments has been in practice for over six decades which is basically single point observations of three-dimensional waves. We need new conceptual advancement and new instrumentation to rejuvenate our research in stagnation. New instruments for spatial wave measurement have been on the horizon.

LIU, P.C. Unrelenting challenges for freaque wave studies in ocean coastal regions: Defining the phenomena. In Coastal Processes III. G.R. Rodriguez, and CA. Brebbia (Eds.) WIT Transactions on Ecology and the Environment Vol 169. WIT Press, Southampton, UK, 13 pp. (2013).

In this paper we point out the lesser known or underexplored aspects of freaque waves and what challenges we are facing. The current study of freaque waves has been an active research field over the last two decades or so. There have been significant advancements especially in connection with the study of nonlinear physics. We have explored what we do or do not know; in this paper, we present the unrelenting challenges that we are still facing.

LUO, L., J. WANG, D.J. SCHWAB, H.A. VANDERPLOEG, G.A. LESHKEVICH, X. BAI, H. HU, and D. Wang. Simulating the 1998 spring bloom in Lake Michigan using a coupled physical-biological model. Journal of Geophysical Research 117(C10011):14 pp. (DOI:10.1029/2012JC008216) (2012).

[1] A coupled physical-biological model is used to simulate the ecosystem characteristics in Lake Michigan. The physical model is the unstructured grid, Finite-Volume Coastal Ocean Model (FVCOM). The biological model is a NPZD model, including phosphorus as the nutrient, which is the limiting element in Lake Michigan, phytoplankton, zooplankton and detritus. The models are driven by observed hourly meteorological forcing in 1998 and the model results are calibrated by satellite and in situ data. The main physical and ecological phenomena in the spring of 1998 are captured. During March to May, a circle-like phytoplankton bloom appears in southern Lake Michigan, which looks like a ‘doughnut’. The formation mechanisms of the prolonged spring bloom are investigated. It is confirmed that the phytoplankton bloom is forced by rapidly increasing temperature and light intensity in spring. The thermal front that develops in spring inhibits the transport of nutrients and phytoplankton from the nearshore to the deeper water. The wind-driven gyre circulation in southern Lake Michigan induces significant offshore transport, which contributes to the establishment of the circular bloom.

Madenjian, C.P., S.A. POTHOVEN, and Y.C. Kao. Reevaluation of lake trout and lake whitefish bioenergetics models. Journal of Great Lakes Research 39:358-364 (DOI:10.1016/j.jglr.2013.03.011) (2013).

Using a corrected algorithm for balancing the energy budget, we reevaluated the Wisconsin bioenergetics model for lake trout (Salvelinus namaycush) in the laboratory and for lake whitefish (Coregonus clupeaformis) in the laboratory and in the field. For lake trout, results showed that the bioenergetics model slightly overestimated food consumption by the lake trout when they were fed low and intermediate rations, whereas the model predicted food consumption by lake trout fed ad libitum without any detectable bias. The slight bias in model predictions for lake trout on restricted rations may have been an artifact of the feeding schedule for these fish, and we would therefore recommend application of the Wisconsin lake trout bioenergetics model to lake trout populations in the field without any revisions to the model. Use of the Wisconsin bioenergetics model for coregonids resulted in overestimation of food consumption by lake whitefish both in the laboratory and in the field by between 20 and 30%, on average. This overestimation of food consumption was most likely due to overestimation of respiration rate. We therefore adjusted the respiration component of the bioenergetics model to obtain a good fit to the observed consumption in our laboratory tanks. The adjusted model predicted the consumption in the laboratory and the field without any detectable bias. Until a detailed lake whitefish respiration study can be conducted, we recommend application of our adjusted version of the Wisconsin generalized coregonid bioenergetics model to lake whitefish populations in the field.

MARSHALL, A., E. Laporte, S. Rutherford, and R.A. STURTEVANT. In a data dilemma? A series of data sets and inquiry tools that furthers Great Lakes literacy. The Earth Scientist XXIX(3):6-10 (2013).

Using real data in science classrooms is a powerful way to encourage inquiry and teach process skills. However, many educators have found geoscience data difficult to access and use. As part of a NOAA Environmental Literacy Grant, the Teaching with Great Lakes Data website ( was developed using scientific data about the Great Lakes. This online resource contains data sets formatted for use by teachers, as well as structured lessons and tools for graphing and guided inquiry.

