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

Summary

   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).