Checking the Pulse of Lake Erie
Edited by
M. Munawar and R. Heath
Ecovision World Monograph Series
Physical and chemical regimes
Lake Erie Thermal Structure: Variability, Trends and Potential Changes
William M. Schertzer*, Paul F. Hamblin, and David C.L. Lam
National Water Research Institute, Canada Centre for Inland Waters
867 Lakeshore Rd., Burlington, Ontario, Canada, L7R 4A6
*Corresponding author: william.schertzer@ec.gc.ca
Principal features of the thermal structure of Lake Erie are described along with an assessment of trends, variability and potential changes. We discuss the historical perspective of observations, long-term temperature and heat storage characteristics resulting from radiative and turbulent heat exchanges, and primary characteristics of the annual thermal cycle including the thermal bar, thermocline dynamics and time of over-turn. The long-term data record clearly demonstrates that there are years with a lack of data representativeness both spatially and temporally. Such problems make it difficult to rely on the observational record alone for analysis of temperature related priority issues. Limitations in spatial and temporal databases necessitate the development and application of a hierarchy of thermal models for simulating / forecasting lake temperature fields. Surface temperature observations do not show a statistically significant trend, however, some years, especially in the 1990s, do have large departures (e.g. 5-7 Co) from the long-term mean temperatures. More research is required to establish the degree of correspondence between these large departures and such factors as ENSO events or anthropogenic changes. Preliminary research combining thermal models with climate warming scenarios (e.g. climate analogs; 2 x CO2 GCM scenarios; climate transposition scenarios) have indicated that the thermal structure of Lake Erie can be significantly changed. Such changes include, for example, reduction in ice cover, longer stratification season and a possible change from dimictic to monomictic conditions, which have implications for other ecosystem components, water quality and many priority issues related to this lake. Based on the climatological record of surface temperatures, the near-term period (i.e. 3-5 years) in Lake Erie may experience variable temperatures with extremes greater than 2Co from the long-term mean similar to the 1990s. Longer-term projections, based on climate change modelling, indicate that with increasing atmospheric concentrations of “green-house gases” significant changes to the lake thermal components are possible. Uncertainties and limitations of data and modelling are assessed with recommendations for future research.
Keywords: thermal cycle, models, climate warming
Lake Erie Hydrodynamics: Regime, Variability and Potential Changes
Paul F. Hamblin and William M. Schertzer*
National Water Research Institute, Canada Centre for Inland Waters
867 Lakeshore Rd., Burlington, Ontario, Canada, L7R 4A6
*Corresponding author: william.schertzer@ec.gc.ca
A review of key hydrodynamical processes in Lake Erie is presented along with trends, variability, and possible changes. Primary focus is on knowledge gained from past physical limnological observations, modelling, and current state of knowledge on possible changes in currents and circulation which may result from climate warming. The circulation of Lake Erie is shown to be complex, largely because of physiography. Specialized observation programs during stratified and unstratified periods have been successful in identifying large-scale circulation patterns including the occurrence of clockwise and anti-clockwise gyres. Research has also documented inter-basin exchange of water and materials, current oscillations, flushing and diffusion time scales, upwelling, surface waves, and turbulence. Modelling has been particularly useful in helping to simulate the 2- and 3-dimensional flow fields and there have been improvements leading to first generation forecast capability for this lake. Knowledge of the complexities of water movements is found to be important for understanding ecological problems (e.g. fish-kills, hypolimnetic anoxia, etc.). Further improvements in instrumentation such as the acoustic doppler current profiler have shown promise in measurement of flows in the upper reaches of the water column. Recommendations for increased spatial and temporal observation of key meteorological components are presented. More research is required to allow projection of possible changes in Lake Erie hydrodynamical processes which may result from changes in climatic forcing. It is suggested that radical changes in thermal structure (e.g. dimictic to monomictic states) will exert a profound influence on winter circulation and mixing. Further, weaker wind forcing expected from climate change in combination with increased bottom friction due to the presence of mussels may lead to a reduction in the strength of lake circulation and mixing which could have consequences on the biology and chemistry of lake Erie.
Keywords: meteorological forcing, currents, climate change
Analysis of Late 90s Phosphorus Loading Pulse to Lake Erie
D.M. Dolan1, and R.P. Richards2*
1University of Wisconsin – Green Bay, Natural and Applied Sciences, 2420 Nicolet Dr., Green Bay, WI 54311.
2National Center for Water Quality Research, Heidelberg College, 310 E Market St., Tiffin, OH 44883, USA
*Corresponding author: prichard@heidelberg.edu
The total phosphorous (TP) load estimates to Lake Erie for each year have been compared to the target load from the Great Lakes Water Quality Agreement of 11,000 metric tons per year. The estimates for 1997 and 1998 exceeded the target load mainly due to elevated tributary loads. Five tributaries in Northern Ohio and Southeast Michigan have been monitored intensively for several years before and after this “pulse” in loading. While increased rainfall in these years was a major contributor to the unusually large loading, another factor was that the slopes in the TP-flow relationships for each of these five tributary sub-basins were usually larger in the winter. This suggests that, in addition to frequency and duration, the timing (i.e., winter vs. summer) of storms may have been responsible for this loading “pulse”. Various statistical models have been applied to the Lake Erie tributary data for the years 1996 through 2001 for these sub-basins. The results show different seasonal relationships within each tributary.
