The Northern Basins: the Vansjø-Hobøl catchment

River Hobølelva

The MARS project has now been running for a little over six months, and many of the planned experiments and models are beginning to take shape.  Over the coming weeks we’ll write about many of the freshwater research projects being carried out by MARS researchers across Europe to investigate the impact of multiple stresses – such as pollution and flooding – on freshwaters.

This week we profile the Vansjø-Hobøl catchment in Southern Norway, known in MARS as ‘The Northern Basins’.  Computer modelling work in the catchment by MARS teams in Wales, Finland, Estonia and Norway is being co-ordinated by researcher Raoul-Marie Couture at NIVA, and is intended to help understand and predict the impact of multiple stressors on freshwaters in Northern Europe.  In this post we outline the environmental issues in the catchment, and next week we’ll describe the models used by Raoul and his team to help find potential solutions to them.

Map of the Vansjø-Hobøl Catchment, Norway. Image: Skarbøvik and Bechmann (2010). Bioforsk Report vol. 5

The Vansjø-Hobøl catchment

The Northern Basins modelling work will be carried out in the Vansjø-Hobøl catchment in Southern Norway.  The catchment – which has been heavily studied by EU projects such as REFRESH and EUROHARP and as a pilot project for the Water Framework Directive in Norway – extends across 690 km² with a large lake in the south – Lake Vansjø – providing drinking water for over 60,000 people.  The catchment is largely covered by forest, and around 15% of the land area is used for (largely arable) agriculture – around five times higher than the average for the rest of Norway.

Multiple stresses

The catchment – with major rivers such as the Hobølelva and the Mosseelva – has particular problems with water quality caused by pollution from agricultural runoff and sewage treatment plants.  Similarly, regular floods (predicted to increase in size and frequency under future climate change) on the rivers in the catchment erode away at banks largely made of marine clay which is rich in the phosphorus-rich mineral apatite.

When combined with runoff of fertilisers from agricultural land, this means that freshwaters in the Vansjø-Hobøl catchment frequently experience high levels of phosphorous and suspendedsediment, which can cause eutrophication and algal blooms that threaten biodiversity, drinking water availability and the safety of freshwaters for swimming.

Current initiatives to improve water quality

Numerous initiatives have been put in place in recent years to improve water quality in the Vansjø-Hobøl catchment.  These include: avoiding ploughing fields during autumn so that vegetation naturally reduces soil erosion during stormy winter months; the creation of sediment and pollution buffer zones using by planting riverside vegetation and creating new wetlands and ponds; the reduction of agricultural fertiliser use; and improving sewage treatment plants.

Landslide in the Vansjø catchment in 2005. Image: Eva Skarbøvik