Hydrologic and material budgets for a small Sonoran Desert watershed during three consecutive cloudburst floods

Abstract

Precipitation and runoff chemistry were monitored during three successive summer storms on a small Sonoran Desert catchment. Both nitrogen and phosphorus concentrations in precipitation were high (1·38 and 0·21 mg/1 respectively) yet lower than in runoff water (2·77 and 0·39 mg/1). However, 75–90 per cent of precipitation did not run off and the storm events represented net inputs of dissolved N and P to the watershed. Antecedent storms influence both water chemistry and nutrient budgets and greatly deplete transportable particulates. Because precipitation in the Sonoran Desert is variable both temporally and spatially, caution should be excercised in attempting to construct ‘typical year’ watershed nutrient budgets. Despite low rainfall and sporadic runoff, hydrologic fluxes of nitrogen and phosphorus in desert watersheds are comparable to those of mesic regions. Chloride, H+, and SO42– were retained by the watershed during these storms while HCO3− and dissolved and particulate organic matter were exported at rates higher than input by precipitation. Total dissolved solids entering in precipitation were three times export in stream flow while total particulate output greatly exceeded input in rain.