Upcoming land use and climate change as well as legal requirements (e.g. the European WFD) pose new challenges for the assessment and sustainable management of water quality of surface waters as well as groundwater bodies on the catchment scale. Therefore models are needed with predictive capabilities under changing land use and climate conditions which fulfill the increasing needs for decision making. Additionally, water quality assessment covers the chemical and ecological status and needs to link the hydrological view on aquatic ecology. However, water quality calculations are affected by errors in input data, model errors, inappropriate model complexity and process knowledge. Therefore there is a strong need for advances in water quality models and to quantify and reduce uncertainties in water quality predictions. A key question in choosing or developing a water quality model is how complex the model structure should be to suit the needs in evaluating the management measures to be implemented. How can the model help in optimizing the measurements? This issue is closely related to data requirements and monitoring schemes for a sound assessment of water quality and model application. Present data often suffer from insufficient temporal and/or spatial resolution, short duration of observations or not harmonized analytical methods. This session aims to get together scientist working on experimental as well as on modelling studies to improve the prediction and management of water quality constituents (e.g. for dissolved oxygen, nutrients, organic matter, algae or sediments) at the catchment scale. Contributions are welcome which focus on the following particular issues:

- Experimental and modelling studies on the identification of hot spots and pathways of nutrients and pollutants from land to water or from water to land
- Assessment of in-stream processes for the transport and fate of nutrients and pollutants
- New approaches to develop efficient water quality monitoring schemes
- Advanced modelling tools integrating catchment as well as in-stream processes
- Observational and modelling studies at catchment scale that relate and quantify water quality changes to changing landuse and climate
- Quantification of uncertainties of water quality models
- Upscaling methodologies and dependencies between models and scales
- Catchment management: pollution reduction measures, scenario analysis for catchment management
- New techniques of stakeholder involvement (e.g. Bayesian Network) to determine control parameters responsible for transport and fate of nutrients and pollutants at the catchment scale
- Measurements and modelling of abiotic and biotic interaction and feedback involved in the transport and fate of nutrients and pollutants at the catchment scale


Solicited speaker: Georgia Destouni (Stockholm University) and Nandita Basu (University of Iowa)