|Capitalized names represent GLERL authors.|
ANDERSON, E.J., D.J. SCHWAB, and G.A. LANG. Real-time hydraulic and hydrodynamic model of the St. Clair River, Lake St. Clair, Detroit River system. Journal of Hydraulic Engineering August 2010:507-518 (2010). https://www.glerl.noaa.gov/pubs/fulltext/2010/20100017.pdf
The Huron-Erie Corridor serves as a major waterway in the Great Lakes and is the connecting channel between Lake Huron and Lake Erie. The system consists of the St. Clair River, Lake St. Clair, and the Detroit River, and serves as a recreational waterway, source of drinking water for Detroit and surrounding cities, as well as the only shipping channel to Lakes Huron, Michigan, and Superior. This paper describes a three-dimensional unsteady model of the combined system and its application to real-time predictions of physical conditions over the corridor. The hydrodynamic model produces nowcasts eight times per day and 48 h forecasts twice a day. Comparisons between model simulations and observed values show average differences of 3 cm for water levels and 12 cm/s for along-channel currents in the St. Clair River _compared to mean current values of 1.7 m/s_ for the period of September 2007 to August 2008. Simulations reveal a spatially and temporally variable circulation in Lake St. Clair as well as significant changes in flow rate and distribution through the St. Clair Delta not accounted for in previous models.
ASSEL, R.A. Contemporary Lake Superior ice cover climatology. In State of Lake Superior. M. Munawar and I.F. Munawar (eds.). Aquatic Ecosystem Health and Management Society, Ecovision World Monograph Series, Canada, 51-66 pp. (2009). https://www.glerl.noaa.gov/pubs/fulltext/2009/20090048.pdf
A brief discussion of Lake Superior ice cover climatology (Phillips, 1978) was included in an issue of the Journal of Great Lakes Research dedicated to the Limnology of Lake Superior (Munawar, 1978) almost three decades ago. Much additional information (and analysis) of Great Lakes ice cover has been collected (and published) since then. The objective here is to describe Lake Superior's contemporary ice cover climatology given additional information and publications since Phillips (1978). The annual cycle of ice formation and loss on Lake Superior affects physical processes in and on the lake (Croley and Assel, 1994; Schertzer, 1978) and in the adjacent atmospheric boundary layer (Norton and Bolsenga, 1993; Eichenlaub, 1979) and thus the economy of the Great Lakes region and the ecology of the Great Lakes. Lake ice is an index of winter regional climate and climate change (Assel and Robertson, 1995; Magnuson et aI., 2000). The timing and extent of ice formation affects the flora and fauna of the winter lake ecosystem (e.g., Vanderploeg et aI., 1992; Brown et aI., 1993; Magnuson et aI., 1997; Assel, 1999) as well as the regional economy (Niimi, 1982). Anomalous contemporary Great Lakes ice cycles have been documented in earlier studies (Quinn et aI., 1978; Assel et aI., 1985; Assel and Norton 1991; Assel et aI., 1996; Assel et aI., 2000). Empirical freezing degree-day models were developed to simulate past ice cover (Assel, 1990) and potential future ice cover under GeM modeled greenhouse-warming scenarios (Assel 1991; Lofgren et aI., 2002). Other studies have identified Great Lakes ice cover and winter severity anomalies associated with large scale atmospheric circulation patterns (Rodionov et aI., 2001; Rodionov and Assel, 2000). Recently, over 1200 historical ice charts (from 1973 to 2002) were digitized and analyzed to produce ice charts that portray spatial patterns of dates of first ice, last ice, ice duration, computer animations of the daily progression of ice cover for each winter, weekly statistics on the spatial distribution patterns of Great Lakes ice cover concentration, and daily lake-averaged ice cover for each winter (Assel, 2003a). The contemporary ice cover climatology for Lake Superior ice cycles is reviewed within the context of lake bathymetry. Long-term averages of date of first ice, date of last ice, and ice duration are presented. The seasonal progression of lake averaged ice cover for discrete depth ranges and the spatial patterns of ice cover for early, mid, and late winter and for early spring for mild, typical, and severe winters are described and discussed. Results of a study on expected ice cover over the rest of the 21st century under two greenhouse warming scenarios are discussed briefly.
Basu, N., and J.A. HEAD. Mammalian wildlife as complementary models in environmental neurotoxicology. Neurotoxicology and Teratology 32:114-119 (2010). 20100040DNP.pdf
The purpose of this paper is to highlight the benefits of mammalian wildlife as models in environmental neurotoxicology. This is first addressed by discussing the general advantages of using mammalian wildlife as models, and highlighting how studies on mammalian wildlife can complement neurotoxicological studies in laboratory animals and humans. Second, specific examples are provided using three persistent, environmental contaminants of neurotoxic concern to humans, namely methylmercury (MeHg), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs). Through these examples we show that studies on mammalian wildlife can provide important, real-world information on bioavailability, environmental exposures, early and sub-clinical effects (e.g., alterations in brain neurochemistry and neuroendocrine hormones), and clinical neurotoxicity (structural and functional damage). In many cases neurotoxicological outcomes are similar across mammalian species adding weight of evidence to causal relationships. Our review highlights that an opportunity exists to use mammalian wildlife to better understand the human health risks posed by environmental neurotoxicants.
Boss, E., L. Taylor, S. Gilbert, K. Gundersen, N. HAWLEY, C. Janzen, T.H. JOHENGEN, H. Percell, C. Robertson, D. Schar, G.J. Smith, and M.N. Tamburri. Comparison of inherent optical properties as a surrogate for particulate matter concentration in coastal waters. Limnology and Oceanography: Methods 7:803-811 (2009). https://www.glerl.noaa.gov/pubs/fulltext/2009/20090042.pdf
Particulate matter concentration (PM, often referred to as total suspended solids [TSS]) is an important parameter in the evaluation of water quality. Several optical measurements used to provide an estimate of water turbidity have also been used to estimate PM, among them light transmission, backscattering, and side-scattering. Here we analyze such measurements performed by the Alliance for Coastal Technologies (ACT) at various coastal locations to establish whether a given optical method performs better than others for the estimation of PM. All the technologies were found to perform well, predicting PM within less than 55% relative difference for 95% of samples (n = 85, four locations). Backscattering performed best as a predictor of PM, predicting PM with less than 37% relative difference for 95% of samples. The correlation coefficient (R) was between 0.96 and 0.98 for all methods with PM data ranging between 1.2 to 82.4 g m–3. In addition, co-located measurements of backscattering and attenuation improves PM prediction and provides compositional information about the suspended particles; when their ratio is high, the bulk particulate matter is dominated by inorganic material while when low, dominated by organic material.
CAVALETTO, J.F., H.A. VANDERPLOEG, R. Pichlová-Ptá?níková, S.A. POTHOVEN, J.R. LIEBIG, and G.L. FAHNENSTIEL. Temporal and spatial separation allow coexistence of predatory cladocerans: Leptodora kindtii, Bythotrephes longimanus, and Cercopagis pengoi in southeastern Lake Michigan. Journal of Great Lakes Research 36:65-73 (2010). 20100023DNP.pdf
The predatory cladocerans, Leptodora kindtii, Bythotrephes longimanus, and Cercopagis pengoi coexist in the waters of southeastern Lake Michigan near Muskegon, Michigan. Leptodora is indigenous, whereas Bythotrephes and Cercopagis are nonindigenous and became established in 1986 and 2000, respectively. To observe seasonal changes in their abundances, and relationships to each other, cladocerans were collected from 1994 to 2008 at an offshore (110-m) site, from 1998 to 2008 at a transitional (45-m) site and from 1999 to 2008 at a nearshore (15-m) site. Bythotrephes was most abundant at the offshore site compared to Leptodora and Cercopagis. Bythotrephes peak abundances usually occurred in autumn at all sites. Cercopagis tended to be more abundant at the nearshore site, and peak densities occurred in summer. At the mid-depth site, similar abundances occurred for all three predatory cladocerans, however, the date of peak abundance was usually earliest for Cercopagis, followed by Leptodora, and latest for Bythotrephes. In recent years, 2007 and 2008, densities of all three predatory cladocerans have increased. Temperature preference, fish predation, and competition between the invertebrate predators may all be important in allowing the dominance of one species over the other seasonally or spatially.
Cha, Y.K., C.A. STOW, K.H. Reckhow, C. DeMARCHI, and T.F. JOHENGEN. Phosphorus load estimation in the Saginaw River, MI using a Bayesian hierarchical/multilevel model. Water Research 44:3270-3282 (2010). 20100008DNP.pdf
We propose the use of Bayesian hierarchical/multilevel ratio approach to estimate the annual riverine phosphorus loads in the Saginaw River, Michigan, from 1968 to 2008. The ratio estimator is known to be an unbiased, precise approach for differing floweconcentration relationships and sampling schemes. A Bayesian model can explicitly address the uncertainty in prediction by using a posterior predictive distribution, while in comparison, a Bayesian hierarchical technique can overcome the limitation of interpreting the estimated annual loads inferred from small sample sizes by borrowing strength from the underlying population shared by the years of interest. Thus, by combining the ratio estimator with the Bayesian hierarchical modeling framework, long-term loads estimation can be addressed with explicit quantification of uncertainty. Our study results indicate a slight decrease in total phosphorus load early in the series. The estimated ratio parameter, which can be interpreted as flow weighted concentration, shows a clearer decrease, damping the noise that yearly flow variation adds to the load. Despite the reductions, it is not likely that Saginaw Bay meets with its target phosphorus load, 440 tonnes/yr. Throughout the decades, the probabilities of the Saginaw Bay not complying with the target load are estimated as 1.00, 0.50, 0.57 and 0.36 in 1977, 1987, 1997, and 2007, respectively. We show that the Bayesian hierarchical model results in reasonable goodness-of-fits to the observations whether or not individual loads are aggregated. Also, this modeling approach can substantially reduce uncertainties associated with small sample sizes both in the estimated parameters and loads.
CHAIMOWITZ, L.A. Great Lakes restoration at the National Oceanic and Atmospheric Administration. Fact Sheet. NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 2 pp. (2010). https://www.glerl.noaa.gov/pubs/brochures/GLRI.pdf
In a world where the demand for fresh surface water increases every year, the restoration and protection of the Great Lakes is vital, as the lakes contain 20 percent of the world’s and 95 percent of the U.S. fresh surface water supply. Recognizing the significance of the Great Lakes to our nation and the need for action, President Obama has made restoring the Great Lakes a national priority. Through this commitment to restoring the Great Lakes, $475 million was invested in the region in 2010, by way of the Great Lakes Restoration Initiative (GLRI). As one of 15 Federal Agencies collaborating with U.S. EPA to implement this effort, the National Oceanic and Atmospheric Administration (NOAA) was allocated $29.72 million to help accomplish restoration goals using its ground-breaking science, data products and services, prediction, and partnerships. NOAA is making significant contributions to the GLRI through each of the projects listed below. By expanding and enhancing many well-established programs, and by advancing the science in many areas that have been identified as critical to the success of the Initiative, NOAA is adhering to the GLRI principles of accountability, action, and urgency.
Cloran, C.E., G.A. BURTON, C.R. Hammerschmidt, W.K. Taulbee, K.W. Custer, and K.L. Bowman. Effects of suspended solids and dissolved organic carbon on nickel toxicity. Environmental Toxicology and Chemistry 29(8):1781-1787 (2010). 20100037DNP.pdf
Nickel (Ni) is a common and potentially toxic heavy metal in many fluvial ecosystems. We examined the potentially competitive and complementary roles of suspended sediment and a dissolved organic ligand, humate, in affecting the partitioning and toxicity of Ni to a model organism, Daphnia magna, in both batch and stream-recirculating flume (SRF) tests. Sediments included a fine grained deposit, montmorillonite, and kaolinite. Survival of D. magna was unaffected by the range of suspended solids used in the present study (8–249 mg/L). However, exposure to suspended solids that were amended with Ni had a deleterious effect on test organism survival, which is attributed to partitioning of Ni into the aqueous phase. At comparable levels of dissolved Ni, survival of D. magna was reduced in tests with Ni-amended suspended solids compared to Ni-only aqueous exposures, suggesting potentiation between these two aquatic contaminants. Addition of humate attenuated toxicity to D. magna in both Ni-only and Ni-amended suspended sediment exposures. These results indicate that organic ligands and suspended solids have important functions in affecting the bioavailability and toxicity of Ni to aquatic organisms and should be incorporated into predictive models to protect ecosystem quality.
CONSTANT, S.A. Marine Instrumentation and Technology at NOAA's Great Lakes Environmental Research Laboratory. Fact Sheet. NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 2 pp. (2010). https://www.glerl.noaa.gov/pubs/brochures/mil/milprojects.pdf
The Marine Instrumentation Lab (MIL) located at NOAA’s Great Lakes Environmental Research Lab (GLERL) is committed to the development, implementation, and technical support of marine instrumentation to enhance GLERL science in the Great Lakes and Marine ecosystems.
