Comparison of soil organic carbon dynamics in forested riparian wetlands and adjacent uplands

Wetland riparian soils typically have greater C pools than adjacent uplands, yet quantifying soil organic C (SOC) sequestration in riparian systems remains difficult. Quantification of major inputs and losses of autochthonous SOC through process-based measurements would allow for better comparisons between riparian and upland systems. In this study, we quantified major soil C fluxes within five paired headwater riparian and upland sites in Rhode Island. The difference between total C inputs and losses were used to construct net annual landscape-scale SOC sequestration rates. Annual SOC inputs were statistically similar between landscapes, with the exception of those from understory herbaceous vegetation, which were significantly greater (p < 0.001) in riparian zones than uplands. Mean annual C losses via soil respiration were also statistically similar between landscapes, but estimates of microbial respiration (actual loss of SOC) were significantly less (p < 0.01) in riparian ecosystems. Thus, riparian forests had greater net annual SOC sequestration (range 2.4-3.4 Mg C ha^-1yr^-1) than paired upland sites (range 0.4-2.1 Mg C ha^-1yr^-1). Our results suggest that process-based SOC sequestration measures can yield similar results to traditional methods, such as chronosequences, but our averaged estimates (2.0 Mg C ha^-1yr^-1) were greater than those typically reported using alternate approaches.