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WATER RESOURCES RESEARCH, VOL. 41, W05009, doi:10.1029/2004WR003507, 2005

Solute transport and storage mechanisms in wetlands of the Everglades, south Florida

Judson W. Harvey

U.S. Geological Survey, Reston, Virginia, USA


James E. Saiers

School of Environmental Studies, Yale University, New Haven, Connecticut, USA


Jessica T. Newlin

U.S. Geological Survey, Reston, Virginia, USA


Abstract

Solute transport and storage processes in wetlands play an important role in biogeochemical cycling and in wetland water quality functions. In the wetlands of the Everglades, there are few data or guidelines to characterize transport through the heterogeneous flow environment. Our goal was to conduct a tracer study to help quantify solute exchange between the relatively fast flowing water in the open part of the water column and much more slowly moving water in thick floating vegetation and in the pore water of the underlying peat. We performed a tracer experiment that consisted of a constant-rate injection of a sodium bromide (NaBr) solution for 22 hours into a 3 m wide, open-ended flume channel in Everglades National Park. Arrival of the bromide tracer was monitored at an array of surface water and subsurface samplers for 48 hours at a distance of 6.8 m downstream of the injection. A one-dimensional transport model was used in combination with an optimization code to identify the values of transport parameters that best explained the tracer observations. Parameters included dimensions and mass transfer coefficients describing exchange with both short (hours) and longer (tens of hours) storage zones as well as the average rates of advection and longitudinal dispersion in the open part of the water column (referred to as the “main flow zone”). Comparison with a more detailed set of tracer measurements tested how well the model's storage zones approximated the average characteristics of tracer movement into and out of the layer of thick floating vegetation and the pore water in the underlying peat. The rate at which the relatively fast moving water in the open water column was exchanged with slowly moving water in the layer of floating vegetation and in sediment pore water amounted to 50 and 3% h−1, respectively. Storage processes decreased the depth-averaged velocity of surface water by 50% relative to the water velocity in the open part of the water column. As a result, flow measurements made with other methods that only work in the open part of the water column (e.g., acoustic Doppler) would have overestimated the true depth-averaged velocity by a factor of 2. We hypothesize that solute exchange and storage in zones of floating vegetation and peat pore water increase contact time of solutes with biogeochemically active surfaces in this heterogeneous wetland environment.

Received 20 July 2004; accepted 4 February 2005; published 12 May 2005.

Keywords: wetlands; surface water tracer; solute transport; hyporheic zone; Everglades; OTIS.

Index Terms: 1830 Hydrology: Groundwater/surface water interaction; 1890 Hydrology: Wetlands (0497); 1820 Hydrology: Floodplain dynamics; 1813 Hydrology: Eco-hydrology; 1847 Hydrology: Modeling.

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Citation: Harvey, J. W., J. E. Saiers, and J. T. Newlin (2005), Solute transport and storage mechanisms in wetlands of the Everglades, south Florida, Water Resour. Res., 41, W05009, doi:10.1029/2004WR003507.