Lipid-degrading enzyme activities associated with distribution and degradation of fatty acids in the mixing zone of Altamaha estuarine sediments

To examine the relationship between lipid-degrading enzyme activities and lipid composition in estuarine sediments, lipase activities and fatty acids in surface sediments at different stations along the Altamaha River were determined during a high discharge period. Freshwater sandy sediments from upstream stations were characterized by low organic carbon and low lipid contents. Sediments from the strong mixing zone, where salinities were highly variable, were characterized by high organic carbon and high lipid contents with a predominance of long chain (>C20) saturated fatty acids, derived from terrestrial plants. At the river mouth, total fatty acids in the sediments were at intermediate concentrations, with a predominance of algal fatty acids. Lipase activity in the Altamaha River sediments was associated with certain fatty acid subgroups, i.e. monounsaturated, short-chain saturated, and branched-chain fatty acids. This indicates that these lipases probably were produced by bacteria. There was no significant correlation between lipase activity and terrestrial plant fatty acids (long-chain saturates) or algal fatty acids (polyunsaturates). A 3 month incubation of Altamaha River sediment, collected from the strong mixing zone, was carried out to determine changes in lipase activities and degradation rates of the various fatty acids. Solvent-extractable fatty acids were more readily degraded than bound fatty acids (fatty acids released from the extracted-sediment residue by saponification). Chain length and degree of unsaturation, which were linked to the lipid source, affected fatty acid degradation rates. The presence of water overlying sediment resulted in increased sediment lipase activity during incubation, presumably due to stimulation of microbial processes at the sediment–water interface.