Baseflow and Stormflow Transport of Nutrients from Mixed Agricultural Watersheds

Many of the reported nutrient losses from agricultural areas, especially where artificial subsurface drainage is not present, have been from surface runoff. In unglaciated, well drained silt loams in eastcentral Ohio, a portion of the infiltrated rainfall moves through the soil returning to the surface at springs or seep areas. Such return flow often creates a constant baseflow in multi-hectare watersheds. The purposes of this study were to compare relative water and nutrient transports via storm runoff with amounts removed in continuous baseflow and to evaluate the influence of different management practices on such transport. Baseflow and storm runoff from four watersheds with different land use practices were measured, sampled, and analyzed for these comparisons. In two watersheds, 123 and 32.1 ha in size, containing woodland, pasture, and row crops, the majority of N moved from the watersheds in the storm runoff; however, 25 to 50% of the N transport was via baseflow. Using 10-yr averages, 5.0 and 2.8 kg/ha of mineral N were annually transported from the 123-ha watershed via 242 and 196 mM of storm runoff and baseflow, respectively; from the 32-ha watershed, 3.6 and 3.2 kg/ha of mineral N were annually transported via 144 and 198 mm of storm runoff and baseflow, respectively. Mineral N transport from a 28.8-ha poor practice pasture watershed and from a 17.7-ha wooded watershed was less than above, but the proportions in storm runoff and baseflow were similar. Although stormflow was the larger transport pathway for nutrients leaving a watershed, a sizable portion of the nutrients can be carried with the baseflow. This comparison of watersheds in an unglaciated area indicates that there is a negligible difference in the quality of water leaving an unfertilized wooded area or unfertilized pasture or a watershed that receives fertilization on 55% of its area. Joint contribution from USDA-ARS and OSU/OARDC.