Diffuse pollution is a challenge for environmental management: the problem is seen as originating from an extensive area and there are limited funds available to undertake mitigation works. This combination of factors means that it is important to target the mitigation works within the landscape to ensure maximum benefit. IHRR researchers at Durham University have been working with researchers at Lancaster, Reading and Bristol to build solutions to these problems at the national, regional and local scales. These tools enable the assessment of the landscape dynamics and the identification of the optimal placement of mitigation features, such as new woodland planting, for maximum benefit. These tools can also identify sites and measures most likely to give multiple benefits in terms of biodiversity improvements, diffuse pollution risk reduction and flood risk reduction.

National scale nutrient export modelling with the NERC Environmental Virtual Observatory

IHRR is working with Reading and Bristol Universities, BGS and Hutton, to develop a UK-wide model of diffuse pollution export of nitrogen and phosphorus to river channels and to the marine environment. This model is based on the amount of loading of nutrients a place receives and how easy it is for this point to export the material to the rivers. The amount of loading is determined from the type and intensity of agriculture taking place and hence takes into account the type and number of livestock and the arable crops grown. The amount of this loading that is likely to be exported is determined by a local factors such as rainfall and geology.

Example national maps for nutrient loading from agricultual census

Developed as part of the NERC Environmental Virtual Observatory (pilot) project, this model will enable the investigation of the potential impacts of policy changes at the national scale on the export of nutrients and will allow for the identification of potential diffuse pollution hotspots that require the attention of more detailed investigations.

Regional scale modelling with SCIMAP

The SCIMAP diffuse pollution risk mapping approach provides a consistent overview of the spatial pattern of the sources of diffuse pollution and their potential connections to the rivers. This approach was developed by Durham and Lancaster Universities in collaboration with EA / Defra and the Rivers Trusts in the UK (such as Eden, West Country and Ribble Rivers Trusts). It is based on the critical source area concept whereby you need both a source of pollutants and an active connection to the receiving waters for there to be a problem. SCIMAP does take a different approach to the diffuse pollution problem when compared to other models. The traditional approach is to predict the exact amount of nutrient reaching a stream in mg / l in response to a certain storm event and then try to use this information to manage the landscape.

SCIMAP takes an alternative approach and focuses on the question ‘what to do where?’ and does not try to make predictions in real world units but abstracts the problem to non-physical ‘risk’ units. SCIMAP also works on a time-integrated basis so that actions at the identified locations are predicted to have the best impacts across the range of storm events. The approach therefore identifies the stream, fields and parts of fields where the observed in-stream nutrients or fine sediment most likely originate from. SCIMAP produces maps of the point erosion risk and hydrological connectivity and these maps are then combined to give the final risk map.

SCIMAP applciation to the Morland Beck catchment in Cumbria, UK.

The SCIMAP risk maps give information on the most likely sources of diffuse pollution in the catchment. For a point where there is an observed problem, the tributary highlighted in red are where you would go and look at first. SCIMAP does not say that there is a definitely problem at this location, rather it directs you where to look first. These high-risk sites may be well managed with mitigation features in place, which are not represented in the land cover or terrain datasets. In this case, you can move onto the next highlighted area.

Local scale modelling with CRUM3

An approach that we are developing for the focus catchments in EdenDTC is the use of the CRUM3 hydrological simulation model to make predictions of the locations of overland flow and soil through flow under both current and projected future climates. This tackling of the potential changes in hydrological connectivity under projected climate change is designed to help ensure that the mitigation features that we install today are robust under possible future climatic conditions.

CRUM3 is a model that describes the flows of water across the landscape using a set of physically-based mathematical equations with the river catchment divided into a grid of model cells. At each of these cells, the processes of interception, infiltration, runoff and soil through flow are represented. The model then routes these water fluxes across the hill slopes to the river channels and then though to the catchment outlet. The model has been modified to store the amount of water flowing though each cell and hence can predict the spatial pattern of overland flow and soil through flow. The CRUM3 can use the UKCP09 (UK Climate Projections) Weather Generator outputs to then make projections for how these patterns may change in the future.

CRUM3 predictions of overland flow and soil through flow for the Uper River Rye catchment, North Yorkshire, UK

Conclusion

These tools give a range of methods of identifying where diffuse pollution problems may be coming from within the landscape. Using this knowledge, environmental managers can target mitigation works in the most effective locations. This targeting approach minimises both the mitigation costs and the impact on the farmers in the agricultural landscape.