Aquatic food webs are supported by primary production from within the system (autochthony) as well as organic matter produced outside of and transported into the system (allochthony). Zooplankton use allochthonous resources, especially in systems with high terrestrial loading and moderate to low internal primary production. We hypothesized that due to high terrestrial loads and remnant submerged terrestrial material, allochthonous resource use by zooplankton would be significant in all reservoirs and would decline along an increasing reservoir age gradient. Using hydrogen stable isotopes and a Bayesian mixing model, we estimated the contribution of allochthonous sources to organic matter pools and crustaceous zooplankton biomass for ten reservoirs. Dissolved organic matter (DOM) in all systems was dominated by allochthonous sources (posterior distribution median [92% allochthonous), while particulate organic matter (POM) composition varied (2-68% allochthonous) and had a lower allochthonous fraction in older reservoirs. There was no relationship between zooplankton allochthony and reservoir age. Crustaceous zooplankton allochthony varied among systems from 26 to 94%, and Chaoborus allochthony, measured in four reservoirs, was similarly variable (33-94%). Consumer allochthony was higher than POM allochthony in some reservoirs, potentially due to terrestrial DOM pathways being important and/or algal resources being inedible (e.g., cyanobacteria). As with many lakes, in the reservoirs we studied, allochthonous inputs account for a significant fraction of the organic matter of basal consumers.
Due to an error in model transcription, the dietary water fraction was only applied to the zooplankton and Chaoborus algal fraction in the mixing model. The dietary water correction should have also been applied to the terrestrial fraction. The updated zooplankton and Chaoborus allochthony values are reported below along with corrected versions of Figs. 2 and 4. In the corrected model, the values for zooplankton and Chaoborus allochthony decreased approximately 15% but the patterns among reservoirs, the regression analysis, and the conclusion remain unchanged.Crustaceous zooplankton allochthony varied among systems from 11 to 79%, and Chaoborus allochthony, measured in four reservoirs, was similarly variable (22-80%). The allochthonous fraction of zooplankton was variable but usually\50% in all but two reservoirs. For most reservoirs the four pools of organic matter considered in this study (POM, DOM, zooplankton, Chaoborus) were over 20% allochthonous based on median values, but some zooplankton distributions had high uncertainty.The online version of the original article can be found under
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