Epsilon Archive for Student Projects

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.