Seasonal contribution of terrestrial organic matter and biological oxygen demand to the Baltic Sea from three contrasting river catchments

[摘要] To examine the potential influence of terrestrially derived DOM on the BalticSea, a year-long study of dissolved organic matter (DOM) was performed inthree river catchments in Sweden. One catchment drains into the Bothnian Sea,while two southern catchments drain into the Baltic proper. Dissolved organiccarbon (DOC) concentrations were positively correlated with discharge fromforested catchments over the year. While the overall concentrations of DOCwere several times higher in the southern two catchments, higher discharge inthe northern catchment resulted in the annual loadings of DOC being on thesame order of magnitude for all three catchments. Biological oxygen demand(BOD) was used as a proxy for the lability of carbon in the system. The rangeof BOD values was similar for all three catchments, however, the ratio of BODto DOC (an indication of the labile fraction) in Ume river was four timeshigher than in the southern two catchments. Total annual BOD loading to theBaltic Sea was twice as high in the northern catchment than in the twosouthern catchments. Lower winter temperatures and preservation of organicmatter in the northern catchment combined with an intense spring flood helpto explain the higher concentrations of labile carbon in the northerncatchment. Lower lability of DOM as well as higher colour in the southerncatchments suggest that wetlands (i.e. peat bogs) may be the dominant sourceof DOM in these catchments, particularly in periods of low flow. With climatechange expected to increase precipitation events and temperatures across theregion, the supply and quality of DOM delivered to the Baltic Sea can also beexpected to change. Our results indicate that DOM supply to the Baltic Seafrom boreal rivers will be more stable throughout the year, and potentiallyhave a lower bioavailability.

[学科分类] 地球化学与岩石