Monitoring and modeling pesticide fate in surface waters at the catchment scale

In this paper, a state-of-the-art is given of the current knowledge related to the occurrence and sources of pesticides in surface waters. An emphasis is put on sources and transport routes that contribute most to the pesticide loads found in river systems. Possible mitigation measures are described. Once pesticides have entered a river system, they are exposed to different physical, chemical and microbial processes which determine their fate. As mathematical models can describe the fate of pesticides in river systems and can be used for the control of environmental pollution and management of resources, an overview is given of available watershed and in-river water quality models able to predict pesticide concentrations in surface waters. Advantages and disadvantages of simple screening tools and complex watershed models are discussed. Finally, some recommendations are made concerning monitoring, modeling and their combined use in order to achieve the water quality goals set by the EU Water Framework Directive.