The effects of land use and regional hydrology on surface water quality in the upper San Pedro River, Arizona, United States of America

The purpose of this study is to examine the effects of land use and hydrology on surface water quality in a semi-arid watershed. Six synoptic sampling events were performed along the upper San Pedro River, AZ, USA before, during, and after the 2002 monsoon season. Water samples were analyzed for conservative solutes, nutrients, and organic matter. During non-monsoon baseflow periods, conservative solutes indicated limited hydrologic connection between regions. Protected reaches had significantly higher DOC concentrations and agricultural reaches had significantly higher DON and NO3-N levels. In contrast, solute concentrations during the monsoon season indicated all regions were hydrologically linked. DOM and NO3-N concentrations increased as terrestrially derived solutes were flushed into the stream. Nutrient loads were variable suggesting that changes in nutrient concentrations were related to individual reaches. This research demonstrates that hydrologic flowpaths and land cover are important controls on surface water quality at the reach and river scales.