Estimation of Critical Loads of. Sulfur and Nitrogen for the Korean Ecosystem

抄録

The critical loads of sulfur and nitrogen and their exceedances by the sulfur and nitrogen deposition of 1994-1998 were mapped for South Korea for the first time with a spatial resolution of 11km×14km (0.12 5° Long.×0.125° Lat.) using the steady-state mass balance model. The Korean soil and geological maps with the map scale of 1: 250, 000 and the Korean forestry statistical yearbooks were used as basis for the estimations of weathering rate of base cations, critical alkalinity leaching, denitrification fraction and uptakes of base cation and nitrogen. Wet depositions of sulfur, nitrogen and non-sea-salt base cations were derived from measured concentrations in precipitation and precipitation rates using optimum regression equations while dry depositions of sulfur and base cations were estimated using the inferential method. However, dry deposition of nitrogen due to NO, NO₂, NH₃ and NH₄⁺ species was estimated using the MM5 numerical model, a modified Regional Acid deposition Model (RADM) and the K-mean clustering technique using three consecutive days of gridded daily mean 850 hPa geopotential height fields without precipitation on the last day over South Korea for 5 years. The predominant ranges of base cation deposition, weathering and uptake were estimated to be 300-500 eq ha^-1 yr^-1, 200-500 eq ha^-1 yr^-1 and 200-400 eq ha^-1 yr^-1, respectively. Critical alkalinity leaching was mainly in the range of 1, 0002, 000 eq ha^-1 yr^-1. Consequently, a large percentage of the maximum critical load of sulfur was found to be in the range of 1, 0002, 000 eq ha^-1 yr^-1. The estimated predominant ranges of nitrogen immobilization and uptake were 120-180 eq ha^-1 yr^-1 and 300-400 eq ha^-1 yr^-1, respectively, indicating low values of the minimum critical load of nitrogen. The maximum critical load of nitrogen was found to be relatively high (predominantly 2, 0004, 000 eq ha^-1 yr^-1) while the critical load of nutrient nitrogen was low (predominantly 400-800 eq ha^-1 yr^-1). Exceedance of the maximum critical load of sulfur was found at 85% of the Korean ecosystems considered mainly in the southeastern part of Korea, whereas that of the critical load of nutrient nitrogen was found in the whole Korean ecosystems. This implies that Korean ecosystems are very susceptible to the combined loadings of sulfur and nitrogen.