The impact of climate change on nutrient flows in the catchment of the River Kokemäenjoki

Description of case study area

The study area, Kokemäenjoki river basin, is the fourth largest catchment in Finland with a total surface area of 27 000 km2 and an average water discharge of 230 m3 s-1. The land use in the area varies from intense agriculture to almost totally forested areas, and the population density from sparse (<10 inhabitants km-2) in remote rural areas to city densities, with Tampere being the largest one with its ca. 200 000 inhabitants. The industry is variable, big pulp and paper mills being histori-cally the most critical for the development of present trophic status in surface waters in many areas of the river system. Nutrient loading from point sources to rivers and lakes and further to the Baltic Sea has decreased since the early 1970s due to the improved wastewater purification of municipali-ties and industry.Today, the main challenge in Finland for controlling eutrophication is diffuse nu-trient loading which originates from agriculture, forestry and scattered settlements. The Kokemäenjoki river basin, is characterized by a high proportion of lakes (11 % of total area). Most of the lakes are small (< 5 km2) and humic; the colour of water typically varies between 30 and 90 mg Pt l-1. The catchment area is divided into nine sub-catchments, which are characterized of varying nutrient concentrations. The concentrations do not consistently increase along the flow of water from headwaters to the estuary which demonstrates the retention capacity of lake basins and rivers. At the outflows of watercourses situated in the northern parts of the catchment, where point source loading or intense agriculture are of minor importance, the nutrient concentrations are fairly low. In contrast, in the southern watercourses where the recipient waters have been loaded with industrial and/or municipal waste waters for decades or diffuse loading from agriculture is severe, the N and P concentrations in the outflows are high. During the last six years (2000-2005) total nutrient loading via the River Kokemäenjoki to the Bothnian Sea has varied between 0.4 and 1.5 t P d-1 and between 13 and 38 t N d-1 (Finnish Envi-ronment Institute, unpubl. results). Today, loading from point sources, i.e. industrial and municipal waste waters, represent only 10% of that measured in 1970's. Consequently, in lakes and rivers a slow downward trend can be seen in total P concentrations, whereas the decrease in total N concen-trations has not been so obvious.

The river Kokemäenjoki

The borders of the river Kokemäenjoki catchment. Discharge of water was modelled in the whole area. Green colour indicates the part of the catchment in which also water quality was modelled

Results of the case study

In the modelling case study, results of previous research projects could be utilized and thus an as-sessment of the impacts of climate change could be made in a relatively short time of the ASTRA project. Climate change will have impacts both on inland waters and on the Baltic Sea. The model-ling system consisted of three parts: a runoff model, a nutrient transport model and a river-lake model. The Rossby Centre coupled Regional Climate Model (RCAO) was used for the discharge simulations. The boundary conditions were taken from two global climate models: Hadley Centre (HadAM3H) and Max Planck Institut für Meteorologie (ECHAM4/OPYC3). The emission scenar-ios A2 and B2 from the IPCC's report were used. The nutrient transport model applied was CATCHLOAD developed at PREC. The river-lake model applied was based on a general advec-tion-dispersion equation with a sink term for describing nutrient sedimentation.
According to the modelling calculations, there will be a considerable change in the seasonal dynam-ics of nutrient loading. Annual loading will increase regardless of the climate model or the emission scenario used. Wintertime loading will be greater than today whereas the spring peak will be lower and take place earlier than in the present climate.

Total phosphorus flow at the outlet the river Kokemäenjoki catchment. Average monthly val-ues (kg/d) with different models and scenarios. The black line (Ref) represents the present climatic situation.

Total nitrogen flow at the outlet the river Kokemäenjoki catchment. Average monthly values (kg/d) with different models and scenarios. The black line (Ref) represents the present climatic situation.

Regional seminars

In the seminars, lectures on adaptation to and possibilities of mitigation of climate change were pre-sented. Representatives of Finnish ministries and other authorities and prominent scientists were invited as lecturers. The seminars were arranged in January and November 2006, and April and October 2007. The topics were actively discussed. The most important expected impacts of climate change in Pirkanmaa are increased floods, changes in agriculture and forestry, increased eutrophica-tion of waters and changes in recreational use of nature. Participants of the seminars were regional stakeholders: local communities and the Regional Council of Pirkanmaa, regional governmental authorities, universities of the region as well as non-governmental organizations. In the last fourth seminar which was also open to the citizens of the region, information about the findings of ASTRA was distributed.

Pirkanmaa Regional Environment Centre (PREC)

PREC is a governmental organisation working under the Ministry of Environment, Finland (partly under the Ministry of Agriculture and Forestry). The mandate of PREC covers environmental pro-tection, protection of biodiversity, sustainable use of natural resources, land use and protection of valuable buildings, responsibility for environmental impact assessment (EIA), and gathering, proc-essing and distribution of environmental information in its region. Total amount of employees at PREC is about 140.

Persons from PREC participating in the ASTRA project on a beach of the Baltic Sea. From the left: Jari Rauhala, Heikki Kaipainen, Ämer Bilaletdin, Tom Frisk and Arto Paananen

Contact information

Pirkanmaa Regional Environment Centre, P.O.Box 297, FI-33101 Tampere, Finland Research Professor, Dr Tom Frisk (tom.frisk at


 © GTK, 2007