Lake ecosystems can receive high inputs of terrestrial organic matter (t-OM) that microbes make available to higher trophic level consumers. Finnish Dutch research group examined terrestrial reliance of 19 consumer groups from 35 boreal lakes using stable isotopes of hydrogen. According to the study, benthic macroinvertebrates and the benthivorous fish reliance to terrestrial energy (allochthony) was higher compared to pelagic plankton and planktivorous fish. Consumer allochthony decreased along the environmental gradient from forested to agricultural catchments, likely due to alteration in the origin of lake organic matter.

The team measured stable isotopes of hydrogen from 19 different consumer groups, from algae to top predators, from 35 boreal lakes and estimated consumer reliance on terrestrial energy using Bayesian mixing models.

- We found great differences in energy dynamics of dystrophic and eutrophic lakes. Agriculture in the catchment areas decreases consumer allochthony at all trophic levels and feeding guilds due to increased algal production while high forest coverage promotes consumer allochthony, says Postdoctoral Researcher Ossi Keva, who worked at the University of Jyväskylä during the research.

Energy from food webs is reflected in fishes

Energy and biomass transfer in lake food webs can be studied with stable isotopes. Stable isotopes of hydrogen are particularly useful for differentiating aquatic and terrestrial biomass as water loss by transpiration leads to strong enrichment in the heavy isotope in terrestrial plants, a process that is absent for submerged aquatic primary producers. Dissolved and particulate organic matter in lakes can originate both from aquatic and terrestrial primary production. Some microbes are able to assimilate dissolved organic matter and thus channeling the energy to higher trophic levels through predator prey interactions.

- Across the study lakes, pelagic zooplankton derived their energy mainly from algal production, but major part of benthic macroinvertebrate energy were terrestrial origin. These patterns were also reflected in the origin of planktivorous and benthivorous fish energy according to their feeding guilds, explains Keva.

Changes in lake organic matter origin

The study shows that catchment area land-use influence the origin of lake dissolved and particulate organic matter pool. Lakes with high coverage of agriculture area in their catchment are usually more eutrophic and thus the organic matter there is mainly algal origin. On the other hand, the organic matter pool in dystrophic lakes in forested areas is relatively more terrestrial originated. Therefore, aquatic consumer reliance on terrestrial energy is altered across an environmental gradient – consumer allochthony decreases from drown dystrophic lakes towards eutrophic lakes.

- The study highlights that catchment area land-use affect the transport of organic matter from donor terrestrial landscapes to recipient lake ecosystems, lake organic matter pool origin, lake energy dynamics and thus the function the aquatic food webs, tells Keva.

Researchers from Finland and Netherlands collaborated to the consumer allochthony study.

The research was published in Nature Communications on 15 of April 2025.