Hydrological catchment analysis from characterisation of organic matter in stream water

Abstract: Organic matter (OM) in aquatic systems is a complex field which have rapidly developed during the last decade due to the introduction of high resolution mass spectrometers. The composition of OM in the aquatic environment is directly dependent on factors such as oxygen supply, pH and the flow rate in the local system. Furthermore, the OM is closely linked to negative effects on these systems such as eutrophication and brownification, which in many cases are caused by human activity through climate change, water management and changes in land use patterns. This thesis focuses on the composition of organic matter in the aquatic environment in relation to land use and water management. The aim of this work is characterising of OM from water draining distinctly different sub-catchments and using the internal OM composition as a tracer for different catchment characteristics. Stream water was sampled and analysed for OM using direct-sample-analysis Time-of-flight mass spectrometry (DSA-TOF-MS) and Total-organiccarbon (TOC) analysis from streams draining the different sub-catchments. The results were then linked to the different sampling locations through comparisons of mass spectra, Principlecomponent statistics and molecular formula correlations. The result show that three different sub-catchments could be distinguished by OM quantification and characterisation. However, it was not possible use characterised mass peaks as a downstream tracer, which can probably be explained by the complex degradation, transformation and sedimentation processes interacting with the OM in the catchment. Improved methodology and further studies to map the processes affecting the OM in the aquatic system is necessary to be able to use the internal organic chemistry as a marker for the status of the system.