Runoff Water Quality from a Sierran Upland Forest, Transition Ecotone, and Riparian Wet Meadow

High concentrations of inorganic N, P, and S have been reported in overland and litter interflow within forested uplands of the Tahoe basin and surrounding watersheds. In this study we compared runoff nutrient concentration and load as well as soil nutrient fluxes at three watershed locations; an upland forest, a transitional ecotone consisting of forest and meadow vegetation, and a down gradient riparian wet meadow immediately adjacent to Sagehen Creek at the U.C. Berkeley Sagehen Experimental Forest near Truckee, CA. Three parallel transects (one at each watershed location) consisting of four sampling points each were delineated. Runoff collectors, rain gages, snowmelt collectors, and resin capsules were installed along each transect. Runoff, precipitation, snowmelt, and groundwater samples were collected and analyzed for NO3--N, NH4+-N, PO43--P, and SO42-. Both discharge concentrations and loads were statistically similar among the upland forest, ecotone, and riparian wet meadow locations, indicating little effect from differences in ecological or physical processes. Model estimated data trends, however, suggested the presence of higher discharge concentrations of NH4+ N for upland and wet meadow sites compared with the transition ecotone, and higher discharge loads of NO3--N from the wet meadow compared with either the upland or transition ecotone sites. Overall, the wet meadow riparian zone at our Sierra Nevada study location did not appear to be as effective at intercepting and retaining high nutrient loads as commonly presumed, and by virtue of the observed data trends in some instances, may have been a contributing source.