Differences in Ecosystem Carbon and Nitrogen Storage of an Artificial Wetland and Local Wetlands in Southern California

Wetland ecosystems are among the most biologically productive ecosystems on Earth, yet they are being lost and degraded at an alarming rate. A growing trend to offset this loss is to construct artificial wetlands to replace the destroyed natural wetlands, yet our understanding of how to construct artificial wetlands, and make them functional, is vastly underdeveloped. This study sampled stocks of nitrogen (N) and carbon (C) in an artificial wetland on the California State University San Marcos (CSUSM) campus and compared them to stocks from local wetlands. Samples were taken from both plant biomass and soil to assess the stocks of C and N throughout the wetlands. Plant cover was also measured at each site via a line-intercept method. We hypothesized that C and N stocks would be significantly lower in the artificial wetland than the natural wetlands due to the young age of the artificial wetland while plant cover and biodiversity (species richness) would be similar across all wetlands. The study revealed a large degree of variation among the three wetlands and that soil and vegetation C and N stocks of the CSUSM wetland appeared to plateau after 11 years. However, the CSUSM wetland C and N stocks and plant cover were higher than, or comparable to, the two local wetlands. Plant species composition was unique for each wetland, with only five species shared among two or more sites. The local wetlands showed a great deal of variation between themselves. Batiquitos showed very low soil and plant C and N stocks, while the site at Cannon Road had much higher stocks, especially in its plant biomass. While this study demonstrated that CSUSM was functioning at least on par with local wetlands, it also raises a number of implications regarding the functional status of wetlands in California. The two local wetlands have a history of anthropogenic disturbance and alteration. California wetlands, both those sampled in this study and those from other studies, showed high variability amongst themselves. In some comparisons, artificial wetlands seem to sequester nutrients even better than a natural wetland, but in other comparisons, failed to match nutrient stocks. This high variability can originate from differences in wetland hydrology, plant abundance and species composition, differences in surrounding terrain, and anthropogenic alterations. California wetlands had much lower nutrient stocks compared to wetlands in other parts of the U.S., which is presumably caused by regional differences in hydrology.