Browsing by Author "Galkin, Annukka"

The arctic region is sensitive to climate change impacts. Arctic lakes are typically transparent and shallow. Environmental changes occurring in the catchment reflect to DOC (dissolved organic carbon) and nutrients concentration of arctic lakes. Furthermore, productivity of lakes, organic matter transport and mineralization will change. This thesis examines how the catchment characteristics currently impact the limnology of arctic lakes and assess future changes when temperature and precipitation will increase. Special attention is given to DOC due to its strong impact on the lake ecosystem. Water and sediment samples were collected from 31 lakes from Ivalo to Utsjoki (68°47' and 69°55') at the end of July 2014. pH was measured in situ and the vegetation type of catchment was observed. LOI 550- % (loss-on-ignition) and chlorophyll-a-sediment were measured from surface sediment (0-2 cm). DOC, TP (total phosphorus), TN (total nitrogen), chl-a-water (chlorophyll-a-water), CDOM (colored dissolved organic carbon) components C1-C4,C6, SUVA (specific UV-absorbance), FI-index (fluorescence index) and HI-index (humification index) were measured from water samples from the epilimnion. Catchment variables were analyzed by using GIS (geographical information system) to determine boundaries, area, topography and altitude of catchments. Based on general map raster of National land survey of Finland © wetland- %, forest- %, tundra- % and lake- % were digitized. Vegetation type was determined based on general map raster and field observations. The July mean temperature during 1984–2013 was calculated based on mean temperature raster of Finnish meteorological institute ©. Principal component analysis (PCA) was used to determine catchment variables which most impact the limnology. Based on principal component analysis results the most effective catchment variable is wetland -% which has a strong impact on DOC, nutrients, chlorophyll-a-water, CDOM components C1-C4, C6 and HI-index. Wetlands are important source of DOC and nutrients to the lakes and the impact of wetland- % is stronger than vegetation type hence DOC-gradient follows wetland- %. On the other hand, tree line and dwarf birch catchments without wetlands are seen clearly in results as lakes with low DOC and nutrient concentrations. Climate change affects catchments and is assumed that release of DOC and nutrients from wetlands and forested areas will increase. Longer ice-free period increases the length of the growing season and will likely, together with increased nutrients, result in a higher water column production in arctic lakes. On the other hand, increased DOC in water column will decrease the amount of light and the production will decrease. Thus, we can expect that the area of tundra vegetation will decrease and dwarf birch will spread to tundra. In addition, the density of trees in forested areas will increase and the tree line will shift northward and higher up the fjells. Environmental changes have substantial impact on the lakes and catchments studied in this thesis. DOC, nutrients and production will probably increase in the studied lakes.