Groundwater’s significance to changing hydrology, water chemistry, and biological communities of a floodplain ecosystem, Everglades, South Florida, USA

Abstract

The Everglades (Florida, USA) is one of the world's larger subtropical peatlands with biological communities adapted to waters low in total dissolved solids and nutrients. Detecting how the pre-drainage hydrological system has been altered is crucial to preserving its functional attributes. However, reliable tools for hindcasting historic conditions in the Everglades are limited. A recent synthesis demonstrates that the proportion of surface-water inflows has increased relative to precipitation, accounting for 33% of total inputs compared with 18% historically. The largest new source of water is canal drainage from areas of former wetlands converted to agriculture. Interactions between groundwater and surface water have also increased, due to increasing vertical hydraulic gradients resulting from topographic and water-level alterations on the otherwise extremely flat landscape. Environmental solute tracer data were used to determine groundwater's changing role, from a freshwater storage reservoir that sustained the Everglades ecosystem during dry periods to a reservoir of increasingly degraded water quality. Although some of this degradation is attributable to increased discharge of deep saline groundwater, other mineral sources such as fertilizer additives and peat oxidation have made a greater contribution to water-quality changes that are altering mineralsensitive biological communities.

Modeling calcification periods of <i>Cytheridella ilosvayi</i> from Florida based on isotopic signatures and hydrological data

“…2). The major water source for any surface or subsurface water in South Florida is precipitation (Meyers et al, 1993;Sacks, 2002;Wilcox et al, 2004;Price and Swart, 2006;Harvey and McCormick, 2009). Further, the whole area of South Florida is pervaded by a complex groundwater system that can be divided into three hydrogeological units: the surficial, the intermediate, and the Floridian aquifer system (Maddox et al, 1992).…”

“…This results in increasing river runoff from June to September and the drying up of great areas of South Florida during the end of the dry season (Duever et al, 1994). Periodic water supply to conservation areas in the central part of the Everglades may modify natural water level variations south of Lake Okeechobee (e.g., Harvey and McCormick, 2009). …”

“…Precipitation determines the isotopic composition (δD, δ 18 O) of surface water and groundwater in Florida, as it is the major water source for the whole region (Meyers et al, 1993;Sacks and Tihansky, 1996;Sacks, 2002;Wilcox et al, 2004;Price and Swart, 2006;Harvey and McCormick, 2009). It has an annual weighted mean value of −12.9 ‰ for δD prec and −2.98 ‰ for δ 18 O prec (Price et al, 2008).…”

“…Water bodies affected by evaporation show increased δD and δ 18 O values along a local evaporation line (e.g., Meyers et al, 1993;Sacks, 2002;Harvey and McCormick, 2009). The variation in evaporation follows a seasonal pattern, with the lowest monthly evaporation occurring from December to February when solar radiation is the lowest, and the highest evaporation occurring from May to August (German, 2000).…”

“…The following assumptions were made for the comparison between δ 18 O ostr and δ 18 O calcite : (1) changes in the δ 18 O water composition of rivers are induced by changes in the δ 18 O prec composition (Meyers et al, 1993;Sacks and Tihansky, 1996;Sacks, 2002;Wilcox et al, 2004;Price and Swart, 2006;Harvey and McCormick, 2009); (2) evaporation is of minor importance for river water and is seasonally constant (Gremillion and Wanielista, 2000; Dutton et al, 2005); (3) the δ 18 O ostr variation is environmentally induced; (4) if calcification is seasonally restricted, the last molting period for a whole C. ilosvayi population to reach the adult stage lasts 1 month at maximum; (5) and there is a constant positive vital effect for the species of about +1 ‰ (Escobar et al, 2012).…”