Michalak, A.M., E.J. ANDERSON, D. BELETSKY, S. Boland, N.S. Bosch, T.B. Bridgeman, J.D. Chaffin, K. Cho, R. Confesor, I. Daloglu, J.V. DePinto, M.A. Evans, G.L. FAHNENSTIEL, L. He, J.C. Ho, L. Jenkins, T.H. JOHENGEN, K.C. Kuo, E. Laporte, X. Liu, M. McWilliams, M.R. Moore, D.J. Posselt, R.P. Richards, D. Scavia, A.L. Steiner, E. Verhamme, D.M. Wright, and M.A. Zagorski. Record-setting algal bloom in Lake Erie caused by agricultural and meteorological trends consistent with expected future conditions. Proceedings of the National Academy of Sciences 110(16):6448-6452 (DOI:10.1073/pnas.1216006110) (2013).

In 2011, Lake Erie experienced the largest harmful algal bloom in its recorded history, with a peak intensity over three times greater than any previously observed bloom. Here we show that long-term trends in agricultural practices are consistent with increasing phosphorus loading to the western basin of the lake, and that these trends, coupled with meteorological conditions in spring 2011, produced record-breaking nutrient loads. An extended period of weak lake circulation then led to abnormally long residence times that incubated the bloom, and warm and quiescent conditions after bloom onset allowed algae to remain near the top of the water column and prevented flushing of nutrients from the system. We further find that all of these factors are consistent with expected future conditions. If a scientifically guided management plan to mitigate these impacts is not implemented, we can therefore expect this bloom to be a harbinger of future blooms in Lake Erie.

Moll, R.A., C.E. Sellinger, E.S. RUTHERFORD, J.L. Johnson, M.R. Fainter, and J.E. Gannon. The Great Lakes: An overview of their formation, geology, physics, and chemistry. In Great Lakes Fisheries Policy and Management: A Binational Perspective. W.W. Taylor, A.J. Lynch, and N.J. Leonard (Eds.). Michigan State University Press, East Lansing, MI, pp. 3-29 (2013).

The Laurentian Great Lakes are the crown jewels of the freshwater systems of North America. These five large lakes, their associated lakes, and their connecting channels (fig. 1) hold about 23,000 km3 of water— enough to cover the contiguous United States to a depth of about 3 meters (Great Lakes Environmental Atlas 1995). They comprise a series of ecosystems unique in the world and are the subject of considerable study, regulation, and observation. They also possess physical, chemical, and biological characteristics unique among all the largest lakes on the planet. Yet for all their immense size and grandeur, the Great Lakes have not been protected from anthropogenic perturbations, which have changed them on a basin-wide scale. The fishes of the Great Lakes, like all the aquatic flora and fauna, are completely dependent on their surroundings for their long-term survival. The primary objective of this chapter is to provide a broad-brush review of the key non-biological aspects of the Great Lakes that, in turn, provide the essential habitat for the fishes. Without the unique geology, physics, and chemistry of the lakes, as described in this chapter, the likewise unique fishes of the lakes could not survive or continue to evolve. This chapter includes three sections: Lake Formation and Geology, Overview of the Great Lakes’ Physical Characteristics, and Great Lakes Water Chemistry. These sections discuss a wide variety of topics but place emphasis on changes to the Great Lakes over the past forty years. Examples used in this chapter come from all five Great Lakes but do not cover every aspect of the geology, physics, or chemistry for each lake. Representative information is presented to demonstrate general trends of the Great Lakes with the understanding that each Great Lake has followed a different course in the past two hundred years. Each section is intended to provide background information that, in turn, sets the stage for the richer discussion of Great Lakes fishes found in the succeeding chapters.

NELSON, D., H. Elmer, and P. Robinson. Planning for climate change in the Laurentian Great Lakes basin. A NOAA needs assessment - Final Report. NOAA Technical Memorandum GLERL-158. NOAA Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 34 pp. (2013).

The NOAA Great Lakes Regional Collaboration Team, Old Woman Creek National Estuarine Research Reserve and Great Lakes Sea Grant Network, and in collaboration with the Great Lakes and Saint Lawrence Cities Initiative, have worked collaboratively to determine what is needed to increase adaptive capacity in Great Lakes communities to anticipated changes in climate. The primary objective for conducting this study is to increase adaptive capacity by informing and developing climate change adaptation training workshops. To ensure that training meets priority needs and provides accessible and applicable tools and resources, these organizations have collaborated to conduct a needs assessment: a comprehensive front-end evaluation of the climate change adaptation training and information needs of Great Lakes coastal communities. Presented here are the results of a needs assessment completed in 2011, engaging nearly 700 stakeholders across the Basin through interviews, focus groups, and an online survey.

NOAA Great Lakes Regional Collaboration Team. Guide to NOAA response and communication protocols for human-caused and natural disasters in the Great Lakes. NOAA Technical Memorandum GLERL-159. NOAA Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 31 pp. (2013).

