应用动态模型确定酸沉降临界负荷的探讨

Calculating Critical Load of Acid Deposition with Dynamic Model

任何一个天然生态系统都是一个稳定系统 .在一定酸沉降量的作用下 ,生态系统最终会平衡在一个新的稳定状态 .动态模型可以模拟不同酸沉降量下生态系统化学状态的变化趋势 .根据信号与系统理论 ,这种趋势可以用一阶指数衰减函数进行模拟 ,以得到系统达到稳定状态时的化学指标值 .根据不同酸沉降量和所对应的稳态化学指标值之间的剂量 响应曲线 ,可以求出当系统稳态化学指标值达到临界化学值时的酸沉降量 ,即为系统的酸沉降临界负荷 .应用这种方法 ,以MAGIC模型为例 ,计算了四川峨眉山顶水和重庆南山湖泊的硫沉降临界负荷 ,分别为 1 5 4和 6 5 1keq·(hm2 ·a) - 1.通过和MAGIC计算的目标负荷及SSWC方法计算的临界负荷相比较 。

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·(hm 2·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.