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[7] The tracer experiment was conducted in Shark River Slough, which is the main surface water drainage way in Everglades National Park that delivers freshwater flow from the central Everglades to coastal waters in Whitewater Bay and the Gulf of Mexico. The experiment was conducted in flume "A" (25°38'31.2"N, 80°43'20.4"W), which is one of the three flumes in the park managed by researchers at Florida International University (Figure 1 and Figure 2). The flume facility is oriented parallel to the average flow direction and consists of four side-by-side channels, each 3.0 m wide, extending for 100 m in a southerly direction. The channels remain open at both ends, which allows Everglades surface water to flow through the channels at ambient rates. Plastic sidewalls and floating walkways keep the water in the individual channels separated, and allow access to measurement points without disturbance to flow or to the peat sediment. Other details on the construction, operation, and results from flume research are given by Noe et al. [2002]. Our injection was conducted on 20 November 2002 in the westernmost channel of the flume (Figure 1 and Figure 2b). Surface water was 60 cm deep at the time of the experiment, and a typical assemblage of Everglades slough vegetation was present (Figure 2c). Emergent macrophytes were dominated by the rooted Eleocharis cellulosa (806 stems m^-2) and Eleocharis elongata (341 stems m^-2), while several species of submerged aquatic plants were dominated by Utricularia purpurea and Utricularia foliasa. The submerged macrophytes floated beneath the water surface in a layer that was 20 cm thick at the time of the experiment. Periphyton (a matrix of algae and heterotrophic microbes) was also present as a mat floating in the top 2 cm of the water column, and also as thin coatings ("sweaters") on Eleocharis stems. At the sediment surface is a layer of flocculent organic detritus (referred to as "floc") that was approximately 3 cm thick at the time of the experiment. Beneath the floc is peat, which is similar in constitution to floc but is finer grained and more consolidated. The rooted macrophytes are anchored in the peat, which is approximately 50 cm in thickness and underlain by limestone at the location of the experiment. There are few published data describing physical and hydrological characteristics of Everglades peat. Recent measurements from the experimental flume suggest that Everglades floc and peat typically have bulk densities of 0.01 and 0.06 g cm^-3, respectively, and porosities of 0.99 and 0.88, respectively [Jones et al., 1999]. Similar peat in the interior of Water Conservation Area 2A in the central Everglades had a hydraulic conductivity of 7x10^-4 cm s^-1 [Harvey et al., 2004]. No measurements of hydraulic conductivity are available for Everglades floc, although it is reasonable to expect (given its lower bulk density and higher porosity compared with peat) that the hydraulic conductivity of floc is greater.