This Guide is designed to enhance coordination of NOAA’s diverse expertise, services, and resources when responding to a Great Lakes natural or anthropogenic emergency that involves a threat or damage to human health or life, to property, or to the environment. This Guide addresses the following emergencies: 1) an oil spill, hazardous chemical release, or maritime accident; 2) a large-scale fire event; 3) a large-scale or high-impact weather event; or 4) a radiological release. For many emergencies, only one NOAA Line Office is needed to provide an effective response. When two or more NOAA Line Offices are involved in a large-scale event, however, clear and efficient communication and coordination are needed to simultaneously provide a high level of service and efficiently utilize NOAA’s own expertise and resources. The focus of this Guide is on communication and collaboration among NOAA’s Line Offices and programs. Although effective communication among federal, state, and local agencies and within each NOAA Line Office is critical to response outcomes, it is beyond the scope of this document. The ultimate objective of the Guide is to advance communication and better integrate line office capabilities to support a “One NOAA” response to emergency events; it is not to challenge existing mandates.

Nold, S.C., M.J. Bellecourt, S.T. Kendall, S.A. RUBERG, T.G. Sanders, J. Val Klump, and B.A. Biddanda. Underwater sinkhole sediments sequester Lake Huron's carbon. Biogeochemistry February 2013:16 pp. (DOI:10.1007/s10533-013-9830-8) (2013).

Lake Huron’s submerged sinkhole habitats are impacted by high-conductivity groundwater that allows photosynthetic cyanobacterial mats to form over thick, carbon-rich sediments. To better understand nutrient cycling in these habitats, we measured the stable isotopic content of carbon and nitrogen in organic and inorganic carbon pools in Middle Island sinkhole, a ~23 m deep feature influenced by both groundwater and overlying lake water. Two distinct sources of dissolved CO2 (DIC) were available to primary producers. Lake water DIC (δ13C = -0.1%) differed by +5.9% from groundwater DIC (δ13C = -6.0 %). Organic carbon fixed by primary producers reflected the two DIC sources. Phytoplankton utilizing lake water DIC were more enriched in 13C (δ13C = -22.2 to -23.2%) than mat cyanobacteria utilizing groundwater DIC (δ13C = -26.3 to -30.0%). Sinkhole sediments displayed an isotopic signature (δ13C = -23.1%) more similar to sedimenting phytoplankton than the cyanobacterial mat. Corroborated by sediment C/N ratios, these data suggest that the carbon deposited in sinkhole sediments originates primarily from planktonic rather than benthic sources. 210Pb/137Cs radiodating suggests rapid sediment accumulation and sub-bottom imaging indicated a massive deposit of organic carbon beneath the sediment surface. We conclude that submerged sinkholes may therefore act as nutrient sinks within the larger lake ecosystem.

POTHOVEN, S.A., and G.L. FAHNENSTIEL. Recent change in summer chlorophyll a dynamics of southeastern Lake Michigan. Journal of Great Lakes Research 39(2):287-294 (DOI:10.1016/j.jglr.2013.02.005) (2013).

Six offshore stations in southeastern Lake Michigan were sampled during a pre quagga mussel Dreissena rostriformis bugensis period (1995–2000) and a post quagga mussel period (2007–2011). Chlorophyll a fluorescence profiles were used to characterize chlorophyll a concentrations during early (June–July) and late (August–September) summer stratification. During the early summer period the average whole water column chlorophyll a, the deep chlorophyll maximum, and the size of deep chlorophyll layer decreased 50%, 55%, and 92%, respectively, between 1995–2000 and 2007–2011. By contrast, in late summer there were no changes in these metrics between periods. Surface mixed layer chlorophyll a in early and late summer did not differ between time periods. On the other hand, chlorophyll a in the near bottom zone (bottom 20 m) declined 63% and 54% between 1995–2000 and 2007–2011 in early and late summer respectively. Changes in total phosphorus between 1995–2000 and 2007–2011were less dramatic, with declines of 22–27% in early summer and 11–30% in late summer. Changes in the chlorophyll a conditions were attributed to dreissenid mussels, which reduced material available from the spring bloom and disrupted the horizontal transport of nutrients to the offshore. Although light availability increased (i.e., increased secchi depths), reduced nutrient availability and spring diatom abundance resulted in a much smaller deep chlorophyll layer in 2007–2011.

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

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

POTHOVEN, S.A., T.O. Hook, T.F. NALEPA, M.V. Thomas, and J. DYBLE. Changes in zooplankton community structure associated with the disappearance of invasive alewife in Saginaw Bay, Lake Huron. Aquatic Ecology 47(1):1-12 (DOI:10.1007/s10452-012-9420-1) (2013).

