The L-31E Surface Water Rediversion Pilot Project: Phase 1 Final Report

Southeast Environmental Research Program; Ross, Michael; Meeder, John; Ruiz, Pablo; Renshaw, Amy; Telesnicki, Guy; Alvord, Jennifer; Jacobson, Myrna; Byrnes, Michael; Atlas, Zachary; Reed, David; Fry, Brian; Lewin, Matthew; Weekley, Carl

The Biscayne Bay SWIM Plan (SFWMD 1994) recommended restoring wetland habitats and mitigating the effects of canal point discharges of freshwater. To that end the South Florida Water Management District, in collaboration with the National Park Service and Florida International University, initiated a demonstration project in 1993 to redistribute some freshwater flow from the South Dade canal system to mangrove wetlands fringing the southwestern Bay. The ultimate objective of the project was to provide guidance that would allow managers to recreate a more natural sheet flow to Biscayne National Park, thereby reducing the effects of sudden releases that now occur through existing coastal structures. A secondary objective was to restore, to the degree feasible, the original coastal ecosystems that prevailed prior to construction of the canal system. Throughout the southern Biscayne Bay watershed, existing coastal wetland communities have been cut off from sheet flow for decades. Mangrove species are quite capable of functioning in intermediate salinities, but the effects of increasing quantities of fresh water, nutrients, and possibly contaminants on ecosystem function is unknown. Better understanding of ecosystem responses to small-scale releases is necessary before extending diversions of canal water to other South Dade coastal wetlands. This knowledge should include an understanding of the effects of diversion on: (a) swamp and near shore water chemistry and hydrology; (b) soil development and microbiological processes; (c) wetland vegetation composition, structure, and production; (d) abundance of epiphytic and epibenthic invertebrates; (e) zonation, production, and phenology of primary producers in the near shore environment; and (f) exchanges between near shore and mangrove ecosystems These responses should be understood in a historical context, and within the context of the current South Dade landscape as a whole. It is also recognized that the character of treatment responses is frequently complicated by ecosystem responses to periodic natural disturbances. A team from Florida International University, Southeast Environmental Research Program (SERP) was chosen to carry out the monitoring activities associated with the demonstration project. The area chosen for the project was the coastal mangrove ecosystem bounded by the Mowry, L-31 E, and Military Canals on the south, west, and north, respectively, as well as adjacent portions of Biscayne Bay (Figure A-1-l) Before establishing the monitoring design, FlU (a) reviewed all ground and SUI face water quality data available from the general area (described in Section B-1 ), (b) developed maps representing current and historical vegetation of the study area and adjacent lands, based on existing aerial photos (Section C-1), (c) sampled and described wetland soils, emphasizing a coastal gradient that prevailed throughout the area (Section E), and (d) determined the suitability of alternative study units by completing detailed topographic surveys (Section A-2).