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Presented at the NABS Annual meeting, Pittsburgh, Pennsylvania, 2002
in Hyporheic Processes
HYPORHEIC INVERTEBRATES AFFECT NITROGEN CYCLING AND RESPIRATION IN STREAM SEDIMENT MICROCOSMS.
M.C. Marshall and R.O. Hall, Jr.. Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071
Many researchers assume that because of their small contribution to biomass and respiration in sediments, hyporheic invertebrates do not affect ecosystem processes, while others suggest they are important. Little empirical research has actually attempted to examine these effects in stream sediments. We used laboratory stream-sediment-filled flow-through microcosms (45 cm2 X 50 cm) to estimate the effects of mixed interstitial invertebrate assemblages (3 biomass treatments X 5 replicates) on nitrogen cycling and respiration. Average invertebrate biomasses in low and high invertebrate treatments were 0.20 and 19 mg DW L-1, respectively. Although we found high variation in response variables among replicates, invertebrate effects were still quantifiable among treatments. Average net nitrate uptake/regeneration decreased 0.0024 min-1 for each mg increase in dry invertebrate biomass, showing invertebrates suppressed uptake of nitrate or stimulated in situ nitrate production. Average respiration (corrected for sediment organic matter) and coarse particulate organic matter (CPOM) increased 33% and 51%, respectively, with increasing invertebrate biomass, suggesting direct contribution to hyporheic metabolism and/or stimulation of microbial activity and an accumulation of CPOM driven by invertebrates. These results are among the first experimental evidence of invertebrate effects on ecosystem level processes in hyporheic microcosms and suggest some contribution to lotic ecosystem functioning.
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