We evaluated the response of the zooplankton community Saginaw Bay, Lake Huron to the disappearance of the planktivore alewife Alosa pseudoharengus using data collected in 1991–1996 (pre-alewife decline) and 2009–2010 (post alewife decline). Bosmina longirostris, Diaptomidae, Cyclops, and Daphnia galeata contributed greatly to the separation of the two time periods with Diaptomidae and D. galeata increasing and Cyclops and B. longirostris decreasing, although B. longirostris remained the dominant species. Peak densities of zooplankton occurred in early summer (June) in the 1990s and in early fall (October) in 2009–2010. For the analysis of environmental variables on a bay-wide, annual basis, abundance of alewife, age-0 yellow perch Perca flavescens and Bythotrephes captured much of the variation in annual zooplankton community structure. Abundances of Bythotrephes and age-0 yellow perch were both higher in 2009–2010 than in 1991–1996. Some changes such as increasing proportions of calanoid copepods reflect a more oligotrophic community and are potentially indicative of resource driven changes rather than direct or indirect impacts of the alewife disappearance.

POTHOVEN, S.A., H.A. VANDERPLOEG, T.O. Hook, and S.A. Ludsin. Hypoxia modifies planktivore-zooplankton interactions in Lake Erie. Canadian Journal of Fisheries and Aquatic Sciences 69:2018-2028 (DOI:10.1139/cjfas-2012-0144) (2012).

We evaluated vertical distributions of fish and zooplankton, planktivore consumption, and prey production in Lake Erie during 2005 to determine how hypolimnetic hypoxia alters fish (i.e., rainbow smelt (Osmerus mordax) and emerald shiners (Notropis atherinoides)) and invertebrate planktivore (i.e., Bythotrephes longimanus and Leptodora kindtii) relationships with their mesozooplankton prey. Hypoxia concentrated 45%–76% of fish into a narrow (_2 m) metalimnetic layer, but only 3%–13% of zooplankton production was in this layer. The epilimnion may have served to some degree as a refuge for mesozooplankton because high temperatures may have excluded rainbow smelt. High concentrations of fish above the hypolimnion likely resulted in increased competition for large prey (i.e., predatory claodcerans). Although hypoxia did not result in overall high predation demands by planktivores relative to total zooplankton production, planktivore consumption rates within the metalimnion exceeded zooplankton production in that layer.

ROCKWELL, D.C., K.B. CAMPBELL, G.A. LANG, D.J. SCHWAB, G. Mann, and R. Wagenmaker. Beach water quality decision support system. NOAA Technical Memorandum GLERL-156. NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 64 pp. (2013).

The need for rapid assessment of bacterial contamination at beaches is well known. Bacterial concentrations change rapidly (Bohm, Whitman et al. 1995, Olyphant and Whitman 2004, Whitman and Nevers 2008). The “persistence model” regulates today’s swimming with yesterday’s Escherichia coli (E. coli) measurement. As a result, this beach management tool is known to be less protective of human health than desired but was still used at over 500 beaches in 2010. One method for meeting this problem has been to develop rapid analytical methods taking two hours of laboratory analytical time. This approach is becoming operationally available but at higher analytical cost (Setty 2012) than the slower cultural methods currently employed. These rapid analytical methods provide beach managers with the capability to advise swimmers about E. coli concentrations on the same day, but only if sampling, transportation, and data management time components can be completed within four hours, giving an overall time of 6 hours. This requires early field sampling and laboratories close to the beaches being sampled. Another approach is to use Nowcast predictive models that can provide estimations of E. coli during the same day (Francy 2009) by measuring easily determined variables that can be correlated with E. coli bacterial concentrations. The Nowcast predictive models were being used at 10 beaches in 2010 (Adam Mednick, personal communication). It is expected that Nowcast predictive models will be expanded in 2011 to more than 20 beaches because of Great Lake Restoration Initiative funding. This technical memorandum is based primarily on the final grant report to Ed Pniak, GLRI Project Officer, Michigan Project Lead, U.S. EPA, Region 5, Water Division, State and Tribal Programs Branch for GL-00E00658. The grant is titled “60 Hour Beach Forecasting Models.” The principle investigators are Allen Burton, Kent Campbell, and David Rockwell. This technical memorandum provides beach managers with a tool to forecast several days in advance the likelihood of E. coli concentrations exceeding the state single sample regulatory standard. This predictive beach water quality management tool is the only beach management decision support system (DSS) capable of forecasting several days in advance the beach water quality bacterial concentrations because it limits the explanatory variables to those variables for which the National Weather Service (NWS) is able to make forecasts. The forecast DSS was applied to 35 sampling locations at 24 beaches during the 2010 swimming season. The results of Grant GL-00E00658 showed the forecast DSS provided the same or better beach management decision support than the persistence model at 71% (25 of the 35) of the sampling sites. In addition, the stratification of beach sampling sites based on 5% of the samples exceeding the state regulatory standard single sample maximum of 235 counts/100 ml improved the forecast DSS. The forecast DSS for the beaches meeting this criteria provided better (70%) beach management support or the same (15%) beach management support than the persistence model for a total of 85% (23 of the 27) of the sampling sites. The evaluation of the percent of samples exceeding the state regulatory standard allows the beach manager to readily determine if the beach is more suitable for the forecast DSS tool. Forecast DSS has the potential to provide the swimming community with information several days in advance, allowing the planning of their water recreational activities and reducing the risk of swimming in bacterially contaminated water while maximizing the opportunity to use the water recreational facilities. Lastly, application of the forecast DSS to all monitored beaches with two or more samples per week in 2010 could have led to about a 23% reduction (862 swimming advisory days) of the 3766 reported (NRDC 2011). The lost value of swimming for the Great Lake recreational swimmers ranges from $11.3M to $117M for these days when swimming is banned (Shaikh 2006 and Rabinovici et al. 2004).

