Lake browning in the northern hemisphere is endangering crucial ecosystem services. Darker water decreases fish and primary production as well as touristic and recreational values. It furthermore requires intensive treatment to receive safe drinking water. Brownification is connected to iron and coloured dissolved organic carbon (DOC). In Sweden, spruce plantations leak DOC, possibly depending in their DOC rate on tree age. Whereas wetlands are known to purify water and might contribute to the degradation of DOC. This thesis aims to investigate how different land use types and other parameters affect water colour. Ditches flowing through old spruce forests, young spruce forests, and peat wetlands in the Lake Bolmen catchment, southwestern Sweden, were sampled at in- and outlet. Highly significantly positive relationships between DOC, iron and absorbance were found. The relationship was strongest between DOC and absorbance (R² = 0.88; p < 0.001) and weakest between DOC and iron (R² = 0.54; p < 0.001). High variability led to no significant differences in the release of DOC and iron between the three land use types. However, older forests tended to increase DOC and iron loading compared to younger forests. This study suggests that not only spruce forests in general are affecting the brownification, but that several different factors like age and underlying soil type might play a critical role.

Increased DOC and Fe concentrations from terrestrial landscapes has led to the browning of boreal surface waters. The negative societal and ecological impacts of brownification are increased cost of water purification, increased presences of algae and cyanobacteria, loss of ecosystem services and reduced recreational value. Impacts of climate change, changes in land use and reduced sulfur deposition have been identified as drivers of brownification. While it has been recognized that DOC and Fe from terrestrial landscapes is increasing, little has been done to understand the impact of different land use practices on brownification. This research aims at evaluating the DOC and Fe runoff from spruce plantations, clear-cuts and wetland landscapes and determining the export of DOC from these landscapes into humic lakes. To do that, streams running through these three different land use types were sampled for water colour, pH, temperature, conductivity, DOC and Fe both at upstream and downstream of each land use type. Further, water discharge was calculated with the help of flow speed measurements and stream profiling (width, depth and channel shape). DOC (but not Fe) concentrations changed significantly depending on land use type. Wetlands lead to reduced DOC concentrations, whereas especially spruce plantations lead to increased stream water DOC concentrations.

<p>The aim of this thesis was to determine whether there has been a trend of increasing or decreasing water colour, absorbance, in Lake Mälaren during the last 35 years and whether it could be correlated with water discharge. The discharge was accounted for using regression analysis. The data material was analyzed for trends using a nonparametric test, the so-called seasonal Mann- Kendall test. The regression model could only account for a small (maximum of 24%) variation due to discharge. Thisindicates that discharge single-handedly can not explain the variation in absorbance. The trend analysis indicated a significant yearly increase in absorbance of 0.93% - 2.43% yr-¹ for three out of four investigated sub-basins, namely, Galten, Ekoln and Skarven. This strongly implies that there has been an increase of absorbance and a change in the amount of organic material in Lake Mälaren during the last 35 years.</p>

The aim of this study was to investigate whether the water chemistry in lake Lillsjön have changed significantly due to human impact of surrounding areas. Lake Lillsjön is located outside the central parts of Östersund. It is an important recrational area, and has great natural values, among other things it is habitat for several species of Chara stoneworts. Chara requires clear calcareous water, high pH, relatively low levels of nitrate-nitrogen and low phosphorus concentrations. Lake Lillsjöns is recepient for surface water from a nearby commercial and industrial area, as well as melt water from an adjecent snow dump. Compared to ten other Chara-lakes in the region, lake Lillsjön shows higher concentration of total phosphorus and higher water colour. The study concludes that the surface water from surrounding areas, as well as melting water from the snow dump, are the main sources of the higher concentration of total phosphorus in lake Lillsjön. While the colour of the incoming water only shows a weak difference compared to the water colour of the reference lakes, the source of the higher water colour cannot be established. The water of lake Lillsjön can not be consider a suitable habitat for Chara.

The aim of this thesis was to determine whether there has been a trend of increasing or decreasing water colour, absorbance, in Lake Mälaren during the last 35 years and whether it could be correlated with water discharge. The discharge was accounted for using regression analysis. The data material was analyzed for trends using a nonparametric test, the so-called seasonal Mann- Kendall test. The regression model could only account for a small (maximum of 24%) variation due to discharge. Thisindicates that discharge single-handedly can not explain the variation in absorbance. The trend analysis indicated a significant yearly increase in absorbance of 0.93% - 2.43% yr-1 for three out of four investigated sub-basins, namely, Galten, Ekoln and Skarven. This strongly implies that there has been an increase of absorbance and a change in the amount of organic material in Lake Mälaren during the last 35 years.

This diploma thesis is focused on the study of the influence of advanced oxidation processes on degradation of organic dyes. The field of AOP – very effective physically-chemical methods of wastewater treatment – includes application of strong oxidation agents, UV and ionizing radiation and electrical discharges. For this thesis, two of these methods were chosen – the application of oxidation agent (ozone) and UV radiation. Along with electrolysis, which is mentioned rather marginally in this thesis (it is the subject of the previous thesis), these phenomena are products of electrical discharge in water, where they participate in the processes of degradation in a different way. For all measurement series, two direct azo dyes were chosen as model substances – C.I. Direct Blue 106 and C.I. Direct Red 79. The ozonizer, in which either oxygen or synthetic or technical air were loaded as carrier gases, was used for degradation of dyes by ozone. The generated ozone was loaded into the bubbling vessel with dye solution of different initial concentration (10–130 mg.dm-3), which was followed by other bubbling vessel with KI solution for the next analytical determination of the amount of generated ozone. The other parameters changed were the gas flow (1–2 dm3.min-1), ozonizer output (minimal and maximal), type of dye, pH value of the solution (neutral or acid) and additional electrolyte (NaCl, Na2SO4 or any). The reactor for the study of the influence of UV radiation on degradation of dyes was an UV sterilizer into which the equivalent volume of dye solution was added. The possibilities of experimental settings were limited and only the type of dye, an additional electrolyte and pH value of the dye solution were adjusted (as in the case of ozone). Several series of samples were measured with various input conditions which more or less influenced the degradation of investigated dyes in this experiment. It was found that for both used methods the Direct Blue 106 dye was more degradable (with significantly better results for ozone than for UV radiation). The degradation of Direct Red 79 dye proceeded only by ozone treatment, in the case of the application of UV radiation no degradation occurred. By investigation of the influence of initial concentration of dye on its degradation, it was confirmed that with the initial concentration enhancement the final concentration rises as well, whereas in low concentrations (10–50 mg.dm-3) the initial concentration has no effect. The addition of an electrolyte had an accelerating effect on dye degradation in both methods (NaCl and also Na2SO4 showed similar results though the degradation proceeded in different ways). The addition of HCl accelerated the degradation only in the case of UV radiation; during the application of ozone the pH level of the system did not have any influence on the degradation. Oxygen and synthetic air had the strongest effect on ozone degradation (comparable results); in the case of technical air the final dye concentration was higher up to 30 %. The gas flow of 1.5 dm3.min-1 was stated as optimal with the ozonizer output 30 W (maximal). At minimal power the ozonizer produced very low amount of ozone.