Water Quality Monitoring in the Execution of Canal Remediation Methods in the Florida Keys

Monitoring data indicate relatively high nutrient concentrations in waters close to shore along the Florida Keys, and corresponding responses from the system, such as higher phytoplankton biomass, turbidity and light attenuation as well as lower oxygenation and lower salinities of the water column. These changes, associated to human impact, have become more obvious near canal mouths. Waters close to shore show characteristics closely related to those in residential canals, affected by quick movement of infiltrated runoff and wastewaters (septic tanks), tides and high water table. Many canals do not meet the minimum water quality (WQ) criteria established by the State of Florida and are a potential source of contaminants to near shore waters designated as Outstanding Florida Waters. Canal remediation is being conducted by the Monroe County targeting poor circulation and organic matter accumulation. The restoration technologies include reduction in weed wrack, enhanced circulation, organic removal and partial backfilling. The objective of WQ monitoring is to measure the status and trends of WQ parameters to evaluate progress toward achieving and maintaining WQ standards and protecting/restoring the living marine resources. Monitoring followed a Before-and-After-Control-Impact scheme (BACI). Field measurements, included diel observations and vertical profiles of physical-chemical properties (salinity, DO, %DO saturation, temperature and turbidity) and nutrient analysis. Comparing profiles between remediated and control canals indicated similar patterns in physicochemical properties, and suggesting larger seasonal than spatial variability. BACI diel observations, in surface and bottom waters of remediated canals indicated little difference for surface waters, but significant improvements for bottom waters. Most surface waters are well oxygenated, while bottom waters show a significant increase in DO following culvert installation.