The impact of storm events on solute exports from a glaciated forested watershed in western New York, USA

This study analysed the importance of precipitation events from May 2003 to April 2004 on surface water chemistry and solute export from a 696 ha glaciated forested watershed in western New York State, USA. The specific objectives of the study were to determine: (a) the temporal patterns of solutes within individual storm events; (b) the impact of precipitation events on seasonal and annual export budgets; and (c) how solute concentrations and loads varied for precipitation events among seasons as functions of storm intensity and antecedent moisture conditions. Analysis of solute trajectories showed that NH 4 + , total Al and dissolved organic nitrogen (DON) peaked on the hydrograph rising limb, whereas dissolved organic carbon (DOC) concentrations peaked following the discharge peak. Sulphate and base-cations displayed a dilution pattern with a minimum around peak discharge. End-member mixing analysis showed that throughfall contributions were highest on the rising limb, whereas valley-bottom riparian waters peaked following the discharge peak. The trajectories of NO 3 - concentrations varied with season, indicating the influence of biotic processes on the generation, and hence flux, of this solute. Storm events had the greatest impact on the annual budgets for NH 4 + , K + , total dissolved Al, DON and DOC. Storm events during summer had the greatest impact on seasonal solute budgets. Summer events had the highest hourly discharges and high concentrations of solutes. However, NO 3 - and DOC exports during a spring snowmelt event were considerably more than those observed for large events during other periods of the year. Comparisons among storms showed that season, precipitation amount, and antecedent moisture conditions affected solute concentrations and loads. Concentrations of solutes were elevated for storms that occurred after dry antecedent conditions. Seven of the largest storms accounted for only 15% of the annual discharge, but were responsible for 34%, 19%, 64%, 13%, 39% and 24% of the annual exports of NH 4 + , K + , Al, NO 3 - , DON and DOC respectively. These results suggest that the intense and infrequent storms predicted for future climate-change scenarios will likely increase the exports of solutes like DOC, DON, NH 4 + , Al and K + from watersheds.

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