Whole-Lake Sugar Addition Demonstrates Trophic Transfer of Dissolved Organic Carbon to Top Consumers
Terrestrial dissolved organic carbon (DOC) provides an external carbon source to lake ecosystems. However, there is ongoing debate about whether external DOC that enters a lake can pass up the food web to support top consumers. We show, from experimental manipulation of a whole lake, that externally loaded DOC can contribute appreciably to fish biomass. Monthly additions of cane sugar with a distinct carbon stable isotope value during 2 years rapidly enriched the 13C content of zooplankton and macroinvertebrates, with a more gradual 13C enrichment of fish. After sugar addition stopped, the 13C content of consumers reverted towards original values. A simple isotope mixing model indicated that by the end of the sugar addition almost 20% of fish carbon in the lake was derived from the added sugar. Our results provide the first direct experimental demonstration at relevant ecological spatial and temporal scales that externally loaded DOC to lakes can indeed transfer to top consumers.
Keywordslakes fish macroinvertebrates zooplankton food webs allochthony cane sugar stable isotopes
This work was funded by Academy of Finland Grants 114604 and 137671 to RJ. We are grateful for the support from staff and facilities at Lammi Biological Station, University of Helsinki, and the Evo Station of the Natural Resources Institute Finland.
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