DeMARCHI, C., Q. Dai, M.E. Mello, and T.S. HUNTER. Uncertainty quantification in the net basin supply of Lake Erie and Lake Michigan. SimHydro 2010: Hydraulic Modeling and Uncertainty, Sophia-Antipolis, Nice, France, June 2-4, 2010. Hydraulic Engineering Company of France, International Association of Hydraulic Research and Engineering, 19 pp. (2010). https://www.glerl.noaa.gov/pubs/fulltext/2010/20100014.pdf
This paper analyzes the uncertainty in the widely used NOAA Great Lakes Environmental Research Laboratory (GLERL) estimates of two key components of the Great Lakes' net basin supply (NBS): over-lake precipitation and tributary flow. GLERL estimates over-lake precipitation using Thiessen Polygon interpolation of gage data, which is affected by the lack of gages on the lakes themselves and the scarcity of gages in parts of the draining basin. Recently, estimates based on merging precipitation radar data and rain gage data proved to be a better alternative to the traditional estimate methods for some of the lakes. We compared traditional over-lake precipitation models with the radar-based estimates for 2002-2007, computed the relative error distribution, and used it for modeling the uncertainty in historical over-lake precipitation estimates, indicating that uncertainty is around ±30% for Lake Erie to around ±25% for Lake Michigan. Tributary runoff should be the least uncertain component in the Great Lakes NBS estimates, but the partial monitoring of most lake basins requires its consideration. We analyzed the algorithm used by GLERL to produce the tributary flow data. We modeled the uncertainty in each single sub-basin runoff estimate and evaluated the overall uncertainty in tributary runoff to a lake using a Monte Carlo technique. Results indicate that it is around 23% for both lakes. The uncertainty of the overall NBS is also presented complementing these results with literature values for the uncertainty on evaporation.
DeMARCHI, C., W. Tao, T.F. JOHENGEN, and C.A. STOW. Uncertainty in phosphorus load estimation from a large watershed in the Great Lakes basin. SimHydro 2010: Hydraulic Modeling and Uncertainty, Sophia-Antipolis, Nice, France, June 2-4, 2010. Hydraulic Engineering Company of France, International Association of Hydraulic Research and Engineering, 13 pp. (2010). https://www.glerl.noaa.gov/pubs/fulltext/2010/20100013.pdf
Saginaw Bay is a large and shallow embayment in western Lake Huron used for drinking water supply, recreation, fishing, tourism, and navigation. Over time, high nutrient loading from agricultural runoff, industrial pollution, and public wastewater systems in its watershed caused eutrophication of the bay. To improve this situation, a target Total Phosphorus (TP) load of 440 metric tons/yr was established for Saginaw Bay and the resulting reduction of phosphorus output from point sources lead to diminishing eutrophication. However, eutrophication symptoms have recently returned to Saginaw Bay. In this paper we present a regression model developed to evaluate the current nutrient loads using the relatively few water quality measurements and daily discharge data available for the basin. The regression model accounts for the effect of discharge on TP concentration, including rising and receding flood phases and previous storms, as well as seasonality and long-term trends in pollution generation. The model tracks TP dynamics well (correlation with observed 1998-2008 daily concentrations and loads at the outlet of Saginaw River is 0.84 and 0.96 respectively) and indicates that the target load of 440 metric tons has been met only during dry years. The ability to closely replicate the observed TP concentrations results in a model uncertainty of annual TP loads of less than 6%. However, a Monte Carlo analysis of the propagation of the errors in the observed concentrations and discharges used for calibrating and driving the model shows that the uncertainty in annual load estimates due to these factors is above 10%.
FAHNENSTIEL, G.L., T.F. NALEPA, S.A. POTHOVEN, H.J. Carrick, and D. Scavia. Lake Michigan lower food web: Long-term observations and Dreissena impact. Journal of Great Lakes Research 36:1-4 (2010). 20100026DNP.pdf
Lake Michigan has a long history of non-indigenous introductions that have caused significant ecological change. Here we present a summary of eight papers that document recent changes and the current state of the lower food web of southern Lake Michigan after the establishment of large dreissenid populations. Results are based on long-term data sets collected by federal and academic research and monitoring programs that place recent changes into a historic context. Dramatic and significant changes in the lower food web, such as the loss of the spring diatom bloom, large declines in phytoplankton productivity, and a decline of Mysis populations, were directly or indirectly attributed to the expansion of Dreissena rostriformis bugensis. Total phosphorus concentrations and loadings also have decreased in the last 20 years. Changes in the Lake Michigan ecosystem induced by D. r. bugensis have produced conditions in the offshore pelagic region that are similar to oligotrophic Lake Superior. The future state of the lower food web in southern Lake Michigan is difficult to predict, mainly because population trends of D. r. bugensis in cold, offshore regions are unknown. Hence, monitoring programs designed to collect long-term, consistent data on the lower food web of Lake Michigan are essential.
FAHNENSTIEL, G.L., S.A. POTHOVEN, T.F. NALEPA, H.A. VANDERPLOEG, D.M. Klarer, and D. Scavia. Recent changes in primary production and phytoplankton in the offshore region of southeastern Lake Michigan. Journal of Great Lakes Research 36:20-29 (2010). 20100028DNP.pdf
Phytoplankton abundance, composition, and productivity were monitored on a bi-weekly basis from March/April through November/December at two offshore stations in southeastern Lake Michigan in 1983–1987, 1995–1998 and 2007–2008 (exception 1983–1984 which were sampled from May to August). During the spring isothermal mixing period, surface-mixed layer (SML) chlorophyll a and phytoplankton biomass (carbon) and water column primary productivity decreased substantially in 2007–2008 as compared to 1995–1998 (66%, 87%, and 70% decrease, respectively). Smaller or no decreases were noted between 1983–1987 and 1995–1998 (chlorophyll a 23% decrease, phytoplankton biomass 5% increase, and production 22% decrease). Phytoplankton composition also changed during the spring isothermal mixing period in 2007–2008 as compared to 1983–1987 and 1995–1998; all phytoplankton groups with the exception of cyanobacteria and chlorophytes exhibited dramatic reductions in 2007–2008. The pronounced changes in phytoplankton properties during spring mixing in 2007–2008 were attributed to the filtering activities of the quagga mussel (Dreissena rostriformis bugensis). During mid- and late thermal stratification periods, SML phytoplankton chlorophyll a and phytoplankton carbon and water column primary production exhibited only one significant change across all decades (mid stratification production in 2007–2008 as compared to 1995–1998 and 1983–1987). Phytoplankton compositional changes in the SML also were limited during thermal stratification. The size of the deep chlorophyll layer (DCL) in 2007–2008 was similar to or smaller than those in 1983–1987 and 1995–1998. However, phytoplankton composition in the DCL changed as net diatoms constituted b5% of total phytoplankton in the 2007–2008 DCL but over 50% in 1983–1987 and 1995–1998.
Fishman, D.B., S.A. Alderstein, H.A. VANDERPLOEG, G.L. FAHNENSTIEL, and D. Scavia. Causes of phytoplankton changes in Saginaw Bay, Lake Huron during the zebra mussel invasion. Journal of Great Lakes Research 35:482-495 (2009). 20090041DNP.pdf
Colonization of the Laurentian Great Lakes by the invasive mussel Dreissena polymorpha was a significant ecological disturbance. The invasion reached Saginaw Bay, Lake Huron, in 1991 and initially cleared the waters and lowered algal biomass. However, an unexpected result occurred 3 years after the initial invasion with the return of nuisance summer blooms of cyanobacteria, a problem that had been successfully addressed with the implementation of phosphorus controls in the late 1970s. A multi-class phytoplankton model was developed and tested against field observations and then used to explore the causes of these temporal changes. Model scenarios suggest that changes in the phytoplankton community can be linked to three zebra mussel-mediated effects: (1) removal of particles resulting in clearer water, (2) increased recycle of available phosphorus throughout the summer, and (3) selective rejection of certain Microcystis strains. Light inhibition of certain phytoplankton assemblages and the subsequent alteration of competitive dynamics is a novel result of this model. These results enhance our understanding of the significant role of zebra mussels in altering lower trophic level dynamics of Saginaw Bay and suggest that their physical reengineering of the aquatic environment was the major force driving changes in the phytoplankton community composition.
GRONEWOLD, A.D., and I.M. Alameddine. Propagating data uncertainty and variability to flow predictions in ungauged basins. 2010 International Congress on Environmental Modeling and Software, Modeling for Environment's Sake, Fifth Biennial Meeting, Ottawa, Ontario, Canada, July 5-8, 2010. International Environmental Modeling and Software Society (iEMSs), 8 pp. (2010). https://www.glerl.noaa.gov/pubs/fulltext/2010/20100016.pdf
Explicitly acknowledging uncertainty and variability in model-based hydrological forecasts is a challenging task. Many basins are either ungauged, are undergoing rapid land use change, or are in regions expected to experience significant climate change. These factors, in addition to uncertainty in monitoring data and model structure, collectively contribute to discrepancies between model predictions and observations. Few hydrological modeling studies, however, routinely quantify data uncertainty. Furthermore, few studies compare model forecasts to observations while considering intrinsic uncertainty in the model itself. To bridge this research gap, we test a series of rainfall-runoff models within gauged and ungauged basins in Eastern North Carolina (US). In the model calibration phase, we propagate data uncertainty into model forecasts within a Bayesian framework. We then assess model suitability by examining the distribution of Bayesian posterior p-values (defined as the model-derived probability of a flow measurement as or more extreme than that observed). Evaluating model performance in this way helps identify potential sources of model bias and error, and clearly demonstrates the magnitude of those errors relative to the various potential sources of variability and uncertainty in the model forecast.
GRONEWOLD, A.D., and M.E. Borsuk. Improving water quality assessments through a hierarchical Bayesian analysis of variability. Environmental Science and Technology 44(20):7858-7864 (DOI:10.1021/es100657p) (2010). https://pubs.acs.org/articlesonrequest/AOR-Nc6WeG4aTR6HMQsKKMeB 20100036DNP.pdf
Water quality measurement error and variability, while well documented in laboratory-scale studies, is rarely acknowledged or explicitly resolved in most model-based water body assessments, including those conducted in compliance with the United States Environmental Protection Agency (USEPA) Total Maximum Daily Load (TMDL) program. Consequently, proposed pollutant loading reductions in TMDLs and similar water quality management programs may be biased, resulting in either slower-than-expected rates of water quality restoration and designated use reinstatement or, in some cases, overly conservative management decisions. To address this problem, we present a hierarchical Bayesian approach for relating actual in situ or model-predicted pollutant concentrations to multiple sampling and analysis procedures, each with distinct sources of variability. We apply this method to recently approved TMDLs to investigate whether appropriate accounting for measurement error and variability will lead to different management decisions. We find that required pollutant loading reductions may in fact vary depending not only on how measurement variability is addressed but also on which water quality analysis procedure is used to assess standard compliance. As a general strategy, our Bayesian approach to quantifying variability may represent an alternative to the common practice of addressing all forms of uncertainty through an arbitrary margin of safety (MOS).
GRONEWOLD, A.D., L. Myers, J. Swall, and R. Noble. Addressing uncertainty in fecal indicator bacteria dark inactivation rates. Water Research 44:13 pp. (DOI:10.1016/j.watres.2010.08.029) (2010). 20100035DNP.pdf
Assessing the potential threat of fecal contamination in surface water often depends on model forecasts which assume that fecal indicator bacteria (FIB, a proxy for the concentration of pathogens found in fecal contamination from warm-blooded animals) are lost or removed from the water column at a certain rate (often referred to as an “inactivation” rate). In efforts to reduce human health risks in these water bodies, regulators enforce limits on easily-measured FIB concentrations, commonly reported as most probable number (MPN) and colony forming unit (CFU) values. Accurate assessment of the potential threat of fecal contamination, therefore, depends on propagating uncertainty surrounding “true” FIB concentrations into MPN and CFU values, inactivation rates, model forecasts, and management decisions. Here, we explore how empirical relationships between FIB inactivation rates and extrinsic factors might vary depending on how uncertainty in MPN values is expressed. Using water samples collected from the Neuse River Estuary (NRE) in eastern North Carolina, we compare Escherichia coli (EC) and Enterococcus (ENT) dark inactivation rates derived from two statistical models of first-order loss; a conventional model employing ordinary least-squares (OLS) regression with MPN values, and a novel Bayesian model utilizing the pattern of positive wells in an IDEXX Quanti-Tray_/2000 test. While our results suggest that EC dark inactivation rates tend to decrease as initial EC concentrations decrease and that ENT dark inactivation rates are relatively consistent across different ENT concentrations, we find these relationships depend upon model selection and model calibration procedures. We also find that our proposed Bayesian model provides a more defensible approach to quantifying uncertainty in microbiological assessments of water quality than the conventional MPN-based model, and that our proposed model represents a new strategy for developing robust relationships between environmental factors and FIB inactivation rates, and for reducing uncertainty in water resource management decisions.
