Experiments that introduce dissolved or particulate tracers into flowing water are useful to characterize rates of material movement and mixing. Parameters determined from tracer experiments, such as advection and dispersion, are especially needed in models that simulate the effects of flow and mass transport on biogeochemical reactions and water quality. Presently, there are few data or guidelines available to understand mechanisms that control transport of materials with flowing water in the Everglades. Recently, a group of USGS and university researchers conducted a tracer experiment in central Shark Slough at one of the Florida International University (FIU) phosphorus dosing flume facilities. Each flume consists of 4 side-by-side channels, each enclosing a 3-m wide by 100-m long flow-way oriented with the natural direction of surface-water flow. More about flume design and results of the lowlevel phosphorus dosing can be found at several FIU websites (http://www.fiu.edu/~ecosyst/index.htm).

This abstract provides a brief description of a tracer experiment conducted from November 20-22, 2002 in flume A. The purpose of the experiment was to characterize transport of both solutes and fine-particles in Shark Slough, including surface-water exchange with subsurface water in the floc and underlying peat. The experiment was conducted in the westernmost channel of flume A. That channel receives the ‘middle’ level of phosphorus dosing being applied to determine the effects of added phosphorus on the Everglades ecosystem. At the time of the experiment, visible differences in macrophyte density were not apparent in the experimental channel when compared with areas immediately outside the flume. The depth of surface water was approximately 60 cm at the time of the tracer test and the location of the injection was 0.75-m upgradient of the 0-m reference point in the channel, which is the location where the ‘mixing’ reach for phosphorus dosing ends and the front edge of vegetation begins. The experiment consisted of a constant-rate injection for 22 hours of a sodium bromide (NaBr) solution made up in 0.2 um filtered Everglades water. The injection was accomplished using two metering pumps to deliver the tracer; dividing the flow between four soaker hoses (2.65-m long) stationed horizontally across the channels at evenly spaced depths. After termination of the NaBr injection, fine particles composed of titanium dioxide (TiO₂) were injected into the flume for a period of six hours. The TiO₂, which has a density of 3.9 g/cm³, was suspended in filtered Everglades surface water by stirring and delivered by metered injection through a single slotted tube, oriented horizontally and positioned at a depth of 30 cm. Sampling for the tracers began before the start of the NaBr injection and lasted for 48 hours. Concentrations of both dissolved and particulate tracers were monitored at four stations at distances of 6.8, 26, 43, and 86m down the channel from the injection site. At each monitoring station, small-volume (20-ml) water samples were repeatedly collected by suction at seven discrete points, which characterized horizontal and vertical variability in tracer distribution across the channel. In addition to sampling surface water, porewater was sampled at two locations at a distance of 6.3 m downstream from the injection site. Analysis of bromide concentration in each sample is being conducted by ion chromatography, while concentrations of TiO₂ particles are being determined by inductively coupled plasma-atomic emission spectrometry following acid digestion of the particles.

Results from the experiment are not available at this time, due to the limited number of analyses completed. A full presentation of findings will be prepared upon completion of the sample processing and simulation modeling. In addition to providing fundamental information about transport processes in the Everglades, the expectation is that results can be combined with complementary data to better characterize rates of biogeochemical reactions in the Everglades. Parameters describing solute and particle transport will also be available as inputs for the water-quality and landscape-process models that are currently guiding restoration planning in the Everglades.

Contact: Harvey, Judson W., U.S. Geological Survey, 12201 Sunrise Valley Drive, Mail Stop 430, Reston, VA 20192; Phone: (703) 648-5876; Fax: (703) 648-5484; jwharvey@usgs.gov; Water Quality and Water Treatment Technologies

(This abstract was taken from the Greater Everglades Ecosystem Restoration (GEER) Open File Report 03-54)

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