Food Web Structure and Phosphorus Cycling in Lakes

Abstract

We assessed the effects of trophic structure on phosphorus (P) recycling by fishes, Chaoborus, and zooplankton in lakes with different food web configurations. Fishes in a piscivoredominated system recycled little P compared to that regenerated by zooplankton and Chaoborus. In a plan ktivore-dominated lake, excretion by fishes (especially young of year) dominated P recycling to algae; Chaoborus and zooplankton recycling was decreased due to intense predation by fishes. The sum of P incorporated into primary production and lost to sedimentation in the piscivore-dominated lake was only 77% of that in the planktivore-dominated lake, Our analyses suggest that the 30% greater primary production in the planktivore-dominated system may be accounted for by the greater than 40% increase in estimated P recycling that was directly due to differences in food web structure, Diel vertical migrations by Chaoborus concentrated P excretion in the epilimnion during night hours. In the plan ktivore-dominated system, Chaoborus migrations further affected spatial dynamics of P recycling by concentrating excreted P in the lower depths of the epilimnion. Diel vertical migrations by zooplankton had little effect on the spatial and temporal dynamics of P recycling except to dampen the effects of the Chaoborus migrations.