Runoff from simulated rainfall in 2 montane riparian communities.

Abstract

Riparian ecosystems are the final terrestrial zone before runoff water enters a stream. They provide the last opportunity to decrease non-point source pollution delivery to streams by removing sediments from overland water flow from uplands and roads. To quantify processes of sediment transport, filtration and deposition, it is necessary to determine runoff characteristics for the area. A rotating boom rainfall simulator was used to evaluate the effects of 3 vegetation height treatments (control, 10-cm stubble height, and clipped to the soil surface) in 2 montane riparian plant communities (grass and sedge) on runoff characteristics. Each rainfall simulation event consisted of 2 phases, a dry run of about 60 min followed by a wet run approximately 30 min later. There were no differences in time to runoff initiation for either dry or wet runs that could be attributed to vegetation height treatments for either plant community. It usually required more time for runoff to be initiated in the sedge community compared to the grass community. Generally, there were lower equilibrium runoff percentages from dry runs in the sedge community compared with the grass community. These differences were less during wet runs. Several runoff parameters had characteristics of runoff from water repellent soils. The organic layer on the soil surface exhibited signs of water repellency that reduced the water infiltration rate during the initial stages of a rainfall simulation. These results indicate that runoff and infiltration processes in the surface organic horizon of riparian zones may not respond in the classical manner. This characteristic has important implications if criteria developed in areas with less organic matter on the soil surface are used to manage overland flow in the zone. Additional studies are needed to fully describe infiltration and runoff processes in riparian plant communities.