Florida Coastal Everglades Long Term Ecological Research
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Hydrology Cross-Cutting Theme
(Phase II, 2007-2012)

Hypotheses and Proposed Work for FCE II (2006-2012)

General Question: How will the interaction of surface and groundwater inflows, tidal energy and seawater intrusion, local rainfall, and evapotranspiration control [physical and chemical] hydrologic conditions in the oligohaline ecotone under conditions of increasing freshwater inflows from the Everglades?

Specific Research Question 1: How will changing inflows from the upstream Everglades affect the position of the salinity mixing zone and alter geochemical conditions in the ecotone by suppressing brackish groundwater discharge?

Approach - We will use continuous measurements of surface water levels at our SRS and TS/Ph sites and data from over 40 surface water monitoring stations (maintained by ENP and USGS) and surface water discharge data from canal inflow points (SFWMD & ENP) and from stations in the TS/Ph ecotone (USGS) to detect changes in inflows from upstream freshwater environments. We will track the location of the oligohaline ecotone with surface water salinity data from our water quality monitoring sites. Monthly observations of groundwater salinity in existing wells and new wells in both ecotone regions will be used to quantify the extent of seawater intrusion in the underlying aquifer. Wells into shallow soil and upper bedrock already exist at sites SRS-3, SRS-4 and SRS-6 (USGS), and we will sample them in collaboration with T.Smith (USGS). We will install an additional cluster of shallow monitoring wells in the soils and into the top of bedrock at SRS-5 to complete the groundwater monitoring along this transect. In Taylor Slough, a shallow and deep bedrock well cluster exist near TS/Ph-3 (3.6 m and 8.8 m) and TS/Ph-6 (0.6 m and 6.7 m). We will install soil and shallow bedrock wells at TS/Ph-7, and soil wells at TS/Ph-3 and 6. The USGS is collecting daily salinity data in the groundwater at their existing wells, and we will collect the same data at our wells. Both datasets will be used to detect short-term changes in salinity at these sites. We will quantify groundwater discharge with a combination of geophysical and geochemical methods: 1) mass-balance mixing models of major cations and anions run monthly and seasonally to determine the proportions of brackish groundwater discharge and surface seawater in the surface water environments (Price et al. 2006); 2) synoptic surveys of 222Rn and streaming resistivity (Swarzenski & Kindinger 2003; Swarzenski et al. 2004); and 3) subsurface heat flux measurement from thermocouple sensor arrays that we will install at various depths in the soil combined with heat flux modeling as developed for river systems (Stonestrom & Constantz 2003) and near-shore marine systems (Taniguchi et al. 2003).

Specific Research Question 2: How will changing freshwater inflows affect water residence times in the oligohaline ecotones of Taylor and Shark River Sloughs?

Approach - We will estimate water residence times with water budgets and geochemical mass-balance mixing models. In both cases, the hydrology and modeling/synthesis groups will work closely together. Water budgets will be calculated from measurements of rainfall, evapotranspiration, surface water flow, groundwater inputs, and marine inputs to both ecotone regions. Rainfall data will come from our freshwater FCE sites and nearby ENP monitoring stations. We will measure evapotranspiration in the SRS ecotone using techniques similar to the eddy-covariance tower that we currently operate at SRS-6 in cooperation with the University of Virginia. We will estimate evapotranspiration in the TS/Ph ecotone by installing an ET 106 Weather Station (Campbell Scientific, Logan, Utah), computing reference evapotranspiration using the FAO Penman-Montieth equation (Allen et al. 2004), and computing actual evapotranspiration from reference evapotranspiration by crop coefficients calibrated for natural vegetation at our sites (e.g., Barnes & Tarboton 2002). We are currently monitoring surface water flow at several sites, including SRS-1, and will install SONTEK Argonaut acoustic flow meters at SRS-3, SRS-4, and TS/Ph-3 to collect continuous flow measurements. The USGS is currently monitoring surface water flows at various creeks in the southern Everglades, and gauges are presently located on Taylor River near our TS/Ph-6 & 7 sites (C.Hittle, USGS). We will continue to use these data to calculate nutrient fluxes and water budgets at each site and fluxes of water and nutrients between the ecotones and upstream/downstream systems. The geochemical mass-balance mixing methods will use chloride, deuterium, and/or oxygen-18 models (Price 2001; Swart & Price 2002) and analysis of naturally-occurring Ra isotopes (223,224,226,228Ra) in surface water and groundwater (Swarzenski et al. 2006). We will also periodically use inert tracers, such as SF6, to determine large-scale surface water advection and dispersion patterns (Ho et al. 2002; Caplow et al. 2003) in the tidal channels of both ecotones. We are currently testing these tracer methods in freshwater Everglades marshes.
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National Science Foundation logo This material is based upon work supported by the National Science Foundation through the Florida Coastal Everglades Long-Term Ecological Research program under Cooperative Agreements #DEB-1237517, #DBI-0620409, and #DEB-9910514. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
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