Roswell, C.R., S.A. POTHOVEN, and T.O. Hook. Spatio-temporal, ontogenetic and interindividual variation of age-0 diets in a population of yellow perch. Ecology of Freshwater Fish 22(3):479-493 (DOI:10.1111/eff.12041) (2013).

Dietary niches of fishes have traditionally been evaluated at the population level, with diet pattern central tendencies compared spatio-temporally among habitats and populations. More recently, however, studies have emphasized the importance of within-population diet variation and niche partitioning. Several studies have examined diets of young yellow perch (Perca flavescens) at the population level and have described an ontogenetic transition from zooplankton to benthic prey during the first year of life. However, independent of ontogenetic diet shifts, intrapopulation variation of young yellow perch diets remains largely unexplored. We quantified patterns of diet composition in age-0 yellow perch collected from Saginaw Bay, Lake Huron, USA during July–October, 2009 and 2010. We observed substantial variation in diet composition among individuals across and within sites, but found relatively weak evidence indicating an ontogenetic diet shift. Zooplankton were the dominant prey for age-0 yellow perch on most occasions, and individual diets were composed primarily of either zooplankton (e.g. Daphnia spp., Calanoida) or benthic (i.e. Chironomidae larvae, Chydoridae) prey. These patterns were not simply attributable to differences in prey availability and ontogenetic diet shifts, because a) not only diet composition, but also prey selectivity (Chesson’s a) varied among sites and b) individual and spatial diet differences were evident independent of ontogeny. Within-cohort differences in diet composition may be an important, but often overlooked, phenomenon with implications for cumulative trophic interactions and intracohort growth and survival among young fish.

Russoniello, C.J., C. Fernandez, J.F. BRATTON, J. Banaszak, D. Krantz, A.S. Andres, L.F. Konikow, and H.A. Michael. Geologic effects on groundwater salinity and discharge into an estuary. Journal of Hydrology 498:1-12 (DOI:10.1016/j.jhydrol.2013.05.049) (2013).

Submarine groundwater discharge (SGD) can be an important pathway for transport of nutrients and contaminants to estuaries. A better understanding of the geologic and hydrologic controls on these fluxes is critical for their estimation and management. We examined geologic features, porewater salinity, and SGD rates and patterns at an estuarine study site. Seismic data showed the existence of paleovalleys infilled with estuarine mud and peat that extend hundreds of meters offshore. A low-salinity groundwater plume beneath this low-permeability fill was mapped with continuous resistivity profiling. Extensive direct SGD measurements with seepage meters (n = 551) showed fresh groundwater discharge patterns that correlated well with shallow porewater salinity and the hydrogeophysical framework. Small-scale variability in fresh and saline discharge indicates influence of meter-scale geologic heterogeneity, while site-scale discharge patterns are evidence of the influence of the paleovalley feature. Beneath the paleovalley fill, fresh groundwater flows offshore and mixes with saltwater before discharging along paleovalley flanks. On the adjacent drowned interfluve where low-permeability fill is absent, fresh groundwater discharge is focused at the shoreline. Shallow saltwater exchange was greatest across sandy sediments and where fresh SGD was low. The geologic control of groundwater flowpaths and discharge salinity demonstrated in this work are likely to affect geochemical reactions and the chemical loads delivered by SGD to coastal surface waters. Because similar processes are likely to exist in other estuaries where drowned paleovalleys commonly cross modern shorelines, the existence and implications of complex hydrogeology are important considerations for studies of groundwater fluxes and related management decisions.

Shuchman, R.A., and G.A. LESHKEVICH. Foreword for Special Issue of JGLR on Remote Sensing. Journal of Great Lakes Research 39(Supplement 1):1 (DOI:10.1016/j.jglr.2013.07.001) (2013).