Hammerschmidt, C.R., and G.A. BURTON. Measurements of acid volatile sulfide and simultaneously extracted metals are irreproducible among laboratories. Environmental Toxicology and Chemistry 29(7):1453-1456 (2010). 20100038DNP.pdf
Partitioning with solid phases is a principal control on availability and associated toxicity of metals to aquatic biota. In anoxic sediments, environmentally active fractions of sulfide and associated metals are defined operationally as acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM). Ratios of these chemical parameters are often used in establishing equilibrium partitioning sediment benchmarks for toxicity and, therefore, require analytical accuracy to be useful. To investigate the reproducibility and accuracy of AVS and SEM measurements, we distributed subsamples of four physicochemically disparate stream sediments to seven independent laboratories, including our own, for analysis of both AVS and SEM (Cd, Cu, Pb, Ni, and Zn). Synthesis of these results shows that AVS varied from 70 to 3,500_and SEM ranged from 17 to 60_among laboratories for each of the four sediments. Inadequate detection limits for AVS precluded calculation of SEM:AVS ratios for two of the deposits, whereas the ratio varied more than 50-fold among laboratories for the other two sediments. This work highlights the need for improved quality control and standardization of methods for determination of AVS and SEM in sediments, and suggests that predictions of metal toxicity in sediments can be laboratory specific, which raises concerns on the use of the AVS:SEM model for risk assessments and regulatory decisions.
HAWLEY, N., C.K. Harris, B.M. Lesht, and A.H. CLITES. Sensitivity of a Lake Michigan sediment transport model for Lake Michigan. Journal of Great Lakes Research 35:560-576 (2009). 20090040DNP.pdf
A two-dimensional (vertical and cross-shore) sediment transport model was applied to several transects in southern Lake Michigan using observations of waves and currents recorded during the spring of 2000. Conditions during this period included several storms that are among the largest observed in the lake. The observations were used to examine the sensitivity of the model to variations in the input parameters (waves, currents, initial bottom sediment size distribution, settling velocity, and bottom stress required for erosion). The results show that changing the physical forcing (waves and currents) or the initial bottom sediment size distribution affected the results more than varying the particle properties (settling velocity and critical shear stress) or the size classes used to describe the size distribution. This indicates that for this model specification of input parameters are of first order importance and should be specified with some confidence before adding additional complexity by including processes such as flocculation and bed consolidation.
HAYHOE, K., J. VANDORN, T.E. CROLEY II, N. Schlegal, and D. Wuebbles. Regional climate change projections for Chicago and the US Great Lakes. Journal of Great Lakes Research 36:7-21 (DOI:10.1016/j.jglr.2010.03.012) (2010). 20100055DNP.pdf
Assessing regional impacts of climate change beginswith development of climate projections at relevant temporal and spatial scales. Here, proven statistical downscaling methods are applied to relatively coarse-scale atmosphere–ocean general circulation model (AOGCM) output to improve the simulation and resolution of spatial and temporal variability in temperature and precipitation across the US Great Lakes region. The absolute magnitude of change expected over the coming century depends on the sensitivity of the climate system to human forcing and on the trajectory of anthropogenic greenhouse gas emissions. Annual temperatures in the region are projected to increase 1.4±0.6 °C over the near-term (2010–2039), by 2.0±0.7 °C under lower and 3±1 °C under higher emissions by midcentury (2040–2069), and by 3±1 °C under lower and 5.0±1.2 °C under higher emissions by end-of-century (2070–2099), relative to the historical reference period 1961–1990. Simulations also highlight seasonal and geographical differences in warming, consistent with recent trends. Increases in winter and spring precipitation of up to 20% under lower and 30% under higher emissions are projected by end-of-century, while projections for summer and fall remain inconsistent. Competing effects of shifting precipitation and warmer temperatures suggest little change in Great Lake levels over much of the century until the end of the century, when net decreases are expected under higher emissions. Overall, these projections suggest the potential for considerable changes to climate in the US Great Lakes region; changes that could be mitigated by reducing global emissions to follow a lower as opposed to a higher emissions trajectory over the coming century.
HEAD, J.A., R. Farmahin, A.S. Kehoe, J.M. O'Brien, J.L. Shutt, and S.W. Kennedy. Characterization of the avian aryl hydrocarbon receptor 1 from blood using non-lethal sampling methods. Ecotoxicology:7 pp. (DOI:10.1007/s10646-010-0541-9) (2010). 20100041DNP.pdf
The amino acid sequence of the aryl hydrocarbon receptor 1 ligand binding domain (AHR1 LBD) is an important determinant of sensitivity to dioxin-like compounds in avian species. We are interested in surveying AHR1 LBD sequences in a large number of birds as a means of identifying species that are particularly sensitive to dioxin-like compounds. Our original method for determining AHR1 LBD genotype used liver tissue and required lethal sampling. Here we present two alternate methods for determining AHR1 LBD genotype which use non-lethal sampling and are more appropriate for ecologically sensitive species. First, we establish that AHR1 LBD mRNA is expressed in avian blood and test a variety of blood collection and handling protocols in order to establish a method that is convenient for field collections. Our findings also identify which types of archival blood samples might be appropriate for AHR1 LBD sequence determination. Second, we present a method for obtaining AHR1 LBD coding sequences from DNA. A DNA-based method is advantageous because DNA can be isolated from many tissue types, is more stable than RNA, and requires less specific sample handling and preservation. This work extends applicability of a genetic screen for dioxin sensitivity to a larger number of species and sample types including endangered species and potentially museum specimens.
HEAD, J.A., and S.W. Kennedy. Correlation between an in vitro and an in invo measure of dioxin sensitivity in birds. Ecotoxicology 19:377-381 (DOI:10.1007/S10646-009-0421-3) (2010). 20100042DNP.pdf
We describe a statistically significant correlation between two well-characterized responses to dioxin-like compounds in birds; induction of 7-ethoxyresorufin-O-deethylase (EROD) activity in cultured hepatocytes, and embryo mortality. Data were obtained from a review of the literature. EROD EC50 values for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 6 polychlorinated biphenyls (PCBs) were strongly correlated with LD50 values in chicken embryos (r2 = 0.93, P\0.005). Similarly, EROD EC50 values for TCDD and a potent dioxin-like compound, PCB 126, were correlated with embryonic LD50 values in different species of birds (chicken, ring-necked pheasant, turkey, double-crested cormorant, and common tern) (r2 = 0.92, P\0.005). Our findings contribute to a developing understanding of the molecular basis for differential dioxin sensitivity in birds, and validate the EROD bioassay as a useful predictive tool for ecological risk assessment.
HU, H., and J. WANG. Modeling effects of tidal and wave mixing on circulation and thermohaline structures in the Bering Sea: Process studies. Journal of Geophysical Research 115, C01006:23 pp. (DOI:10.1029/2008JC005175) (2010). 20100002DNP.pdf https://www.agu.org/journals/jc/jc1001/2008JC005175/
Ocean circulation and the tidal current in the Bering Sea are simulated simultaneously using a coupled ice-ocean model (CIOM) with tidal and parameterized wave mixing to investigate several important physical processes. The simulated circulation pattern in the deep basin is relatively stable, cyclonic, and has little seasonal change. The Bering Slope Current is estimated at 5 Sv and the Kamchatka Current at 20 Sv. The modeled volume transports through the Aleutian passes compared reasonably well with observations. It is confirmed that subtidal clockwise circulation around St. George and St. Paul islands are driven by tidal rectification. The simulation results show that wind-wave mixing and tidal stirring are the main factors controlling the formation of the upper and the bottom mixed layers, respectively. The mechanism of thermocline and the cold pool (summer minimum-temperature water) formation in the middle shelf are investigated in depth. The CIOM reproduces the cold winter-convective water in the middle shelf that forms the bottom cold pool, which persists throughout the summer until sea surface cooling and strong wind mixing in fall, leading to an unstable vertical water column and eventually to vertically well-mixed water in the winter. Sensitivity experiments show that tidal and wind-wave mixing are two important factors in accurately estimating the volume of the cold pool, which is the ideal marine habitat for cold water species.
Ivan, L.N., E.S. RUTHERFORD, C. Riseng, and J.T. Tyler. Density, production, and survival of walleye (Sander vitreus) eggs in the Muskegon River, Michigan. Journal of Great Lakes Research 36:328-337 (2010). 20100019DNP.pdf
Walleye (Sander vitreus) is an important sport fish in the Great Lakes that is experiencing low reproductive success after severe population declines starting in the late 1940s. In the Muskegon River, Michigan, natural reproduction of walleyes remains low and is largely supplemented by stocking. To determine factors influencing walleye reproductive success in the Muskegon River, we estimated walleye egg survival using in situ egg incubators covered with nitex screening (2003–2004) and estimated density and survival of fertilized eggs caught on furnace filter traps across different substrate types (2005–2006). We compared physical habitat suitability for walleye eggs under high and low flow scenarios. Density of walleye eggs was highest in regions of gravel/cobble substrates. Egg survival was higher in egg incubators (24–49.5%) than on furnace filter traps (2.0%), suggesting predation is an important source of walleye egg mortality in the Muskegon River. Cold water temperatures that extended developmental stage durations may also be an important source of egg mortality. The dynamic habitat suitability model predicted low suitability for eggs due to poor temperature and velocity conditions. Despite low egg survival rates, 40 million to 1 billion eggs were estimated to hatch. The low natural reproduction of walleyes in the Muskegon River is likely due to a combination of low walleye egg survival and failure of walleye larvae to reach their nursery grounds in Muskegon Lake.
Jaeger Miehls, A.L., D.M. MASON, K.A. Frank, A.E. Krause, S.D. PEACOR, and W.W. Taylor. Invasive species impacts on ecosystem structure and function: A comparison of Oneida Lake, New York, USA, before and after zebra mussel invasion. Ecological Modelling 220:3194-3209 (DOI:10.1016/j.ecolmodel.2009.07.020) (2009). 20090036DNP.pdf
Exotic species invasion is widely considered to affect ecosystem structure and function. Yet, few contemporary approaches can assess the effects of exotic species invasion at such an inclusive level. Our research presents one of the first attempts to examine the effects of an exotic species at the ecosystem level in a quantifiable manner. We used ecological network analysis (ENA) and a social network analysis (SNA) method called cohesion analysis to examine the effect of zebra mussel (Dreissena polymorpha) invasion on the Oneida Lake, New York, USA, food web. We used ENA to quantify ecosystem function through an analysis of food web carbon transfer that explicitly incorporated flow over all food web paths (direct and indirect). The cohesion analysis assessed ecosystem structure through an organization of food web members into subgroups of strongly interacting predators and prey. Our analysis detected effects of zebra mussel invasion throughout the entire Oneida Lake food web, including changes in trophic flow efficiency (i.e., carbon flow among trophic levels) and alterations of food web organization (i.e., paths of carbon flow) and ecosystem activity (i.e., total carbon flow). ENA indicated that zebra mussels altered food web function by shunting carbon from pelagic to benthic pathways, increasing dissipative flow loss, and decreasing ecosystem activity. SNA revealed the strength of zebra mussel perturbation as evidenced by a reorganization of food web subgroup structure, with a decrease in importance of pelagic pathways, a concomitant rise of benthic pathways, and a reorganization of interactions between top predator fish. Together, these analyses allowed for a holistic understanding of the effects of zebra mussel invasion on the Oneida Lake food web.
Jaeger Miehls, A.L., D.M. MASON, K.A. Frank, A.E. Krause, S.D. PEACOR, and W.W. Taylor. Invasive species impacts on ecosystem structure and function: A comparison of the Bay of Quinte, Canada, and Oneida Lake, USA before and after zebra mussel invasion. Ecological Modelling 220:3182-3193 (DOI:10.1016/j.ecolmodel.2009.07.013) (2009). 20090037DNP.pdf
As invasion rates of exotic species increase, an ecosystem level understanding of their impacts is imperative for predicting future spread and consequences.We have previously shown that network analyses are powerful tools for understanding the effects of exotic species perturbation on ecosystems. We now use the network analysis approach to compare how the same perturbation affects another ecosystem of similar trophic status.We compared food web characteristics of the Bay of Quinte, Lake Ontario (Canada), to previous research on Oneida Lake, New York (USA) before and after zebra mussel (Dreissena polymorpha) invasion. We used ecological network analysis (ENA) to rigorously quantify ecosystem function through an analysis of direct and indirect foodweb transfers.We used a social network analysis method, cohesion analysis (CA), to assess ecosystem structure by organizing food web members into subgroups of strongly interacting predators and prey. Together, ENA and CA allowed us to understand how food web structure and function respond simultaneously to perturbation. In general, zebra mussel effects on the Bay of Quinte, when compared to Oneida Lake,were similar in direction, but greater in magnitude. Both systems underwent functional changes involving focused flow through a small number of taxa and increased use of benthic sources of production; additionally, both systems structurally changed with subgroup membership changing considerably (33% in Oneida Lake) or being disrupted entirely (in the Bay of Quinte). However, the response of total ecosystem activity (as measured by carbon flow) differed between both systems, with increasing activity in the Bay of Quinte, and decreasing activity in Oneida Lake. Thus, these analyses revealed parallel effects of zebra mussel invasion in ecosystems of similar trophic status, yet they also suggested that important differences may exist. As exotic species continue to disrupt the structure and function of our native ecosystems, food web network analyses will be useful for understanding their far-reaching effects.
