Carbon and nitrogen storage of constructed and natural freshwater wetlands in southern California

Artificial wetlands are often constructed to replace degraded natural wetlands; however, it is unclear whether constructed wetlands can become functionally equivalent to natural wetlands. We used measurements of soil and plant nitrogen (N) and carbon (C) storage as indicators of initial function in an artificial wetland in southern California, and compared them to the C and N stocks of local naturally occurring wetlands. We hypothesized that C and N stocks would be significantly lower in the constructed wetland. Soil and vegetation C and N stocks of the constructed wetland increased rapidly but plateaued after 6 years, and soil C and N stocks of the constructed wetland were higher than, or comparable to, local natural wetlands. Limited comparisons between constructed and natural freshwater wetlands reported in the literature illustrated high variability in ecosystem C and N storage, but soil C and N stocks in artificial wetlands were significantly lower than in natural wetlands. Southern California wetlands had lower soil C and N storage compared to other temperate zone wetlands, which may be due to the highly variable rainfall and flow regimes of semi-arid wetlands in southern California.