Choice of control of sulfur and/or nitrogen deposition based on critical loads

Abstract

In order to design more reasonable and effective acid deposition control policies, the critical load function (CLF) was established and a two-dimensional critical load function figure was drawn based on the steady-state mass balance (SMB) method. The figure could be divided into five different regions: critical load region (non-control region), S deposition control region, N deposition control region, S and N deposition selective control region and S and N deposition simultaneous control region. According to the region into which the deposition point fell, we could choose the corresponding control approach. With further consideration of high base cation deposition (BCdep) in China, a three-dimensional critical load function surface could be drawn by taking BCdep as a variable. As a case study, critical loads of sulfur and nitrogen for the lateritic red earth in Guangzhou were calculated with current deposition data, vegetation data and soil data obtained by field sampling and laboratory analysis. Results showed that the current deposition point fell into the critical load region and a 75% reduction in BCdep caused the deposition point falling into S deposition control region, which indicated the importance of controlling sulfur deposition. While taking the critical load of nutrient nitrogen into account, the current deposition point fell into N deposition control region and with the reduction of BCdep, the deposition point entered S and N deposition simultaneous control region, which meant sulfur and nitrogen deposition should be controlled at the same time.