Interacting watershed size and landcover influences on habitat and biota of Lake Superior coastal wetlands

Coastal wetlands are important contributors to large-lake productivity and biodiversity and mediators of lake - watershed interactions. This study explores whether the size of the watershed in which coastal wetlands are embedded (a measure of strength of connection to the terrestrial landscape) influences their background condition and response to anthropogenic landuse. Water quality, substrate, vegetation structure, and composition of zoobenthos, turtles, crayfish, and fish were characterized in 32 Lake Superior coastal wetlands in the summers of 2000-2001, and related to watershed size categories via ANOVA and to watershed development (percent agricultural and urban landuse) via linear regression. Lake Superior coastal wetlands had relatively low levels of watershed development - apparently not enough to significantly alter fish composition. However, watershed development was associated with significant changes in substrate, turbidity, plant structure, and zoobenthos, and in most cases these effects were stronger in wetlands having big rather than small watersheds. An alternate classification contrasting exposure to versus protection from river influences was not effective at resolving responses to watershed development. Watershed size had little effect on background conditions in minimally disturbed wetlands, although turtles were more abundant in large-watershed wetlands. The role of watershed size in mediating responses to landuse merits further study, but our findings suggest that receiving inflows from bigger watersheds affects coastal wetlands primarily by amplifying transmission of disturbance rather than via direct impacts of flow.