Hydrologic Response of Four Ecological Sites to Natural Rainfall Events Within a Semiarid Watershed

Abstract

Understanding the capture and redistribution of water within ecological sites should improve our understanding of the function of rangeland watersheds. We compare ecological site physical properties, runoff events, and precipitation event characteristics to assess the variability in hydrologic response of four ecological sites to natural rainfall events in a semiarid watershed in southeast Wyoming, United States. Ecological sites were selected on the basis of their extent of areal coverage in the watershed and their perceived importance in watershed scale hydrologic response. At each study site, four 12-m2 runoff plots were installed with collection troughs to capture and quantify the rate and amount of runoff. A tension infiltrometer was used to measure effective saturated hydraulic conductivity at the point scale, and a data-logging rain gauge was installed at each site to measure rainfall. One-way analysis of variance (α = 0.05) was used to compare the hydrologic characteristics of ecological sties. Amounts and intensities of rainfall required to generate runoff, timing of overland flow, and peak runoff rates differed (P < 0.05) among sites in their current state. We found differences in effective hydraulic conductivity, 20.30 mm hr−1 on shallow loamy site up to 50.40 mm hr−1 on the coarse upland, and plot water storage potential, which varied from 101.8 mm on the shallow loamy site to 472.0 mm on the loamy upland site, due to differences in soil depth and porosity among sites. After normalizing runoff according to rainfall depth, we found no statistical difference (P > 0.05) in the volumes of runoff produced by different sites. The amount of runoff generated on all sites was very small, indicating high infiltration and limited ponding and overland flow. Ecological sites were shown to have different hydrologic response characteristics (i.e., timing of runoff), suggesting that they can be used to better quantify and understand the variability in hydrology in rangeland watersheds.