Keywords: nutrients, tributaries, storm events
Modelling Phosphorus and Dissolved Oxygen Conditions Pre- and Post- Dreissena Arrival in Lake Erie
D.C.L. Lam1*, W.M. Schertzer1, R.C. McCrimmon1, M. Charlton1, S. Millard2
1National Water Research Institute (NWRI), P.O. Box 5050, Burlington, Ontario, Canada, L7R 4A6
2Great Lakes Laboratory for Fisheries & Aquatic Sciences, P.O. Box 5050, Burlington, Ontario, Canada, L7R 4A6
*Corresponding author: David.Lam@ec.gc.ca
Using the NWRI nine-box water quality model calibrated for pre- Dreissena years, with the model coefficients unchanged, we demonstrate that changes in phosphorus and dissolved oxygen in post- Dreissena years can be detected by the deviation of computed results from observed data. Through sensitivity analysis, we exclude other possible mechanisms to conclude that Dreissena can affect the total phosphorus concentration in Lake Erie, notably a concentration decrease in the east basin. On the other hand, changes in dissolved oxygen in the central basin hypolimnion are influenced less by Dreissena, as the model was able to simulate the observed oxygen concentration in Post- Dreissena years, using the original formulation on oxygen, thermal layer thicknesses and sediment oxygen demand and in the absence of a new Dreissena submodel. The impact of these and other findings on the phosphorus-dissolved oxygen relationship and its implication to the Lake Erie lakewide management plan is discussed using the results of this study.
Changes in Water Quality of Maumee Bay 1928-2003
D. Moorhead*, T. Bridgeman and J. Morris
Department of Earth, Ecological and Environmental Sciences, and the Lake Erie Center, University of Toledo, Toledo, Ohio 43606-3390
*Corresponding author: Daryl.Moorhead@utoledo.edu
The recent publication, State of Lake Erie, (Munawar et al. 1999), provides a thorough synthesis of historic information, complete with hypotheses regarding likely changes in the lake in response to continuing changes in land use, water quality and exotic species invasions. It outlines a conceptual model of the Great Lakes as a very dynamic freshwater system that has experienced considerable change on both historic and geologic time scales, due to a combination of glacial and human activities (Leach 1999). Lake Erie, in particular, has undergone great changes within the last century, as coastal swamps were drained and upland forests cleared for agriculture, cities and industries proliferated, and numerous exotic species became established (Arnott and Vanni 1996, Klerks et al. 1996, Richards et al. 2002a). It is the shallowest, most southern, most productive, most exploited and possibly the most impacted of the Great Lakes. Lake Erie became increasingly eutrophic with human development in the region (Leach 1999) and now is experiencing “oligotrophication” (Dermott and Munawar 1993, Ackerman et al. 2001) as nutrient inputs decline (Rasul et al. 1999) and zebra mussel (Dressina polymorpha) populations expand (Nicholls et al. 1999). The most dynamic part of this very dynamic lake is probably the western basin, which is the shallowest region of the lake and receives the largest inflows of water, sediments and nutrients entering Lake Erie, via the Detroit and Maumee Rivers (Rasul et al. 1999).
The Maumee Bay in particular, represents an especially dynamic microcosm within the Lake Erie ecosystem. The Maumee River drains the largest watershed feeding Lake Erie (ca. 17,000 km2), and enters the lake in the Maumee Bay, which serves as the connection between the largest river entering the Great Lakes and the rest of Lake Erie. The watershed is dominated by traditional row-crop agriculture (corn and soy beans), which covers about 75% of its area (Baker 1985). Although the Maumee River contributes only 3% of the water that flows into the western basin of Lake Erie, it contributes more than half the input of suspended solids (Herdendorf and Krieger 1989, Rasul et al. 1999) as well as an estimated 2,240 tons of phosphorus (Baker 1985). A recent suite of articles summarized results of the Lake Erie Agricultural Systems for Environmental Quality (LEASEQ) project, which included detailed evaluations of changes in land use patterns and water quality of the Maumee watershed over 1975-1995 (Richards et al. 2002a). Non-point sources, primarily agricultural lands, provide most of the phosphorus and sediments entering the lake (Baker and Richards 2002). However, changes in agricultural practices during this time included increasing soil conservation practices and declining fertilizer sales, which are likely to affect water quality (Richards et al. 2002b). Indeed, Calhoun et al. (2002) found that soluble reactive phosphorus (SRP) concentrations in river waters declined with falling fertilizer sales. Richards and Baker (2002) also found significant reductions in SRP, total phosphorus, and total Kjedahl nitrogen concentrations, which they attributed to changes in manure and fertilizer application. In total, Baker and Richards (2002) estimated that annual export of total phosphorus and SRP from watershed soils declined by 25-40% and 60-89%, respectively, during this period, although loading is still quite high compared to other Midwestern watersheds.
