From Greenland to Green Lakes: Cultural Eutrophication and the Loss of Benthic Pathways in Lakes

Benthic community responses to lake eutrophication are poorly understood relative to pelagic responses. We compared phytoplankton and periphyton productivity along a eutrophication gradient in Greenland, U.S., and Danish lakes. Phytoplankton productivity increased along the phosphorus gradient (total phosphorus [TP] = 2-430 mg m-3), but whole-lake benthic algal productivity decreased, substantially depressing increases in primary productivity at the whole-lake scale. In shallow, oligotrophic Greenland lakes, periphyton was responsible for 80-98% of primary production, whereas in Danish lakes with TP > 100 mg m-3, phytoplankton were responsible for nearly 100% of primary production. Benthic contributions ranged from 5 to 80% depending on morphometry and littoral habitat composition in lakes with intermediate phosphorus concentrations. Thus, eutrophication was characterized by a switch from benthic to pelagic dominance of primary productivity. Carbon stable isotope analysis showed that the redistribution of primary production entailed a similar shift from periphyton to phytoplankton in the diets of zoobenthos. Benthic and pelagic habitats were energetically linked through food web interactions, but eutrophication eroded the benthic primary production pathway.