Differential support of lake food webs by three types of terrestrial organic carbon

Abstract

Organic carbon inputs from outside of ecosystem boundaries potentially subsidize recipient food webs. Four whole‐lake additions of dissolved inorganic 13 C were made to reveal the pathways of subsidies to lakes from terrestrial dissolved organic carbon (t‐DOC), terrestrial particulate organic carbon (t‐POC) and terrestrial prey items. Terrestrial DOC, the largest input, was a major subsidy of pelagic bacterial respiration, but little of this bacterial C was passed up the food web. Zooplankton received Chaoborus and fishes. This route supplied 33–73% of carbon flow to zooplankton and 20–50% to fishes in non‐fertilized lakes. Terrestrial prey, by far the smallest input, provided some fishes with >20% of their carbon. The results show that impacts of cross‐ecosystem subsidies depend on characteristics of the imported material, the route of entry into the food web, the types of consumers present, and the productivity of the recipient system.

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