Fatty acids, fatty alcohols and sterols were quantified in surface sediment samples taken from the Mawddach Estuary and from the Clyde Sea to assess the spatial variability. These biomarkers were also quantified in sediment cores from the Conwy Estuary and Loch Riddon to investigate their temporal variability. These biomarkers are valuable tracers to assess organic matter sources in different marine environments. Traditional biomarker approaches such as Alcohol Source Indices (ASI) and Sterol Source Indices (SSI) based on the ratio between terrestrial and marine fatty alcohols and sterols were developed to see the influence of terrestrial organic matter within marine sediments. Other ratios based on short/long, odd/even and coprostanol/cholesterol highlighted the bacterial/sewage derived organic matter and their distribution. This approach also shows the degradation of marine derived lipids with time as seen in the core samples.
Principal Component Analysis (PCA), factor analysis and cluster analysis were used to classify these biomarkers according to their primary source such as terrestrial, marine, bacteria and sewage. PCA based on the proportion data rather than raw data clearly shows the compound separations according to their geochemical sources. PCA of fatty alcohols and fatty acids also provide more information on secondary processes. However, in the Conwy core, PCA was not able to separate the marine and bacterial derived markers. Cluster analysis with Ward's method differentiated the Clyde Sea sediment samples and the Loch Riddon core into two regions: 1) Samples that were influenced by marine and
bacterial organic matter, and 2) Samples that were dominated by terrestrial inputs. Two and three factors were extracted from factor analysis conducted on the Mawddach Estuary and the Loch Riddon core. Three significant sources in the Mawddach were marine/bacterial, sewage and terrestrial. In the Loch Riddon core, bacterial/marine and terrestrial became the significant sources. To quantify the contribution or transportation of organic matter in these sampling sites, Partial Least Squares (PLS) path model were developed. PLS successfully quantified the decrease of organic matter down the core, as well as the contribution of organic matter due to current movements, river runoff and tidal
exchange.