3.0 Sedimentation of Long Point Bay

3.3 Human causes of Increased sedimentation

The primary causes of increased Long Point Bay sedimentation and turbidity are intensive agriculture in the Big Creek watershed (Downey et al. 1994). Once forests are removed and land is cultivated, soils are much more susceptible to erosion, particularly during heavy storms. Inland wetlands act as sediment traps, thereby reducing the amount of sediment that is transported to downstream receiving waters such as Long Point Bay. Consequently, the drainage of wetlands throughout the Big Creek catchment during the past 100-150 years has probably also resulted in a substantial increase in the amount of sediment that is transported to the Big Creek Marsh and the Inner Bay. However, Old Norfolk county has retained a higher proportion of riparian vegetation than many other regions of southern Ontario, and very few farmers plough their fields in the fall (Chapter 9). Also, tobacco farming, which is the most prevalent farming practice in the Big Creek watershed, requires a winter cover crop, and this also decreases rates of soil erosion. Consequently, while farming is the major cause of increased sedimentation in the Big Creek watershed, retention of large amounts of riparian forests, combined with responsible farming practices, has resulted in Big Creek having a lower sediment load (per unit area of catchment) than many other Lake Erie tributaries (Table 3.2).

The boat channels at Port Dover, Port Rowan, and Nanticoke, as well as numerous channels used throughout the marshes, are all dredged periodically. This and the natural gas extraction throughout the Bay cause sediments to be re-suspended and relocated, and this also increases water turbidity. The construction of shore protection works, marinas, cottage development and removal of vegetation for water access, has also increased the rates of erosion and the turbidity on Long Point Bay (Stenson 1993; Downey et al. 1994). However, the contribution of these activities to the sedimentation and turbidity of Long Point Bay is probably minimal compared to inputs from Big Creek.