SS3.07 Headwater Ecosystems in Forested Landscapes and Beyond
Date: Wednesday, June 12, 2002
Location: Poster Session - VCC
 
KreutzweiserDP, Canadian Forest Service, Sault Ste. Marie, Canada, dkreutzw@nrcan.gc.ca
Capell, S, S, Canadian Forest Service, Sault Ste. Marie, Canada, scapell@nrcan.gc.ca
 
BENTHIC MICROBIAL UTILIZATION OF DIFFERENTIAL DOM SOURCES IN HEADWATER STREAMS
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Terrestrial organic matter inputs to forested headwater streams have been shown to be important drivers of aquatic microbial community dynamics. However, studies have reported conflicting results with regard to the importance of terrestrially-derived dissolved organic matter (DOM) to attached microbial communities in streams. We conducted stream-side mesocosm experiments in a low-order forest watershed to directly examine responses by microbial communities on standardised substrates to different terrestrial and aquatic sources of DOM. Community respiration (oxygen uptake), CFU density, leaf decomposition, and microbial metabolic profiles in sole carbon source utilization assays were measured. Stream benthic microbial communities responded immediately and positively to increases in terrestrially-derived DOM. Respiration activity and density estimates increased significantly, but there was no significant change in community metabolic profile. Responses were greater to DOM extracted from upper soil horizons than from deeper soils. Community respiration and bacterial abundance also increased in response to an aquatic DOM source, but were accompanied by a significant change in community metabolic profiles. Results provide direct experimental evidence that benthic microbial communities of headwater streams are pre-adapted to rapidly utilise terrestrial DOM.