The impact of the Maumee River on Lake Erie is undoubtedly substantial, but impacts on Maumee Bay are probably even greater. The bay has an average depth of 1.7 m, with hydraulic retention of about 5 days, compared to 53 days for the western basin and 1008 days for the Lake Erie (Herdendorf and Krieger 1989). Hence, inputs are high relative to turnover, sediments are prone to re-suspension by wind, and seiche activity can alter water depth (and volume) within a few hours. The river carries high, albeit variable loads of sediment and nutrients (Moog and Whiting 2002a, Baker and Richards 2002) into the bay, likely defining a “loading gradient” from the river mouth into the larger, western basin of Lake Erie. This gradient may serve as a spatial surrogate of the temporal gradient of the benthification process occurring throughout the lake. In any case, the Maumee Bay is where inputs from the Maumee River mix with waters from the western basin of Lake Erie, before entering the western basin. Thus, the river-bay-lake continuum may have a substantial impact on water quality in the rest of Lake Erie (Mortimer 1987, Bartish 1987).
Relatively few studies of the water quality in Maumee Bay have been published to date and observations on water quality have been made only sporadically since the late 1920s. However, the last 30 years have been a period of transition for the Maumee River and the rest of Lake Erie, so it is likely that Maumee Bay has also undergone many changes. Improved sewage treatment, invasion by zebra mussels, and reductions in both point-source pollution and nutrient input likely affected water quality. Fortunately, Dr. Peter Fraleigh conducted intensive monitoring studies in the bay during this time frame. Although data he collected in 1974 and 1977 were previously reported (Fraleigh et al. 1975, 1979), we are unaware of any publications reporting the data collected in 1994. The latter observations were retained on the original field and laboratory data recording sheets, along with the personal notes of Fraleigh, at the Lake Erie Center (University of Toledo). These data also can be combined with both earlier and more recent observations to help interpret some of the changes taking place in the bay (Table 1).
Keywords: Lake Erie, historic trends, spatial trends, nutrients, sediment loading
Water Use for Irrigation Agriculture in Ohio’s Lake Erie Basin and its Potential Impact on Lake Erie Water Quality
Timothy T. Loftus1,2 and R. Peter Richards1*
1National Center for Water Quality Research, Heidelberg College, 310 E Market St., Tiffin, OH 44883, USA
2Current address: Northeastern Illinois Planning Commission, 222 S Riverside Plaza, Suite 1800, Chicago, IL 60606
*Corresponding author: prichard@heidelberg.edu
Section 6217 of the Coastal Zone Act Reauthorization Amendments of 1990 (CZARA) requires that states develop and submit a Coastal Nonpoint Pollution Control Program. Management measures must be specified in state programs for restoring and protecting coastal waters from specific categories of nonpoint source pollution. Irrigation is one of several potential sources of agriculture-related nonpoint-source pollution. In this study, water withdrawals and returns within the Ohio Lake Erie Basin were evaluated to determine their potential impact on the water quality of Lake Erie, and support a policy choice by the State of Ohio: whether or not the water quality impacts are sufficient to justify implementation of the relevant Section 6217 management measures. Data for the years 1991–2002 included surface and groundwater withdrawal volumes, return flows, and number and type of users. Statistical and spatial analyses indicated that current levels of irrigation do not have a discernable impact on Lake Erie water quality. Net water use for irrigation is less than that for most industrial and municipal uses for which data were available. Other findings include important differences between water use for crops and nurseries, and upward trends in irrigation withdrawals, especially for nurseries. Spatial analysis reveals several areas of concentrated withdrawals. Future research should consider the seasonality of irrigation agriculture and other hydrological variables of interest, and focus on understanding the potential for local impacts of irrigation on surface and ground water resources.
Keywords: Great Lakes, Coastal Zone Act, water resources management, farming practices
Current Knowledge of Trace Metal Biogeochemistry in the Water Column of Lake Erie
Michael R. Twiss
Department of Biology/Clarkson Center for the Environment,
Clarkson University, Potsdam, New York 13699, USA
The historical record of reliable analytical measurements of trace metal concentrations in the water column of Lake Erie dates back only 15 years to the publication of the first measurements made using stringent trace metal clean sampling protocols. The results of these and later efforts revealed that the concentrations of dissolved trace metals were much lower than previously thought to have existed in these waters – accordingly, the perceived role that these elements play in Lake Erie has radically changed. Plankton are widely considered to be the most important factor controlling the residence time of trace metals in the water column. Evidence suggests that some metals (Zn, Fe) may at times be low enough to cause physiological adaptations in plankton; the influence of other metals has not yet been examined. The Lake Erie trace metal data set is limited to primarily total dissolved concentrations. Measurements are available for Cd, Cr, Co, Cu, Cs, Fe, Hg, Pb, Ni, Tl, and Zn. Important information regarding chemical speciation of most of these elements is lacking, yet needed. In addition, the data set represents measurements made almost exclusively during the summer months ? hence, the current restricted view of trace metal biogeochemistry in the lake cannot allow proper risk assessment. Determinations of the chemical speciation of several bioactive trace metals (Cd, Co, Ni, Cu, Zn, Fe, Mn) will provide important information regarding the interaction of these elements with plankton.
