Biogeochemical Processes at the Sediment-water Interface, Bombah Broadwater Myall Lakes  

Authors / CoAuthors

Heggie, D.T. | Logan, G.A. | Smith, C.S. | Fredericks, D.J. | Palmer, D.W.

Abstract

Benthic nutrient fluxes from the sediments were measured at three Sites in the Bombah Broadwater of Myall Lakes during the winter (June) of 2000. Surface sediments (0-1 cm) and two cores were collected at each site and processed for measurements of carbon and nitrogen isotopic composition of the OM (organic matter), biomarkers and bulk sediment composition (OM and major cations). Pore waters were extracted from sediments and measured for both organic and inorganic metabolites. Biomarker, benthic flux data and the compositions of inorganic metabolites in pore waters indicated that Redfield OM (organic matter) was predominant in the sediments and mostly diatomaceous and probably responsible for the observed release of nutrients from the sediments to t he overlying waters. Carbon degradation rates in the sediments, during these winter month, varied between 5-47 mmol m-2 d-1 (60-564 µg m-2d-1) and were highest in the muddy sediments (mean = 21.3 +/-12.7 mmol m-2 d-1) as compared to the sandy sediments (mean = 11.6 +/-4.8 mmol m-2 d-1). DIN fluxes were less than those predicted from CO2 fluxes and Redfield stoichiometry and the `missing nitrogen' (subsequently determined by mass spectrometry as N2) was indicative of denitrification in the surface sediments. Rates of denitrification calculated from N2 directly and from `missing N' were similar and up to 5.1 mmol N m-2 d-1. There was no evidence of organic metabolite fluxes although the organic and inorganic metabolite concentrations were similar in the pore waters. Denitrification efficiencies were high (mean = 80 +/- 4%) in the sandy sediments and lower (although there was considerable variability) in the muddy sediments (mean =38% +/- 9%). Most DIP (generally > 70%) liberated to pore waters during OM degradation was not released into overlying waters but remained trapped and enriched in surface sediments. Benthic nutrient fluxes (average DIN/DIP = 131) were preferentially enriched in N compared to the OM (N/P = 16) raining into the sediments. Adjective biophysical processes (not diffusive) dominated the fluxes of metabolites across the sediment -water interface.

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nonGeographicDataset

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64204

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• External PublicationScientific Journal Paper

( Theme )

• geochemistry

( Theme )

• coasts

( Theme )

• environmental

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• water resources

Australian and New Zealand Standard Research Classification (ANZSRC)

• Earth Sciences

• Published_Internal

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2006-05-08T00:00:00

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