Effect of Drainage Flow on Phosphorus Concentrations in a Water Conservation Area Canal in South Florida.

The Loxahatchee National Wildlife Refuge is one of three conservation areas in South Florida designed to provide water storage and flood control, as well as habitat for native fish and wildlife populations.  Most of the Everglades, including the refuge, developed as a rainfall-driven system with surface waters low in nutrients and inorganic ions.  There is concern that increases in outflow from Stormwater Treatment Area 1E (STA-1E) may suspend and transport light organic sediments and nutrients in the receiving canal that may negatively impact the fragile ecosystem inside the refuge.  The objective of this study was to measure the effect of STA-1E outflow on different P species and other selected water properties in the L40 Canal.  Six water surveys under flow drainage conditions (16,508 – 163,448 m³ h^-1) and three under no flow conditions were conducted in 2006.  Total P concentrations from samples collected under flow conditions averaged 77 µg L^-1, compared to 56 µg L^-1 during no flow.  Phosphorus concentrations from individual surveys showed higher differences in P species concentrations depending on intensity of drainage flow and timing during the rainy season.  Contribution of total dissolved P to total P in the water column ranged from as low as 21% (18 µg L^-1) on samples from a low drainage event early in the rainy season (34,544 m³ h^-1) to as high as 75% (83 µg L^-1) in samples from one of the highest drainage events (163,448 m³ h^-1) in 2006.  In contrast, particulate P concentrations were considerable higher early in the rainy season (79% of total P, 71 µg L^-1), with concentrations considerably decreasing toward the end of the rainy season.  These results suggest that the net contribution of particulate P most likely resulted from the remobilization of biological generated particulate matter accumulated in the canal during the quiescent dry season.