JOSEPH, S.T. Harmful algal blooms and muck: What's the difference? Fact Sheet. NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 2 pp. (2009). https://www.glerl.noaa.gov/pubs/brochures/HAB_Muck.pdf
Harmful algal blooms and muck, otherwise known as Cladophora, can be mistaken for each other simply because people may associate an algal bloom with either type. However, both represent significantly different species. Unlike green algae such as Cladophora, blue-green algae is technically not an algae, but is a bacteria known as cyanobacteria that photosynthesizes like algae do. Blue-green harmful algal blooms (HABs) and green algae blooms can be found in similar locations. However, the two species differ in appearance and in factors that influence their growth and movement in the Great Lakes.
JOSEPH, S.T. Harmful algal blooms in the Great Lakes. Fact Sheet. NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 2 pp. (2009). https://www.glerl.noaa.gov/pubs/brochures/bluegreenalgae_factsheet.pdf
There are many species of single-celled organisms living in the Great Lakes, including algae. When certain conditions are present, such as high nutrient or light levels, these organisms can reproduce rapidly. This dense population of algae is called a bloom. Some of these blooms are harmless, but when the blooming organisms contain toxins, other noxious chemicals, or pathogens, it is known as a harmful algal bloom, or HAB. HABs can cause the death of nearby fish and foul up nearby coastlines, and produce harmful conditions to marine life as well as humans.
Kerfoot, W.C., J. Jeong, and J.A. ROBBINS. Lake Superior mining and the proposed mercury zero-discharge region. In State of Lake Superior. M. Munawar and I.F. Munawar (eds.). Aquatic Ecosystem Health and Management Society, Ecovision World Monograph Series, Canada, 153-216 pp. (2009). 20090050DNP.pdf
A century and a half ago, mining activity spread across the U.S. and Canadian shorelines of the northern Great Lakes. Most early efforts were ephemeral, as local operations rose and fell in boom-bust cycles. Yet some regional activities persisted for decades to centuries, creating infrastructures of roads, towns, and supporting industry (Benedict, 1952; Lankton, 1991, 1997; Mouat, 2000). Both short- and long-term operations contributed to a metal legacy that lies scattered about watersheds and along the shorelines of Lake Superior (Kerfoot and Nriagu, 1999). Two early investigators of Lake Superior sediments, Nussman (1965) and Kemp et al. (1978), suspected that copper enrichments in lake sediments originated from several intensively mined regions: the Keweenaw Peninsula of Michigan and the Thunder Bay, Marathon, Wawa, and Sault Ste. Marie regions of Ontario, Canada. Sediment investigations around the Keweenaw region have confirmed copper mining impacts on Lake Superior sediments (Kerfoot et al. 1994, 1999a; 1999 IAGLR Special Issue, Volume 25, No.4). Between 1865 and 1968, approximately 360 million metric tons (Mt) of stamp sands were discharged from native copper stamp mills into interior waterways and along Lake Superior shorelines. The extensive tailing piles prompted establishment of a Superfund Site within the Torch Lake Area Of Concern (AOC), one of the largest remediation efforts in the Great Lakes (368 sq. miles, 800 acres of tailing piles throughout the Keweenaw Peninsula; 1998-present; a 5-8 year, $15.2 million remediation effort; USEPA 2001).
Kerfoot, W.C., F. Yousef, S.A. Green, J.W. Budd, D.J. SCHWAB, and H.A. VANDERPLOEG. Approaching storm: Disappearing winter bloom in Lake Michigan. Journal of Great Lakes Research 36:30-41 (2010). 20100029DNP.pdf
Between 1990 and 2001, late-winter phytoplankton blooms were common in parts of the lower Great Lakes (southern Lake Michigan, Saginaw Bay and southern Lake Huron, and western Lake Erie), providing resources for over-wintering zooplankton. In Lake Michigan up to 2001, detailed remote sensing and ship studies documented well-developed late-winter blooms in the southern gyre (circular bloom termed the ‘doughnut’). However, from 2001 to 2008, the winter blooms in Lake Michigan also supported early season veliger larvae from the introduced, cold-water adapted “profunda” morph of quagga mussels (Dreissena rostriformis bugensis). Remote sensing and ship studies revealed that settled mussels caused an extraordinary increase in water transparency and a simultaneous decrease of Chl a in the late-winter bloom. Before quagga mussels in 2001, water transparency was 74–85% at deep-water sites, whereas it increased progressively to 89% by 2006 and 94–96% by 2008. Chlorophyll a concentrations in the gyre rings were 1.1–2.6 μg/L in 2001, declining to 0.5–1.7 μg/L by 2006 and 0.4–1.5 μg/L by 2008. The reduction of Chl a in the winter bloom rings from 2001 to 2008 was 56–78% for the western limb and 74–75% for the eastern limb. Zooplankton species abundance, composition and abundance also changed, as cyclopoid copepods became very scarce and overwintering omnivorous calanoid copepods declined. Reduction in late-winter phytoplankton and zooplankton poses a serious threat to open-water food webs.
Lamon, E.C., and C.A. STOW. Lake Superior water level fluctuation and climatic factors: A dynamic linear model analysis. Journal of Great Lakes Research 36:172-178 (2010). 20100006DNP.pdf
We use Dynamic Linear Models (DLM) to analyze the time series of annual average Lake Superior water levels from 1860 to 2007, as well as annual averages of climate drivers including precipitation (1900–2007), evaporation and net precipitation (1951–2007). Our results indicate strong evidence favoring the presence of a systematic trend over a random walk for Lake Superior water levels, and this trend has been negative in recent decades. We then show decisive evidence, in terms of improved predictive performance, favoring a model in which the trend component is replaced with regression components consisting of climatic drivers as predictor variables. Because these models use lagged values of precipitation or net precipitation as predictors, the models can be used to forecast water levels, with the associated uncertainty, several years into the future. We use several of the best fit models and compare one (2008) and two step-ahead (2009) forecasts. The 2008 forecasts compare very well with the observed 2008 water level; the two step-ahead 2009 forecasts are offered as testable hypotheses. The Bayesian context in which these models are developed provides a rigorous framework for data assimilation and regular model updating.
Lee, J.-H., C.A. STOW, and P.F. LANDRUM. Bayesian multilevel discrete interval hazard analysis to predict DDE mortality in Hyalella azteca based on body residues. Environmental Toxicology and Chemistry 28:2458 (2009). 20090035DNP.pdf
We exposed Hyalella azteca to p,p'-dichlorodiphenyldichloroethylene for intervals of 1 to 4 d and followed mortality out to 10 d. Mortality was determined as the cessation of heartbeat; dead organism body residue was determined daily. To model mortality probability, body residues of the living organisms were estimated using published kinetic data with concentration-dependent rate constants. The estimated residues compared favorably with measured residues in the dead organisms (predicted body residue = 1.302 ± 0.142 measured body residue + 10.351 ± 15.766, r2 = 0.64, n = 50). The response data were collected at discrete intervals; thus, it was not possible to determine the exact time of death for organisms. Consequently, we analyzed the mortality data using discrete interval analysis, in a Bayesian hierarchical framework, with body residue as the dose metric. The predicted body residues to produce mortality were similar across the duration of exposure when postexposure mortality was considered. The concentration for 50% mortality was 0.47 μmol/g (148.6 μg/g, range 0.32–0.66 μmol/g), and predictions of response indicted 95% (range 73–99.9%) mortality at 0.79 μmol/g (250 μg/g) and 4% (range 1.2–9.6%) mortality at 0.16 μmol/g (50 μg/g). The lethal residue for 50% mortality based on interval analysis for short-term exposures with postexposure mortality resulted in values similar to long-term continuous exposures for exposure durations of more than 600 h.
LIU, P.C. What do we know about freaque waves in nature? Fourth International Conference of the Frontiers of Nonlinear Physics, Nizhny Novgorod, St. Petersburg, Russia, July 13-20, 2010. Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novogorod, Russia, 96-97 pp. (2010). https://www.glerl.noaa.gov/pubs/fulltext/2010/20100021.pdf
There are always freaque wave encounters being reported in the news all around the world. However, regardless of when or where it was reported as taking place, the question posed by the title of this paper is really predicated by another rather more fundamental question: Do we really know what kind of freaque wave was encountered? Frankly, the answer must be no! We know that something happened, but no one really knows what, why, or how it happened. Encounters are reported quite frequently nowadays. Freaque waves (freak or rogue waves) have become somewhat of a standard nomenclature being used in news reports to describe any kind of wave-related incident. So generally, we know something happened, but most likely we have no way of knowing what kind of wave condition it was, why, or how it was encountered. For instance, in the case of the Cruise Ship MS Louis Majesty that encountered freaque waves in the northern Mediterranean near Marseille, France in early March 2010. As was reported in news reports worldwide, two passengers were swept to their death, and as many as 14 were injured when freaque waves crashed into a vessel that was carrying 1,350 passengers and 580 crew members. According to a Louis Cruise Lines spokesman the ship was hit by three "abnormally high" waves up to 26 feet high that broke glass windshields in the forward section. The waves hit as high as deck 5 on the 10-deck ship. All kinds of news reports and commentaries on this case have been published online or in print since then. At one time, Google Search indicated that there were about 1,300 articles available. Unfortunately, despite all of those reports, some complete with eye witness interviews and "expert" opinions and analysis, there was no clear information regarding wave conditions beyond the cruise ship spokesman's announcement of three 26 feet high waves. So in this case, as in many other cases, we know freaque waves were probably encountered, but we don't know the details of how, what, and why!
LIU, P.C., C.H. Wu, K.R. MacHutchon, and D.J. SCHWAB. An analysis of measurement from a 3D oceanic wave field. WIT Transactions on Ecology and the Environment 126:15-26 (DOI:10.2495/CP090021) (2009). 20090038DNP.pdf
We present here a preliminary examination and analysis of a small suite of 3D wave data to explore what new insight or inference we can garner – particularly toward the realm where conventional approaches have not yet been. While we caught a few glimpses that might indicate a need for new conceptualizations, it by no means negates the vast positive contributions that the conventional approaches have allowed us to make in the past century. We feel it is timely to encourage further 3D ocean wave measurement and thereby facilitate fresh new states of study and to enhance our understanding of ocean waves.
Liu, z., S.H. Choudhry, M. XIA, J. Holt, C.M. Wallen, S. Yuk, and S.C. Sanborn. Water quality assessment of coastal Caloosahatchee River. Journal of Environmental Science and Health Part A 44:972-984 (DOI:10.1080/10934520902996872) (2009). 20090051DNP.pdf
Caloosahatchee River watershed and estuary has experienced a general decline in the water quality over the last several decades due to agriculture practices, development, and other human activities. The objective of this study is to assess the water quality condition in coastal Caloosahatchee River watershed by analyzing the data collected by South Florida Water Management District and Lee County. Results indicated that during 1995 to 2006, averaged annually, Lake Okeechobee released 1124 million m3 of freshwater into the Caloosahatchee River, whereas the average annual freshwater discharge out of the Caloosahatchee River was approximately 2277 million m3. Lake Okeechobee might have more impacts on the water quality condition of Caloosahatchee River in dry season than wet season. The loads ratios of Lake Okeechobee to those out of Caloosahatchee River were much higher in dry season than wet season for flow (72% to 36%), total phosphorus (63% to 20%), total nitrogen (72% to 41%), organic nitrogen (85% to 47%), and NH3 (78% to 39%). In the coastal watershed area where the urban area is concentrated, of the total 5453 water samples, 74% of them have dissolved oxygen concentration less than 5 mg L−1, the United States Environmental Protection Agency and Florida Department of Environmental Protection water quality standard. Only in January is the average monthly dissolved oxygen concentration higher than 5 mg L−1.
