Controls of stream water chemistry were examined at eight catchments along a snow and rain transition at Providence (1,500 - 2,100 m) and Bull (2,000 - 2,500 m) at the Kings River Experimental Watersheds (KREW), an integrated ecosystem project for long-term research on nested headwater streams in the Southern Sierra Nevada. KREW is also the site of the Southern Sierra Critical Zone Observatory (CZO). Chemical data of stream water from water years 2004-2006 indicated that ionic concentrations in stream water were strongly correlated with catchment elevations, but the correlations varied among solutes. The mean annual ionic concentrations of major cations (Ca2+, Mg2+ and Na+) strongly decreased with an increase in the mean catchment elevations (R2 = 0.74-0.93, n = 24, p < 0.001), showing stronger geochemical weathering at catchments of lower elevations with greater groundwater discharge due to more rain than snow. Ionic concentrations of NH4+ and major anions (Cl-, NO3-, SO42-, and PO43-) in stream water showed isolated peaks with the first significant rainfall event in October each year at both Providence and Bull catchments, caused by high contents of pollutants in the atmosphere over a long, dry summer. The mean annual concentrations of SO42- and TIN (NO3- + NH4+) increased over the mean catchment elevations (R2 = 0.43 and 0.20, respectively) due to an increase in snowmelt runoff. However, the mean annual ionic concentrations of PO43- decreased over the mean catchment elevations, with a strong correlation at the basis of individual water years (R2 > 0.86, n = 8, p < 0.001). It is indicated that there was more labile P in soils at lower elevations than higher elevations. With the upwards shift of snow and rain line over time due to the climate warming, the exports of P and major cations and the retention of N would be increased in catchments of snow and rain transition.
Liu, F., Hunsaker, C.T., Bales, R.C. (2009): Controls of Stream Water Chemistry in Small catchments Across Snow/Rain Transition in the Southern Sierra, California . Fall meeting, American Geophysical Union, December 2009. 90(52). Abstract H33H-0987. .