Nitrogen and sulfur compounds are emitted as pollutants into the atmosphere by a variety of sources including industry, power plants, automobiles and agriculture. Nitrogen is emitted as nitrogen oxides (NOx), released during the combustion of fuels, and ammonia (NH3), released from fertilized fields, feedlots, and other agricultural activities. Sulfur is primarily emitted as sulfur dioxide (SO2), released when coal is burned in powerplants. After transport and transformation in the atmosphere these compounds may be deposited into ecosystems by wet deposition (rain, snow, etc.) or dry deposition (dust or dryfall) as nitrates (NO3-), sulfates (SO42-), or ammonium ions (NH4+). Potential effects include acidification of lakes, streams, and soils, disruption of soil nutrient cycling, degradation of water quality, and loss of biodiversity. Certain ecosystems are more sensistive to atmospheric deposition than others. Areas with low nitrogen assimilating capacity (short growing seasons or sparse vegetation, for example) or low acid-buffering capacity (low in base cations like calcium and magnesium) are particularly vulnerable.