Skip to main content
Login | Suomeksi | På svenska | In English

Browsing by Subject "dissolved organic matter"

Sort by: Order: Results:

  • Tuomela, Nea (2022)
    Climate change causes changes in the Arctic lakes, such as shortening of the ice-covered period and changes in hydrology as well as vegetation of the drainage area around the lakes. With these shifts in the function of the ecosystems, dissolved organic matter drainage from terrestrial sources is expected to increase. Terrestrial, allochthonous DOM is more refractory, higher molecular weight organic matter, which is less available to bacterial consumption. Alterations in the DOM pool of the lake may change the bacterial community composition, which could in turn alter the lake ecosystem. Four ice-covered lakes in Kilpisjärvi region were sampled in spring 2021. Water samples were filtered and analyzed for dissolved and particulate nutrients and carbon. Coloured dissolved organic matter and fluorescent dissolved organic matter properties were defined. Bacterial community composition was determined with multiplex polymerase chain reaction and sequences analyzed with DADA2 pipeline. Principal component analysis (PCOA) was done to visualize differences between lakes, and distance-based redundancy analysis (dbRDA) was used to detect any associations between dissolved organic matter properties and bacterial community composition. The lakes had low nutrient and carbon concentrations and had mainly similar properties of dissolved organic matter. However, P3 surface water had higher nitrate and total dissolved nitrogen concentrations. Optical properties in P3 surface water, Peak T, Peak M, biological index and humification index, indicated autochthonous production and lability of organic matter. This was reflected also in bacterial community composition by higher relative abundance of Gammaproteobacteriales. Lake P3 had also higher relative abundance of Cyanobacteria, which could be the cause for labile organic matter in the site. Sites P2 and P3 had similar bacterial community compositions, which is likely due to the sites forming a lake chain and sharing the same catchment area. The sites were oligotrophic and low nutrient environments as expected in the arctic environment. One of the sites had indications of more labile organic matter, which was reflected in the bacterial community structures. In the future shorter ice-cover period may induce autochthonous production such as Cyanobacteria, which reflects in the bacterial community. Changes in the DOM properties and bacterial communities can alter the whole food chain. with A more comprehensive study on this issue could be useful way of understanding the carbon cycling and impacts of climate change to the subarctic lakes.
  • Grönroos, Jonas (2022)
    Exchanges between DOM and POM play an important role in the carbon cycling of freshwater ecosystems. Flocculation is a process where aggregates of DOM are formed and moved from a liquid phase to a solid phase. For colloids to form flocs, the negative surface charge of the present organic colloids needs to be destabilized. This process is generally dependent on salinity, but other compounds affecting the ionic strength of the solution can influence these processes. Gypsum is applied to Finnish fields to reduce the amount of nutrient leaching from agricultural soils. Gypsum treatment effectively reduces the runoff of both particulate and dissolved phosphorus from agricultural fields. Gypsum treatments are performed in areas where the soil contains over 30% clay minerals, making gypsum usage highly relevant in the Archipelago Sea area. This thesis aimed to find out how gypsum additions influence flocculation processes and DOM characteristics of terrestrial organic matter in boreal rivers. The study focused on the implications of gypsum use in waterways from areas with agricultural activities. Three core experiments were conducted to investigate the effects of several variables on flocculation dynamics. This study provides some preliminary insights into the influence of gypsum on biogeochemical processes in rivers. Gypsum additions were found to influence the flocculation processes of terrestrial organic matter in boreal aquatic environments. The most notable effect of gypsum additions was the enhanced floc formation, creating an increased flux of organic material onto the sediment surface. This has potential implications for microbial and benthic food webs, meaning that gypsum use is something that may need to be considered when assessing the impact of agriculture on the biogeochemical processes of waterways. Gypsum additions were also found the influence the characteristics of the remaining DOM pool. With the current knowledge, the positive aspects of gypsum use heavily outweigh the negative ones.