Big Creek runs north of the Big Creek Marsh and discharges its runoff directly into the Inner Bay of Long Point. However, a few channels provide movement of the creek water into the marsh, which, with the exception of a few small culverts, does not have a direct outlet to the Bay itself. The nutrient dynamics of coastal wetlands differ from those of inland wetlands where the majority of nutrients are retained and peat tends to accumulate as a nutrient sink (Sloey et al. 1978). Nevertheless, causeway construction in 1925 closed most of the outlet of Big Creek Marsh to Long Point Bay and Lake Erie (Figure 1.1), thereby increasing the proportion of nutrients retained within the marsh (see Heath 1992). Consequently, Big Creek Marsh has a very high tendency to retain both nutrients and metals and this has resulted in its being eutrophic.
Several nutrient transformation processes within marshes (sorption, coprecipitation, active uptake, nitrification and denitrification) remove phosphorus and nitrogen and other suspended loads from the water and deliver them to the substrate and biota, much of which is eventually incorporated to support new microbial and plant growth (Sloey et al. 1978). Excesses are eventually exported down-gradient (Wetzel 1992). This is supported by the fact that the N, P, and K concentrations in Big Creek are higher than in the marsh and in the Inner Bay (Wade 1979). Big Creek Marsh serves as a regulator of the nutrients, organic matter and sediment-associated contaminants transported from Big Creek into Long Point Bay (Murdoch 1981). While the high nutrient load in Big Creek runoff makes Big Creek Marsh very productive, the closed nature of the system and susceptibility of wetlands to pesticide contamination make responsible agricultural activities in the catchment paramount to the long-term ecological functioning of Big Creek Marsh.
The Long Point causeway probably impedes the transfer of nutrients from the Inner Bay and Lake Erie to the Big Creek Marsh, while providing protection from destructive wave energy and ice scouring. However, Big Creek Marsh still experiences the effects of short term (seiches) and long term (successive years of high or low precipitation) changes in Lake Erie water levels, which are necessary to sustain productivity (Ball 1985; Kaminski et al. 1989; Neill 1990). Lake Erie has a much stronger influence on the ecology of the Inner Bay than does Big Creek Marsh.
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