Upscaling riparian lowland buffer zone flow dynamics in the Danish nitrogen model

The importance of riparian lowland buffer zones on surface and ground-water quality has recently received greater attention within Denmark. Significant funding has been made available to re-establish riparian lowlands to reduce nitrate loading to streams, as well as reducing GHG emissions. Surface water nitrate loads are currently estimated using the national nitrogen model, the scale of this model is unable to capture the flow dynamics of small-scale riparian lowlands. Therefore, the model is unable to account for the spatial and temporal variation in the nitrate reduction in the riparian lowlands. Consequently, the current focus is on upscaling the hydrological impacts of riparian lowlands so they may be incorporated into the national scale model in a consistent and transparent way.

Key to quantifying the impacts of riparian lowlands on the surface water nitrate loading is partitioning flow pathways, e.g., surface runoff, groundwater discharge, and drain flow. For example, the likelihood of nitrate reduction within a riparian lowland dominated by surface runoff is low, conversely if groundwater discharge dominants the likelihood is higher. Determining a relationship between the small-scale riparian flow pathways and larger scale landscape features, such as drainage area, slope, and aquifer geometry, may provide a means to upscale and quantify the reduction capacity of a lowland riparian zone.

Numerous field scale riparian lowland investigations have focused on describing the hydraulic processes, but very few investigations have attempted to quantify the flow pathways and/or provide insight into how this information may be used at a larger scale. This investigation will aim to simulate and quantify the observed flow pathways at the field scale for two field sites in Jutland (Fensholt and Holtum), Denmark. These simulations will aid in identifying the keys landscape features which can be used to determine the reduction capacity of riparian lowlands at the national scale.