Lu, Y., P.A. Meyers, T.H. JOHENGEN, B.J. EADIE, J.A. ROBBINS, and H. Han. Delta 15N values in Lake Erie sediments as indicators of nitrogen biogeochemical dynamics during cultural eutrophication. Chemical Geology 273:107 (2010). 20100007DNP.pdf
We have measured the stable nitrogen isotope values (δ15N) in two sediment cores sampled 15 years apart (1988 and 2003) from the Eastern Basin of Lake Erie and compared them to the total phosphorus (TP) and biogenic silica (BSi) concentrations in the 2003 core. Changes in the TP, BSi and total nitrogen (TN) accumulations in the 2003 core correspond to three stages in the trophic history of the lake that include the onset (∼1910 to ∼1950), peak (~1950 to ∼1970), and amelioration (∼1970 to 2003) of eutrophication owing to accelerated nutrient loading. Decreasing BSi:TP atomic ratios (BSi:TPat) from ∼1910 to ∼1970 suggest a gradual Si drawdown in the lake during its progressive eutrophication, which led to Si limitation and reduced diatom settling rates. δ15N values show pronounced variability in ∼1950 to ∼1970, which corresponds with rapid increases in N from runoffs from the lake catchment. A trend of gradually increasing δ15N values from ∼1910 to ∼1970 is likely the result of denitrification associated with the development of anoxic bottom waters in the Central Basin of the lake. This study illustrates the complexity of extracting environmental information from δ15N values in sediments and confirms the need for further studies of the multiple processes and their interactions that contribute to lacustrine δ15N records.
Ludsin, S.A., X. Zhang, S.B. Brandt, M.R. Roman, W.C. Boicourt, D.M. MASON, and M. Costantini. Hypoxia-avoidance by planktivorous fish in Chesapeake Bay: implications for food web interactions and fish recruitment. Journal of Experimental Marine Biology and Ecology 381:S121-131 (2009). 20090047DNP.pdf
Chesapeake Bay has been experiencing severe eutrophication-driven bottom hypoxia for several decades, yet the effects of hypoxia on its food webs, especially its pelagic components, remain largely enigmatic. To better understand how hypoxia influences the interaction and spatial overlap between planktivorous fishes (e.g., bay anchovy Anchoa mitchilli) and their mesozooplankton prey (e.g., Acartia tonsa), we contrasted the spatial distributions of these food-web components along the Bay's entire north–south axis during spring, summer, and fall 1996, 1997, and 2000, and along several cross-Bay transects during summer of these same years. Pelagic fish biomass was estimated with a surface-towed split-beam echosounder. Dissolved oxygen and mesozooplankton biomass were simultaneously quantified using a towed, undulating ScanFish sensor package. Results indicate that hypoxia can disrupt the diel vertical migration behavior of planktivorous fishes in Chesapeake Bay during summer by reducing access to bottom waters and forcing fish to reside in well oxygenated surface or nearshore waters. In turn, reduced access to bottom waters reduces spatial overlap with mesozooplankton prey, which appear to use the hypoxic zone as a refuge. Ultimately, we discuss how these hypoxia-driven changes in behavior and spatial overlap may influence food web interactions and bay anchovy recruitment in Chesapeake Bay
Madenjian, C., S.A. POTHOVEN, P.J. Schneeberger, M.P. Ebener, L.C. Mohr, T.F. NALEPA, and J.R. Bence. Dreissenid mussels are not a "dead end" in Great Lakes food webs. Journal of Great Lakes Research 36:73-77 (2010). 20100009DNP.pdf
Dreissenid mussels have been regarded as a “dead end” in Great Lakes food webs because the degree of predation on dreissenid mussels, on a lakewide basis, is believed to be low. Waterfowl predation on dreissenid mussels in the Great Lakes has primarily been confined to bays, and therefore its effects on the dreissenid mussel population have been localized rather than operating on a lakewide level. Based on results from a previous study, annual consumption of dreissenid mussels by the round goby (Neogobius melanostomus) population in central Lake Erie averaged only 6 kilotonnes (kt; 1 kt=one thousand metric tons) during 1995–2002. In contrast, our coupling of lake whitefish (Coregonus clupeaformis) population models with a lake whitefish bioenergetics model revealed that lake whitefish populations in Lakes Michigan and Huron consumed 109 and 820 kt, respectively, of dreissenid mussels each year. Our results indicated that lake whitefish can be an important predator on dreissenid mussels in the Great Lakes, and that dreissenid mussels do not represent a “dead end” in Great Lakes food webs. The Lake Michigan dreissenid mussel population has been estimated to be growing more than three times faster than the Lake Huron dreissenid mussel population during the 2000s. One plausible explanation for the higher population growth rate in Lake Michigan would be the substantially higher predation rate by lake whitefish on dreissenid mussels in Lake Huron.
Mida, J.L., D. Scavia, G.L. FAHNENSTIEL, S.A. POTHOVEN, H.A. VANDERPLOEG, and D.M. Dolan. Long-term and recent changes in southern Lake Michigan water quality with implications for present trophic status. Journal of Great Lakes Research 36:42-49 (2010). 20100030DNP.pdf
Southern Lake Michigan has changed in response to alterations in nutrients and invasive species. NOAA and EPA monitoring results are used to examine those changes. NOAA provides detailed seasonal resolution, but limited spatial coverage, whereas the EPA provides more spatial coverage, but limited seasonal resolution. We compare changes in total phosphorus (TP), silica, nitrate plus nitrite, and chlorophyll concentrations from before and after the invasion by the quagga mussel (Dreissena rostriformis bugensis). Although TP at NOAA stations was consistently higher than at EPA stations, both confirm declines in spring and summer surface mixed layer (SML) conditions. Chlorophyll differed at EPA and NOAA stations before quagga mussel invasion, but not after the invasion. Spring chlorophyll decreased at NOAA stations after the invasion, but summer conditions did not change at either set of stations. Pre-invasion silica at NOAA stations was slightly higher than at EPA stations, and the lake's Si reservoir increased over the study period. Basin-scale spring Si increased gradually, whereas summer SML Si increased dramatically after 2003, likely reflecting reduced diatom production. Basin-scale nitrate increased significantly from pre- to post-invasion in both spring and summer. Summer nitrate utilization declined drastically in recent years, likely reflecting reduced phytoplankton production. TP loads decreased; however, the timing of changes in chlorophyll and Si and nitrate utilization suggest the recent increase in dreissenid filtering dramatically reduced spring phytoplankton abundance and production across the entire southern basin. The offshore pelagic zone of the historically mesotrophic southern Lake Michigan is now similar to oligotrophic Lake Superior.
Mizobata, K., K. Shimada, R. Woodgate, S. Saitoh, and J. WANG. Estimation of heat flux through the eastern Bering Strait. Journal of Oceanography 66:405-424 (2010). 20100018DNP.pdf
We estimated the northward heat flux through the eastern channel of the Bering Strait during the ice-free seasons between 1999 and 2008. This is likely about half of the total heat flux through the strait. The net volume transport and heat flux through the eastern channel of the strait were estimated from multiple linear regression models with in-situ/satellite remotely sensed datasets and NCEP reanalysis 10 m wind. The net volume transport was well explained by the west-east slope of sea level anomaly and NNW wind component at the strait. On the heat flux, the contributions of both barotropic and baroclinic components were taken into account. Estimated volume transport and vertical profile of temperature were used to calculate northward heat flux through the eastern channel of the strait. The magnitude of the estimated heat flux is comparable to estimates from in-situ measurements. Averaged heat flux in the eastern Bering Strait between 2004 and 2007 was about 1.9 times larger than that between 2000 and 2003. Maximum heat flux occurred in 2004, and same magnitude of heat flux was estimated from 2005 to 2007. This resulted not only from the increase in northward volume transport but also anomalous warm water intrusion from the Bering Sea. Our results suggest a candidate among the important parameters controlling heat budget, which contributes to the Arctic sea ice reduction, whereas more studies are required to confirm that this mechanism is actually responsible for the interannual and longer timescale variability.
NALEPA, T.F. An overview of the spread, distribution, and ecological impacts of the quagga mussel, Dreissena rostriformis bugensis, with possible implications to the Colorado River system. Proceedings, Colorado River Basin Science and Resource Management Symposium. Coming Together, Coordination of Science and Restoration Activities for the Colorado River Ecosystem, Scottsdale, AZ, November 18-20, 2008. U.S. Geological Survey Scientific Investigations Report 2010-5135, 372 pp. (2010). https://www.glerl.noaa.gov/pubs/fulltext/2010/20100039.pdf
The quagga mussel (Dreissena rostriformis bugensis) was first found in the Great Lakes in 1989 and has since spread to all five lakes. Although its spread through the system was slower than that of the zebra mussel (Dreissena polymorpha), once established, it replaced zebra mussels in nearshore regions and is colonizing deep regions where zebra mussels were never found. Outside the Great Lakes Basin, quagga mussels do not appear to be increasing to any extent in the Ohio and Mississippi Rivers, even after being present in these rivers for over a decade. In contrast, numbers in the Colorado River system have continued to increase since the quagga mussel was first reported. It will likely become very abundant in all the reservoirs within the Colorado River system, but attain limited numbers in the mainstem. Ecological impacts associated with the expansion of quagga mussels in the Great Lakes have been profound. Filtering activities of mussel populations have promoted the growth of nuisance benthic algae and blooms of toxic cyanobacteria. In addition, the increase in quagga mussels has led to a major disruption of energy flow though the food web. An understanding of food webs in the Colorado River system, particularly the role of keystone species, will help define future ecological impacts of quagga mussels in this system.
NALEPA, T.F., D.L. FANSLOW, and S.A. POTHOVEN. Recent changes in density, biomass, recruitment, size structure, and nutritional state of Dreissena populations in southern Lake Michigan. Journal of Great Lakes Research 36:5-19 (2010). https://www.glerl.noaa.gov/pubs/fulltext/2010/20100027.pdf
Trends in density, biomass, population structure, and nutritional state of Dreissena polymorpha and Dreissena rostriformis bugensis were examined in southern Lake Michigan between the 1990s and 2008. Density and biomass of D. polymorpha increased to a peak in the early 2000s and then declined. In contrast, D. rostriformis bugensis was first found in the southern basin in 2001 and has continued to increase in density or biomass at all depths ever since. In 2008, maximum mean density of D. rostriformis bugensis occurred at 16–30 m (19,000/m2), but maximum biomass (AFDW) occurred at 31–50 m (43.9 g/m2). D. rostriformis bugensis has only recently (since 2005) began to increase at depths N50 m. When both species were present in 2004 at depths b50 m, a condition index (CI) for D. rostriformis bugensis was 27% higher, and shell weight per shell length was 48% lower compared to D. polymorpha. For D. rostriformis bugensis, CI decreased in 2008 compared to 2004 at 25 m and 45 m, but biochemical content (lipid, glycogen) did not. Seasonal changes in both RNA/DNA ratio (growth) and ETS (metabolic activity) in D. rostriformis bugensis were unaffected by reproductive activity, and only ETS appeared to change seasonally relative to bottom temperatures. Spawning of D. rostriformis bugensis occurred in late summer at 25 m, but occurred in spring at 45 m. Veliger densities peaked in both spring and late summer at both depths. Future population expansion (biomass) is expected to be most rapid at depths N50 m.
NEKOUEE, N. Dynamics and numerical modeling of river plumes in lakes. NOAA Technical Memorandum GLERL-151. NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 185 plus Appendices pp. (2010). https://www.glerl.noaa.gov/pubs/tech_reports/glerl-151/tm-151.pdf
Models of the fate and transport of river plumes and the bacteria they carry into lakes are developed. They are needed to enable informed decisions about beach closures to avoid economic losses, and to help design water intakes and operate combined sewer overflow schemes to obviate exposure of the public to potential pathogens. This study advances our understanding of river plumes dynamics in coastal waters by means of field studies and numerical techniques. Extensive field measurements were carried out in the swimming seasons of 2006 and 2007 on the Grand River plume as it enters Lake Michigan. They included simultaneous aerial photography, measurements of lake physical properties, the addition of artificial tracers to track the plume, and bacterial sampling. Our observed results show more flow classes than included in previous studies (e.g. CORMIX). Onshore wind can have a significant effect on the plume and whether it impacts the shoreline. A new classification scheme based on the relative magnitude of plume-crossflow length scale and Richardson number based on the wind speed is devised. Previous studies on lateral spreading are complemented with a new relationship in the near field. The plume thickness decreased rapidly with distance from the river mouth and a new non-dimensional relationship to predict thickness is developed. Empirical near field models for surface buoyant plumes are reviewed and a near field trajectory and dilution model for large aspect ratio surface discharge channels is devised. Bacterial reductions due to dilution were generally small (less than 10:1) up to 4.5 km from the river mouth. E. coli decay rates were significantly affected by solar radiation and ranged from 0.2 to 2.2 day-1 which were within the range of previous studies in Lake Michigan. Total coliform survived longer than E. coli suggesting different die-off mechanisms. Mathematical models of the bacterial transport are developed that employ a nested modeling scheme to represent the 3D hydrodynamic processes of surface river discharges in the Great Lakes. A particle tracking model is used that provides the capability to track a decaying tracer and better quantify mixing due to turbulent diffusion. Particle tracking models have considerable advantages over gradient diffusion models in simulating bacterial behavior nearshore that results in an improved representation of bacteria diffusion, decay and transport. Due to the complexity and wide variation of the time and length scale of the hydrodynamic and turbulent processes in the near field (where plume mixing is dominated by initial momentum and buoyancy) and far field (where plume mixing is dominated by ambient turbulence), a coupling technique is adapted. The far field random walk particle tracking model incorporates the empirical near field model. It simulates the transport, diffusion and decay of bacteria as discrete particles and employs the near field output as the source and transports the particles based on ambient currents predicted by the 3D hydrodynamic model. The coupled model improves dilution predictions in the near field. The new techniques advance our knowledge of the nearshore fate and transport of bacteria in the Great Lakes and can be ultimately applied to the NOAA Great Lakes Coastal Forecasting System to provide a reliable prediction tool for bacterial transport in recreational waters.
