Organic matter and benthic metabolism in euphotic sediments along shallow sub-tropical estuaries, northern New South Wales, Australia

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 33:137-154 (2003) - doi:10.3354/ame033137 Organic matter and benthic metabolism in euphotic sediments along shallow sub-tropical estuaries, northern New South Wales, Australia Angus J. P. Ferguson*, Bradley D. Eyre, Jennita M. Gay Centre for Coastal Management, Southern Cross University, PO Box 157, East Lismore 2480, New South Wales, Australia *Email: aferguso@scu.edu.au ABSTRACT: Sediment organic matter (OM), chloropigments and benthic metabolism (oxygen, carbon dioxide and alkalinity fluxes) were investigated along 3 sub-tropical Australian estuaries during different seasons. Significant rates of benthic productivity occurred throughout the year in the study estuaries, especially in the lower reaches where sediments were commonly net autotrophic. Benthic microalgae (BMA) contributed up to 20% of the total carbon content in the lower estuary sands, while organic matter was dominated by phytodetritus and allochthonous material in the middle to upper estuaries. Sediment oxygen demand (SOD) incubations were carried out on surface sediments to investigate labile carbon contents. SOD normalised to sediment carbon content (SOD mol C-1) confirmed a much higher proportion of labile OM in the lower estuary sediments due to a predominance of living BMA, while the OM pool in the upper and middle estuaries was relatively more degraded. SOD mol C-1 correlated well with both the C:N and the chlorophyll:pheophytin ratios of surface sediments, providing 3 independent measures of sediment OM quality. Comparisons between SOD and benthic community respiration rates (O2 fluxes) measured in sediment core incubations suggested that oxygen demand due to the oxidation of reduced sulphur compounds formed a significant fraction of the O2 flux, and that fluxes may be enhanced by bioturbation. O2 and TCO2 respiration rates were overall poorly correlated and suggested that benthic metabolism is characterised by periods of anaerobic mineralisation (TCO2:O2 > 2) during periods of high OM supply, followed by aerobic respiration and reoxidation (TCO2:O2 ≈ 1 to 2) as OM supply waned. At many sites throughout the study TCO2:O2 flux ratios were less than 1 and coupled with alkalinity uptakes, indicating that either sulphide oxidation or nitrification may be significant influences on the benthic fluxes. These processes cause a net drawdown on O2 effluxes that can lead to significant underestimations of benthic productivity. As such, the use of CO2 and O2 fluxes yield distinctly different measures of benthic metabolism. KEY WORDS: Organic matter · Benthic metabolism · Respiratory quotient · Chlorophyll · Benthic microalgae Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 33, No. 2. Online publication date: October 14, 2003 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2003 Inter-Research.