Hydrologic responses of a montane riparian ecosystem following cattle use

Abstract

Riparian areas link streams with their terrestrial catchments and decrease water pollution by trapping sediments from upland sources before they reach streams or lakes. Livestock grazing in riparian areas is a controversial practice. If not properly managed, cattle can cause degradation to both the riparian zone and adjacent water body. Vegetative, soil microtopographical, microchannel and hydrograph parameters were measured in a montane riparian community in northern Colorado to quantify the effects of cattle on overland flow and runoff characteristics. Treatments were cattle grazing plus trampling, cattle trampling, mowing, and a control. Water was applied to plots (3 m x 10 m) at a rate of 100 mm hr(-1) using a rainfall simulator. Concurrently, overland flow was introduced at the upper end of the plots at an equivalent rate of 25 mm hr(-1). A high intensity-short duration grazing treatment was used for the cattle-treated plots. Reduction in vegetation stem density and aboveground biomass by cattle decreased microchannel sinuosity and drainage density. Cattle-treated plots had greater flow velocities and depths in microchannels compared with mowed and control plots. Reduced stem density and aboveground biomass by grazing left fewer obstacles to divert flows, which decreased microchannel sinuosity and drainage density. Flows were concentrated into fewer microchannels with deeper flows. Microchannel characteristics were not significant factors affecting total runoff. Stem density and rainfall intensity were the most important factors in predicting runoff characteristics and total runoff. Results from this study have improved our understanding of flow and runoff processes following cattle use of a riparian ecosystem.