Aqueous‐ and Sediment‐Phase Nitrogen Yields from Five Southern Pine Watersheds

Abstract Nitrogen (N) in solution and associated with suspended sediments in stormflow from five reforested watersheds (1.5–2.8 ha) in northern Mississippi was determined during the 1975 water year. Samples were collected using Coshocton wheel samplers set below 0.91‐m H‐flumes. Mean yearly solution NH 4 ‐N and NO 3 ‐N concentrations, 0.20 and 0.01 mg/liter, respectively, did not differ among watersheds. Sediment‐N concentrations ranged from 2,410 to 6,080 µg/g and were 5.4 to 10.0 times those in the watershed soils. The N enrichment of sediment relative to soil was attributed to selective erosion of fine sediments (clay) and/or deposition of coarse sediments in transport. Significant differences in sediment N yields among the five watersheds were related to stormflow volume, sediment concentration, and sediment N concentration. Nitrogen was transported from the watersheds about equally in the sediment and solution phases. Mean solution NH 4 ‐N and NO 3 ‐N yields for the water year were 422 and 28 g/ha, respectively, for the five watersheds; mean sediment N yield was 395 g/ha. For the year, 8–17% of the precipitation was measured as stormflow; the remainder was deep seepage and evapotranspiration since there was essentially no baseflow.