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

Abstract

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.

Keywords:

• Great Lakes
• watershed landuse
• hydrology
• water quality
• zoobenthos
• fish
• turtles

Acknowledgements

We thank Matthew Starry for additional GIS processing, and Michael Sierszen, John Morrice, and Jack Kelly for discussions and feedback on various aspects of this work. Comments from two anonymous reviewers helped to improve the manuscript. Although this work was fully funded by the U.S. Environmental Protection Agency, the views expressed are those of the authors and do not necessarily reflect the views or policies of the Agency.

This article not subject to United States copyright law.

Notes

¹Trebitz et al., 2009 (N = 58, correlation vs.% developed land)

²Uzarski et al., 2004 (N = 22, correlation vs.% agricultural or urban land)

³Crosbie and Chow-Fraser, 1999 (N = 22, ordination vs.% agricultural land)

⁴Lougheed et al., 2001 (N = 62, ordination vs.% agricultural or urban land)

⁵DeCatanzaro and Chow-Fraser, 2010 (N = 77, linear regression vs. road density).