After receiving the acid waters from years of washing lead batteries, the cypress-gum swamps downstream from the Sapp operations ﬁltered and stored much of the lead (Chapter 6). Many trees had been killed, and the swamps were full of dead wood and detritus. Chemical studies (Chapter 6) showed lead present in tiny amounts in the waters, but larger amounts were chemically bound in the organic sediments. This chapter describes a simulation model of lead and its simpliﬁed representation of the storages and ﬂows within the swamp ecosystems. First we describe our concept of how the swamp operates in processing lead by discussing parts and processes in a simpliﬁed model. The systems diagram of that model (Figure 8.1) helps you visualize how this model is structured. Causal relationships are listed in Table 8.1. Some of the details are in Appendix 8.