Pangle, K.L., and S.D. PEACOR. Temperature gradients, not food resource gradients, affect growth rate of migrating Daphnia mendotae in Lake Michigan. Journal of Great Lakes Research 36:345-350 (2010). 20100020DNP.pdf
Zooplankton production plays a critical role in the Great Lakes ecosystem, and vertical migration, which is exhibited by many zooplankton species, could affect production. We examined the effects of water temperature and food resource gradients on the growth rate of zooplankton undergoing vertical migration in Lake Michigan. In three laboratory experiments, juvenile Daphnia mendotae, native herbivorous cladocerans, were incubated for 5 days at water temperatures associated with the epilimnion and deep chlorophyll maxima (DCM) of Lake Michigan and were fed food resources collected directly from these regions. Growth rate strongly depended on water temperature, as Daphnia incubated at the epilimnetic temperature (21 °C) grew 42% faster than those at the DCM temperature (8 °C). Growth rate of Daphnia that alternated between the two temperatures every 12 h (0.108 day−1) was similar to the arithmetic average growth rate of the two water temperature treatment extremes (0.110 day−1), suggesting fluctuating temperatures alone do not substantially influence Daphnia growth. In contrast, food resources derived from different depths did not affect growth rate, nor was there a significant interaction between food resource origin and water temperature effects. Our results indicate that vertical migration will reduce growth rate, and hence zooplankton production, through reduced temperature, not from changes in resources. Consideration of the effects of vertical migration, especially given the known variability in this behavior, may substantially improve zooplankton production estimates in the Great Lakes.
POTHOVEN, S.A., G.L. FAHNENSTIEL, and H.A. VANDERPLOEG. Temporal trends in Mysis relicta abundance, production, and life-history characteristics in southeastern Lake Michigan. Journal of Great Lakes Research 36:60-64 (2010). https://www.glerl.noaa.gov/pubs/fulltext/2010/20100022.pdf
The density and life history characteristics of Mysis relicta were evaluated at a 110-m and 45-m station in southeast Lake Michigan during spring, summer, and fall for two time periods, 1995–2002 and 2007–2008. Mysis were more abundant during 1995–2002 than 2007–2008 for all seasons and depths, with average declines across seasons of 81% at 45 m and 70% at 110 m. Offshore densities of Mysis in 2007–2008 were similar to published densities within the same region during 1985–1989, but under differing ecosystem conditions (e.g. higher fish biomass and primary production in the 1980 s). Growth averaged 0.032 ± 0.002 mm/day in both 1995–2002 and 2007–2008, and the proportion of females with broods (overall 7%) did not differ between time periods. Mean brood size adjusted for length did not differ between 1995–2002 (17±0.6) and 2007–2008 (15±1.3). The mean length of reproductive females was higher in 2007–2008 (17±0.2) than during 1995–2002 (16±0.1). New recruits (≤4 mm) were collected during each season for each time period, but were lower in abundance in 2007–2008 than in 1995–2002. During spring, there was a significant relationship between offshore water column chlorophyll concentration and Mysis recruit abundance, but not during summer/fall. Declining spring chlorophyll levels may be altering food availability for small mysids in spring, and the decline of the benthic macroinvertebrate Diporeia may be increasing fish predation pressure on Mysis despite declining planktivore abundance.
Raikow, D.F., J.F. Atkinson, and T.E. CROLEY II. Development of resource shed delineation in aquatic ecosystems. Environmental Science and Technology 44:329-334 (DOI:10.1021/es900562t) (2010). 20100003DNP.pdf
We apply a concept derived from food web ecology to largescale spatial patterns of material supply within and between watersheds and coasts by generalizing the definition “resource shed” to source areas for materials supplied to a receptor (e.g., a point location) over a specified time interval. Independent hydrologic and hydrodynamic models, coupled with a particle tracking model, were used to delimit resource shed total spatial extent and relative contributory importance for selected receptors in Lake Erie (North America) over varying time intervals. One resource shed was extended into the Maumee River watershed (OH) by integrating the lake and hydrologic models. Model validation was achieved through comparison with data from the 2005 International Field Years on Lake Erie (IFYLE) study. Resource shed size, orientation, and internal structure varied with receptor location, in-lake circulation, terrestrial precipitation, time interval, and season. River plume extent and interaction were illustrated, and model integration revealed the relative contributory importance of subwatershed catchments to an off-shore receptor.
REICHERT, J.M., B.J. Fryer, K.L. PANGLE, T.B. Johnson, J.T. Tyson, A.B. Drelich, and S.A. LUDSIN. River plume use during the pelagic larval stage benefits recruitment of a lentic fish. Canadian Journal of Fisheries and Aquatic Sciences 67:987-1004 (2010). 20100011DNP.pdf
Similar to coastal marine systems, Lake Erie exhibits open-water river plumes that differ physicochemically and biologically from surrounding waters. To explore their importance to yellow perch (Perca flavescens) recruitment in western Lake Erie, we tested two related hypotheses: 1) contributions of larvae to the juvenile stage (when recruitment is set) would be greater from nutrient-rich Maumee River plume (MRP) waters than less-productive non-MRP waters; and 2) warmer temperatures and higher zooplankton (prey) production in the MRP (versus non-MRP waters) would underlie this expected recruitment difference through “bottom-up” effects on larval growth. Peak larval yellow perch density was 10-fold and 5-fold less in MRP than non-MRP waters during 2006 and 2007, respectively. However, otolith microchemical analyses demonstrated that disproportionally more juvenile recruits emanated from the MRP than non-MRP waters during both years. Although temperature and zooplankton production were higher in the MRP than non-MRP waters during both years, observed recruitment differences were not definitively linked to bottom-up effects. Top-down effects also appeared important, as high turbidity in the MRP may offer a survival advantage by reducing predation mortality on larvae. Our research highlights the need to better understand biophysical coupling in freshwater systems, and demonstrates how stochastic tributary inputs can influence fish recruitment.
ROBERTS, J.J., T.O. Höök, S.A. Ludsin, S.A. POTHOVEN, H.A. VANDERPLOEG, and S.B. Brandt. Effects of hypolimnetic hypoxia on foraging and distributions of Lake Erie yellow perch. Journal of Experimental Marine Biology and Ecology 381:S132-S142 (2009). 20090045DNP.pdf
Bottom hypoxia (< 2 mg O2 L−1) is a widespread phenomenon in marine and freshwater systems, yet the ecological consequences of hypoxia are generally unknown, especially for mobile organisms such as fish. Herein, we explore how a large area of hypolimnetic (i.e., sub-thermocline) hypoxia that develops seasonally in Lake Erie's central basin influences yellow perch (Perca flavescens), a demersal species of both ecological and economic importance. We hypothesized that hypolimnetic hypoxia would negatively affect yellow perch by limiting access to benthic prey and preferred (cool) temperatures. To explore how hypoxia influences yellow perch foraging and migration patterns in central Lake Erie, we collected a suite of biological (i.e., fish with bottom and mid-water trawls, benthic macroinvertebrates using Ponar grabs, and zooplankton via depth-specific pumping) and physical (i.e., temperature and dissolved oxygen) data monthly during June through October 2005. Our results indicate that yellow perch avoid hypoxic bottom waters by either moving horizontally away from the hypoxic zone or migrating above the oxycline. We also found evidence to suggest that individuals that moved above the hypoxic hypolimnetic layer continue to “dive” into the hypoxic layer to feed on benthic invertebrates. Even so, during the height of hypoxia, both the amount and proportion of benthic macroinvertebrates consumed decreased, whereas consumption of zooplankton increased. While hypoxia-induced changes in yellow perch distributions and foraging likely affect individual condition and growth in the short-term, the long-term effects on population production remain equivocal.
Rucinski, D.K., D. BELETSKY, J.V. DePinto, D.J. SCHWAB, and D. Scavia. A simple 1-dimensional, climate based dissolved oxygen model for the central basin of Lake Erie. Journal of Great Lakes Research 36:465-476 (2010). 20100034DNP.pdf
A linked 1-dimensional thermal-dissolved oxygen model was developed and applied in the central basin of Lake Erie. The model was used to quantify the relative contribution of meteorological forcings versus the decomposition of hypolimnetic organic carbon on dissolved oxygen. The model computes daily vertical profiles of temperature, mixing, and dissolved oxygen for the period 1987–2005. Model calibration resulted in good agreement with observations of the thermal structure and oxygen concentrations throughout the period of study. The only calibration parameter, water column oxygen demand (WCOD), varied significantly across years. No significant relationships were found between these rates and the thermal properties; however, there was a significant correlation with soluble reactive phosphorus loading. These results indicate that climate variability alone, expressed as changes in thermal structure, does not account for the interannual variation in hypoxia. Rather, variation in the production of organic matter is a dominant driver, and this appears to have been responsive to changes in phosphorus loads.
Scharold, J.V., S.J. LOZANO, and T.D. Corry. Status of benthic macroinvertebrates in southern nearshore Lake Superior, 1994-2003. In State of Lake Superior. M. Munawar and I.F. Munawar (eds.). Aquatic Ecosystem Health and Management Society, Ecovision World Monograph Series, Canada, 473-492 pp. (2009). https://www.glerl.noaa.gov/pubs/fulltext/2009/20090049.pdf
Benthic macroinvertebrate communities are useful indicators of ecological condition for the Great Lakes (Cook and Johnson, 1974; Wiederholm, 1980). Benthic macro invertebrates are closely associated with lake sediments, and are impacted by changes in physical and chemical characteristics of the sediments and of the overlying water. Benthic organisms play an important role in the ecosystem by influencing sediment-water interactions and by mediating the flow of energy and material between decomposers, primary producers, and higher trophic levels. Because of the sedentary nature and relatively stable population characteristics of benthic communities, their responses integrate environmental conditions in a local area over extended periods of time (Cook and Johnson, 1974).
Shen, C., J. Niu, E.J. ANDERSON, and M.S. Phanikumar. Estimating longitudinal dispersion in rivers using Acoustic Doppler Current Profilers. Advances in Water Resources 33:615-623 (DOI:10.1016/j.advwatres.2010.02.008) (2010).
The longitudinal dispersion coef!cient (D) is an important parameter needed to describe the transport of solutes in rivers and streams. The dispersion coef!cient is generally estimated from tracer studies but the method can be expensive and time consuming, especially for large rivers. A number of empirical relations are available to estimate the dispersion coef!cient; however, these relations are known to produce estimates within an order of magnitude of the tracer value. The focus of this paper is on using the shear-"ow dispersion theory to directly estimate the dispersion coef!cient from velocity measurements obtained using an Acoustic Doppler Current Pro!ler (ADCP). Using tracer and hydrodynamic data collected within the same river reaches, we examined conditions under which the ADCP and tracer methods produced similar results. Since dead zones / transient storage (TS) are known to in"uence the dispersion coef!cient, we assessed the relative importance of dead zones in different stream reaches using two tracer-based approaches: (1) TS modeling which explicitly accounts for dead zones and (2) the advection–dispersion equation (ADE) which does not have separate terms for dead zones. Dispersion coef!cients based on the ADE tend to be relatively high as they describe some of the effects of dead zones as well. Results based on the ADCP method were found to be in good agreement with the ADE estimates indicating that storage zones play an important role in the estimated dispersion coef!cients, especially at high "ows. For the river sites examined in this paper, the tracer estimates of dispersion were close to the median values of the ADCP estimates obtained from multiple datasets within a reach. The ADCP method appears to be an excellent alternative to the traditional tracer-based method if care is taken to avoid spurious data and multiple datasets are used to compute a distance-weighted average or other appropriate measure that represents reach-averaged conditions.
