Water quality in Great Lakes coastal wetlands: Basin-wide patterns and responses to an anthropogenic disturbance gradient

We present water quality data from 58 coastal wetlands, sampled as part of a larger effort investigating effects of nutrient enrichment and habitat disruption in the Laurentian Great Lakes. Our sampling design selected sites from across a gradient of agricultural intensity within combinations of biogeographic ecoprovince and wetland hydromorphic type and captured a large range in water quality. Levels of total nutrients (N and P), and various measures of particulate concentration, water clarity, and ionic strength were strongly associated with agricultural intensity in the watershed, and could be effectively aggregated into an overall principal component-based water quality descriptor. Lake Erie wetlands had the highest nutrient levels and lowest water clarity, while wetlands in Lakes Superior and Huron had the lowest nutrient levels and clearest water. Lake Ontario wetlands had clearer water than would be expected from their nutrient levels and position on the agricultural intensity gradient. Dissolved oxygen, silica, pH, and dissolved organic carbon (DOC) were independent of agricultural intensity but DOC was responsible for low water clarity in some Lake Superior wetlands. Simple classification by hydromorphic type (riverine or protected) did not explain water quality differences among wetlands exposed to similar agricultural intensity levels, so finer hydrologic classification may be desirable. Results are used as a basis for discussing research and information needs underlying development of water quality criteria and monitoring programs for coastal wetlands of the Great Lakes.