In this paper we discuss three rather special characteristics shared by manyudenvironmental problems. Namely, that (i) the environmental variables in which we areudmost interested constitute a stochastic process; (ii) the long-term or limiting behaviorudand the short-term or transient behavior are often both important; and (iii) theudunderlying probability distributions are likely to be influenced by the environmentaludpolicies or remedies that we choose to impose. This third characteristic impliesudthe need to understand the impact of technologies and controls that influenceudthe dynamics of the system. The control theoretic perspective of environmentaludengineering problems has, we believe, received less attention than it deserves inudthe literature. Consequently, after a brief discussion of the exogenous, control-independentudcase we focus on illustrating some special challenges and opportunitiesudembedded in the control-dependent situations.
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