Summary and conclusions, Miljøstyrelsen

Vidensstatus for sammenhængen mellem tilstanden i grundvand og overfladevand

Summary and conclusions

Until now the groundwater and surface water resources in Denmark have been managed separately. As a consequence of this two different monitoring programs for groundwater and surface water exist today, and also the administration of groundwater and surface water is placed in different departments/institutions at the state level as well as at the county level.

This separate way of managing the water resources will be strongly challenged by the new EU Water Framework Directive, which states that surface water and groundwater in the future shall be managed as an integrated resource. The Water Framework Directive states among other things that criteria's for evaluation of the state of groundwater and surface water shall be established with the purpose of assessing how groundwater influences the quantity and quality of surface water as well as the ecological conditions of the surface water.

The objective of this report is to present an overview of the knowledge concerning the groundwater influence on surface water under Danish conditions, and to identify possible areas where the actual knowledge about the interaction between groundwater and surface water is insufficient in relation to the implementation of the Water Framework Directive.

In the Water Framework Directive groundwater is defined as all water found under the upper (unconfined) water table. This means that drainage water is defined as groundwater. Under Danish conditions surface runoff is very limited, with the exceptions of some specific wetlands and situations with frozen soils, so for practical purposes nearly all water in Danish streams originate from groundwater. Correspondingly surface water includes all water which can be seen from the spring to the coastal zone. At the coastal zone the outer boundary is defined as a distance of 1 nautical mile from the coast. This means that many Danish fjords and coastal waters are included under the Water Framework Directive. It should be noticed that water in the unsaturated zone, between the ground surface and the upper water table, is defined as surface water according to the Water Framework Directive.

The interaction between groundwater and surface water is essential for the entire aquatic environment. Some examples are here to be mentioned:

It is well known that groundwater abstraction results in reduced stream water flow, and that e.g. the intensive groundwater abstraction around Copenhagen has caused that many streams in the area mainly conduct wastewater during dry summers. Reduced water flow affects the ecology of the streams. Especially will a reduction of the summer stream flow result in poorer conditions for fish and macro-invertebrates. The administrative practice today where these aspects are taken into consideration is not standardized, and there is a lack of appropriate tools for effect assessments.

The interaction between groundwater and surface is of special importance in areas near the streams, the hyporheic zone. The key to the understanding of the complex processes of flow and solute transport in this zone, is a characterisation of an area in spatial elements that have similar geochemical and hydrological characteristics. The few existing studies show that the geomorphology and the flow pattern on the small scale is very complex.

A comparison of the water quality in groundwater with the ecotoxicological standards shows that for certain heavy metals and organic micro pollutants the concentrations in groundwater are so high that in some places the groundwater quality will determine the surface water quality.

The phosphorus content in the groundwater might in some areas be of decisive importance for the phosphorus transport to lakes, and thus the ecological state of the lakes.

In general in Denmark we have a comprehensive knowledge and data collection within the field of hydrology and aquatic environment, especially compared to many other countries. But a lot of the knowledge we have achieved in the last decades has been during research and monitoring programmes with objectives other that the ones to be pursued within the Water Framework Directive. During the last decades there have been no research programmes focusing directly on the interaction between groundwater and surface water, and the different monitoring programmes have been split into traditional sectors with distinct monitoring programmes for groundwater, for root zone processes, for surface water etc. So in Denmark we have had very little research activities in some areas, while internationally there have been conducted interesting and relevant research activities.

As a result of this there have been identified a number of areas where there is a need for increasing the knowledge to be able to fulfil the Water Framework Directive with a technical and scientific level corresponding to the state-of-the-art. The different subjects, where there is a need for further knowledge either as new basic knowledge or as new tool for operational management, are described in a 'catalogue of ideas' in the main report.

The project group has made at priority list of the many subjects, and divided the subjects into three categories of importance: High (A), Medium (B), and Low (C). There has not been made any priority within the three categories. A summary of the needs of knowledge and their priority are found in the following table.

Priority	Catalogue no.	Subject	Comment
High Priority (A)
High	A-1	Methods for investigation of geology, geochemistry and stream morphology of the hyporheic zone with the purpose of describing water and solute transport in the hyporheic zone.	New basic knowledge and tools. Decisive for groundwater - surface water interaction in hyporheic zone, for quantity as well as quality.
High	A-2	Investigations of flow patterns in the hyporheic zone at field and catchment scale.	New basic knowledge and tools. Decisive for the description of the fate of substances from root zone to stream.
High	A-3	Determination of minimum acceptable stream flow to maintain good ecological quality (and fulfil objectives)	Development of tool(s) for estimation of minimum acceptable stream flow.
High	A-4	The relation between the environmental state of groundwater and lakes.	Methods and prognosis tools for evaluating the effect of changing groundwater conditions on lakes with large groundwater exchange.
High	A-5	Definition of unaffected state.	Development of methods for administrative procedures.
Medium Priority (B)
Medium	B-1	Concentration of polluting substances in groundwater and the effect on surface water compared to ecological standards.	Investigation of the potential influence of groundwater on the surface water quality.
Medium	B-2	Quantification of the water balance and evaporation on catchment scale.	Of decisive importance for the groundwater protection (zonation), estimation of groundwater recharge and nitrate leaching.
Medium	B-3	Phosphorus.	Estimation of reference state and knowledge of importance of groundwater as a transport media to surface water.
Low Priority (C)
Low	C-1	Quantification of regional variations in groundwater flow in space and time.	Development of tools.
Low	C-2	Hydrochemical and biological interaction between stream and hyporheic zone.	Knowledge about interaction between floods, vegetation, groundwater and sedimentation of nutrients in streams, wetlands and the hyporheic zone.
Low	C-3	Transport of nutrients with groundwater to marine areas.	New basic knowledge and tools. Essential for estimation of the transport of nutrients to marine areas.
Low	C-4	Determination of parameters and uncertainties for hydrological models of large complexity.	Of large general importance, e.g. for groundwater protection (zonation) and regional hydrological modelling.
Low	C-5	State of reference and habitat models for streams.	Development of transient habitat models as tools for prediction of e.g. ecological state of reference.