Assessing the biodegradability of terrestrially-derived organic matter in Scottish sea loch sediments

摘要

Lignin oxidation products, oxygen uptake rates, molar organic carbon tonitrogen (OC/N) ratio (from bulk elemental analysis) and Rp values (fromloss on ignition experiments, the ratio of the refractory to total organicmatter, OM) were determined for sediments along transects of Loch Creran andLoch Etive. Lignin data indicated the importance of riverine inputscontributing to land-derived carbon in the lochs as total lignin (Λ, mg/100 mgorganic carbon, OC) decreased from 0.69 to 0.45 and 0.70 to0.29 from the head to outside of Loch Creran and Loch Etive, respectively.In addition, significant correlations of lignin content against total OM andOC (p<0.05) also suggested a distinct contribution of terrestrial OM tocarbon pools in the lochs. The general trend of decreasing oxygen uptakerates 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 OM.Biodegradability of the sedimentary OM was also characterized by theincrease of Rp values from the head to mouth of the lochs: 0.40 to 0.80 inLoch Etive and 0.43 to 0.63 in Loch Creran. Furthermore, the molar OC/Nratio decreased from 11.2 to 6.4 in Loch Creran, and from 17.5 to 8.2 inLoch Etive. Derived rate constants for OM degradation were found to decreasefrom LC0 to LC1, and increase from RE5 to RE6. This work demonstrates thatoxygen uptake rates, Rp values and molar OC/N ratio are able to serve asuseful proxies to indicate the biodegradability of sedimentary OM.