Impacts of flue gas desulfurization (FGD) gypsum on water quality and the algal community in catfish aquaculture ponds

Catfish aquaculture ponds are at high risk of experiencing excessive algal growth, especially cyanobacteria, that can lead to negative water quality issues due to their consistent input through regular feedings and internal cycling of nutrients. Conventional algaecides used in aquaculture, such as copper sulfate, may be effective in the short-term but can potentially lead to developed resistance in phytoplankton over time or harmf u l effects on non-target species. An alternative nutrient management strategy, which has traditionally been used in land-based agriculture, is via flue gas desulfurization (FGD) gypsum, a form of calciu m sulfate that is created as a by-product of carbon-based energy sources. A six-month fiel d experiment was conducted on active catfish aqua-culture ponds at a farm in west Alabama to test the effects of FGD gypsu m on water quality, including its abilit y to manage excessive algal blooms throughout the growing season . In stark contrast to previous results from FGD gypsum application in eutrophic waters, it was discovered that FGD gypsum-treated ponds experienced a large increase in soluble reactive phosphorus (SRP) that led to a spike in phytoplankton abundance, specifically cyanobacteria. Supplementary microcosm experiments aided in determining that FGD gypsu m could extract legacy phosphorus out of the nutrient-rich flocculant sediment found in aquaculture ponds. While these results were unexpected and ultimately undesired, we did discover that the use of FGD gypsu m at the 500 mg/L con-centration does not produce any trace metal contamination in the water column or in the fish tissue. Overall, this experiment discovered new results that FGD gypsu m could produce when used in hypereutrophic waters with nutrient-rich sediments and provides the foundation for futu r e research directions to determine the specific mechanisms behind the interaction of FGD gypsum with the sediment.