The environmental aspect of transboundary aquifer management is often not obvious and straightforward. In this section it is explained how the environmental aspect is related with the notion of sustainability. One way of looking at the environmental aspect of transboundary groundwater management is by considering all possible functions that groundwater and aquifers perform. One of these functions is that it sustains eco-systems. To sustain these groundwater-dependent ecosystems, groundwater resources are partly environmentally committed. Aquifers act as a transfer function that migrate and transform interventions in one location (state) into hydrogeological and environmental consequences in another place (state).
The environmental aspect of transboundary aquifer management is increasingly considered important and has developed in parallel with the notion of sustainability. This notion can be associated with 3 different motivations and hence one can interpret 3 different meanings.
One way of looking at the environmental aspect of groundwater management is by considering all possible functions that groundwater and aquifers perform. The obvious aquifer function is that it holds groundwater that can be consumed or used productively in human activities. In this sense, aquifers are resource pools that need to be developed and managed and the groundwater is valued in its extractive consumptive and productive form.
However, when addressing the environmental aspects of groundwater one needs to look into the more hidden, in-situ functions and values of groundwater and aquifer systems:
An environment assessment in transboundary aquifer manage should ideally incorporate all these functions of aquifers and groundwater. Where are the functions located and how do we value them.
Various types of ecosystems are directly or indirectly dependent on groundwater. River ecosystems are often dependent on a groundwater sustained base-flow guaranteeing a continuous presence and flow of water in the river. Without this continuity most fluvial flora and fauna would not survive. Also lakes and wetlands may be totally or partly groundwater-fed. Without the groundwater influx these lakes and wetlands might dry up or have very shallow water depth resulting in a change of the aquatic ecosystem. Discharging groundwater may have a specific chemical and or temperature signature that favor the development of particular terrestrial ecosystems that would not develop in other habitats.
Basically, incorporating the environmental aspect in groundwater management starts with realizing that ecosystems may be depending on groundwater and that groundwater system alteration affect the functioning of these ecosystems. When developing groundwater resources for productive use in a society one has to assess where and how much groundwater is needed to sustain the ecological functions in the area: or in other words which part of the groundwater flow is environmentally committed.
In a transboundary context it is easy to understand that large-scale interventions in the environment in one state may have large effects on the functioning of ecosystems in nearby states. For example large scale land use change from natural vegetation into agricultural areas may need huge volumes of groundwater for irrigation with a consequent groundwater table drop. Possibly, the groundwater table decline expands into the neighboring country jeopardizing ecosystems such wetlands and others.
In a transboundary context, aquifers could be seen as a sort of transfer function. Interventions (causes) at one place are migrated and transformed in the aquifer in hydrogeological and ecological consequences in another place. Other obvious transfer functions that might work transboundary are winds (airborne emissions of toxic substances) and surface water. With respect to the dynamics of the latter 2 transfer functions, aquifers are rather slow ones.
An environment assessment ideally studies where groundwater-dependent ecosystems are located, how much of the groundwater (flow) is environmentally committed and how the aquifer transfer function relates activities and interventions in one state to ecological consequences in neighboring states.