DRY DEPOSITION OF NITROGEN AND SULFUR TO PONDEROSA AND JEFFREY PINE IN THE SAN-BERNARDINO NATIONAL FOREST IN SOUTHERN CALIFORNIA

Little is known about the concentrations, deposition rates, and effects of nitrogenous and sulfurous compounds in photochemical smog in the San Bernardino National Forest (SBNF) in southern California. Dry deposition of NO3- and NH4+ to foliage of ponderosa pine (Pinus ponderosa Laws.) and Jeffrey pine (Pinus jeffreyi Grev. & Balf.) was correlated (R = 0.83-0.88) with historical average hourly O3 concentrations at 10 sites across an O3 gradient in the SBNF. Mean deposition fluxes of NO3- to ponderosa and Jeffrey pine branches were 0.82 nmol m-2 s-1 at Camp Paivika (CP), a high-pollution site, and 0.19 nmol m-2 s-1 at Camp Osceola (CAO), a low- pollution site. Deposition fluxes of NH4+ were 0.32 nmol m-2 s-1 al CP and 0.17 nmol m-2 s-1 at CAO, while mean values for SO42- were 0.03 at CP and 0.02 nmol m-2 s-1 at CAO. Deposition fluxes to paper and nylon filters were higher in most cases than fluxes to pine branches at the same site. The results of this study suggest that an atmospheric concentration and deposition gradient of N and S compounds occurs along with the west-east O3 gradient in the SBNF. Annual stand-level dry deposition rates for S and N at CP and CAO were estimated. Further studies are needed to determine if high N deposition loads in the SBNF significantly affect plant/soil nutrient relations, tree health, and the response of ponderosa pine to ozone.