Keywords: aquatic chemistry, geochemistry, Great Lakes, phytoplankton, seston
An updated review of contaminant sources and loads in Lake Erie
David Porta* and G. Douglas Haffner
Great Lakes Institute for Environmental Research (GLIER), University of Windsor, 401 Sunset Ave., Windsor, ON N9B 3P4, Canada
*Corresponding author: dporta@uwindsor.ca
Lake Erie is the smallest of the Laurentian Great Lakes and the most heavily affected by anthropogenic activity supporting a population base of over 11 million people. An integrated overview of the chemical contaminants lake wide was implemented to assess the current status of the lake and outline future monitoring and research needs required to address environmental effects of chemical pollutants. A comprehensive database of contaminant concentrations in water, sediment, and biota has been developed for over three decades, but the comparison and integration of available data are difficult to achieve due to the diverse methodologies and different time/spatial scales of the studies. Overall, lake wide declines of polychlorinated biphenyls (PCBs) and mercury are documented while other chemicals such as polybrominated diphenyl ethers (PBDEs) and polycyclic aromatic hydrocarbons (PAHs) continue to exhibit increasing trends. Only a few metal studies have been based on trace metal clean dependable techniques, and this results in most of the available data on toxic metals up to the mid 1990s to be of limited value. The lack of integrated monitoring and research programs combined with quality assurance issues stresses the need for the general adaptation of a new approach if ecosystem management is to be achieved. Furthermore appropriate monitoring, research, and remediation programs must consider chemical pollutants in combination with other lake stressors such as species invasions and climate change in order to predict future trends and effects.
Keywords: Laurentian Great Lakes, toxic metals, persistent organic pollutants, microcystins
Biological regime
A review of planktonic viruses in Lake Erie and their role in phosphorus cycling
Amanda L. Dean1, Julie L. Higgins2, Jennifer M. DeBruyn1, Johanna M. Rinta-Kanto2, Richard A. Bourbonniere3, and Steven W. Wilhelm1,2*
1Department of Ecology and Evolutionary Biology, The University of Tennessee, Knoxville, TN 37996
2Department of Microbiology, The University of Tennessee, Knoxville, TN 37996
3National Water Research Institute, Environment Canada, 867 Lakeshore Road, P.O. Box 5050 Burlington, ON Canada L7R 4A6
*Corresponding author: wilhelm@utk.edu
As pervasive pathogens, viruses that infect members of the microbial community are now included in most analyses of aquatic food webs and nutrient cycles. Here we provide a review of the available information concerning their distribution in the Laurentian Great Lake, Lake Erie, as well as new information from samples collected in July 2003. Results from virus production assays demonstrate that bacterial lysis by viruses released 122 – 1080 nM of phosphorus per day throughout Lake Erie, implying that viruses acted as a major mechanism of phosphorus recycling in the lake. Combining this data with results from previous studies, viruses are shown to be ubiquitous throughout Lake Erie, with a weak correlation between their distribution and the distribution of heterotrophic bacteria. Moreover, evidence suggests that virus production rates are tightly tied to the growth rate of the microbial community, with changes in bacterial growth (brought on by amendments of PO4-P) resulting in increases in virus production in the system. In combination with data compiled from 1997 through 2002, this information is presented to reinforce the importance of viruses as integral components of Lake Erie and other aquatic ecosystems.
Keywords: microbial foodwebs, nutrient recycling, bacteria, bacteriophage
Distribution and apportionment of phosphate between bacterioplankton and phytoplankton in Lake Erie during summer 2003 and 2004
T. T. Meilander* and R. T. Heath
Department of Biological Sciences, Kent State University Kent, OH 44242
*Corresponding author: ttrzebuc@kent.edu
The effects of labile dissolved organic carbon (LDOC) on phosphorus dynamics of plankton were studied at diverse stations during synoptic surveys of Lake Erie aboard the CCGS Limnos in August of 2003 and June, July, and August of 2004. The sites represented diverse LDOC regimes, trophic states, and basin locations. LDOC values ranged from 13.7 to 126.5 µM. At higher LDOC concentrations, a greater portion of the phosphorus pool was distributed to algae, and at lower LDOC concentrations, a greater portion of the phosphorus pool is distributed to bacteria. Bacterial P-quota was greatest at stations with the lowest LDOC concentrations. Phosphate uptake by bacteria was greater at lower LDOC sites and lower at higher LDOC sites. LDOC concentration was not related to trophic state index (TSI), calculated based on chlorophyll a concentrations. These observations support the microbial shunt hypothesis (MSH). Phosphate apportionment to bacteria was consistent and independent of LDOC concentrations. This observation varies from the MSH.
