Dissolved Inorganic and Spectrophotometrically Characterized Dissolved Organic Carbon From Source to sea: Tyne Catchment, UK

Dissolved organic matter (DOM) fluorescence, absorbance and dissolved organic and inorganic carbon (DIC, DOC) were measured from source to sea in the River Tyne catchment, of c. 2935 km2 and encompassing areas of contrasting land use. The catchment has three major tributaries: the North Tyne which has good water quality, high DOC concentrations and visible water colour from the high proportion of peat in its upper catchment; the South Tyne which has good water quality with typical riverine DOC concentrations and drains from limestone uplands; and the Derwent, a more urbanized catchment which is increasingly impacted by treated sewage effluent discharges towards its mouth. Freshwater and estuarine sampling campaigns yield the following results: (1) High absorbance at 340 nm and DOC concentration identify North Tyne waters due to the peaty headwaters, but no downstream trends in these parameters are observed in any of the tributaries, in contrast to the estuary where a rapid decrease is observed in both. (2) Fluorescence demonstrated downstream trends in both intensity and wavelength, especially in the Derwent as it is increasingly impacted by anthropogenic DOM. Elevated protein- like fluorescence intensity also fingerprints sewage effluent within the estuary. (3) The absorbance coefficient at 340 nm was found to have the strongest correlation to DOC concentration greater than all fluorescence intensity parameters measured. However, fluorescence analysis permits the source of the DOM to be determined. (4) With the exception of peat rich headwaters, DIC concentration is always greater than DOC. DIC is primarily in the form HCO3-, with concentrations highest in highly urbanized catchments, typically greater than those observed in catchments with carbonate bedrock, demonstrating a significant and previously unrecognized anthropogenic DIC. (5) Principal components analyses of estuarine samples showed 63.4% of the variability in DOM can be explained by two sets of components, with the first component correlated to the mixing of terrestrial and marine waters and the second component correlated to sources of pollution such as domestic sewage.