Lake Erie Nutrient Loads, 1970–1980

The Buffalo District, Corps of Engineers’ Lake Erie Wastewater Management Study and Heidelberg College's Water Quality Laboratory supported a tributary water quality monitoring program from 1974 to 1980 of the major United States tributaries to Lake Erie. This program was designed to measure nutrient loads by monitoring concentration changes occurring in association with increased streamflow. Soluble orthophosphate loads, chloride loads, and silica loads decreased from 1970 to 1980. Nitrogen species were highly variable and increased over the period. Total phosphorus loads to Lake Erie have decreased during the period as a result of phosphorus removal at wastewater treatment plants. The effect of the phosphorus reductions can be seen in the lake concentrations and were predicted by a three-basin phosphorus budget model developed in the early 1970s. The results show that phosphorus removal programs are having the predicted effect on Lake Erie water quality.     

Burrowing mayfly (Ephemeroptera: Ephemeridae: Hexagenia spp.) bioturbation and bioirrigation: A source of internal phosphorus loading in Lake Erie

Traditional lake eutrophication models predict lower phosphorus concentrations with decreased external loads. However, in lakes where decreased external phosphorus loads are accompanied by increasing phosphorus concentrations, a seeming “trophic paradox” exists. Western Lake Erie is an example of such a paradox. Internal phosphorus loads may help explain this paradox. We examined bioturbation and bioirrigation created from burrowing mayfly, Hexagenia spp., as a possible source of internal phosphorus loading. Phosphorus concentrations of experimental microcosms containing lake sediments, filtered lake water, and nymphs (417/m²) collected from western Lake Erie were compared to control microcosms containing sediments and lake water over a 7-day period. Phosphorus concentrations in microcosms containing Hexagenia were significantly greater than microcosms without nymphs. Further, we estimate the soluble reactive phosphorus flux from the sediments due to Hexagenia is 1.03 mg/m²/day. Thus, Hexagenia are a source of internal phosphorus loading. High densities of Hexagenia nymphs in western Lake Erie may help explain the “trophic paradox.” Furthermore, Hexagenia may be a neglected source of internal phosphorus loading in any lake in which they are abundant. Future studies of phosphorus dynamics in lakes with Hexagenia must account for the ability of these organisms to increase lake internal phosphorus loading.     

Lake Erie Central Basin Total Phosphorus Trend Analysis from 1968 to 1982

The total phosphorus data from 1968 to 1982 in the Lake Erie central basin trend study area was analyzed to determine in-lake responses to the Great Lakes Water Quality Agreement (GLWQA) phosphorus loading reduction program. The available data for each year were divided into five subsets according to time of year and depth of the water column. Each data subset was regressed as a function of time and total phosphorus loadings to Lake Erie. Linear regression analysis indicates that the in-lake phosphorus concentrations have been decreasing and are well correlated with decreased loadings to the lake. The highest rate of phosphorus decrease with time (0.56 ± 0.10 mg · m⁻³ yr⁻¹) was obtained by using epilimnetic concentrations from April to December for each year. This data subset also shows the best correlation with decreasing phosphorus loadings. From 1968 to 1982, Lake Erie offshore phosphorus concentrations responded to decreasing external phosphorus loadings at a rate of 0.45 ± 0.09 mg · m⁻³ per thousand metric tonnes.     

Trends in Total Phosphorus in Canadian Near–Shore Waters of the Laurentian Great Lakes: 1976–1999

Beginning as early as 1976 at many locations, total phosphorus concentrations (TP) were measured weekly in samples collected year-round in the intake water of 18 municipal water treatment plants in Canadian (Ontario) waters of the Laurentian Great Lakes. No consistent long-term trends were evident at two north-shore Lake Superior sampling locations, but there were significant long-term declines in TP measured at all three Lake Huron locations; however, concentrations there have remained relatively constant during the past decade. Declines in TP averaging about 1 μg/L/yr during 1976 to 1990 were prevalent at lower Great Lakes sampling locations and by the early 1990s TP had declined to 15–25 μg/L in Lake Erie and 10–20 μg/L in Lake Ontario. Declines generally levelled out in Lake Ontario after 1990, but TP increased substantially at some Lake Erie locations in the late 1990s. Recent (1996 to 1999) total phosphorus concentrations in north-shore Lake Erie locations in the range of 20 to 30 μg/L were 2 to 3 times higher than at Lake Ontario near-shore locations in the 8 to 11 μg/L range. Rates of decline of TP were generally highest for the March–April period (−1.88, −1.61, and −1.34 μg/L/yr in Lakes Ontario, Erie, and Huron, respectively for 1976 to 1990). The March–April Lake Ontario near-shore rate of TP decline was nearly twice as high as that reported previously for off-shore Lake Ontario (attributed to proximity to P loading sources and to lower net sedimentation losses of P in the near-shore environment). There were substantial declines in chlorophyll-to-TP ratios and in the slopes and Y-intercepts of chlorophyll-TP regressions for both Lake Erie and Lake Ontario following the establishment of dreissenid mussels.     