Keywords: plankton, labile dissolved organic carbon (LDOC), trophic state
An intensive assessment of planktonic communities in the Canadian waters of Lake Erie, 1998.
M. Munawar1*, I.F. Munawar2, M. Fitzpatrick1, H. Niblock1, K. Bowen1, J. Lorimer1
1Fisheries & Oceans Canada, 867 Lakeshore Road, Burlington, Ontario, Canada, L7R 4A6
2Plankton Canada, Burlington, Ontario, Canada
*Corresponding author: munawarm@dfo-mpo.gc.ca
Microbial loop (bacteria, autotrophic picoplankton, and heterotrophic nanoflagellates) phytoplankton, size fractionated primary productivity, and zooplankton from the Canadian waters of Lake Erie was studied at 15 stations on a biweekly basin from April – November 1998 using standard methodologies. Annual mean phytoplankton biomass suggested that the west basin was meso-eutrophic (3.0 g m-3); the central basin was mesotrophic (1.7 g m-3) and east basin was also mesotrophic (1.9 g m-3). The size structure (ESD) indicated a prevalence of nanoplankton (2-20 µm). Chlorophyta was increasingly important in the community structure of all the 3 basins. Species diversity was high across the lake ranging from 183 – 207 identified species. Size fractionated primary productivity was highest in the west basin and nanoplankton was dominant in all three basins. P/B quotients were highest for picoplankton (<2 µm) throughout the lake. Zooplankton biomass was also highest in the west basin, with a decreasing gradient across the lake. Cladocerans dominated the biomass in the west and central basins however Calanoids were most prevalent in the east. Comparisons of trophic interactions revealed some interesting and contrasting predator prey relationships amongst the three basins. Phytoplankton as a primary food resource was plentiful across the lake with sufficient edible forms amenable for grazing including Diatomeae, Chlorophyta and various phytoflagellates. However the composition of the predators was significantly different among basins. In the west basin, herbivorous zooplankton and dreissenid veligers were dominant whereas herbivorous zooplankton and carnivorous zooplankton were prevalent in the central basin. On the other hand, the east basin was overwhelmingly dominated by carnivorous zooplankton. The trophic interactions studied during 1998 present an interesting and complex picture of three lakes contained within a single lake, each with characteristic food web interactions. The intensive sampling, as done in the Lake Erie Biomonitoring (LEB) study of 1998, could serve as a model for future plankton investigations and be supplemented with laboratory grazing experiments in order to fully comprehend the food web dynamics of a lake which is changing rapidly.
Keywords: Great Lakes, trophic interactions, lower food web
A Planktonic Index of Biotic Integrity (P-IBI) for Lake Erie: A new technique for checking the pulse of Lake Erie
D.D. Kane1, S.I. Gordon2, M. Munawar3, M.N. Charlton4, and D.A. Culver1*
1Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, Columbus, Ohio 43210
2Department of City and Regional Planning, The Ohio State University, Columbus, Ohio 43210
3Great Lakes Laboratory for Fisheries and Aquatic Sciences, Department of Fisheries and Oceans,Burlington, Ontario L7R 4A6
4National Water Research Institute, Environment Canada, Burlington, Ontario L7R 4A6
*Corresponding author: culver.3@osu.edu
In order to measure changes in ecosystem health in Lake Erie, we developed a biological water quality assessment tool. The Planktonic Index of Biotic Integrity (P-IBI) was developed using Lake Erie zooplankton and phytoplankton data from 1970 and 1996, validated with respect to total phosphorus and chlorophyll a concentrations, and applied to a number of years of Lake Erie plankton data. P-IBI candidate zooplankton metrics included an abundance ratio of calanoid copepods to cladocerans and cyclopoid copepods, percentage density of large Daphnia, rotifer composition, density of the calanoid copepod Limnocalanus macrurus, percentage biomass of the predatory invasive zooplankters Bythotrephes and Cercopagis, biomass of crustacean zooplankton/ biomass of phytoplankton, and biomass of crustacean zooplankton. Candidate phytoplankton metrics included a generic index of diatoms, abundance ratio of centric diatoms to pennate diatoms, biomass of inedible algae taxa, percentage biomass of bluegreen algae of the total phytoplankton biomass, percentage biomass of the potentially toxic Microcystis, Anabaena, and Aphanizomenon of total phytoplankton biomass, and biomass of edible algae taxa. Discriminant analysis was used to evaluate candidate metrics relative to Lake Erie degradation. Significant metrics for June included biomass of edible algae taxa, percentage Microcystis, Anabaena, and Aphanizomenon of total phytoplankton biomass, and an abundance ratio of calanoids to cladocerans and cyclopoids. The only significant metric for July was the density of Limnocalanus macrurus, while both the zooplankton abundance ratio and crustacean zooplankton biomass were significant metrics for August. The P-IBI showed an increase in water quality between 1970 and the mid-1990’s, with declining water quality in the late 1990’s and 2002.
