Temporal and spatial trends in streamwater nitrate concentrations in the San Bernardino Mountains, southern California

We report streamwater nitrate (NO3-) concentrations for December 1995 to Se ptember 1998 from 19 sampling sites across a N deposition gradient in the S an Bernardino Mountains. Streamwater NO3- concentrations in Devil Canyon (D C), a high-pollution area, and in previously reported data from the San Gab riel Mountains 40 kin northeast of Los Angeles, are the highest value repor ted in North America for undisturbed forest or shrub land watersheds. Conce ntrations in the primary stream draining western DC peaked at 350 mu mol L- 1 in December 1997 and minimum base flow NO3- concentrations were nearly al ways greater than or equal to 80 mu mol L-1. In the San Gorgonio Wilderness (SGW), average NO3- concentrations in four streams along the southern tran sect (moderate N deposition), ranged from 10 to 37 mu mol L-1, while averag e NO3- concentrations were less than or equal to 0.7 mu mol L-1 in seven st reams along the northern transect (low N deposition), Peak NO3- concentrati ons in DC and in the SGW occurred after large winter storms, and a large sp ike in NO3- concentrations (10-370 pmol L-l) in SGW Streams 1 to 5 was obse rved after thundershower activity in July 1997. Streamwater export of NO3-N from Devil Canyon ranged from 3.6 to 11.6 kg ha(-1) yr(-1) during water Se ars 1995 to 1998. This study further indicates that N emissions from fossil fuels and agriculture impact not only air quality, but also water quality from watersheds that are recipients of atmospheric N deposition.