Water column nutrient and dissolved organic carbon concentrations, dissolved organic matter characteristics and bacterial abundance in three Baltic Sea estuaries

These include transformations and degradation by biological and chemical processes, but also the production of fresh organic matter. Since many of these processes occur simultaneously, properties of the DOM pool represent the net changes during the passage along the hydrological path.

We examined changes in multiple DOM characteristics across three Finnish estuarine gradients during spring, summer and autumn: Dissolved organic carbon (DOC) concentration, coloured DOM absorbance and fluorescence, stable carbon isotope signal of DOC and molecular size distribution. Changes in these DOM characteristics with salinity were analysed in relation to residence time (i.e. freshwater transit time), since increased residence time is likely to enhance DOM degradation while stimulating autochthonous DOM production at the same time.