Spatial patterns of Dissolved Organic Matter in Swedish Surface Waters

Abstract: Dissolved organic matter (DOM) in surface water has been widely studied, in part due to its significance for aquatic ecology and drinking water quality. Across Sweden, increases in the total organic carbon (TOC) concentrations and color of surface waters, known as brownification, were noted in the decades before and after year 2000, though recent analysis has found widespread DOM increase to have ceased after 2010. While the overall decadal trends of TOC have gained considerable attention, the spatial patterns in the TOC dynamics of different watercourses may hold clues to the causes of the TOC variation in time as well as in space. Recent developments in digital mapping provide high resolution information on soil moisture and the spatial variation of the extent of river systems. This thesis focused on testing whether the new, high resolution map data can explain spatial and temporal patterns in stream DOM. In addition to the soil moisture map, modeled stream networks were used to more accurately represent the small streams of the headwaters, and locate hydrological connectivity of soils near streams. Data taken from the soil moisture map and modeled stream networks were used as high resolution data in the analysis. In changing the stream initiation size of the modeled streams from 10 ha to a smaller area needed for stream initiation of 2 ha the stream systems length in Sweden showed a mean increase by 41% while increasing stream initiation size to 30ha decreased the stream network length by 46%. Adding high resolution data did not improve the ability of the multivariant model to explain TOC variation and influences that already included catchment characteristics such as meteorological, discharge, soil type and land use data, which could explain 64% of variation. However, on its own high resolution data was able to explain 40% of the variation in TOC and its influences. In conclusion high resolution spatial data of soil moisture and stream length although they could not add new explanatory power, can be used to deepen our understanding of the importance of topographic variables to TOC variation.