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Note: Session titles beginning with an asterisk (*) have student presenters.
AUTHORS: Brian C. Reeder, Morehead State University
ABSTRACT: Earthen hatchery ponds sediments may provide additional nutrients to the water column, and act as a sink for nutrients and excess fertilizer. We examined pond soil nutrient concentrations and P adsorption in five Minor Clark Fish Hatchery earthen ponds in 2008, and again in 2013. Ponds are filled with oligotrophic Cave Run Lake water, fertilized, and drained annually. Pond N and P additions over time have not kept up with soil losses. Soil extractable P concentrations decreased from 37 mg kg-1 to 3.1 mg kg-1 between 2008 and 2013. Soil N decreased from 0.17% to 0.08%. Other soil nutrients (Organic C, Ca, and Mg) remained the same. The loss of soil P was explained by results from P adsorption isotherms using Cave Run lake water, and P-spiked Cave Run Lake water, as equilibrium solutions. Soil collected in 2008 desorbed an average of 4.6 ± 2.3 µg P g-1 under normal fish rearing water quality conditions (<70 µg P L-1; incubations at 0, 3, 7, 33, and 65 µg L-1 P). Using higher concentrations on 2013 soils (8, 96, 150, and 1500 µg P L-1), phosphorus was adsorbed more as P concentrations increased, with greatest adsorption occurring at the highest loading (1,500 µg-P L-1 adsorbed 35.6 ± 0.4 µg P g-1). Phosphorus adsorption was correlated with concentrations of extractable Al and % clay, but not with extractable Fe. Soils collected in 2013 incubated with unspiked Cave Run Lake water (8 µg L-1 P) still desorbed P to the lake water, but at a rate an order of magnitude lower (0.46 ± 0.05 µg P g-1) than 2008 soils. The ability of soils to release P to the water under normal conditions has decreased over time, as pond soils exhausted their extractable and labile P supplies. Regular annual flooding and flushing with low ionic strength water has resulted in P depletion in Minor Clark Fish Hatchery pond soils. Given the relatively low contribution of sediments to pond P budgets during fish rearing, lining ponds could be a worthwhile management strategy.
Wednesday November 1, 2017 10:20am - 10:40am EDT
Jones