Variability in benthic respiration in three southeastern Australian lowland rivers

La Trobe University Faculty of Science, Technology and Engineering Murray Darling Freshwater Research Centre

MDFRC item.

Benthic respiration is an important measure of decomposition processes occurring in streams, but our understanding of benthic respiration in lowland rivers is not well developed, particularly the factors that affect benthic respiration. In our study we measured benthic respiration at three sites in three contrasting lowland rivers in southeastern Australia. On most sampling occasions, rates of oxygen consumption in benthic chambers were linear. However, oxygen consumption rates fitted exponential decay curves during periods of highest microbial activity. Benthic community respiration ranged from 289 to 619 mg O-2 m(2)d(-1) in the Broken River, from 178 to 1438 mg O(2)m(2)d(-1) in the River Murray and from 127 to 2178 mg O-2 m(2) d(-1) in the Ovens River. Benthic respiration was closely correlated with water temperature, but not with sediment carbon content, sediment particle size, water column nutrients or water column dissolved organic carbon concentrations. Average carbon turnover periods were between 1.7 and 6 years for the three rivers, but were as low as 0.1 year immediately following an event that gave rise to mobilization of in-stream dissolved organic carbon, sufficient to produce coloured water. The latter occurred in the Ovens River as a consequence of a rain event during a period of base-flow. Flow regime as such did not have a major impact on benthic community respiration. Induced changes in respiration, by altering flows, would only occur by altering the quality and timing of carbon inputs, since temperature and carbon quality, rather than quantity, appear more important in determining lowland river benthic respiration.