Excess nutrient load in a water body increases primary production and causes eutrophication.
Negative effects of eutrofication include decrease of water transparency, increase of algal blooms, filamentous algae and aquatic macrophytes, wintertime oxygen depletion and changes in fish community, among others.
of the Pasvik watercourse.
In the long time series the changes in the air temperature of the Kola Peninsula may seem small. In the period of 1936–2012 the yearly average temperature has risen only 0.06 °C in ten years. However, in the period of 1976–2012 the yearly average temperature has risen up to 0.6 °С in ten years, which means that the warming intensity is increasing. The highest rise in temperature has been observed in the western parts of the Kola Peninsula in wintertime.
The temperature in the border area is changing
The rise in the yearly average temperature has been studied at the hydrometeorological stations in Janiskoski and Nikel. Warming has been more intensive in the recent decades. However, temperatures are not rising evenly in different seasons as the effects of climate change are the most significant in winter.
At the Nikel station the measured temperatures are higher than in Janiskoski. The measurements of Nikel and Janiskoski stations days with maximal air temperature extremes have become more common and days with minimal air temperature extremes less common since the mid-1970’s. This shows climate warming in the Kola Peninsula. This observation is supported by the measurements of the Norwegian air monitoring station of Svanvik, where a rise in temperature has also been observed.
The border area is very damp as is the whole Murmansk region. The yearly precipitation is 500 mm on average. Since the mid-1970’s the yearly precipitation has increased at the Janiskoski and Nikel monitoring stations. The increase in precipitation has been observed in Janiskoski in all other seasons except winter. In Nikel the amount of precipitation has increased in all seasons, but in the autumn precipitation has increased the most. In the period of 1976–2012 the amount of precipitation has grown 1.8 mm/month in ten years in Janiskoski and 2.4 mm/month in ten years in Nikel.
In winter up to 70–80 % of the winds in the Nikel area blow from the south and in Janiskoski from the southwest. In summer 30–40 % of Nikel winds and 40–50 % of Janiskoski winds blow from the Barents Sea (north and northeast).
The yearly average wind speed is 3.8 m/s in Nikel, varying about 1 m/s seasonally. The wind speed is lower in Janiskoski: the average is 1.8 m/s and the range is about 0.5 m/s. Weak wind in Nikel causes adverse weather conditions which in turn cause increase of contaminants’ concentrations in the ambient air. Such still days have become more common since the mid-1970’s. In Janiskoski the occurrence of stale air is lower than in Nikel.
One of the most important wind system parameters is the average number of days when there are gusts of wind equal to or exceeding a certain value. There is an increase in stormy winds in the winter months as the cyclone processes are the most frequent. In summer the number of stormy days is five times less than in winter. In winter, when the amount of radiation decreases the frequency of ground inversion increases: the lower air stratum becomes less stable and the wind speed decreases. Since the mid-1970’s the number of stormy days at the Nikel and Janiskoski monitoring stations have decreased.
Climate change affects aquatic ecosystems
The present findings indicate that the effects of climate change can already be seen in the Pasvik watercourse. This is evident in the significant increase in summer water temperatures, for instance. It has also been noted that the increase in water temperature has increased the early growth of coregonid fishes. Also, changes in the fish species composition of the littoral zone are evident as the proportion of perch, which is known to benefit from warmer water, in the community has grown.
Mercury concentrations in fish have grown in the latest years as increased precipitation and run-off cause mercury to end up in the watercourses more and more. Climate change can affect the ecosystem resistance and make it more vulnerable to change. However, more information is needed to verify these assumptions. It is also important to take into account other stressors like pollution, water level regulation and biological threats like invasive species.