Soranno, P.A., K.S. Cheruvelil, K.E. Webster, M.T. Bremigan, T. Wagner, and C.A. STOW. Using landscape limnology to classify freshwater ecosystems for multi-ecosystem management and conservation. Bioscience 60(6):440-454 (2010). 20100010DNP.pdf
Governmental entities are responsible for managing and conserving large numbers of lake, river, and wetland ecosystems that can be addressed only rarely on a case-by-case basis. We present a system for predictive classification modeling, grounded in the theoretical foundation of landscape limnology, that creates a tractable number of ecosystem classes to which management actions may be tailored. We demonstrate our system by applying two types of predictive classification modeling approaches to develop nutrient criteria for eutrophication management in 1998 north temperate lakes. Our predictive classification system promotes the effective management of multiple ecosystems across broad geographic scales by explicitly connecting management and conservation goals to the classification modeling approach, considering multiple spatial scales as drivers of ecosystem dynamics, and acknowledging the hierarchical structure of freshwater ecosystems. Such a system is critical for adaptive management of complex mosaics of freshwater ecosystems and for balancing competing needs for ecosystem services in a changing world.
Tao, W., C. DeMARCHI, T.F. JOHENGEN, C. HE, and C.A. STOW. Estimating phosphorus load from a large watershed in the Great Lakes basin. Proceedings of the 2010 International Conference on Challenges in Environmental Science and Computer Engineering (CESCE 2010), Wuhan, China, March 6-7, 2010. IEEE Computer Society's Conference Publishing Services, 427-430 pp. (2010). https://www.glerl.noaa.gov/pubs/fulltext/2010/20100012.pdf
Common ways to quantify watershed nutrient loads include estimating the annual or seasonal loads using simple relations between discharge and load, such as the ratio estimator, and fitting complex nutrient transport models to the observed concentrations. The former approach produces quite uncertain estimates at low temporal resolution when based on typically infrequent routine monitoring data. The second approach may produce more reliable estimates, even at high temporal resolution, but requires a lot of time and auxiliary data. The approach explored in this paper uses linear combination of river discharge at the time of estimate and for antecedent periods to quantify Total Phosphorous (TP) concentration, yielding high resolution load estimates sufficiently reliable for a variety of applications.
Thupaki, P., M.S. Phanikumar, D. BELETSKY, D.J. SCHWAB, M.B. Nevers, and R.L. Whitman. Budget analysis of Escherichia coli at a southern Lake Michigan beach. Environmental Science and Technology 44:1010-1016 (2010). https://www.glerl.noaa.gov/pubs/fulltext/2010/20100043.pdf
Escherichia coli (EC) concentrations at two beaches impacted by river plume dynamics in southern Lake Michigan were analyzed using three-dimensional hydrodynamic and transport models. The relative importance of various physical and biological processes influencing the fate and transport of EC were examined via budget analysis and a first-order sensitivity analysis of model parameters. The along-shore advective flux of EC(CFU/m2 · s) was found to be higher compared to its cross shore counterpart; however, the sum of diffusive and advective components was of a comparable magnitude in both directions showing the importance of cross-shore exchange in EC transport. Examination of individual terms in the EC mass balance equation showed that vertical turbulent mixing in the water column dominated the overall EC transport for the summer conditions simulated. Dilution due to advection and diffusion accounted for a large portion of the total EC budget in the nearshore, and the net EC loss rate within the water column (CFU/m3 · s) was an order of magnitude smaller compared to the horizontal and vertical transport rates. This result has important implications for modeling EC at recreational beaches; however, the assessment of the magnitude of EC loss rate is complicated due to the strong coupling between vertical exchange and depth-dependent EC loss processes such as sunlight inactivation and settling. Sensitivity analysis indicated that solar inactivation has the greatest impact on EC loss rates. Although these results are site-specific, they clearly bring out the relative importance of various processes involved.
VANDERPLOEG, H.A., J.R. LIEBIG, T.F. NALEPA, G.L. FAHNENSTIEL, and S.A. POTHOVEN. Dreissena and the disappearance of the spring phytoplankton bloom in Lake Michigan. Journal of Great Lakes Research 36:50-59 (2010). https://www.glerl.noaa.gov/pubs/fulltext/2010/20100025.pdf
We determined the clearance rates of the profunda morph of the quagga mussel (Dreissena bugensis) using seston and Cryptomonas ozolini, a high-quality algal food, for the temperature range 1–7 °C,which is the full temperature range this morph is likely to experience during isothermal conditions or in the hypolimnion of deep lakes. Experiments at 3 °C with the shallow-water morph of the quagga and the zebra mussel provided very similar results. The clearance rates were combined with dreissenid abundance in 0–30 m, 30–50 m, 50–90 m, and N 90 m depth zones of the southern basin of Lake Michigan to calculate a maximum (using Cryptomonas) and minimum (using seston) fraction of the water column cleared (FC) per day in the different depth zones at 3 °C to determine dreissenid impact on the spring phytoplankton bloom from 1994 to 2008. Starting in 2003 or 2004 with the replacement of zebra mussels by quagga mussels in shallow water and expansion of quagga mussel biomass in deep water, FC began to exceed likely phytoplankton growth in the 30–50 m zone. In 2007–2008, FC greatly exceeded likely phytoplankton growth by a factor of about 5 in the 30- to 50-m depth zone, where dreissenids were extremely abundant. Low FC in the offshore region led to the hypothesis of a mid-depth carbon (C) and phosphorous (P) sink caused by mussel uptake of seston-associated C and P that affected not only the mid-depth region, but also the offshore region “downstream” of the mid-depth zone.
VANDERPLOEG, H.A., S.A. Ludsin, J.F. CAVALETTO, T.O. Höök, S.A. POTHOVEN, S.B. Brandt, J.R. LIEBIG, and G.A. LANG. Hypoxic zones as habitat for zooplankton in Lake Erie: Refuges from predation or exclusion zones? Journal of Experimental Marine Biology and Ecology 381:S108-S120 (2009). 20090043DNP.pdf
Bottom hypoxia has reemerged as a prominent feature of Lake Erie's central basin during late summer. Similar to coastal marine systems, the impacts of hypoxia on pelagic organisms in Lake Erie remain largely enigmatic. During summer 2005 and 2007, we used pump sampling for mesozooplankton and fish acoustics to test the hypothesis that mesozooplankton use hypoxia as a refuge from predation. We explored species-specific diel vertical migration (DVM) of mesozooplankton and spatial overlap with planktivorous fishes at several offshore stations in the central basin of Lake Erie with similar thermal structure, but varying hypolimnetic dissolved oxygen (DO) concentrations (range: 0.3 to 4.6 mg l−1). The tendency of a zooplankter to use the hypolimnion under normoxic conditions and its sensitivity to DO defined its DVM and overlap with fish, which were generally more sensitive to hypoxia than mesozooplankton. The diaptomids (calanoid copepods) and the predatory cladoceran Leptodora kindtii were largely unaffected by hypoxia, using the epilimnion during both day and night. Daphnia mendotae and the predatory cladoceran Bythotrephes longimanus, both of which migrated from the metalimnion and epilimnion to the hypolimnion during the day under normoxic conditions, avoided the hypolimnion at DO levels ≤ 2.0 mg l−1. Dissolved oxygen levels between 1.0 and 1.2 mg l−1 were critical avoidance thresholds for most other mesozooplankton species, with the copepod Mesocyclops edax, a migrator between the epilimnion and hypolimnion, avoiding DO ≤ 1.2 mg l−1. By contrast the cool water, hypolimnetic copepod Diacyclops thomasi and Daphnia longiremis continued to use the hypolimnion during the day until DO became ≤ 1.0 mg l−1. These species aggregated in the metalimnion (primarily) and epilimnion (secondarily) at night. Only Bosmina was found in abundance in the hypolimnion at DO levels equal to 0.3 mg l−1. Hypoxia intolerant species (e.g., D. mendotae, B. longimanus) that were compressed into the thin metalimnion during day likely faced high predation pressure from visual-feeding planktivorous fishes (e.g., rainbow smelt Osmerus mordax, emerald shiners Notropis atherinoides) as well as the predatory cladoceran, B. longimanus. By contrast, hypoxia-tolerant species (e.g., D. thomasi, D. longiremis, and B. longirostris) that remained in the hypolimnion may have found refuge in hypoxic areas with DO N1.0mg l−1, although fishwere occasionally observed making feeding excursions into hypoxic waters.
VANDERPLOEG, H.A., S.A. Ludsin, S.A. RUBERG, T.O. Höök, S.A. POTHOVEN, S.B. Brandt, G.A. LANG, J.R. LIEBIG, and J.F. CAVALETTO. Hypoxia affects spatial distributions and overlap of pelagic fish, zooplankton, and phytoplankton in Lake Erie. Journal of Experimental Marine Biology and Ecology 381:S92-S107 (2009). 20090044DNP.pdf
Bottom hypoxia has reemerged as a prominent feature of Lake Erie's central basin during late summer. Similar to coastal and marine systems, the influence of hypoxia on pelagic organisms remains largely enigmatic in Lake Erie. During 2005, we used a plankton survey system (a sensor package consisting of an optical plankton counter, fluorometer, dissolved oxygen sensor, light sensor, and conductivity–temperature–depth sensor), coupled with a fish hydroacoustics system, to explore how the distribution of phytoplankton (chlorophyll), mesozooplankton, and fish varied vertically and horizontally in relation to oxygen concentrations. To do so, we conducted surveys of the entire water column on a continuous basis during mild (August) and severe (September) hypoxia. Our surveys included two sampling designs: 1) basin-wide transects sampled during day and night to define broad-scale patterns of spatial overlap among pelagic organisms; and 2) shorter (5 km) transects sampled every 4 h over a 24-h period to explore how diel vertical migration and hypoxia interact to affect time-specific spatial overlap among fishes, mesozooplankton, and phytoplankton. Our findings indicated that fish avoided regions of the hypolimnion with dissolved oxygen concentrations > 3 mg l−1 by 1) moving horizontally into areas with higher oxygen, or 2) moving vertically into the metalimnion, where a sharp thermocline and oxycline existed. A portion of the mesozooplankton continued to use the hypoxic hypolimnion as a refuge from fish predation during daytime at oxygen concentrations between 1 and 3 mg l−1; however, there was usually a mesozooplankton maximum in the metalimnion, even when fish were compressed into this region. Prior to development of hypoxia, the metalimnion in some areas may have served as thermal refuge from predation from the epilimnetic planktivore, the emerald shiner, and the hypolimnetic planktivore–benthivore, the rainbow smelt. Overall, the horizontal compression of fish into less hypoxic regions in the deep area of the central basin followed by vertical compression into the metalimnion as hypoxia developed further may have led to local reduction of mesozooplankton prey in these regions. Herein, we discuss the potential implications of these hypoxia-induced impacts for understanding foodweb interactions and fisheries management.
Walker, J.T., C.A. STOW, and C. Geron. Nitrous oxide emissions from the Gulf of Mexico hypoxic zone. Environmental Science and Technology 44:1617-1623 (2010). https://www.glerl.noaa.gov/pubs/fulltext/2010/20100004.pdf
The production of nitrous oxide (N2O), a potent greenhouse gas, in hypoxic coastal zones remains poorly characterized due to a lack of data, though large nitrogen inputs and deoxygenation typical of these systems create the potential for large N2O emissions. We report the first N2O emission measurements from the Gulf of Mexico Hypoxic Zone (GOMHZ), including an estimate of the emission “pulse” associated with the passage of Tropical Storm Edouard in August 2008. Pre-storm emission rates (25-287 nmol m-2 hr-1) and dissolved N2O concentrations (5 - 30 nmol L-1) were higher than values reported for the Caribbean and western Tropical Atlantic, and on the lower end of the range of observations from deeper coastal hypoxic zones. During the storm, N2O rich subsurface water was mixed upward, increasing average surface concentrations and emission rates by 23% and 61%, respectively. Approximately 20% of the N2O within the water column vented to the atmosphere during the storm, equivalent to 13% of the total “hypoxia season” emission. Relationships between N2O, NO3 -, and apparent oxygen utilization (AOU) suggest enhanced post storm N2O production, most likely in response to reoxygenation of the water column and redistribution of organic nitrogen. Our results indicate that mixing related emissions contribute significantly to total seasonal emissions and must therefore be included in emission models and inventories for the GOMHZ and other shallow coastal hypoxic zones.