Keywords: zooplankton, phytoplankton, Great Lakes, water quality
Declining Lake Erie ecosystem health — Evidence from a multi-year, lake-wide, plankton study
Joseph D. Conroy, Douglas D. Kane, and David A. Culver*
Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, Columbus, Ohio
*Corresponding author: culver.3@osu.edu
Recent research indicates that Lake Erie ecosystem health is declining due to increases in total phytoplankton biomass throughout the lake and the recurrence of cyanobacterial blooms in the western basin and nearshore areas of the central and eastern basins. In this paper, we use extensive information on phytoplankton and zooplankton communities collected from 1995 to 2003 to test whether the health of the lower trophic levels in the lake has indeed changed recently. We found that the lake’s total phytoplankton, inedible phytoplankton, cyanophyte, and total crustacean biomasses increased from 1995 to 2003 based on our samples, although linear regression analysis versus year did not fully support this conclusion. A crustacean taxonomic index also indicated the lake is eutrophic, particularly in the western basin. Overall, we found that plankton communities indicate that Lake Erie has better health than at the height of cultural eutrophication, but that the system remains impaired and it is less healthy than it was 10 years ago.
Keywords: phytoplankton, zooplankton, Dreissena, cyanobacteria, eutrophication, algal loading
Changing benthic fauna of Lake Erie between 1993 and 1998
R. Dermott* and J. Dow
Great Lakes Laboratory for Fisheries & Aquatic Sciences, Fisheries & Oceans Canada,867 Lakeshore Road, Burlington, Ontario, Canada. L7R 4A6.
*Corresponding author: dermottr@dfo-mpo.gc.ca
Average benthic density and biomass were greatest in the eastern basin of Lake Erie. Dreissena dominated all areas while the mayfly Hexagenia was common in the west basin. Quagga mussels ( D. bugensis) represented 90 to 100 % of the collected mussels; while Oligochaetes, Pisidium and Chironomus dominated the fauna in the central basin.
Except for the mayflies, benthic density and biomass of the inmvertebrates decreased in the west basin between 1993 and 1998, while dreissenid biomass increased in the central and east basins. No specimens of the amphipod Diporeia were collected in Lake Erie during1998.
Keywords: benthos, Dreissena, biomass
Synergistic changes in the fish community of western Lake Erie as modified by non-indigenous species and environmental fluctuations
Xinhua Zhu 1*, Timothy B. Johnson 2**, and Jeffrey T. Tyson 3
1Department of Biological Sciences, University of Windsor, Windsor, Ontario, Canada N9B 3P4
2Ontario Ministry of Natural Resources, Lake Erie Fisheries Station, Wheatley, Ontario, Canada N0P 2P0
3Sandusky Fisheries Research Unit, Division of Wildlife, Ohio Department of Natural Resources, Sandusky, Ohio, USA 44870
*Corresponding author: jeffrey.zhu@mnr.gov.on.ca
We used a basin-wide bottom trawl dataset, collected annually from 1987 to 2003, to explore relationships between fish community composition and environmental variation in the western basin of Lake Erie. Over 1.6 million individuals representing 18 families, 38 genera, and 55 species were sampled from 1,253 effective trawls. Nine non-indigenous species (NIS) contributed >75% of the total abundance, dominated by white perch, Morone americana, (48.85%) and gizzard shad, Dorosoma cepedianum, (14.65%). Native yellow perch, Perca flavescens, was the next most abundant species, comprising 12.0% of the catch. Species richness did not vary appreciably within the time series, but catch-per-unit-effort (CPUE) was strongly influenced by NIS evenness and bathymetric attributes, which resulted in an increase in diversity indices (H’, D, J, PIE) of fish community through time. Multiple analyses of variance (MANOVA) identified significant interannual and depth-specific variation in water transparency, water temperature, and dissolved oxygen across the western basin. A canonical correspondence analysis (CCA) revealed a close association between clupeid abundance and environmental variation; the relationship was weaker for other soft-finned fish, and virtually absent for spiny-rayed fish. Three species-size groups were discriminated on the basis of feeding mode (planktivore vs. benthivore / omnivore) and thermal preference when the abundance of 18 important species was aligned with environmental gradients. Water transparency was the primary environmental gradient influencing community structure and may alter foraging effectiveness, both in terms of predator avoidance and prey detection. We conclude that synergistic effects of the invasion by dreissenid mussels and round goby invoked environmental fluctuations that altered predator-prey dynamics and thus the stability of fish community in western Lake Erie.
