Assessing nutrient loads from in-situ fertilizer amendments in Willard Spur

A research team studied relationships between nutrient loading and submerged aquatic vegetation (SAV) in the Willard Spur as related to increased nutrient loading by the Perry/Willard Regional Wastewater Treatment Plant (PWRWTP). In-situ plots containing slow-release nutrient amendments were constructed in the Willard Spur in 2012 and 2013. The water and sediment chemistry of the plots was monitored monthly in 2012 and bimonthly in 2013. Another team member a assessed plant health metrics concurrently with surface water and sediment samples to determine short-term response of SAV to increased nutrient loading. In 2012 water and sediment analysis showed amendment affects from fertilizer amendments. In 2013 only the water column was amended. Nutrient concentrations in the water column did not show significant amendment effects, likely due to changes in fertilizer formulation. Laboratory and in-situ mesocosm tests provided surrogate settings in which nutrient release rates were measured under a variety of conditions. Release rate constants were obtained for a range of conditions through multivariate linear regression of data from these tests. Nitrogen isotopes provided evidence of perturbation of the system in the amended plots in 2012 and 2013. SAV health corresponded with the amount of fertilizer added to the plot, indicating that fertilizer amendments successfully bracketed a range of plant responses to nutrient loading. In a separate study, depth profiles of dissolved and solid phase phosphorus and phosphorus mineral concentrations were examined in an impounded wetland before and after being drained and again following re-flooding to explore the potential benefit of periodic drying and oxidation of sediment. Surface water, pore water, and sediment nutrients were measured in order to monitor changes resulting from the drying and reflooding process. The efficacy of Quantitative Evaluation of Minerals by SCANning (QEMSCAN) to determine mineral content in fine-grained sediment was also explored. Changes in phosphorus speciation in surface water, pore water, and sediment were observed in response to the drying and re-flooding process. Surface water dissolved phosphorus increased by 35% and pore water dissolved phosphorus increased by 50 to 125% following re-flooding between depths of 5 and 20 cm. Available phosphorus in the top 3 cm of sediment increased by approximately 10% after re-flooding.