WANG, J. Ice cover on the Great Lakes. Fact Sheet. NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 2 pp. (2010). https://www.glerl.noaa.gov/pubs/brochures/ice/ice.pdf
Ice on the Great Lakes is more than just a signal of winter. In fact, the lakes were formed over several thousands of years as mile-thick layers of glacial ice advanced and retreated, scouring and sculpting the basin. In addition, the ebb and flow of glacial meltwater and rebound of the underlying land from the weight of the massive ice sheets further changed the basin’s shape and drainage patterns. Ice cover still has a major effect on the Great Lakes, making it more important than a connection to the past and a measure of the winter’s harshness. Ice cover has an effect on almost every aspect of life on the Great Lakes, from hydropower generation to commercial shipping to the fishing industry. The amount of ice cover and how long it remains on the lakes during the winter season changes from year to year, and long-term changes may occur because of global warming. Studying, monitoring, and predicting ice is important to determine climate patterns, lake water levels, water movement patterns, water temperature structure, and for predicting spring plankton blooms.
WANG, H.-Y., H.A. Cook, D.W. Einhouse, D.G. Fielder, K.A Kayle, L.G. Rudstam, and T.O. Hook. Maturation schedules of walleye populations in the Great Lakes region: Comparison of maturation indices and evaluation of sampling-induced biases. North American Journal of Fisheries Management 29:1540-1554 (2009). https://www.tandfonline.com/doi/abs/10.1577/M08-156.1
WANG, J., X. BAI, G.A. LESHKEVICH, M.C. COLTON, A.H. CLITES, and B.M. LOFGREN. Severe ice cover on Great Lakes during winter 2008-2009. EOS Transactions 91(5):41-42 (2010). https://www.glerl.noaa.gov/pubs/fulltext/2010/20100005.pdf
The North American Great Lakes contain about 95% of the fresh surface water supply for the United Stales and 20% for the world. Nearly one eighth of the population of the United States and one third of the population of Canada live within their drainage basins. Because of this concentration of population, the ice cover that forms on the Great Lakes each winter and its year-to-year variability affect the regional economy [Niimi, 1982]. Ice cover also affects the lake's abiotic environment and ecosystems [Vanderploeg et al.,1992] in addition to influencing summer hypoxia, lake effect snow inland, water level variability, and the overall hydrologic cycle of the region [Assel et al., 2004] . From the late 1990s to the early 2000s, the volume of lake ice cover was much lower than normal, which enhanced evaporation and led to a significant water level drop, as much as 1.3 meters. Lower water levels have a significant impact on the Great Lakes economy. For example, more than 200 million tons of cargo are shipped every year through the Great Lakes. Since 1998-when water levels took a severe drop, commercial ships have been forced to lighten their loads; for every inch of clearance that these oceangoing vessels sacrificed due to low water levels, each ship lost US $II,000-22,000 in profits. Lake ice loss can cause other problems, including the destruction of the eggs of fall-spawning fish by winter waves and erosion of coastal areas unprotected by shore ice. Ice loss also compromises the safety of people engaging in winter recreational activities, such as snowmobiling or ice fishing.
WANG, J., H. HU, and X. BAI. Modeling Lake Erie ice dynamics: Process studies. Proceedings, 20th Annual IAHR International Symposium on Ice, Lahti, Finland, June 14-18, 2010. IAHR, AIRH, 17 pp. (2010). https://www.glerl.noaa.gov/pubs/fulltext/2010/20100033.pdf
A Great Lakes Ice-circulation Model (GLIM) with a 2-km resolution grid was applied to Lake Erie under hourly high-frequency atmospheric forcing derived from meteorological measurements. After the seasonal cycles of ice concentration, thickness, velocity, and other variables were well reproduced in the 2003/04 ice season in comparison with satellite measurements, process studies were further conducted on ice dynamics. Categories of ice thickness and ice speed were further investigated using available ice drifting measurements. The simulated ice velocity speeds resemble some important features of the observed ice drifts.
WANG, J., H. HU, D.J. SCHWAB, G.A. LESHKEVICH, D. BELETSKY, N. HAWLEY, and A.H. CLITES. Development of the Great Lakes ice circulation model (GLIM): Application to Lake Erie in 2003-2004. Journal of Great Lakes Research 36:425-436 (2010). https://www.glerl.noaa.gov/pubs/fulltext/2010/20100032.pdf
To simulate ice and water circulation in Lake Erie over a yearly cycle, a Great Lakes Ice-circulation Model (GLIM) was developed by applying a Coupled Ice-Ocean Model (CIOM) with a 2-km resolution grid. The hourly surface wind stress and thermodynamic forcings for input into the GLIM are derived from meteorological measurements interpolated onto the 2-km model grids. The seasonal cycles for ice concentration, thickness, velocity, and other variables are well reproduced in the 2003/04 ice season. Satellite measurements of ice cover were used to validate GLIM with a mean bias deviation (MBD) of 7.4%. The seasonal cycle for lake surface temperature is well reproduced in comparison to the satellite measurements with a MBD of 1.5%. Additional sensitivity experiments further confirm the important impacts of ice cover on lake water temperature and water level variations. Furthermore, a period including an extreme cooling (due to a cold air outbreak) and an extreme warming event in February 2004 was examined to test GLIM's response to rapidly-changing synoptic forcing.
Wiley, M.J., D.W. Hyndman, B.C. Pijanowski, A.D. Kendall, C. Riseng, E.S. RUTHERFORD, P.J. Steen, P.L. Richards, P.W. Seelbach, J.M. Koches, and R.R. Rediske. A multi-modeling approach to evaluating climate and land use change impacts in a Great Lakes river basin. Hydrobiologia 657:243-262 (DOI:10.1007/s10750-010-0239-2) (2010). https://www.glerl.noaa.gov/pubs/fulltext/2010/20100044.pdf
River ecosystems are driven by linked physical, chemical, and biological subsystems, which operate over different temporal and spatial domains. This complexity increases uncertainty in ecological forecasts, and impedes preparation for the ecological consequences of climate change. We describe a recently developed ‘‘multi-modeling’’ system for ecological forecasting in a 7600 km2 watershed in the North American Great Lakes Basin. Using a series of linked land cover, climate, hydrologic, hydraulic, thermal, loading, and biological response models, we examined how changes in both land cover and climate may interact to shape the habitat suitability of river segments for common sport fishes and alter patterns of biological integrity. In scenario based modeling, both climate and land use change altered multiple ecosystem properties. Because water temperature has a controlling influence on species distributions, sport fishes were overall more sensitive to climate change than to land cover change. However, community-based biological integrity metrics were more sensitive to land use change than climate change; as were nutrient export rates. We discuss the implications of this result for regional preparations for climate change adaptation, and the extent to which the result may be constrained by our modeling methodology.
Wynne, T.T., R.P. Stumpf, M.C. Tomlinson, and J. DYBLE. Characterizing a cyanobacterial bloom in western Lake Erie using satellite imagery and meteorological data. Limnology and Oceanography 55(5):2025-2036 (2010). https://www.glerl.noaa.gov/pubs/fulltext/2010/20100024.pdf
The distribution and intensity of a bloom of the toxic cyanobacterium, Microcystis aeruginosa, in western Lake Erie was characterized using a combination of satellite ocean-color imagery, field data, and meteorological observations. The bloom was first identified by satellite on 14 August 2008 and persisted for > 2 months. The distribution and intensity of the bloom was estimated using a satellite algorithm that is sensitive to near-surface concentrations of M. aeruginosa. Increases in both area and intensity were most pronounced for wind stress, 0.05 Pa. Area increased while intensity did not change for wind stresses of 0.05–0.1 Pa, and both decreased for wind stress > 0.1 Pa. The recovery in intensity at the surface after strong wind events indicated that high wind stress mixed the bloom through the water column and that it returned to the surface once mixing stopped. This interaction is consistent with the understanding of the buoyancy of these blooms. Cloud cover (reduced light) may have a weak influence on intensity during calm conditions. While water temperature remained > 15oC, the bloom intensified if there were calm conditions. For water temperature < 15oC, the bloom subsided under similar conditions. As a result, wind stress needs to be considered when interpreting satellite imagery of these blooms.
Yurista, P.M., H.A. VANDERPLOEG, J.R. LIEBIG, and J.F. CAVALETTO. Lake Michigan Bythotrephes prey consumption estimates for 1994-2003 using a temperature and size corrected bioenergetic model. Journal of Great Lakes Research 36:74-92 (2010). 20100031DNP.pdf
Bythotrephes were collected on a regular basis at a 110 m deep reference station in Lake Michigan over a 10-year period 1994–2003. The measured population structure in conjunction with an updated bioenergetic model was used to estimate daily predation demands by Bythotrephes on the zooplankton community. The bioenergetic model incorporated the effect of temperature on growth and respiration and used a scalable size structure to adjust for a dynamic range in size across the season. A general linear model was developed to apply the bioenergetic results to routinely collected field data for estimating predation needs. Daily population consumption needs were estimated to be approximately equal to Bythotrephes standing biomass but varied as a function of water temperature and percent instar composition. At a temperature of 18 °C the predation needs of the population were equal to the population biomass. At warmer temperatures (22–24 °C) the daily needs were up to 35% above the population biomass. Within and across years the population was variable, while trend lines from the long-term data indicated biomass and predation needs had an initial peak in mid-August followed by a plateau period with a seasonal high peak mid-October. A decrease in the midseason long-term average size structure suggests that Bythotrephes may experience prey limitation during this time period of the year. Over the course of the 10-year period population cycles and peak biomass were fairly stable with no indication of a change in predation needs.
ZHANG, H., S.A. Ludsin, D.M. MASON, A.T. ADAMACK, S.B. Brandt, X. Zhang, D.G. Kimmel, M.R. Roman, and W.C. Boicourt. Hypoxia driven changes in the behavior and spatial distribution of pelagic fish and mesozooplankton in the northern Gulf of Mexico. Journal of Experimental Marine Biology and Ecology 381:S80-S91 (2009). 20090046DNP.pdf
Hypoxia (<2 mg O2 l−1) is a major global water quality and fisheries management issue in coastal ecosystems. Although the impact of hypoxia on benthic communities has been intensively studied, less is known about hypoxia's effect on pelagic communities. Herein, we explored how hypoxia can influence the horizontal and vertical distribution of pelagic fish, as well as their overlap with mesozooplankton prey in the northern Gulf of Mexico, an area with extensive seasonal hypoxia. Using an undulating Scanfish sensor package (with CTD and optical plankton counter) towed in parallel with a split-beam acoustics system, we simultaneously collected water temperature, dissolved oxygen, salinity, mesozooplankton biomass, and relative fish biomass density data along transects (day and night) during 2003, 2004, and 2006. We used spatial analytical techniques to account for intercorrelation and spatial autocorrelation in data and to discern patterns in the distribution of pelagic organisms. We observed low fish biomass in hypoxic waters, with fish aggregating horizontally at the edges of hypoxic areas. Fish also aggregated immediately above hypoxic bottom waters, but only during years of severe hypoxia. Spatial overlap between fish biomass and mesozooplankton biomass was high during mild hypoxia, but reduced during years of severe hypoxia. Consistent with other coastal systems such as Chesapeake Bay and the Neuse River Estuary, our findings ultimately suggest that hypoxia can reduce the availability of quality habitat for zooplanktivorous fish in the northern Gulf of Mexico by reducing access to bottom habitat and mesozooplankton prey
Zhulidov, A.V., A.V. Kozhara, G.H. Scherbina, T.F. NALEPA, A. Protasov, S.A. Afanasiev, E.G. Pryanichnikova, D.A. Zhulidov, T.Y. Gurtovaya, and D.F. Pavlov. Invasion history, distribution, and relative abundances of Dreissena bugensis in the old world: a synthesis of data. Biological Invasions 12:1923-1940 (2010). 20100015DNP.pdf
We examined trends in expansion patterns and relative abundances of Dreissena bugensis in reservoirs and major river systems in eastern Europe. Based on our own data and data from the literature, it is apparent that trends were variable across river basins and not easily related to environmental conditions. In some cases these did not conform to the patterns typically found for dreissenids. In the early period of expansion beyond its native range in the Dnieper-Bug delta and estuary, D. bugensis rapidly replaced Dreissena polymorpha in the upper Dnieper River system, but increased only gradually and over time became less abundant relative to D. polymorpha in the Don-Manych River system. Contrary to the Dnieper and Don River systems, in the Volga River system considerable spatial variability in relative abundances was apparent, particularly in northern reservoirs. Moreover, even though D. bugensis usually displaces D. polymorpha as the dominant dreissenid, the latter can remain dominant in certain types of habitats where conditions are less favourable for the former. Suggested factors that may be responsible for differences in invasion patterns in the river systems may include differential responses to temperature, or to some other factor(s) associated with geographical latitude, the level of water mineralization, and selective predation by molluscivorous fish. In particular, the northward expansion of D. bugensis seems to be limited by temperature. The lack of long-term data on appropriate scales precludes linking these differences to specific features within the environment, but our comparisons indicate that the expansion of D. bugensis relative to D. polymorpha is more complex than previously believed.
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