The trophic significance of bacteria in a detritus-based stream food web. Ecology 79

Abstract. We compared relative use of streamwater dissolved organic carbon (DOC) by bacteria and the trophic significance of bacteria to invertebrates in two headwater streams at Coweeta Hydrologic Laboratory in North Carolina: a stream with all leaf litter inputs excluded for 1 yr, and a reference stream. Leaf litter standing crop in the treatment stream was,1 % that of the reference stream, and fine benthic organic matter (FBOM) was 50% lower than the reference. We used a whole-stream tracer addition of 13C-1 sodium acetate for 3 wk to label bacteria and hence their consumers during both July and December. Bacterial d13C was measured by collecting respired bacterial carbon. We estimated the contribution of bacterial carbon to consumers using a mixing model for invertebrates and bacteria. The acetate label declined exponentially downstream with a 10-m uptake length in each stream and season. FBOM and biofilm were the only detrital samples to show a strong label; both were more labeled in the litter-excluded stream. Bacteria in the litter-excluded stream had 7–10 times more label than those in the reference stream during both seasons, showing their higher relative use of streamwater DOC. The percentage of inver-tebrate carbon derived from bacteria was.20 % for many taxa. This was significantl