Urban total phosphorus loads to the St. Clair-Detroit River System

The St. Clair-Detroit River System watershed is a large, binational watershed draining into the connecting channel between lakes Huron and Erie. In addition to extensive agricultural lands, it contains large urban areas that discharge phosphorus from point source facilities, runoff of impervious surfaces, and overflows of combined sewers. To help guide actions to reduce phosphorus input to Lake Erie, we analyzed the spatial and temporal dynamics of loads from the three largest urban areas in the watershed (southeast Michigan; Windsor, Ontario; and London, Ontario), and used a previously calibrated storm water management model (SWMM) to explore options for reducing loads around metro Detroit. Point sources in these three urban areas contribute, on average, 81% of the total urban load and 19% of the Detroit River’s total phosphorus (TP) load to Lake Erie, while combined sewer overflows and runoff both contribute about 10% each to the urban load and about 2.5% each to the Detroit River’s load to Lake Erie. Most of the urban load (56%) comes from a single point source, the wastewater treatment facility in Detroit; however, TP loads from that facility have decreased by about 51% since 2008 due to improvements in wastewater treatment. Model simulations suggest that increasing pervious land area or implementing green infrastructure could help reduce combined sewer overflows in certain upper portions of the metro Detroit sewer system, but reductions were much less expressed for wet-weather discharge from the system.     

Is glyphosate an underlying cause of increased dissolved reactive phosphorus loading in the Western Lake Erie basin?

The western Lake Erie basin has been experiencing increasing dissolved reactive phosphorus (DRP) loads since approximately 1994, the causes of which are not well understood. Changing agricultural practices such as no-till agriculture and tile drainage are certain to have an effect on DRP loads. This study examines glyphosate as a potential driver of the observed increase in the western Lake Erie basin DRP loads since 1994 by examining adoption of herbicide-tolerant crops, glyphosate use, and both DRP loads and concentrations from the mid-1990’s to the present. Glyphosate’s widespread usage contributes to DRP loadings and eutrophication in the western Lake Erie basin.     

Lake Erie's ecological history reconstructed from the sedimentary record

We evaluated the recent ecological history of Lake Erie from diatoms and geochemistry in sediment cores. Two major transition points in the ecology of the western basin (WB; 1985 and 2008) and central basin (CB; 1935 and 1982) were defined. Changes in abundance of diatom eutrophic indicators and geochemical markers were interpreted as a degradation in water quality after 1935 due to the effects of increased population, agriculture, and industrialization until abatement measures were enacted in the 1970s and 1980s. Diatom indicators suggested modest recovery from eutrophic conditions in Lake Erie, however diatom-inferred total phosphorus suggested that despite abatement efforts total phosphorus was not reduced below pre-impact levels. The effects on diatoms of increased temperature and dissolved silica also became apparent in the 1980s, and in the WB recent shifts were likely caused by increased pollution and recent climatic warming. Based on stratigraphic changes since 1985, the diatom trajectory suggests the phytoplankton of Lake Erie will likely remain in a state of flux for the near future due to a variety of countervailing impacts including unknown effects of mitigation efforts, legacy pollution, climate change, and changing upstream conditions.     