This special issue of the Journal of Great Lakes Research addresses the use of current state-of-the-art remote sensing technology to make critical observations of the Great Lakes and other large lakes throughout the world. Remote sensing is defined as the acquisition of information about an object or phenomenon without making physical contact with the object and makes use of the electromagnetic spectrum. There are two types of remote sensing; passive and active. Passive remote sensing such as a camera or radiometer detects natural radiation that is reflected or emitted by the object or its surrounding, with sunlight being the most common source of this natural radiation. Active remote sensors such as Lidar, sonar, and Radar emit their own source of radiation to scan an object and utilize the reflected energy or backscatter from the object to obtain the desired measurement. Remote sensing instrumentation used to gain information about the Great Lakes operates at frequencies from tens of KHz, in the case of sonar, to optical, infrared, and microwave frequencies. The remote sensors can be deployed on land, ship or autonomous underwater vehicle, manned and unmanned aircraft, and satellite-based platforms. For example, first launched in 1960, the TIROS series of weather satellites dramatically improved weather forecasting and our understanding of macroscale phenomenon such as global snow cover. Satellites have been routinely imaging the Great Lakes from the early 1970s and thus now provide an extremely important tool to go back in time to document changes in the Great Lakes Basin that are a result of invasive species, climate change, and anthropogenic forcing.

Shuchman, R.A., G.A. LESHKEVICH, M.J. Sayers, T.H. JOHENGEN, C.N. Brooks, and D. Pozdnyakov. An algorithm to retrieve chlorophyll, dissolved organic carbon, and suspended minerals from Great Lakes satellite data. Journal of Great Lakes Research 39(Supplement 1):14-33 (DOI:10.1016/j.jglr.2013.06.017) (2013).

An algorithm that utilizes individual lake hydro-optical (HO) models has been developed for the Great Lakes that uses SeaWiFS, MODIS, or MERIS satellite data to estimate concentrations of chlorophyll, dissolved organic carbon, and suspended minerals. The Color Producing Agent Algorithm (CPA-A) uses a specific HO model for each lake. The HO models provide absorption functions for the Color Producing Agents (CPAs) (chlorophyll (chl), colored dissolved organic matter (as dissolved organic carbon, doc), and suspended minerals (sm)) as well as backscatter for the chlorophyll, and suspended mineral parameters. These models were generated using simultaneous optical data collected with in situ measurements of CPAs collected during research cruises in the Great Lakes using regression analysis as well as using specific absorption and backscatter coefficients at specific chl, doc, and sm concentrations. A single average HO model for the Great Lakes was found to generate insufficiently accurate concentrations for Lakes Michigan, Erie, Superior and Huron. These new individual lake retrievals were evaluated with respect to EPA in situ field observations, as well as compared to the widely used OC3 MODIS retrieval. The new algorithm retrievals provided slightly more accurate chl values for Lakes Michigan, Superior, Huron, and Ontario than those obtained using the OC3 approach as well as providing additional concentration information on doc and sm. The CPA-A chl retrieval for Lake Erie is quite robust, producing reliable chl values in the reported EPA concentration ranges. Atmospheric correction approaches were also evaluated in this study.

Shuchman, R.A., M.J. Sayers, G.L. FAHNENSTIEL, and G.A. LESHKEVICH. A model for determining satellite-derived primary productivity estimates for Lake Michigan. Journal of Great Lakes Research 39(Supplement 1):46-54 (DOI:10.1016/j.jglr.2013.05.001) (2013).

A new MODIS based satellite algorithm to estimate primary production (PP) has been generated and evaluated for Lake Michigan. The Great Lakes Primary Productivity Model (GLPPM) is based on previous models that required extensive in situ data but it can utilize remotely sensed observations as input for some model variables and therefore allows greater spatial resolution for primary productivity estimates. The Color Producing Agent Algorithm (CPA-A) is utilized to obtain robust chlorophyll a values and the NASA KD2M approach is used to obtain the diffuse attenuation coefficient (Kd). Only incident PAR and carbon fixation rates are additionally needed to generate the primary productivity estimate. Comparisons of the satellite derived PP estimates from single monthly images to average monthly field measurements made by NOAA/ GLERL found good agreement between estimates. Satellite derived PP estimates were used to estimate a preliminary Lake Michigan annual primary production of 8.5 Tg C/year. The new algorithm can be easily adapted to work on all the Great Lakes and therefore can be used to generate time series dating back to late 1997 (launch of SeaWiFs). These time series can contribute to improved assessment of Great Lakes primary productivity changes as a result of biological events, such as Dreissenid mussel invasions, climatic change and anthropogenic forcing.

STOW, C.A., and Y.K. Cha. Are chlorophyll a - total phosphorus correlations useful for inference and prediction? Environmental Science & Technology 47(8):3768-3773 (DOI:10.1021/es304997p) (2013).

