3.0 Sedimentation of Long Point Bay

3.2 Sediment characteristics of Big Creek Marsh and Long Point Bay

Most of the Big Creek watershed is rural; consequently, sediment loads to the creek are from diffuse sources. The primary anthropogenic causes of increased sedimentation and turbidity are forest clearing and cultivation of the land. Big Creek runs along the northern border of Big Creek Marsh before draining into the Inner Bay, and consequently influences the sediment characteristics of this wetland. Deforestation associated with European settlement activity initially led to marked changes in the vegetation and sedimentation rate (Reeder and Eisner 1994). This suggests that upland landscape change can play an indirect yet important role in patterns of coastal wetland development. Very little has been published on the chemical quality of sediments or their rates of accrual or depletion in coastal wetlands of the Great Lakes (Mitsch 1992). Sediments that have accumulated within Long Point Bay, increase in depth from east to west, and have resulted in the progressive shallowing of the water (Mudroch 1984). Evidence suggests that the initial aquatic environment was relatively deep and open, and as recently as 1000 BP, the Big Creek Marsh area formed part of the Inner Bay. The construction of the causeway along the eastern boundary of Big Creek in 1925 probably increased the amount of sediment that is retained within the Big Creek Marsh. This can be attributed largely to the fact that a few channels permit creek water to enter the marsh, yet the limited number of small culverts that were built under the causeway have silted in resulting in there being presently no direct outlet from Big Creek Marsh to the Inner Bay. The major size fraction of the sediment in Big Creek Marsh is silt (Murdoch 1980).

Big Creek is also the primary source of suspended sediments to the Inner Bay (Berst and McCrimmon 1966). The continual input of sediments to the Bay, and restricted water circulation, cause sediment to be accumulated and the Inner Bay to become shallower and marshier each year. It has been suggested that the Bay will eventually silt in completely, especially given the fact that the entire eastern basin of Lake Erie continues to experience isostatic lift from the pressure of Pleistocene ice sheets (Heathcote 1981). Surprisingly, with the exception of broad scale sediment characteristics, little is known about the sediment of Long Point Bay. Smith (1979) found that the bottom of the Inner Bay from the western shorelines to about 2 km offshore was primarily mud (Figure 3.1). This can be attributed to the fact that sedimentation near the mouth of Big Creek has created a deltaic deposit (Heathcote 1981). Sandy sediments exist along the north and south shore of Long Point, while sandy mud covers most of the central and northeastern part of the Bay.