Changes in mid-summer water temperature and clarity across the Great Lakes between 1968 and 2002

In recent decades, three important events have likely played a role in changing the water temperature and clarity of the Laurentian Great Lakes: 1) warmer climate, 2) reduced phosphorus loading, and 3) invasion by European Dreissenid mussels. This paper compiled environmental data from government agencies monitoring the middle and lower portions of the Great Lakes basin (lakes Huron, Erie and Ontario) to document changes in aquatic environments between 1968 and 2002. Over this 34-year period, mean annual air temperature increased at an average rate of 0.037 °C/y, resulting in a 1.3 °C increase. Surface water temperature during August has been rising at annual rates of 0.084 °C (Lake Huron) and 0.048 °C (Lake Ontario) resulting in increases of 2.9 °C and 1.6 °C, respectively. In Lake Erie, the trend was also positive, but it was smaller and not significant. Water clarity, measured here by August Secchi depth, increased in all lakes. Secchi depth increased 1.7 m in Lake Huron, 3.1 m in Lake Ontario and 2.4 m in Lake Erie. Prior to the invasion of Dreissenid mussels, increases in Secchi depth were significant (p < 0.05) in lakes Erie and Ontario, suggesting that phosphorus abatement aided water clarity. After Dreissenid mussel invasion, significant increases in Secchi depth were detected in lakes Ontario and Huron.     

Detrended Correspondence Analysis of Phytoplankton Abundance and Distribution in Sandusky Bay and Lake Erie

The purpose of this study was to determine if phytoplankton communities in Sandusky Bay were distinct from those of Lake Erie. Samples were taken from 11 sites along a 50 km transect extending from the lower reaches of the Sandusky River, through Sandusky Bay and into the western basin of Lake Erie to identify factors correlated with identifiable patterns in distribution and abundance of summer phytoplankton. Detrended correspondence analysis (DCA), an ordination technique used to describe patterns in complex data sets, arranged the sample sites along an ordination axis that explained 76% of the variation in the phytoplankton abundance data matrix, and produced the following sequence of ordination axis scores: Sandusky Bay→ Lake Erie→ Sandusky River. DCA axis I scores strongly correlated with total phosphorus, soluble reactive phosphorus, algal phosphatase activity, dissolved oxygen, conductivity, turbidity, and alkalinity, but not chloride concentration, suggesting that phytoplankton abundance and distribution were related to phosphorus availability and not simply due to the passive movement of water along the transect. Bacterial abundance correlated with DCA axis I, suggesting that phytoplankton-bacterial interactions may be important in understanding distributional patterns of Sandusky Bay phytoplankton.     

A Post Audit of a Lake Erie Eutrophication Model

A post audit of a eutrophication-dissolved oxygen model of Lake Erie is presented. The model had been calibrated using data from 1970 and 1975. Projections were then made for use in establishing the IJC target loadings for phosphorus that would essentially eliminate the anoxia in the central basin. In the latter 1970s the phosphorus discharges to Lake Erie dropped substantially due to increased removal from point sources. The observed response of the lake to this change in loading is compared to the predicted response. A 10-year computation from 1970 to 1980 is made using measured lake loadings. Concentrations of total and dissolved phosphorus, nitrate, chlorophyll, dissolved oxygen, and anoxic area are compared to observations. Both agreements and deviations are examined. It is concluded that the IJC target loadings were reasonably accurate forecasts of the loadings required to achieve the goal of elimination of anoxia.     

Validation of a diatom-based index of water quality confirms its utility in monitoring of the Lake Erie's nearshore area

We conducted a validation of the Planktonic Diatom Index (PDI) to demonstrate the utility of a water quality index for the monitoring of Lake Erie's nearshore pelagial zone. Using a large, independent dataset from the Western and Central Basins of Lake Erie for validation ensures realistic assessment of the performance of the index. Diatom-based biomonitoring allows for the inference of integrative information about water quality based on diatom species composition. The PDI is based on the assumption that phosphorus, an established proxy for eutrophication, is instrumental in the structuring of diatom communities. In this study, PDI scores and measured total phosphorus were significantly correlated (r²?=?0.34, r²?=?0.63 outliers removed). However, when samples were considered on a basin-wide basis, the PDI scores were not significantly predicted by measured total phosphorus in the Western Basin. We suggest that snapshot phosphorus measurements are less likely to represent the overall condition in the highly variable, eutrophic Western Basin. When multiple phosphorus measurements were averaged over time, the relationship with the integrative PDI scores was more apparent (r²?=?0.52). Through validation with an independent dataset, we show that the PDI is likely a monitoring tool that provides a robust assessment of water quality in the pelagial zone of the nearshore waters in Lake Erie.     