Correlations between chlorophyll a and total phosphorus in freshwater ecosystems were first documented in the 1960s and have been used since then to infer phosphorus limitation, build simple models, and develop management targets. Often these correlations are considered indicative of a cause−effect relationship. However, many scientists regard the use of these associations for modeling and inference to be misleading due to their potentially spurious nature. Using data from Saginaw Bay, Lake Huron, we examine the relationship among chlorophyll a, total phosphorus, and algal biomass measurements. We apply graphical models and recently developed “structure learning” principles that use conditional dependencies to help identify causal relationships among observational data. The spurious relationship suspected by some is not supported by our data, whereas a direct relationship between chlorophyll a and total phosphorus is always supported, and an additional indirect relationship with an algal biomass intermediary is plausible under some circumstances. Thus, we conclude that these correlations are useful for simple model building but encourage the use of modern statistical methods to avoid common model-assumption violations.

STOW, C.A., and T.O. Hook. Saginaw Bay multiple stressors summary report. NOAA Technical Memorandum GLERL-160. NOAA Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 51 pp. (2013).

This report synthesizes results obtained during a five-year study (2008-2012) on Saginaw Bay, a large embayment on the southwest side of Lake Huron. The report is a summary of findings relevant for management decision making regarding issues related to the fishery and water quality of Saginaw Bay. Because the report is intended as an overview, detailed descriptions of the approaches and methods used are omitted, but can be found in papers published in the peer-reviewed literature, including a special issue in the Journal of Great Lakes Research, scheduled for publication in late 2013.

Sun, Y., M.G. Wells, S.A. Bailey, and E.J. ANDERSON. Physical dispersion and dilution of ballast water discharge in the St. Clair River: Implications for biological invasions. Water Resources Research 49:1-13 (DOI:10.1002/wrcr.20201) (2013).

[1] Ballast-water-vectored biological invasions in water bodies are subject to physical mixing. To investigate how mixing influences ballast water dispersion, we conducted five trials of dye release in the 600_900 m wide St. Clair River (with a mean flow of 5100 m3 s_1) in 2009. Dye-mixed ballast water was discharged from tankers in two nearshore trials, and dye solutions were directly released into the river in three offshore trials. Results confirm that dye was rapidly diluted by jet mixing during ballast water discharge (BWD) and became vertically homogeneous within 500 m downstream. Subsequently, there was two-dimensional mixing downstream with a longitudinal dispersion coefficient Kx _ 100 m2 s_1 and a transverse dispersion coefficient Ky _ 0.5 m2 s_1. The marked difference between Kx and Ky resulted in limited transverse mixing, implying that any nearshore BWD is unlikely to reach the opposite bank in the wide St. Clair River within its total length (_60 km). The peak concentration Cp showed a power-law decay over time t as Cp / tb and b was close to _1, consistent with the Fickian diffusion model. Compared to the offshore trials, the nearshore trials were characterized by significantly slower travel speeds, because of velocity shear across the channel. This is the first field study on mixing of BWD in the context of biological invasions in a river that is large enough to reveal considerable differences in mixing across the channel. These findings shed light on the management of BWD and contaminant spills.

WANG, J., H. HU, J. Goes, J. Miksis-Olds, C. Mouw, E. D'Sa, H. Gomes, D.R. Wang, K. Mizobata, S. Saitoh, and L. LUO. A modeling study of seasonal variations of sea ice and plankton in the Bering and Chukchi Seas during 2007–2008. Journal of Geophysical Research, Oceans 118:1–14 (DOI:10.1029/2012JC008322) (2013).

[1] A nutrient (N), phytoplankton (P), zooplankton (Z), and detritus (D) ecosystem model coupled to an ice-ocean model was applied to the Bering and Chukchi Seas for 2007–2008. The model reasonably reproduces the seasonal cycles of sea ice, phytoplankton, and zooplankton in the Bering–Chukchi Seas. The spatial variation of the phytoplankton bloom was predominantly controlled by the retreat of sea ice and the increased gradient of the water temperature from the south to the north. The model captures the basic structure of the measured nutrients and chl-a along the Bering shelf during 4–23 July 2008, and along the Chukchi shelf during 5–12 August 2007. In summer 2008, the Green Belt bloom was not observed by either the satellite measurements or the model. The model-data comparison and analysis reveal the complexity of the lower trophic dynamics in the Bering and Chukchi Seas. The complexity is due to the nature that the physical and biological components interact at different manners in time and space, even in response to a same climate forcing, over the physically distinct geographic settings such as in the Bering and North Aleutian Slopes, deep Bering basins, Bering shelf, and Chukchi Sea. Sensitivity studies were conducted to reveal the underlying mechanisms (i.e., the bottom-up effects) of the Bering–Chukchi ecosystem in response to changes in light intensity, nutrient input from open boundaries, and air temperature. It was found that (1) a 10% increase in solar radiation or light intensity for the entire year has a small impact on the intensity and timing of the bloom in the physical–biological system since the light is not a limiting factor in the study region; (2) a 20% increase in nutrients from all the open boundaries results in an overall 7% increase in phytoplankton, with the Slope region being the largest, and the Bering shelf and Chukchi being the smallest; and (3) an increase in air temperature by 2_C over the entire calculation period can result in an overall increase in phytoplankton by 11%.

