Small ponds (<1 ha to ≈12 ha) vegetated by dense stands of cypress trees (Taxodium distichum) are common in the southeastern coastal plain of the United States, particularly in Florida, and were evaluated as sites for waste-water recycling. Four swamps were chosen for intensive analysis: two to receive sewage that had been given secondary treatment; one to receive only groundwater, serving as a partial control to distinguish the impacts of nutrient loading and water loading; and one to serve as an undisturbed reference swamp. Six months after the project began, a fire burned one of the sewage swamps and the groundwater swamp. The project therefore continued with an unburned reference swamp, a burned groundwater control swamp, a burned sewage swamp, and an unburned sewage swamp (Table 10.1).

   Most studies, particularly intensive metabolism measurements and determinations of water and nutrient budgets, were concentrated in the reference swamp and the unburned sewage swamp. Additional moderately intensive studies were conducted in an undisturbed cypress strand (a larger, slowly flowing swamp) in south Florida and in a strand near Gainesville that had been receiving barely treated sewage for 40 years. Satellite studies examined specific questions in other local cypress ponds as well as in other kinds of swamps where cypress trees grow, such as river swamps and dwarf cypress savannas. The analysis of the response of cypress ponds to wastewater therefore involved virtually no replication of experimental units. Intensive examination of one treated swamp was augmented by analysis of other sewage swamps, not experimentally manipulated but of longer standing.

   Certain aspects of the study required using the entire basin as a treatment unit: e.g. impact of nutrients and pathogens on regional groundwater supplies; changes in use of the swamps by animal populations, especially vertebrates; and relative magnitudes of potential nutrient storages. Imposing a treatment that generated a significant response in at least one swamp established two ends of a spectrum ( treatment and reference) that allowed major shifts in metabolism and species composition to be detected. The advantage to this approach is the opportunity to collect information on various components within the same treatment unit simultaneously and to observe cross-system interactions. The boundaries of important response variables were established: e.g. changes in net photosynthesis rates (Brown, 1981), decomposition rates (Dierberg and Ewel, 1984), and invertebrate populations (Brightman, 1984) with nutrient loading; as well as relative importance of soil vs vegetation in nutrient storage and the role of denitrification (Dierberg and Brezonik, 1984).

   Another set of projects was subsequently begun to evaluate the impacts on cypress swamps of forest management practices such as drainage, selective logging, and clearcutting. Several swamps in north and central Florida that had already been subjected to such management practices were selected. One study included 15 small swamps in a 4 km² management block. Eleven of these swamps had berms and/or drainage ditches affecting their water fluxes to varying degrees, and four were undisturbed (Marois and Ewel, 1983). In another study, three swamps that had been logged at each of five times (from as recently as a few months to as long as 45 years before) were identified (Terwilliger and Ewel, 1986). Although these studies were not such thorough ecosystem analyses as the wastewater project, they built on the information derived from the earlier intensive study to give a more complete picture of how cypress swamps function. The forest management study therefore contained more replication but less intensive analysis of any single swamp.

   Natural variability and less dramatic perturbations in swamps that were less intensively studied produced a spectrum of ecological conditions and, in some cases, replicates within single levels in the spectrum. Nevertheless, replication of swamps was essential for establishing the variability of geological substrata (Spangler, 1984), ET rates (Brown, 1981; Heimburg, 1984; Ewel, 1985), and fire effects (Ewel and Mitsch, 1978). Additional swamps incorporated into both the wastewater and silviculture studies provided both replication and intermediate points in the spectrum of nutrient responses. They were useful in suggesting the limits of nutrient loading (Lemlich and Ewel, 1984), establishing vegetation composition as an index to hydroperiod (Marois and Ewel, 1983), and describing variability of net productivity rates within and among swamps (Ewel and Wickenheiser, 1990).

   The strategy used to study Florida cypress ponds was to concentrate human and financial resources on a few swamps. In this top-down approach to examining ecosystems, intensive studies on two swamps identified major trends and elucidated important mechanisms, whereas extensive studies on additional swamps determined the variability of many of these responses.