Modelling nitrate river water quality for policy support

Abstract

In response to the need for nitrate policy support in the UK, ADAS UK Ltd. has developed the EveNFlow modelling tool. EveNFlow is conceptually based and allows for surface and subsurface pathways and multiple diffuse sources, associated with different soil‐crop‐livestock combinations. Sources of nitrate losses from agricultural and non‐agricultural land, urban areas and point sources are all represented. The output provides information in the form of daily time‐series at any point along the catchment river network, losses from the base of the soil profile and exported nitrate loads associated with key vectors, e.g. livestock and arable land. In order to model N losses, UK wide GIS datasets for agricultural activity, climate and soil type are used. EveNFlow builds on existing models, either through their coupling or in the form of metamodels. These component models include: SLIMMER; a simple functional N loss model; a crop water use/drainage model based on elements of the MORECS and IRRIGUIDE models, and a series of export coefficients for N potentially available for leaching at the beginning of the drainage season for a range of livestock and crop types from the NEAP‐N model. The final model is capable of simulating a long daily time‐series of flow and nitrate‐N concentrations. As an example, EveNFlow is applied to the Yorkshire Ouse (3315 km²) catchment, UK, and two of its subcatchments, which have contrasting land use and climatic regimes. The results compare favourably with hydrological and chemical data collected over the period 1990–2000 at monitoring sites on these rivers.

Keywords:

• EveNFlow
• nitrate
• water quality
• catchment modelling
• water framework directive
• policy