Florida Coastal Everglades Long Term Ecological Research
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PAST WORKING GROUPS

Hydrology Cross-Cutting Theme
(Phase II, 2007-2012)


Findings

The main goals of the hydrology group were to quantify the major water balance parameters: freshwater inflow from the upstream Everglades; marine water; groundwater, precipitation and evapotranspiration in both Shark and Taylor Sloughs. Groundwater discharge was investigated in terms of surface water quality as well as its potential effects on ecological process. In addition, the role of water management and sealevel rise on water levels and residence times were investigated.



Our results indicate that in each slough, precipitation was the dominant water source while evpotranspiration was the dominant water loss (Zapata-Rios, 2009; Saha et al., in press). Groundwater inputs were found to be a significant contribution to the surface water in both Taylor and Shark Sloughs (Fig. 1). In Taylor Slough, groundwater inputs were the second largest input, accounting for about 25% of the total inputs (Zapata-Rios, 2009), with upstream freshwater flows accounting for only 8% of the surface water. In Shark Slough, groundwater input was equivalent in magnitude to the upstream freshwater flows across Tamiami Trail, representing 19% of the total input (Saha et al., in press). Groundwater inputs are important for the oligohaline ecotone region of the FCE as both fresh and brackish groundwater contains higher concentrations of phosphorus (Price et al., 2006), the limiting nutrient within our ecosystem.
Pie charts of water budget components in Shark and Taylor Sloughs


Figure 1. Pie charts of water budget components in Shark and Taylor Sloughs. Inputs include rain (blue), surface water inflow (red), and groundwater discharge (green). Outputs consist of evapotranspiration (ET, blue), surface water outflow (red), and groundwater seepage (green). Values represent the average percentages of each component for Taylor Slough on a monthly basis between Jan. 2008 - July 2009, and on an annual basis in Shark Slough between 2002-2008.




Marine waters from Florida Bay and the Gulf of Mexico intrude into the coastal aquifer beneath the oligohaline ecotone, causing the groundwater to be brackish (Price et al., 2006). Our investigations have determined that brackish groundwater discharge (GWD) combined with long residence times and evaporation had a greater effect on water chemistry in Taylor Slough which seasonally became hypersaline (Zapata-Rios et al., 2009) as compared to Shark Slough which only became moderately hypersaline (Barr et al., 2009). The highest values of GWD occurred in May-July (Fig. 2) concurrent with the highest levels of evapotranspiration (Saha et al., 2010, Zapata, 2009), solar radiation (Price et al., 2007; Barr et al., 2009), phosphorus concentrations (Koch et al., 2011), and hypersalinity conditions. Ecosystem response was mixed under these conditions, with mangrove physiological functions limited (Barr et al., 2009), but gross primary production becoming elevated (Koch et al., 2011).

Monthly Groundwater discharge to SRS and monthly surface water salinity at the oligohaline ecotone
Figure 2. Monthly Groundwater discharge to SRS and monthly surface water salinity at SH2 (the oligohaline ecotone) averaged over 2003-2008 (Saha et al., in press).


The position of the groundwater mixing zone varies seasonally but has been steadily increasing inland with sealevel rise (Saha et al., 2011). Water levels along the coastline have been increasing since the 1960s at a rate of 2 mm/yr, equivalent to local sealevel rise (Fig. 3a). While, water levels in the upper reaches of Shark Slough have increased at a higher rate (7mm/yr) due to increased releases of fresh surface water across Tamiami Trial (Fig. 3b). Despite the increased releases of freshwater from the upstream Everglades, the resultant water becomes ponded in the upper reaches of Shark Slough due to the presence of sawgrass and floating peryphyton mats within the water column which restrict flow velocities (He et al., 2010). Our results suggest that managed surface water inflows to Shark Slough need to be increased in order to counteract the landward intrusion of seawater (Saha et al., in press).
Estimated residence times in Taylor and Shark Sloughs are variable. Preliminary estimates of residence times in Taylor Slough indicate a bi-modal distribution with peaks at 7 and 180 days, corresponding with periods of high flow and low flow, respectively. In Shark Slough, residence times decreased in a downstream direction from >90 days to about 14 days between SRS-1 and SRS-4 (Fig. 3), due to increased surface water flow velocities in the slough. Within the mangrove ecotone region of Shark River Slough, where tides occur, residence times of 12 days or less were estimated (Wacksman and Chambers, 2005).

References
Barr, J.G., J.D. Fuentes, V. Engel, J.C. Zieman. 2009. Physiological responses of red mangroves to the climate in the Florida Everglades. Journal of Geophysical Research , 114: G02008.

He, G., V. Engel, L. Leonard, A.L. Croft, D.L. Childers, M. Laas, Y. Deng, H. Solo-Gabriele. 2010. Factors Controlling Surface Water Flow in a Low-gradient Subtropical Wetland. Wetlands , 30: 275-286.

Koch, G., D.L. Childers, P.A. Staehr, R.M. Price, S.E. Davis, and E.E. Gaiser, 2011. Analysis of seasonality in Taylor River: When do ecological tipping points occur?. 2011 FCE LTER All Scientists Meeting, Fairchild Tropical Garden, Coral Gables, Florida , January 06-07, 2011.

Price, R.M., P.K. Swart, J.W. Fourqurean. 2006. Coastal groundwater discharge - an additional source of phosphorus for the oligotrophic wetlands of the Everglades. Hydrobiologia , 569(1): 23-36.

Price, R.M., W.K. Nuttle, B.J. Cosby, P.K. Swart. 2007. Variation and Uncertainty in Evaporation from a Subtropical Estuary: Florida Bay. Estuaries and Coasts , 30(3): 497-506.

Saha, A.K., C. Moses, R. M. Price, V. Engel, T. J. Smith III, G. H. Anderson. A hydrological budget (2002-2008) for a large subtropical wetland ecosystem indicates seawater, Estuaries and Coasts. In Press.

Saha, A.K., S.Saha, J. Sadle, J.Jiang, M.S. Ross, R. M. Price, L.S.L.O. Sternberg, K.S. Wendelberger. 2011. Sea level rise and South Florida coastal forests. Climate Change. 107(1-2): 81-108.

Wacksman, J.J. and R.M. Chambers, 2005. Modeling of net ecosystem metabolism in an Everglades tidal river. Society of Wetland Scientists Annual Meeting, Charleston, South Carolina , June 05-10, 2005.
Zapata-Rios, Xavier . 2009. Groundwater/surface water interactions in Taylor Slough-Everglades National Park. Master's thesis, Florida International University.
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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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