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Detention areas are an important part of the agricultural as well as urban landscapes throughout the world fulfilling the water storage and treatment needs. In Florida, they are ubiquitous in the farmed areas as a best management practice (BMP) to retain nutrients lost as a result of the sandy soils, shallow water table, and sub-tropical climate. A measurement study was undertaken to estimate the phosphorus (P) treatment efficiency of two agricultural stormwater detention areas (SDAs) in south Florida and identify modifications to enhance P retention. Located in a sugarcane farm in the C-139 basin, SDA1 was a source of P for year 1 (2008-2009) and a P sink with 54% retention efficiency in year 2 (2009-2010). The release of P during year 1 was attributed to limited to no soil phosphorus storage capacity (SPSC) and excessive dilution of P-laden drainage from a large rainfall event. The second SDA (SDA2), located in a vegetable farm, consistently functioned as a P sink during year 1 (2009-2010) and 2 (2010-2011). At both sites, P load reduction was mainly driven by volume retention, not biochemical processes. Hydraulic and managerial (biomass harvesting and chemical (alum) treatment) modifications were identified as avenues to enhance the P retention efficiency of the SDAs. The hydraulic modifications included dividing the SDA into two cells and raising its storage capacity. These hydraulic modifications have been implemented and a comparison between post and pre-modification water and P fluxes will be conducted to quantify the improvement in P treatment efficiency, if any. |