National Assembly of Service Hydrologists (NASH)
National Conservation and Training Center, Shepherdstown, WV
May 11-14, 2004
Technical session on “Restoration/Water Quality Issues and Case Studies”
“Northern Everglades Hydrology and Water Quality Issues”
Mike Waldon (Senior Hydrologist), Arthur R. Marshall Loxahatchee National Wildlife Refuge, 10216 Lee Rd, Boynton Beach, FL 33437, 561-735-6006
Abstract: The Arthur R. Marshall Loxahatchee National Wildlife Refuge was established in 1951 to preserve over 140,000 acres of remnant Northern Everglades wetlands. The vast majority of the area of the refuge is made up of a levee-encircled wetland, called Water Conservation Area 1 (WCA-1), which is managed by the USFWS under a license agreement with the South Florida Water Management District and the State of Florida. Water levels in WCA-1 are maintained to provide water storage and flood control, as well as habitat for native fish and wildlife populations. Average annual water volume to the refuge is roughly half from stormwater inflows and half from direct precipitation. Constructed wetlands treat some stormwater before discharge into the refuge perimeter canal.
Alterations in hydrology and water quality impact the interior wetlands of the refuge. The levee and perimeter canal bypass discharge around the wetland, resulting in reduced flow velocities, altered flow directions, and changed hydroperiods and hydropatterns throughout the WCA-1 wetland. Loading of phosphorus entering with treated and untreated stormwater runoff flows causes eutrophication of refuge wetlands. Intrusion of canal stormwater also threatens to alter interior rain-dominated water chemistry, which in-turn may cause a change in periphyton community structure.
Impacts also are related to the refuge perimeter canal. Over the past half-century, 4.8 million cubic meters of sediment sequestering 756 metric tons of phosphorus have been deposited in the perimeter canal. These sediments have low bulk density, are high in organic content, and rich in phosphorus. For comparison, 43 metric tons of phosphorus were discharged into the refuge during Florida water year 2003 from stormwater inflows. The refuge is concerned that phosphorus currently sequestered in the canal sediments may be entrained by high velocity canal flows associated with existing and new pumps. Transport of phosphorus-rich sediment porewater into the surface water through groundwater advection or dispersion may also be a significant mechanism.
Extensive Everglades restoration efforts are underway. Success of these efforts requires an integrated system perspective that includes an understanding of Everglades hydrology and water quality.