Water Quality Improvement Benefits of Restored and Natural Wetlands and Riparian Buffers.

We compared nitrogen (N) and phosphorus (P) retention and removal in natural and WRP (Wetland Reserve Program)-restored wetlands and in natural and CRP (Conservation Reserve Program)-restored riparian buffers in Indiana to characterize water quality improvement benefits of restoration practices in the region.  Four soil cores were collected from four plots within each of ten natural and restored wetlands and four natural and restored riparian buffers and were used to measure ambient and potential denitrification, phosphorus sorption index (PSI), and total N and P sequestration in soil. 

Ambient and potential denitrification were 2 to 3 lower in restored sites compared to natural sites.  Denitrification was higher in the riparian sites compared to wetlands, which was attributed to higher NO₃^- levels in the riparian sites.  There was no difference in PSI between natural and restored sites within each system (wetland, riparian), though PSI was five times higher in riparian sites relative to wetlands.  Total N and total P accumulation in the natural wetlands ranged from 3.0 to 8.1, and 0.19 to 0.59 g/m²/yr, respectively, based on ¹³⁷Cs, bulk density, and total N and P concentrations.  In the restored wetlands, total N and P sequestration rates averaged 1.1 and 0.15 g/m²/yr, respectively. 

Our findings suggest that natural wetlands and riparian buffers remove more N from the landscape via denitrification and soil accumulation than restored WRP and CRP sites.  Also, riparian sites remove more P than wetlands, which is likely related to a higher clay content relative to the sandier, wetland soils.  Overall, riparian systems remove more N and P as compared to wetlands.  Given sufficient time to develop, restored WRP and CRP sites may perform ecosystem services comparable to their natural counterparts.