Carbon Availability in Riparian Subsoils

Riparian zones have been identified as important sinks for nitrogen (N) in various landscapes. Microbes that mediate nutrient transformations in the subsurface are frequently limited by available carbon (C). An improved understanding of C-supply to the riparian subsurface therefore presents a promising approach to understanding variation in N-removal within and between sites. Previous research has identified C-rich patches and buried soil horizons as likely C sources for denitrifiers. Our objectives are to: (1) compare C lability among buried horizons and patch types; and (2) assess relationships of C availability with depth. We sampled soil at four sites in Rhode Island and measured potential C availability using aerobic lab incubations. Preliminary data show a steep decline in C availability with depth for Oa and A horizons. C availability is greater for Oa ( ~5-30 ug C/g/d) than A-horizons and root-derived patches ( ~0-4 ug C/g/d). Patches lacking root structures had the lowest C availability ( ~0-1 ug C/g/d). These findings suggest future research priorities should include: (1) developing and testing models to predict the occurrence of buried horizons and root-derived patches among riparian zones; and (2) integrating these models with descriptions of landscape-scale variation in N-fluxes.