The fate of phosphorus in decomposing fish carcasses: a mesocosm experiment

Summary An outdoor mesocosm experiment was conducted to study the process of phosphorus (P) and nitrogen (N) release during fish carcass decomposition and its implications for the functioning of warm, shallow temperate lakes after massive fish kills. Specifically, we compared differences in the fate of P released from carcasses of two fish species that differ in body P concentrations and the ecosystem responses to these fish‐derived nutrient inputs. Nutrients liberated from bluegill ( Lepomis macrochirus ) and gizzard shad ( Dorosoma cepedianum ) carcasses induced phytoplankton blooms and high total P and N concentrations in the water column within a week after carcass addition; these effects persisted for ˜2–3 weeks. Subsequently, water column P was transferred to other ecosystem compartments, primarily sediments and benthic algae. Fish species identity influenced the effects only slightly; decomposition of gizzard shad triggered the highest maximal chlorophyll‐ a concentrations in the water column, while the highest coverage of benthic algae and lowest biomass of periphytic biofilm were found in mesocosms containing bluegill carcasses. Both bluegill and gizzard shad carcasses decomposed completely during the experimental period (˜3 months). Thus, apparently all carcass nutrients were mineralised into bioavailable forms and taken up by other ecosystem compartments. Fallen fish carcasses are not probably to represent long‐term P sinks in warm‐temperate shallow lakes. Decomposition following large mortality events can induce fleeting algal blooms in these ecosystems.