Soil carbon and nutrient and vegetation dynamics of a constructed freshwater wetland on the campus of California State University, San Marcos

Background/Question/Methods: Wetland construction has been increasing over the last 1-2 decades as natural wetlands are degraded by development and wetland construction is viewed as a viable alternative for mitigation.  On the campus of California State University, San Marcos (CSUSM) a 1 ha wetland was constructed in 2004 to mitigate for the filling of a natural wetland during the construction of the CSUSM student dormitories.  Vegetation monitoring by consultants contracted by the California Department of Fish and Game was completed in April 2009 and the wetland mitigation was deemed a success.  However, critical indicators of wetland function, such as soil organic matter (SOM) and nutrient accumulation and cycling, have not been assessed.  Thus, this project uses data collected from 2009 and 2011-12 to assess the accretion of SOM and to assess nutrient storage and cycling as the wetland develops. 

Results/Conclusions: Data collected in 2009 and 2012 indicates that plant cover and leaf area index were nearly identical to that reported for other natural freshwater wetlands, indicating rapid development of the plant community.  However, soil C content was still 3-times lower and total soil N was more than 1 order of magnitude lower in the constructed wetland compared to that reported for natural wetlands.  While sample analysis is ongoing, these results indicate that soil C and N storage are still well below what would be considered for a functional wetland, and suggest that typical indicators of wetland mitigation ”success,” such as plant cover and species distribution, fail to consider aspects of wetland function that may take years to develop in manmade wetlands.