Calculating Critical Load of Acid Deposition with Dynamic Model
应用动态模型确定酸沉降临界负荷的探讨

Any natural ecosystem is a steady system which will ultimately approach a new steady state when it receives a fixed quantity of acid deposition Dynamic models can be used to predict the changing potential of the chemical state of an ecosystem under different acid depositions. According to the theory of signal and system, this potential can be modeled by the first order exponential attenuation function to get the value of chemical index when the ecosystem achieves steady state. A dose response curve can be obtained according to the different quantity of acid deposition and the corresponding steady state values of chemical index. Consequently, the critical load for an ecosystem can be evaluated from the dose response curve, i.e, the quantity of acid deposition under which the steady state value of the chemical index will achieve the critical chemical value. Taking MAGIC as an example, this method was applied to estimate critical loads of S deposition for a water body on Emei Mountain in Sichuan province and a lake on Nanshan Mountain in Chongqing city, the values being 1.54 and 6.51 keq·(hm2·a)-1, respectively. Through comparing the critical loads calculated using the method proposed in this paper with the target loads calculated with MAGIC and the critical loads estimated using SSWC method, it can be concluded that the method proposed in this paper are reasonable in estimating critical loads of acid deposition.