Estimating climate effects on the atmospheric contribution to the potential available inorganic nitrogen in eastern United States soils

Atmospherically deposited inorganic nitrogen (N) is often considered to be the primary means of increasing the nitrogen in natural ecosystems. A modeling study of the relationship of climate to an estimate of available inorganic N in soil solution was made for locations/climates in the eastern United States assuming only wet N deposition and assuming both wet and dry deposition measurements for the period 1986–1995. In the absence of denitrification, dry and cool climate locations increased in available nitrogen over the 10-yr period even if only wet deposition was considered. Locations in humid climates retained little wet N deposition due to both denitrification and leaching. Locations in cool dry climates were more sensitive to maximum denitrification rates than warm or hot climates because the temperatures of the soil in the cool climates often were not high enough to maximize the rate. What wet N deposition occurred tended to be retained within the soil column in cooler climates and during drier parts of the year. The timing and magnitude of the dry deposition strongly influenced the retained N in the soil solution; deposition during dry or cold periods resulted in net N accumulation in the soil solution and deposition during wet periods resulted in net N loss from the soil solution. Dry N deposition was retained in the soil column in warmer climates during drier parts of the year. Results indicated that the retention of atmospherically deposited N in the soil water column may be strongly influenced by the climate of the area, and that N was retained especially in soil columns under dry and cold conditions. Additional modeling with verification is needed to assess the impact organic N exchanges and various vegetation types have on the developed relationships between climate, atmospheric deposition and available N.