Continuous, Pulsed and Disrupted Nutrient Subsidy Effects on Ecosystem Productivity, Stability, and Energy Flow

Resource pulses and subsidies can supply ecosystems with a nutrient source that supports increased productivity. Common carp Cyprinus carpio provide ecosystems with a continuous nutrient subsidy through bioturbation but may initiate a nutrient pulse through carcass decomposition.  We examined how continuous (foraging), pulsed (decomposition) and disrupted (carp removed) subsidies differed in their ability to alter nutrient availability, ecosystem productivity and energy flow.  Nitrogen and phosphorus and primary production were highest in pulsed, intermediate in continuous and lowest for disrupted and control systems.  Continuous, and to a lesser extent pulsed, systems were associated with decreased water clarity and macrophyte coverage.  Nutrient pulses ascended to higher trophic levels and supported greater densities of consumers (i.e., zooplankton and macroinvertebrates).  Biotic and abiotic responses in disrupted systems quickly returned to control levels and water quality improved. Biotic materials collected from pulsed and continuous subsidy systems were enriched in δ¹⁵N suggesting released nutrients supported increased productivity whereas δ¹³C signatures were depleted suggesting a transition to more pelagic energy pathways.  Our results suggest that continuous and pulsed nutrient subsidies vary in their ability to support and sustain ecosystem productivity with resulting variation in food web structure and ecosystem stability.