Deposition and processing of airborne nitrogen pollutants in mediterranean-type ecosystems of southern California

Abstract

Atmospheric nitrogen deposition, associated with chronic urban air pollution, has produced stream water nitrate concentrations as high as 7.0 mg of N L^-l in chaparral watersheds in the San Gabriel Mountains of Los Angeles County, CA. Stream water [NO₃^-] and discharge were greatest at high flow and may contribute significantly to existing groundwater NO₃^- pollution. Annual NO₃^- discharge ranged from 0.04 to 10.0 kg of N ha^-1 over 4 years. Canopy throughfall and precipitation inputs of 23.3 and 8.2 kg of N ha^-1 year^-1 were high relative to other undisturbed ecosystems nationwide. Dry deposition was apparently a major source of the throughfall nitrogen. NO₃^- concentrations from nearby, relatively unpolluted watersheds were lower by 1–3 orders of magnitude. NO₃^- yield was elevated on watersheds where chaparral was converted to grassland in 1960 and may be greatly accelerated after wildfire because of high postfire NH₄⁺ concentrations and rapid nitrification in terrestrial and aquatic ecosystems.

Citation

Riggan, Philip J.; Lockwood, Robert N.; Lopez, Ernest N. 1985. Deposition and Processing of Airborne Nitrogen Pollutants in Mediterranean-Type Ecosystems of Southern California. Envlron. Sci. Technol. 19(9): 781-789