Snowpack storage and release of nitrogen in the Emerald Lake Watershed, Sierra Nevada

Interactions between the storage and release of nitrogen (N) from the seasonal snowpack and basin processes were evaluated from 1985 through 1987 at the Emerald Lake Watershed, located at 2800 m in the southern Sierra Nevada, California. The volume-weighted mean annual concentrations of NH4(+) and NO3(-) in winter snow were <= 5.0 µeq/L and are among the most dilute recorded in the northern hemisphere. However, about 90% of the annual flux on NH4(+) and NO3(-) in wet deposition was supplied during the period of snowmelt runoff, due to the large percentage of annual precipitation that occurred as snow. Dry deposition in N to the seasonal snowpack was not significant relative to wet deposition. Concentrations on NH4(+) and NO3(-) in the first fraction of meltwater were 3-6 fold greater than bulk concentrations measured in co-located snow pits, an ionic pulse. Elution of NO3(-) from the snowpack in the form of an ionic pulse appeared to be the cause of seasonal maxima in NO3(-) concentration in stream waters. In contrast to the export of NO3(-) during snowpack runoff, more than 99% of the ammonium stored in the seasonal snowpack was retained in the basin. The retention of NH4(+) in the basin during snowpack runoff indicates that much of snowpack meltwater infiltrates soils before becoming stream water and that soil processes with relatively fast kinetics must be active at this time.