WP4: Integrated top-down concepts

The main goal of WP 4 is to explore and develop data driven techniques to deconvolute the integral matter flux signals observed in the receiving waters. This top-down approach aims at providing simple and robust methods to predict matter flux dynamics in certain functional zones or small catchments as an alternative to PDE-based and data-hungry numerical models, which are hard to parameterise (cf. WP 3).

One promising approach is the use of residence time distributions (RTDs) to describe matter fluxes in catchments. In contrast to the common assumption that RTDs are static it has been demonstrated that they are in fact dynamic. In addition, nitrate fluxes from an agricultural lowland catchment are proved to be strongly related to the dynamics of RTDs within the catchment and adequately predicted daily nitrate exports.

In this WP the concept of dynamic RTDs as proxies for matter fluxes is tested, refined and improved. Dynamic RTDs are generated using a process based numerical model for a small experimental catchment (Schaferbach), where the required heterogeneous patterns of hydraulic properties are obtained using the approach in WP 3. Functional descriptions are developed for the derived dynamic RTDs. In a second step parameterisations of these functional descriptions are developed based on the observed matter flux response at the catchment outlet and general catchment characteristics.