Exports of dissolved ammonium (NH4 +) during storm events across multiple catchments in a glaciated forested watershed.

Storm event exports of dissolved $$ {\text{NH}}^{ + }_{4} $$ were explored for multiple events in the Point Peter Brook watershed (PPBW), a glaciated, forested watershed located in Western New York, USA. Investigations were performed across four catchments (1.6–696 ha) with varying topography and the extent of surface-saturated areas. While wetland and riparian waters were important sources of $$ {\text{NH}}^{ + }_{4} $$ during non-storm periods, throughfall and litter leachate were the dominant contributors of $$ {\text{NH}}^{ + }_{4} $$ during storm events. Ammonium concentrations in catchment discharge displayed a sinusoidal seasonal pattern with a maximum during early spring (March) and a minimum in late summer (August–September). Storm event concentrations of $$ {\text{NH}}^{ + }_{4} $$ in streamflow were much greater than baseflow values and showed a consistent temporal pattern with an increase in concentrations on the hydrograph rising limb, a peak at or before the discharge peak, followed by a decline in concentrations. Storm event patterns of DON were similar to $$ {\text{NH}}^{ + }_{4} $$ while the patterns of $$ {\text{NO}}^{ - }_{3} $$ differed from $$ {\text{NH}}^{ + }_{4} $$ for the summer and fall events. The storm event expression of $$ {\text{NH}}^{ + }_{4} $$ was attributed to throughfall and throughfall-mediated leaching of the litter layer. The reactive behavior of $$ {\text{NH}}^{ + }_{4} $$ precluded its use in an end member mixing model (EMMA) for predicting streamflow concentrations. While concentrations of $$ {\text{NH}}^{ + }_{4} $$ in precipitation and streamflow were high for the spring events, exports of $$ {\text{NH}}^{ + }_{4} $$ in streamflow were highest for the large and intense storm events. Baseflow $$ {\text{NH}}^{ + }_{4} $$ concentrations increased with the percent wetland/saturated area in the catchment but the same trend did not hold for storm-event concentrations. [ABSTRACT FROM AUTHOR]