The subsurface water system role for surface and coastal water pollution

This paper addresses two main questions: 1. What is the role and importance of the subsurface water system (soil water and groundwater) for determining nutrient and pollutant loading in surface and coastal waters, and the responses of this loading to different source abatement measures? 2. Is present water flow and quality monitoring sufficient for accurate understanding of this subsurface water system role? Simulation results for nitrogen loading in the Swedish Norrström drainage basin indicate that slow reversible mass transfer and transport processes in the subsurface may be essential for determining future surface and coastal water loads and their responses to various source abatement measures. Subsurface and surface water monitoring exemplification for Sweden and the whole Baltic Sea Drainage Basin, however, indicates important data gaps, which may make it difficult or impossible to discriminate among different possible interpretations and model quantifications of the subsurface water system processes and their contributions to nutrient and pollutant loading in surface and coastal waters.