Wehrly, K.E., L. Wang, D. Infante, C. Joseph, A. Cooper, L. Stanfield, and E.S. RUTHERFORD. Landscape change and its influence on aquatic habitats and fisheries in the Great Lakes basin. In Great Lakes Fisheries Policy and Management: A Binational Perspective. W.W. Taylor, A.J. Lynch, and N.J. Leonard (Eds.). Michigan State University Press, East Lansing, MI, pp. 81-103 (2013).

The Laurentian Great Lakes are an economically and ecologically valuable resource. The lakes supply water for municipalities and industry, provide fishing and boating opportunities for residents and tourists, and serve as a key shipping route linking the agricultural, mining, and manufacturing centers of the basin to the world. The lakes also support a diverse array of aquatic life. Owing to their large spatial extent and geologic history, the Great Lakes exhibit considerable variation in climate and bathymetry that naturally maintains differences in temperature, water quality, and biological assemblages both within and among the lakes. Humans have altered Great Lakes ecosystems through exploitation and management of fish stocks, introduction of invasive species intentionally and unintentionally, and alteration of the landscape. Much of the management and research dealing with human impacts on the Great Lakes has primarily focused on fisheries issues in the pelagic zone and on impacts of invasive species. Comparatively little work has addressed landscape change and its influences on aquatic habitats and fisheries. The Laurentian Great Lakes, like other aquatic ecosystems, are strongly influenced by

Wynne, T.T., R.P. Stumpf, M.C. Tomlinson, G.L. FAHNENSTIEL, J. DYBLE, D.J. SCHWAB, and S.J. JOSHI. Evolution of a cyanobacterial bloom forecast system in western Lake Erie: Development and initial evaluation. Journal of Great Lakes Research 39(Supplement 1):90-99 (DOI:10.1016/j/jglr.2012.10.003) (2013).

In the summer of 2008 the National Oceanic and Atmospheric Administration began monitoring cyanobacterial blooms in Lake Erie using high temporal resolution satellite imagery. In 2009, a forecast of bloom transport was also developed using a hydrodynamic model to forecast the trajectory of the bloom. These forecasts have been disseminated from 2008 to the present in the form of a bulletin, which is emailed to local managers, health departments, researchers and other stakeholders. The number of bulletins issued each year, as well as the number of subscribers that receive the weekly bulletins, has increased significantly every year that the system has been in place. This manuscript discusses results from the first 3 years that the forecasts were distributed (2008–2010), describes the components of the forecasts, and will conclude with possible improvements that could be made to the forecast system. Harmful algal blooms of the genus Microcystis were found in all 3 years, and the development of these blooms was associated with water temperatures >18 °C and wind stresses b0.04 Pa. Wind stresses >0.1 Pa were associated with bloom dispersement as were temperatures b18 °C. The present forecasting system was deemed adequate, but improvements in the use of additional remote sensing products and post-processing would yield a more accurate forecast.

Zhulidov, A.V., A.V. Kozhara, T.F. NALEPA, T.Y. Gurtovaya, and D.A. Zhulidov. Relative abundance of two dreissenid species, Dreissena polymorpha and Dreissena rostriformis bugensis in the lower Don River system, Russia. Aquatic Invasions 8(3):311-318 (DOI:10.3391/ai.2013.8.3.07) (2013).

Relative abundance of two dreissenid species, Dreissena rostriformis bugensis and Dreissena polymorpha, in the total dreissenid community was calculated for 15 sites in the lower Don River system, Russia, between 1977 and 2010 to determine relative trends in their sympatric occurrence. The proportion of D. r. bugensis first increased at most stations reaching a maximum by 1999. However, after 1999, this species consistently decreased at 14 of the 15 sites. Degree of decline seems to correlate strongly to calcium content and total mineral content of the water. At sites in the Manych River with a higher Ca2+ and total mineral content, the proportion of D. r. bugensis in the total dreissenid population declined from 65–75% in 1999 to 14–22% by 2009–2010, whereas at sites in the Don River with lower Ca2+ and total mineral content its proportion declined from 25–50% to only 1 %. However, Ca2+ and total mineral content cannot explain the synchronous and consistent long-term decrease in relative numbers as observed. D. r. bugensis normally displaces D. polymorpha over time due to superior physiological characteristics. Reasons for the decline of D. r. bugensis in the total dreissenid community are unclear, but given its synchronicity despite different times of invasion and hence species interactions we assume a macroregional factor affecting all the populations examined.

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