Keywords: canonical correspondence analysis, species richness, feeding mode, thermal preference, water transparency
Application of the Primary Production Required model for managing commercial fisheries in western Lake Erie
Mark A.J. Fitzpatrick1, Mohiuddin Munawar2 and G. Douglas Haffner1*
1University of Windsor, Great Lakes Institute for Environmental Research, Windsor, ON, Canada, N9B 3P4
2Fisheries & Oceans Canada, Great Lakes Laboratory for Fisheries and Aquatic Sciences, Burlington, ON, Canada, L7R 4A6
*Corresponding author: haffner@uwindsor.ca
The Primary Production Required (PPR) model, first developed by Pauly and Christensen (1995) was applied to historic commercial fisheries catch data from Lake Erie (1950 – 2000) and current commercial catch data from the western basin of Lake Erie (2000 – 2002). The rate of energy transfer between trophic levels was determined to be 10% and equal to global estimates. Our calculations suggested that lakewide PPR reached as high as 50% of the available primary production in 1956 and, following the collapse of the blue pike (Sander vitreus glaucus) fishery, oscillated from 10 – 20 % up to 2000. In the west basin, we estimated that PPR declined from 53 – 32% of the available primary production between 2000 and 2002, corresponding to a reduction in walleye (Sander vitreus) quotas. All of these values are considerably higher than the benchmark of 8% PPR established for sustainable fisheries. The results of the PPR approach suggest that autochthonous energy may not be sufficient to support the commercial fishery. The relative importance of autochthonous and allochthonous carbon inputs, with respect to meeting the energy requirements of the fishery, needs to be investigated.
Keywords: phytoplankton, carbon uptake, autochthonous energy, sustainable fisheries, Great Lakes
Lake Erie Colonial Waterbirds, 1974-2002: Trends in Populations, Contaminant Levels, and Stable Isotope Indicators of Diet
C. E. Hebert1*, D.V. Weseloh2, T. Havelka2, C. Pekarik3, J.L. Shutt1, and F. Cuthbert4
1Canadian Wildlife Service, National Wildlife Research Centre, 1125 Colonel By Drive, Ottawa, ON K1A 0H3
2Canadian Wildlife Service, 4905 Dufferin St., Downsview ON M3H 5T4
3Canadian Wildlife Service, 867 Lakeshore Rd., P.O. Box 5050, Burlington ON L7R 4A6
4University of Minnesota, Department of Fisheries and Wildlife, 1980 Folwell Ave., St. Paul MN 55108
*Corresponding author: Craig.Hebert@ec.gc.ca
Censuses conducted over the last 25 years indicate that breeding populations of colonial-nesting birds on Lake Erie have changed. During the most recent census (1997-2001) twelve species were confirmed nesting on the lake. The most abundant species was the Ring-billed Gull with 68,000 nests lake-wide. Breeding populations of Ring-billed Gulls and Herring Gulls increased from Census 1 (1977-78) to Census 2 (1990-92), and then showed slight increases (Ring-billed Gulls) or decreases (Herring Gulls). Double-crested Cormorant nests increased from 57 during Census 1 to 1,956 during Census 2, to 9,257 nests during the most recent survey. This translated into an annual population increase of 23% from Census 1 to Census 3. Common Tern populations declined through time, exclusively as a result of decreases in the Canadian breeding population. Breeding populations of Black-crowned Night-Herons also declined through time. Statistical analysis of organochlorine levels in Herring Gull eggs suggested that the rate of temporal decline of most contaminants has been constant or has increased during the period 1974-2002. Stable isotope analysis of eggs revealed changes in the diet of Lake Erie Herring Gulls that likely reflected declines in the availability of fish prey.
Keywords: Laurentian Great Lakes, fish-eating birds, piscivorous birds, aquatic birds, organochlorines, d15N.
Current issues
Life in the Dead Zone: exploring microbial communities in the oxygen depleted waters of Lake Erie
Tracey T. Meilander1*, Mohiuddin Munawar2, Mark A. J. Fitzpatrick2, and Robert T. Heath1
1Department of Biological Sciences, Kent State University, Kent, OH 44242
2Fisheries and Oceans Canada, Great Lakes Laboratory for Fisheries and Aquatic Sciences, Burlington, ON L7R 4A6
*Corresponding author: ttrzebuc@kent.edu
Areas of hypoxia and anoxia in aquatic ecosystems are often called “dead zones” because low oxygen concentrations prevent survival of higher organisms, especially fish. The purpose of this investigation was to compare two sites in Lake Erie, a central basin site with a record of hypoxia and an eastern basin site without hypoxia, in order to investigate microbial processes under oxygen-stressed conditions. This research was conducted during June, July, and August of 2004 aboard the CCGS Limnos. Phytoplankton communities in the productive surface waters appear to be meso-oligotrophic and weakly P-limited based on particulate phosphorus concentration and phosphate uptake velocities. The structure and function of the microbial community, including heterotrophic bacteria, phytoplankton, autotrophic picoplankton, and heterotrophic nanoflagellates, were analyzed. Microbial biomass and activity did not appear to be impacted by hypoxic conditions in August. Throughout the season, microbial community biomass and activity in the central basin hypolimnion was equal to or greater than that in the eastern basin. Bacterial productivity and growth efficiency peaked in July in the central basin hypolimnion, possibly as a precursor to August hypoxia. All size fractions of primary productivity were greater in the central basin. This suggests that even hypolimnetic phytoplankton remain active, thereby retaining the capability to photosynthesize. The Lake Erie “dead zone” is very much “alive” for members of the microbial community which maintain the ability to survive and thrive in the oxygen-stressed hypolimnion of the central basin. The continued use of the term “dead zone” to describe hypoxia is discouraged.
