UV Effects on Aquatic Microbial Food Webs in Northern Lakes and Rivers

Abstract

Lakes, ponds and rivers occur throughout the arctic and subarctic landscape and provide the habitat for a variety of aquatic life including zooplankton, insects, fish and birds. The base of the food webs supporting these animal populations is still poorly understood, but at many sites examined to date the biomass and energy flow in the lower food web is mostly associated with microscopic species of diverse nutritional modes: photosynthetic bacteria and micro-algae; heterotrophic and chemotrophic bacteria; phagotrophic flagellates, ciliates and amoeboid protozoa; parasitic organisms including viruses; and mixotrophic protists that can obtain their carbon and energy supply by heterotrophic processes as well as by photosynthesis. These organisms collectively form the microbial food web (Fig. 7.1) that recycles nutrients and passes on carbon and other elements to higher trophic levels. In deeper lakes and rivers this microbial community is mostly planktonic and is distributed throughout the water column In shallow-water systems, which are especially abundant throughout the North (e.g., thaw ponds on the tundra, polar desert streams), these diverse functional groups are most abundant in the benthic mats or films that form the periphyton over the surface of rocks, sediment and submerged plants such as aquatic mosses. Even in deeper lakes, the benthic microbial communities play a major role in biomass production and biogeochemical transformations.