Broad-Scale Patterns in CDOM and Total Organic Matter Concentrations of Inland Waters – Insights from Remote Sensing and GIS

Sammanfattning: The rise in CDOM (coloured dissloved organic matter) is likely to be relatively more pronounced in remote northern regions. However, there is a lack of monitoring to confirm this. For this reason, there is a strong incentive to develop remote sensing-based methods to map CDOM in lakes across broader geographical scales and to include geograghic contex in such analysis. There is a lack of understanding of the mechanisms behind changes in water colour (i.e. CDOM) at large scales. The CDOM variations could be due to varying drivers, such as climate and landscape patterns or catchment features. This means that currently, we do not know the extent to which aquatic ecosystems need conservation efforts, such as management of the surrounding vegetation, to prevent CDOM leakage. Thus, there is need to better understand the drivers behind CDOM changes in inland waters.Over the last few decades, remote sensing technologies and methods have developed dramatically for terrestrial ecosystems. Coupled with the broader availability of remote sensing data, free access to different data sources and the increased resolution of satellite platforms, remote sensing technology now has a significant impact on land monitoring. Due to the increasing demand for high-quality remote sensing data, the technology continues to improve, which makes remote sensing critical for reducing time and funding costs. Similar to these advances in terrestrial remote sensing, there is an increasing potential to provide information about inland waters by using remote sensing. For instance, recent advancements in designing remote sensors, such as the Landsat 8 operational land imager (OLI) and Sentinel-2 multispectral instrument (MSI), have solved past radiometric sensitivity issues and provide high spatial resolution. This thesis explored CDOM patterns on spatial and temporal scales. The overall aim was to investigate the capabilities of remote sensing (RS) and geographic information systems (GIS) to extend CDOM patterns from a regional to a broad scale. Different study sites in Europe, mainly Northern Scandinavia, including large numbers of lakes and rivers, were tested on different scales.The results shows how climate changes (from wet to dry) can result in a combination of changes in hydrology, vegetation type and productivity, which can lead to intra-annual variations in the CDOM of recipient waters. It is also shown that drought can temporarily decrease values of CDOM in boreal lakes. In addition, it is demonstrated that combining remote sensing and GIS tools is an effective way to reveal the impact of different catchment parameters and morphometry on lake CDOM concentration. Moreover, the thesis shows that utlizing long-term remote sensing records of CDOM from the last few decades is a successful approach to fill the gaps of the missing lake data from in situ assessments. Finally, the results helped to explore links between water browning and the organic matter degradation rates in temperate European rivers at a continental scale. In conclusion, this thesis demonstrates the pogential use of remote sensing for mapping CDOM in a wide range of inland waters that are situated in complex, inaccessible regions that are not well- monitored.