Keywords: bacterioplankton, phytoplankton, microbial loop, hypoxia, phosphorus dynamics
Abundance of healthy phytoplankton in the hypoxic waters of Central Lake Erie during the summer of 2004
Iftekhar F. Munawar1, M. Munawar2*, M. Fitzpatrick2, J. Lorimer2
1Plankton Canada, Burlington, Ontario, Canada
2Fisheries & Oceans Canada, Canada Centre for Inland Waters, 867 Lakeshore Rd., Burlington, ON, L7R 2A6, Canada
*Corresponding author: munawarm@dfo-mpo.gc.ca
Phytoplankton samples were collected from three depths (epilimnion, metalimnion and hypolimnion) at a single station in the central basin of Lake Erie during the summer of 2004 (July and August). This area of the central basin has a long history of hypoxia. Oxygen stress (Dissolved Oxygen < 4 µg l-1) was observed only during August in the hypolimnion and not in July. A substantial amount of phytoplankton was recorded in the hypoxic stratum (1.3 g m-3) dominated by Chlorophyta (34%) and other phytoflagellates. A large number of species (111) were identified in the hypoxic stratum. The most prevalent (as biomass) were a mixture of species belonging to Cyanophyta, Chlorophyta, Chrysophyceae, Cryptophyceae and Dinophyceae (Chroococcus dispersus var. minor, Tetraëdron minimum, Chrysochromulina parva, Rhodomonas minuta and Gymnodinium helveticum). These species are common in the Great Lakes and occur in diverse nutrient conditions. Importantly, these species do not characterize either eutrophic or oligotrophic conditions. Some species, including Rhodomonas minuta and Chrysochromulina parva, were recorded in all strata, while others such as Cyclotella atomus and C. glomerata were found only in the epilimnion. P/B quotients were highest for picoplankton and lowest for nanoplankton and their distribution in the water column did not seem to be affected by hypoxic conditions. The detailed phytoplankton biomass, species composition and P/B ratios presented in this study confirm that the hypoxic zone is viable and supports a large number of photosynthetically active species. The plankton identified in the oxic and hypoxic strata were similar in composition. Furthermore, the hypoxic samples did not contain dead settling algae but in fact were active and viable. Our findings support the conclusions of Meilander et al. (2008) that the oxygen stressed hypolimnion observed in the summer of 2004 harboured a healthy phytoplankton community, which is anything but dead.
Keywords: hypolimnion, Dead Zone, algae, oxic, microbial, oxygen, Great Lakes
Nonindigenous species in Lake Erie: A chronicle of established and projected aquatic invaders
Sarah A. Bailey*, David W. Kelly, Derek K. Gray, Kanavillil Nandakumar, Hugh J. MacIsaac
Great Lakes Institute for Environmental Research, University of Windsor,Windsor, ON, N9B 3P4, Canada
Lake Erie has an extensive history of human-mediated perturbation, ranging from habitat destruction to nutrient and contaminant loadings and introduction of nonindigenous species (NIS). Currently, at least 72 NIS of aquatic vertebrate and invertebrate animals, protists, algae and submerged macrophytes are established in Lake Erie. Fishes and algae are represented by the most NIS (16 species each), followed by molluscs (13 species), crustaceans (10 species) and submerged macrophytes (7 species). In addition, 10 NIS of protists, bryozoans, hydrozoans and insects are established in the lake. Both the taxonomic composition of new NIS and pathway of introduction have varied temporally. Before 1880, aquatic invaders consisted primarily of fishes that were deliberately introduced. Molluscs were the principal invaders between 1881 and 1920, and were introduced by a variety of mechanisms including ships’ solid ballast and aquarium releases. After 1920, a wide variety of aquatic NIS were introduced via an array of vectors, although ballast water was the predominant pathway (responsible for 66% of invasions after 1960). NIS continue to establish in Lake Erie at a rate of one invader per year; and until the numerous pathways of introduction are addressed, it is expected that the lake remains at risk of further invasion.
Keywords: biological invasion; exotic species; invasion pathways