An empirical inferential method of estimating nitrogen deposition to Mediterranean-type ecosystems: the San Bernardino Mountains case study

- New approach for estimating atmospheric N inputs to terrestrial ecosystems.
- Fine spatial scale of N deposition estimates in complex mountain terrain.
- N deposition estimates similar to throughfall and big-leaf inferential methods.
- Large areas of San Bernardino Mountains exceed critical loads for nutrient N.

The empirical inferential method (EIM) allows for spatially and temporally-dense estimates of atmospheric nitrogen (N) deposition to Mediterranean ecosystems. This method, set within a GIS platform, is based on ambient concentrations of NH3, NO, NO2 and HNO3; surface conductance of NH4+ and NO3−; stomatal conductance of NH3, NO, NO2 and HNO3; and satellite-derived LAI. Estimated deposition is based on data collected during 2002-2006 in the San Bernardino Mountains (SBM) of southern California. Approximately 2/3 of dry N deposition was to plant surfaces and 1/3 as stomatal uptake. Summer-season N deposition ranged from <3 kg ha−1 in the eastern SBM to ∼60 kg ha−1 in the western SBM near the Los Angeles Basin and compared well with the throughfall and big-leaf micrometeorological inferential methods. Extrapolating summertime N deposition estimates to annual values showed large areas of the SBM exceeding critical loads for nutrient N in chaparral and mixed conifer forests.