The application of oyster and seagrass models to evaluate alternative inflow scenarios related to Everglades restoration

Abstract

The South Florida landscape is highly engineered featuring ∼3380km of canals, ∼1225 water control structures, >70 pumping stations, managed wetlands, densely populated coastal watersheds, and impacted estuaries. Landscape scale agricultural and urban modifications require flood control which sometimes results in the release of excess freshwater that potentially damages estuarine ecology. The Central Everglades Planning Project (CEPP) is a partnership between the U.S. Army Corps of Engineers and the South Florida Water Management District focused on restoring natural patterns of freshwater flow to the Everglades and associated estuaries. One of the primary project goals is to reduce deleterious inflows eastward to the St. Lucie Estuary (SLE) and westward to the Caloosahatchee River Estuary (CRE) by diverting freshwater south from Lake Okeechobee. Performance evaluation of the CEPP relies upon integrated modeling which links the watershed engineering projects to estuarine salinities and biotic responses. The objective of this study was to utilize seagrass and oyster models to evaluate the effectiveness of alternative inflow scenarios. There are three different scenarios: the existing condition base (ECB), the future without proposed CEPP projects (FWO) but with other landscape features that could alter freshwater inflows, and alternative 4R (ALT4R) that incorporates a suite of restoration projects including those associated with the CEPP. Each of these inflow scenarios was used to generate daily salinity time series from 1965 to 2005 at multiple locations in the SLE and CRE which were used to run site-specific seagrass and oyster models. The hydrodynamic and ecological effects of freshwater inflow were greater in the SLE compared to the much larger CRE. Predicted densities of oysters (individualsm−2) and seagrass (shootsm−2) were greater in the wet season (May–Oct) vs. the dry season (Nov–Apr) in both estuaries. Oyster and seagrass densities increased under the ALT4R inflow scenario that mitigated high inflows to the estuaries in the wet season. This result improved environmental conditions while increasing freshwater availability for other parts of the Greater Everglades and the southern estuaries such as Florida Bay and Biscayne Bay.