Detroit River phosphorus loads: Anatomy of a binational watershed

As a result of increased harmful algal blooms and hypoxia in Lake Erie, the US and Canada revised their phosphorus loading targets under the 2012 Great Lakes Water Quality Agreement. The focus of this paper is the Detroit River and its watershed, a source of 25% of the total phosphorus (TP) load to Lake Erie. Its load declined 37% since 1998, due chiefly to improvements at the regional Great Lakes Water Authority Water Resource Recovery Facility (WRRF) in Detroit and phosphorus sequestered by zebra and quagga mussels in Lake Huron. In addition to the 54% of the load from Lake Huron, nonpoint sources contribute 57% of the TP load and 50% of the dissolved reactive phosphorus load, with the remaining balance from point sources. After Lake Huron, the largest source is the WRRF, which has already reduced its load by over 40%. Currently, loads from Lake Huron and further reductions from the WRRF are not part of the reduction strategy, therefore remaining watershed sources will need to decline by 72% to meet the Water Quality Agreement target - a daunting challenge. Because other urban sources are very small, most of the reduction would have to come from agriculturally-dominated lands. The most effective way to reduce those loads is to apply combinations of practices like cover crops, buffer strips, wetlands, and applying fertilizer below the soil surface on the lands with the highest phosphorus losses. However, our simulations suggest even extensive conservation on those lands may not be enough.     

The Zebra Mussel Dreissena polymorpha Found in North America in 1986 and 1987

The zebra mussel Dreissena polymorpha was first detected in the western basin of Lake Erie, Ontario, Canada, on natural gas wellheads and well markers between April and November 1986. It was found again in 1987 on the north shore of Lake Erie in a water treatment plant, and in vessel fouling. The population increased in Lake Erie in 1988. Dreissena may have spread from Lake Erie to Lake St. Clair, where it was then discovered on 1 June 1988.     

A hydrodynamic approach to modeling phosphorus distribution in Lake Erie

The purpose of this paper is to show how a high-resolution numerical circulation model of Lake Erie can be used to gain insight into the spatial and temporal variability of phosphorus (and by inference, other components of the lower food web) in the lake. The computer model simulates the detailed spatial and temporal distribution of total phosphorus in Lake Erie during 1994 based on tributary and atmospheric loading, hydrodynamic transport, and basin-dependent net apparent settling. Phosphorus loads to the lake in 1994 were relatively low, about 30% lower than the average loads for the past 30 years. Results of the model simulations are presented in terms of maps of 1) annually averaged phosphorus concentration, 2) temporal variability of phosphorus concentration, and 3) relative contribution of annual phosphorus load from specific tributaries. Model results illustrate that significant nearshore to offshore gradients occur in the vicinity of tributary mouths and their along-shore plumes. For instance, the annually averaged phosphorus concentration can vary by a factor of 10 from one end of the lake to the other. Phosphorus levels at some points in the lake can change by a factor of 10 in a matter of hours. Variance in phosphorus levels is up to 100 times higher near major tributary mouths than it is in offshore waters. The model is also used to estimate the spatial distribution of phosphorus variability and to produce maps of the relative contribution of individual tributaries to the annual average concentration at each point in the lake.     

Estimating the Extent of Reduction Needed to Statistically Demonstrate Reduced Non-Point Phosphorus Loading to Lake Erie

The need to reduce non-point phosphorus contributions to Lake Erie has led to extensive efforts to implement conservation tillage in the Lake Erie basin. Because annual loads are highly variable, statistical approaches will be required to document the success of conservation tillage and other best management practices in reducing loads. Important management issues are how large a reduction will be required, and how long it will take to achieve the needed reduction. In response to these issues, a method is presented for estimating the amount of change needed to establish a statistically significant reduction, based on the standard t-test. Analysis of data from the Sandusky River, a north-central Ohio tributary of Lake Erie, indicates that the necessary change is about 35% of the current loads. When the loads are adjusted for variations in discharge, the necessary change can be reduced to about 20%. Based on projections of the Army Corps of Engineers of adoption rates of conservation tillage, and the associated effects on phosphorus loads, a 35% change would take 25 years or more, but a 20% change would occur by the end of 8 years. The documentation of these changes will require high quality monitoring data, collected before and during the implementation period with the same sampling strategy.     

