Effects of resource pulse magnitude on nutrient availability, productivity, stability, and food web dynamics in experimental aquatic ecosystems

Abstract

Resource pulses provide short-duration, large-magnitude resources that influence ecosystem productivity, structure, and function. However, little empirical evidence is available evaluating how lake ecosystems respond to varying resource pulse magnitudes. We used mesocosms inoculated with primary producers and consumers to compare resource pulses of 0, 25, 50, 100, and 250 kg/ha of common carp Cyprinus carpio to simulate post-winterkill fish biomass in shallow lakes. Ecosystem responses to a gradient of resource pulse magnitudes typically had the greatest effects on nutrient availability and primary producers with fewer detectable effects for consumers. Total phosphorus, total Kjeldahl nitrogen, nitrate, phytoplankton, and periphyton productions increased as a result of the resource pulse, whereas copepods were the only consumer observed to elicit a positive response. In contrast, pulse magnitude had little effect on ecosystem stability, trophic position, or energy flow, potentially due to the low biomass of pulse magnitudes introduced. Resource pulses of moderate or large size generally increased nutrient availability and primary productivity while decreasing water clarity, suggesting that resource pulses can be an important factor influencing shallow eutrophic lakes but that effects may not be proportional to pulse size.