age conditions, surface water and groundwater were relatively small components of the Everglades water inputs (see Table 4-1; Harvey and McCormick, 2009).

The rainfall input is characterized by low ionic strength (median specific conductance of <20 microsiemens per centimeter [µS/cm]) and generally low concentrations of all major ions (i.e., largely <1 parts per million [ppm, or milligrams per liter], except for sulfate and chloride, because of marine aerosol influences). Rain-fed areas of the Everglades (e.g., the interior of the Arthur R. Marshall Loxahatchee National Wildlife Refuge [LNWR]) have conductivities of <100 µS/cm. Rainfall is also notably low in nitrogen and phosphorus; estimates of phosphorus concentrations and loading in rainwater range from 30 parts per billion (ppb) (Davis, 1994) to more recent measurements of 9 to 10 ppb (Ahn and James, 2001; Richardson, 2008).

Water quality data going back to 1978 show that the interior portions of the Water Conservation Areas (WCAs) and Everglades National Park are uniformly at or below 10 ppb total phosphorus (TP). Water samples taken between 1978 and 2003 in Everglades National Park have geometric mean TP concentrations of 4.5-5.6 ppb and geometric mean total nitrogen (TN) concentrations of 0.9-1.4 ppm (Payne and Weaver, 2004). A study conducted in 1953, prior to the intensive agricultural development of the Everglades Agricultural Area (EAA) but after construction of the major canals, showed “dissolved phosphorus” concentrations of 3–7 ppb in the Tamiami Trail canal and the lower portions of the canals bordering what is now WCA-3B, with concentrations about an order of magnitude higher in samples closer to Lake Okeechobee (Odum, 1953). In the absence of explicit data from the pre-drainage period, one can assume that the rain-driven system would have had similar water quality characteristics (i.e., low alkalinity, low total nitrogen and phosphorus concentrations) derived primarily from atmospheric deposition. Any phosphorus inputs from Lake Okeechobee overflows were generally thought to have been assimilated by the former pond apple swamp that existed between the lake and the sawgrass plains (Noe et al., 2001).

LEGAL CONTEXT FOR WATER QUALITY IN THE SOUTH FLORIDA ECOSYSTEM

Water quality criteria and standards (see Box 5-1) in the South Florida ecosystem are governed by a mix of federal and state statutes, implementing regulations, and judicial consent decrees. Current and proposed standards are fiercely contested, and active litigation in federal courts continues to create uncertainty as to which regulations will apply to future restoration plans. Because these criteria and standards have important implications for the CERP as it moves forward, the current legal and regulatory context is described in this section.

Current standards, including designated uses and supporting criteria, are designed to limit the nutrient content of waters (especially phosphorus) flowing



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