Coastal wetlands on Lake Superior are hydrologically complex ecosystems situated at the interface of upland catchments and the oligotrophic lake. Little is known about nutrient dynamics within coastal wetlands or their role in modifying or contributing to nutrient fluxes from watersheds to Lake Superior. We conducted an intensive study of Lost Creek Wetland (LCW) near Cornucopia, WI, with the objective of determining influences of temporal variability in hydrology on dynamics and retention of N and P. We measured hydrologic inputs and distributions of inorganic and organic forms of nitrogen and phosphorus within LCW under hydrologic conditions ranging from summer base flow to spring snow melt. Our study confirms that the interrelationship between hydrologic connections to lake and tributary and seasonal variations in hydrology can regulate internal nutrient dynamics of coastal wetlands. The strength of hydrologic linkage of LCW to Lake Superior and tributary varied greatly among seasons, resulting in shifts in the relative importance of these nutrient sources and influencing spatial distribution of nutrients within the wetland. Ratios of inorganic nitrogen and phosphorus in the wetland were consistently low (< 16) indicating a potential for nitrogen limitation. Retention of inorganic nitrogen ranged from 11% to 94% and was positively related to hydraulic residence time which ranged from < 1 day during snow melt to 26 days in summer. Retention of total and soluble reactive phosphorus was generally lower than retention of inorganic nitrogen and was not related to hydraulic residence time.
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We thank Martin Auer, John Brazner, Pat Chow-Fraser, Jim Latimer, and one anonymous reviewer for thoughtful and constructive reviews of this manuscript. We also thank Susan Siragusa, Andrea Grygo, Meaghan Tredrea, and Scott Johnson for assistance with field sampling and chemical analysis. This research was funded by the U.S. Environmental Protection Agency. It has been subjected to review by EPA’s National Health and Environmental Effects Research Laboratory and approved for publication. Approval does not signify that the contents reflect the views of the Agency nor does mention of trade names or commercial products constitute endorsement or recommendation for use.
- Coastal wetlands