Effects of Resource Pulses on Nutrient Availability, Ecosystem Productivity, and Temporal Variability Following a Stochastic Disturbance in Eutrophic Glacial Lakes

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Hypoxia in shallow lakes represents a stochastic disturbance that may elicit a resource pulse through fish decomposition, altering nutrient availability and temporal variability of ecosystem productivity. We measured nutrient availability, primary and secondary production, and temporal variability from April through September in no, moderate, and high carrion lakes following winter 2007–2008 and used a repeated-measures ANOVA and impact trend-by-time analyses to evaluate how increasing levels of fish carrion influence recipient ecosystems. Lakes with carrion had higher nutrient concentrations, pH, turbidity, chlorophyll-a, and zooplankton and benthic invertebrates and less periphyton compared to no carrion lakes. Phytoplankton was positively related to carrion biomass but the association diminished through time suggesting recovery from the initial nutrient pulse. In contrast, total Kjeldahl nitrogen, turbidity, and macroinvertebrates were positively related to carrion biomass and the slope increased throughout the summer suggesting an increasing pulse effect through time. Initially, zooplankton density was negatively related to carrion biomass but then became positively related to carrion biomass. Regression slope between zooplankton and carrion biomass peaked in June before decreasing in late summer, suggesting recovery from the pulse. Combined, our results suggest that nutrients released during fish decomposition following stochastic disturbances represent an important pulse in eutrophic lakes that further enriches productivity.





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