Abstract
Diffuse agricultural pollution is widely recognized as a significant threat to the quality of water resources. Metaldehyde is a soluble synthetic aldehyde pesticide used globally in agriculture which has caused recent concern due to high observed levels (exceeding the European and UK standards for pesticides in drinking water value of 0.1 µg/l) in surface waters utilized for potable water supply. This paper describes the development of a new travel time based physically distributed metaldehyde prediction model which aims to describe the short term fluctuations of metaldehyde concentrations in surface waters caused by rainfall runoff events. This will enable water infrastructure operators to consider informed control decisions in order to improve the quality of abstracted surface water. The methodology is developed and trailed within a case study catchment in the UK. The new approach integrates spatially and temporally disaggregated surface runoff generation, routing and build-up/wash-off concepts using a simple structure in a GIS environment to build a metaldehyde concentration prediction model. The use of 1 km2 resolution radar rainfall data and identification of high risk areas in the catchment provide an approach which considers the spatio-temporal variations of pollutant generation and transport in the catchment. The model is calibrated and validated using available catchment flow and a new metaldehyde concentration dataset acquired using automatic samplers over four rainfall events. An average coefficient of determination and model efficiency of 0.75 and 0.46 respectively have been obtained for the rainfall events used to validate the model. This shows the capability of the model for the intended purpose of predicting the arrival of peak metaldehyde concentrations at surface water abstraction sites and informing abstraction decisions.
Highlights
Diffuse pollution is a significant threat to the quality of surface water systems, with agricultural runoff commonly recognised as posing the greatest risk (Grayson et al, 2008)
Flow data recorded by a gauging station located at the outlet of the catchment is acquired from Environment Agency and is used to calibrate and validate the travel time computation technique used in the surface runoff model
Diffuse agricultural pollution is known to be a significant concern to the quality of surface water, with implications for drinking water supply
Summary
Diffuse pollution is a significant threat to the quality of surface water systems, with agricultural runoff commonly recognised as posing the greatest risk (Grayson et al, 2008). Observed levels of diffuse agricultural pollutants in surface water have increased as pesticide application rates have intensified, detection methods have improved and new products emerge onto the market (Loucks et al, 2005). D’Arcy et al (1998) recommends that efforts to tackle diffuse pollution problems are best taken at catchment scale (as promoted by the Water Framework Directive) to help avoid the need for energy and cost intensive engineered treatment solutions. Current understanding of short term pollutant dynamics in catchments caused by rainfall/runoff processes is limited due to the scarce availability of water quality data at suitable temporal resolutions (Bach et al, 2001)
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