Throughfall and fog deposition of nitrogen and sulfur at an N-limited and N-saturated site in the San Bernardino Mountains, southern California

Inorganic nitrogen (N) and sulfur (S) deposition in bulk throughfall and fo g were determined at two sites located at opposite ends (42 km apart) of a pollution gradient in the San Bernardino Mountains. Plot-level averages for total annual N and S deposition in throughfall in 1996 were 18.8 and 2.9 k g,ha(1), respectively, at Camp Paivika (CP) and 2.9 and 0.4 kg,ha(1), respe ctively, at Barton Flats (BF). Deposition of N in throughfall in the four t ransects at CP ranged from 12.1 to 31.7 kg,ha(1)year(1). Spatial variabilit y was high because of heterogenous canopy cover and varying exposure to air pollution. Annual estimated stand-level deposition of N and S in fog were 10.9 and 1.9 kg,ha(1), respectively, at CP, and 0.6 and 0.2 kg,ha(1), respe ctively, at BF. We estimated that N deposition in fog contributed 35% of th e total annual N deposition at CP and 13% at BF. Analogous values for S wer e 39% at CP and 26% at BF. Ammonium deposition in throughfall and fog at CP were 72 and 122% as high as NO3- deposition because of elevated NH3 emissi ons from dairy farms in the Chino-Norco area 34 km southwest of CP.