Pacific Southwest

Title: Evidence for nitrogen saturation in the San Bernardino Mountains in southern California

Author: Fenn, Mark A.; Poth, Mark A.; Johnson, Dale W.

Date: 1996

Source: Forest Ecology and Management 82:211-230

Description: Elevated N deposition has occurred in the Los Angeles Basin in southern California for at least the last 40 years. Elevated streamwater NO; fluxes and high nitric oxide (NO) fluxes from soil, indicators of N saturation, have recently been reported for chaparral watersheds exposed to chronic N deposition in the San Gabriel Mountains north/northeast of Los Angeles. A number of nutritional and edaphic parameters across a deposition gradient in the San Bernardino Mountains (SBM) support the hypothesis that the mixed conifer forest in the western end of the range is also N saturated. Concentrations of NO₃^- in the soil solution or in soil extracts during the summer months were 14 to 44 times higher at Camp Paivika (CP), a western high N deposition site, than at Camp Osceola (CAO) or Barton Flats (BF), eastern low-pollution sites. Accumulation of NO₃^- in foliage of bracken fern (Pteridium aquilinum var. pubescens Underw.) and overstory species was also much greater at CP than at CA0 and a site near BF. Nitric oxide fluxes in mid-August from relatively dry soil at CP were ca. 20 times higher than for typical forests in North America. Nitrous oxide (N₂O) emissions, on the other hand, were low in the SBM sites. However, emissions of NO and N₂O were several-fold higher at CP than at BF, a relatively low-pollution site. High NO emissions from otherwise undisturbed and well-drained forest soils of the western US may prove useful as a diagnostic indicator of N saturation. Nitrogen mineralization was greater at CP and Dogwood (high-pollution sites) than at CA0 and Heartbar (low-pollution sites).

Keywords: Nitrogen trace gases, nitrate accumulation, nutrient ratio

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Citation

Fenn, Mark A.; Poth, Mark A.; Johnson, Dale W.  1996.  Evidence for nitrogen saturation in the San Bernardino Mountains in southern California.   Forest Ecology and Management 82:211-230.