3.0 Sedimentation of Long Point Bay

3.4 Potential impacts of increased sedimentation on waterfowl habitat

Sedimentation is a natural process. However, increased rates of sedimentation resulting from human activities can increase water turbidity, adversely affect water quality, influence the composition of wetland sediments, and ultimately affect the rate of wetland succession.

Increased water turbidity results in decreased light penetration. As plants require light for photosynthesis, any increase in turbidity can affect the species composition and abundance of submerged aquatic plants, thereby influencing the availability of foods to migrating waterfowl. For instance, wild celery, an important food for Canvasbacks at Long Point, only grows well in relatively clear water. Increased turbidity also decreases the light available to other aquatic organisms, such as invertebrates.

Contaminants (metals, pesticides) and nutrients (phosphorus, nitrogen) readily attach to, and are transported by sediments. A large portion of sediment-associated contaminants and nutrients can be released into receiving waters (e.g. Big Creek Marsh and the Inner Bay) through desorption in microbial processes (Downey et al. 1994). Fine, clay-sized sediment in particular, because of its large surface area, readily absorbs contaminants and nutrients (Lee et al. 1981); 90% of the sediment deposited into Lake Erie is either fine-grained clay or silt (Kemp et al. 1976). As wind-generated surface waves serve to periodically re-suspend fine sediments, deposited material can act as a continual source of contaminants and nutrients (Luettich Jr. et al. 1990; Matisoff and Eaker 1992). This can be problematic because both contaminants and nutrients can seriously impede the ecological function of wetland ecosystems (details are discussed in Chapter 4). One major problem associated with sediment-associated contaminants is that they can remain within the aquatic system for many years. For instance, extensive use of DDT to control cutworm and hornworm in the Big Creek drainage basin prior to 1970 was still detectable in Big Creek and Big Creek Marsh sediments over a decade later (Murdoch 1980).

Not only do intensive farming practices result in the loss of valuable topsoil, they also contribute to the gradual infilling of Big Creek Marsh and the Inner Bay through increased sedimentation. This adversely affects commercial, industrial and recreational water uses (Environment Canada 1993), while decreasing the life expectancy of the Inner Bay as a suitable waterfowl staging area. Since many species of Great Lakes fish use coarse substrates as spawning and nursery habitat, the increased deposition of fine sediments in the Inner Bay will also adversely affect recreational and commercial fishing. While the rate of accumulation has not been adequately studied at Long Point over time, it is known that sediment accumulation on Old Woman Creek Estuary in western lake Erie increased from 0.76 mm/yr prior to the advent of row-crop agriculture in the 1800s, to about 10 mm/yr in the early 1990s (Matisoff and Eaker 1992). This may be cause for concern at Long Point, as there has been a substantial increase in corn production in the Big Creek catchment over the past forty years (see Chapter 9).