Welcome to MARS

The Vansjø-Hobøl 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 fertilizers from agricultural land, this means that freshwaters in the Vansjø-Hobøl catchment frequently experience high levels of phosphorous and suspended sediment, which can cause eutrophication and algal blooms that threaten biodiversity, drinking water availability and the safety of freshwaters for swimming.

Several stressors

The MARS-project uses computer models to understand how rivers and lakes in the catchment respond to stress – largely nutrient pollution – both now and in the future. These models are used to simulate the impact of different scenarios – for example, increased rainfall, air temperatures or fertiliser pollution – on freshwater ecosystems. Models are designed using observations taken in the field and laboratory on how different aspects of the environment respond to change and stress, and then use a complex set of calculations to simulate environments under a variety of different scenarios.

The Vansjø-Hobøl catchment is 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 Raoul-Marie Couture, researcher at NIVA, and is intended to help understand and predict the impact of multiple stressors on freshwaters in Northern Europe. In total, 16 catchments throughout Europe are being coordinated in the project.

Models are extremely important in providing guidance to environmental managers and policy makers in responding to environmental issues and predicting what impacts management is likely to have.

- MARS is a motivating challenge because we have to use our most recent models for water quality in a totally new way, Couture told the Freshwaterblog.

- We will have to predict the response of biological indicators of water quality, consider the communication of results and uncertainty to stakeholders, and also say something on how the economic value of ecosystem services may change in response to environmental stresses. This forces me to reach out to biologists, social scientists and economists early on in the project.

INCA and MyLake

The MARS team uses two computer models to understand and predict how water quality in the catchment might respond to future environmental change, at both the catchment and lake scale.

The INCA (‘Integrated Catchment’) model is being used to understand the sources, distribution and impact of phosphorous through the Vansjø-Hobøl catchment. The INCA model tracks the flow and quality of water through the catchment, showing the dynamic, day-to-day fluctuations of these parameters in response to human-caused stresses such as agricultural pollution or sewage discharges. INCA can also be used to model the impact of long-term environmental and land-use changes – such as climate change and afforestation – on freshwaters in a catchment. It can model the dilution, natural decay and transformation (e.g. uptake by vegetation) of different chemicals – in MARS’s case for phosphorous, nitrogen and carbon – in water flows.

The dynamics and functioning of lakes in the Vansjø-Hobøl catchment will be modelled using the MyLake model developed by NIVA in Norway. MyLake is a “multi-year lake simulation model” that simulates the daily vertical distribution of lake water temperature, the evolution of seasonal lake ice and snow cover, sediment-water interactions and phosphorus-phytoplankton dynamics. These variables can be modelled through time by using known environmental factors such as the shape and depth of the lake (its ‘morphometry’), atmospheric conditions such as temperature, pressure and wind, and the amount of sediment and nutrients already in the lake (called ‘loading’ by ecologists).

As for the INCA catchment model, MARS’s focus is on phosphorous dynamics in the lakes and on the biological and physical processes controlling algal growth which can lead to harmful blooms. The MyLake model is particularly useful to policy makers as it allows for analyses to be made of the uncertainties in its predictions, and of the sensitivities of the model to the different input parameters.

The innovative link

In this 2014 paper, Couture and colleagues describe how the two models can be linked. Their key observation is that because the models run their analysis on a day-to-day basis using the same factors – phosphorus concentration and water quantity – they can be used in tandem to analyse both the lake and the catchment under the same scenarios, allowing for more thorough predictions of ecosystem responses to stress. Their paper’s conclusion is that both land use and climate change can increase the frequency of algal blooms, but that suitable management can overcome any detrimental effect of climate change if appropriately implemented.

The NIVA-scientist emphasized the novel, cross-disciplinary nature of this work.

- This idea of linking models is not new; in fact most complex models are made of connected modules. However in MARS we will link models that would not normally be used together as one: including hydrological models, biological response models, and economic valuation models.

>> Read the scientific article: Modelling phosphorus loading and algal blooms in a Nordic agricultural catchment-lake system under changing land-use and climate

>> Read more about ‘The Northern Basins’ at the Freshwaterblog