Atmospheric Deposition

Abstract

Atmospheric deposition plays a key role in the biogeochemistry of temperate, tropical, and boreal forests. Many essential macro- and micronutrients as well as pollutants are delivered from the atmosphere to forest ecosystems: (1) dissolved in rain and snow (wet deposition); (2) directly as particles and gases (dry deposition); and (3) dissolved in cloud droplets (cloud, occult, or fog deposition, hereafter referred to as cloud). Here we refer to total atmospheric deposition as the sum of wet, dry, and for some ecosystems, cloud inputs. Substances deposited to forests in any of these three forms can add to soil element pools, while many are immediately labile and thus can be taken up by forest vegetation. Therefore, inputs from the atmosphere can be quantitatively significant relative to the annual nutrient demand for forest growth (Schlesinger 1997), and to watershed input–output budgets (Weathers and Lovett 1998). Conversely, nutrients and pollutants supplied in excess of forest requirements can have adverse ecological effects on sensitive species, soils, and surface waters draining forest watersheds (Likens et al. 1996).