3rd UF Water Institute Symposium Abstract

Submitter's Name Jennifer Mitchell
Session Name Posters - Understanding Natural, Anthropogenic and Legacy Sources of Nutrients
Category Understanding natural, anthropogenic and legacy sources of nutrients
Poster Number 63
Author(s) Jennifer  Mitchell,  Alachua County EPD (Presenting Author)
  Mark Clark,  UF Soil and water science
  Jim  Myles, Alachua County DEP
  The Influence of Stormwater Pond Substrate on Surface Water Phosphorus Dynamics across Alachua County
  Sizing and design of stormwater basins in the past has primarily focused on quantity of water storage; however, water quality leaving these ponds is of increasing importance as numeric nutrient criteria (NNC) are implemented . Phosphorus is often the limiting nutrient for plant growth in freshwater systems and is often a target for management. Phosphorous management in the landscape is often focused on fertilizer and animal waste management, but in areas with naturally high phosphatic geology, increasing the exposure of this material to weathering during development could result in increased surface water phosphorus levels. . To evaluate the potential influence phosphatic soils may have on stormwater basin water quality as well a preliminary survey of 15 stormwater ponds across Alachua County was conducted in Fall of 2011. Ponds were selected based on their location in the county and accessibility. Phosphorus (P) rich Hawthorne series clays underlie the eastern section of the county, while the western side has rapid infiltration rates resulting from the lack of a confining layer.. In this study we calculated soil P storage capacity (SPSC) of the newly accreted surface layer and the underlying native soil to use as a possible index of P flux potential. These two layers were easily identified and separated. Melich-1 extractions were conducted for P, aluminum (Al), iron (Fe), calcium (Ca), and magnesium (Mg). Water extratable P was also determined on these samples. Intact soil cores collected from three locations within each basin were incubated with rain water for up to 14 days. Based on the SPSC values using Fe, Al, Ca, and Mg and small change in surface water soluble reactive P (SRP) concentration over the incubation these stormwater wetlands should serve as a sink for P. Interestingly the cores with the greatest P flux were from the basins which were not flooded during sampling, indicating the importance of reducing conditions for P storage. Despite some soils having up to 1000 mg/kg of Melich-1 extractable P, concentrations of Fe, Al, Mg, and Ca were in similar abundance and prevent release of P when soils remained under flooded conditions.