Monitoring Cladophora Growth Conditions and the Effect of Phosphorus Additions at a Shoreline Site in Northeastern Lake Erie

A study to measure environmental conditions, Cladophora standing crop, internal nutrient levels, and the effect of the addition of phosphorus to Cladophora growth at a single location on the north shore in the eastern basin of Lake Erie is described. In 1979, the mean standing crop for depths 0.5–3 m was 431 gDW/m² as measured at the time of maximum standing crop in early July. Thereafter, the alga was sloughed and carried ashore causing a rapid decline in standing crop. These events coincided with the attainment of lake temperatures exceeding 20° C. Total phosphorus concentrations averaged about 18 μg P/L while soluble reactive phosphorus levels remained near the limit of detection. Stoichiometric ratios of nitrate nitrogen to soluble reactive phosphorus approximated 150:1, suggestive of phosphorus limited conditions. Internal phosphorus and nitrogen levels averaged about 0.06% and 1.80%, respectively. In 1980, phosphorus (0.34 kg/day) was discharged at the 0.5 m depth commencing July 19. No response was noted until the water temperature dropped below 20° C in September when a rapid regrowth occurred, apparently in response to the nutrient addition. It is concluded that Cladophora grows in response to available phosphorus in the eastern basin of Lake Erie and that limitation of this nutrient may be expected to reduce Cladophora growth.     

The Status of Limnocalanus macrurus (Copepoda: Calanoida: Centropagidae) in Lake Erie

The calanoid copepod Limnocalanus macrurus showed large declines in abundance and a narrowing of spatial distribution with the onset of cultural eutrophication and increases in rainbow smelt (Osmerus mordax) abundances in Lake Erie in the mid 20th century. Since 1995, however, Limnocalanus macrurus appears to have repopulated in western Lake Erie to levels of abundance that have not been observed since the late 1930s. We hypothesize that phosphorus abatement and the subsequent decrease in low dissolved oxygen events have assisted this resurgence. However, Limnocalanus macrurus abundances have not increased in the central and eastern basins, even though water quality has improved there too. High densities of rainbow smelt and associated smelt predation pressure in the central and eastern basins may be responsible for the low numbers in these basins.     

Updated phosphorus loads from Lake Huron and the Detroit River: Implications

The binational Great Lakes Water Quality Agreement (GLWQA) revised Lake Erie’s phosphorus (P) loading targets, including a 40% western and central basin total P (TP) load reduction from 2008 levels. Because the Detroit and Maumee River loads are roughly equal and contribute almost 90% of the TP load to the western basin and 54% to the whole lake, they have drawn significant policy attention. The Maumee is the primary driver of western basin harmful algal blooms, and the Detroit and Maumee rivers are key drivers of central basin hypoxia and overall western and central basin eutrophication. So, accurate estimates of those loads are particularly important. While daily measurements constrain Maumee load estimates, complex flows near the Detroit River mouth, along with varying Lake Erie water levels and corresponding back flows, make measurements there a questionable representation of loading conditions. Because of this, the Detroit River load is generally estimated by adding loads from Lake Huron to those from the watersheds of the St. Clair and Detroit rivers and Lake St. Clair. However, recent research showed the load from Lake Huron has been significantly underestimated. Herein, I compare different load estimates from Lake Huron and the Detroit River, justify revised higher loads from Lake Huron with a historical reconstruction, and discuss the implications for Lake Erie models and loading targets.     

Re-eutrophication of Lake Erie: Correlations between tributary nutrient loads and phytoplankton biomass

Both abiotic and biotic explanations have been proposed to explain recent recurrent nuisance/harmful algal blooms in the western basin and central basin of Lake Erie. We used two long-term (> 10 years) datasets to test (1) whether Lake Erie total phytoplankton biomass and cyanobacterial biomass changed over time and (2) whether phytoplankton abundance was influenced by soluble reactive phosphorus or nitrate loading from agriculturally-dominated tributaries (Maumee and Sandusky rivers). We found that whereas total phytoplankton biomass decreased in Lake Erie's western basin from 1970 to 1987, it increased starting in the mid-1990s. Total phytoplankton and cyanobacterial seasonal (May–October) arithmetic mean wet-weight biomasses each significantly increased with increased water-year total soluble reactive phosphorus load from the Maumee River and the sum of soluble reactive phosphorus load from the Maumee and Sandusky rivers, but not for the Sandusky River alone during 1996–2006. During this same time period, neither total phytoplankton nor cyanobacterial biomass was correlated with nitrate load. Consequently, recently increased tributary soluble reactive phosphorus loads from the Maumee River likely contributed greatly to increased western basin and (central basin) cyanobacterial biomass and more frequent occurrence of harmful algal blooms. Managers thus must incorporate the form of and source location from which nutrients are delivered to lakes into their management plans, rather than solely considering total (both in terms of form and amount) nutrient load to the whole lake. Further, future studies need to address the relative contributions of not only external loads, but also sources of internal loading.