Assessing the biodegradability of terrestrially-derived organic matter in Scottish sea loch sediments
Résumé
Lignin oxidation products were used to determine the sources, transport and distribution of terrestrially-derived organic matter (OM) in two Scottish sea lochs, Loch Creran and Loch Etive. Oxygen uptake rates, molar OC/N ratios (from bulk elemental analysis) and Rp values (from loss on ignition experiments, the ratio of the refractory to total OM) were also determined for sediments along transects of the lochs. Lignin data indicate the importance of riverine inputs, contributing land-derived carbon to the lochs as total lignin (?, mg/100 mg organic carbon, OC) decreased from 0.69 to 0.45 and 0.70 to 0.29 from the head to outside of Lochs Creran and Etive, respectively. In addition, significant correlations for lignin content against total OM and OC (p<0.05) also suggest a distinct contribution of terrestrial OM to carbon pools in the lochs. The general trend of decreasing oxygen uptake rates from the head (20.8 mmole m?2 day?1) to mouth (9.4 mmole m?2 day?1) of Loch Creran indicates decomposition of some terrestrial OM. Biodegradability of the sediment OM was also characterized by the increase of Rp values from the head to mouth of the lochs: 0.40 to 0.80 for Etive and 0.43 to 0.63 in Creran. Further, the molar OC/N ratio decreased from 11.2 to 6.4 in Creran, and from 17.5 to 8.2 in Etive. Our results show that the relatively fresh, terrestrially-derived OM, which is still susceptible to mineralization, plays an important role in fuelling the biogeochemical cycling of carbon in both systems. This work also demonstrates that oxygen uptake rate, Rp value and molar OC/N ratio are able to serve as useful proxies to indicate sediment biodegradability.
Origine : Accord explicite pour ce dépôt
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