Summary
Large areas of California forests and other ecosystems are exceeding critical deposition loads for atmospheric nitrogen inputs. Ecological effects of these excess atmospheric nitrogen inputs are most commonly related to "nitrogen as a nutrient" effects, or eutrophication responses. Because of the dilute waters of high-elevation lakes in the Sierra Nevada of California, the acid neutralizing capacity of these water bodies is very low. As a result, even low levels of nitrogen or sulfur deposition from air pollution results in vulnerability to acidification. Sixteen percent of the 208 lakes from Class I and II Wilderness areas studied were in exceedance of the critical load for acidification. The most vulnerable lakes were located in the Sierra and Stanislaus national forests. Atmospheric deposition inputs are projected to exceed the estimated critical loads of the more sensitive lakes and catchments in this area for the foreseeable future, even though nitrogen oxide emissions in California from the transportation sector have decreased dramatically in recent years.
