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publications > paper > ground water recharge and discharge in the central everglades > results
Ground Water Recharge and Discharge in the Central EvergladesResultsTable 2. In the WCA-2A interior, 19 measurements were made at four sites in the wetland interior, and near the WCA-2A levee seven measurements were made at one site. In ENR, 17 measurements were made at six sites. No obvious vertical pattern was seen in the vertical distribution of Kpeat estimates (Figure 4), which supports the simple approach of using the geometric mean of all Kpeat estimates from a site as a reasonable characterization of vertical hydraulic conductivity at the site. There was a trend toward higher values of Kpeat in the WCA-2A interior (geometric mean of 55 cm/day) compared with ENR (6 cm/day). Values of Kpeat at sites near the Hillsboro levee in WCA-2A (24 cm/day) were intermediate between interior WCA-2A and ENR. A tendency toward lower Kpeat values in ENR may be the result of irreversible compaction of peat that probably occurred there due to decades of drainage and farming before the site was reconverted to a wetland (Harvey et al. 2002). That interpretation is consistent with bulk density measurements which indicate that peat sediments in ENR are a factor of three denser than in the WCA-2A interior. Finding lower Kpeat near the WCA-2A levee compared to values from the WCA-2A interior is consistent with the higher bulk density of peat measured near the levee (Table 2), which may be the result of interactions with the nearby canal, where frequent overbank flooding over the past 30 years is likely to have delivered large amounts of fine-grained mineral sediments into the wetlands. Probably as a result of being less disturbed by human activities, interior areas of WCA-2A appeared to have a higher Kpeat that was more representative of predrainage conditions in the central Everglades (Gleason and Stone 1994).At some sites, we also estimated hydraulic conductivity in the fresh water marl/sand layer immediately underlying the peat. Average hydraulic conductivities in transitional layers at WCA-2A interior, WCA-2A levee,
and ENR sites were 61, 6, and 18 cm/day, respectively (Figure 4 and Table 2). K in the transitional layer therefore did
not differ greatly from Kpeat above. K values were 2000 and
900 cm/day near the top of the surficial aquifer at WCA-2A and ENR, respectively (Harvey et al. 2000). Finding that hydraulic conductivity in the surficial aquifer was one to two orders of magnitude higher than in the peat or fresh water marl/sand transition layer indicated that peat, along with the transitional matrix, function together as a layer restricting vertical fluxes of water by recharge and discharge.
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U.S. Department of the Interior, U.S. Geological Survey
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Last updated: 12 January, 2005 @ 10:12 AM(KP)
