Sustainable aquifers
Today, many of the concerns about groundwater resources are related to their future sustainability. The sustainability of groundwater resources depends on many factors, most of them influenced by climate change. Do you want to know more about sustainable aquifers? Continue reading this post...
Content
Dynamics of aquifers
Under pre-exploitation conditions, an aquifer is in a state of equilibrium. But, what does that mean? Basically, that at a given average time, the amount of water recharging the aquifer is approximately equal to the amount of water discharged from it. Therefore, the water stored in the aquifer is constant, or varies around a certain average condition, in response to annual or longer-term climatic conditions. The diagram shown in Figure 1 illustrates the equilibrium condition described.
Figure 1 Aquifer under in equilibrium conditions (Source: modified from USGS, 1999).
The possible sources of recharge and discharge for the aquifers, under equilibrium conditions, are shown in Table 1.
Table 1 Potential sources of aquifer recharge and discharge under equilibrium conditions (Source: USGS, 1999).
Recharge | Discharge |
Recharge from precipitation percolating through the unsaturated zone to the water table. | Discharge into streams, lakes, wetlands, saltwater bodies (bays, estuaries or oceans), and springs. |
Recharge of lost streams, lakes and wetlands. | Groundwater evapotranspiration. |
However, humans change the flow system of a certain sector, due to the pumping of water from the aquifer, and the modification of recharge patterns due to irrigation and the construction of urban developments, as well as changes in the type of vegetation. This is what is called "the anthropogenic effect" on an aquifer.
Pumping effect
Focusing our attention on the effects of groundwater extraction, it is possible to conclude that the source of water for pumping must be contributed to the aquifer by:
- More water entering the aquifer (i.e., increased recharge).
- Less water leaving the aquifer (i.e., a decrease in discharge).
- Drawdown of water stored in the aquifer.
- Some combination of the above three.
Schematically, the pumping effect can be depicted as illustrated in Figure 2, which represents a developing aquifer.
Figure 2 Developing aquifer (Source: modified from USGS, 1999).
It is clear that changes in the system allow the extraction of water. That is, the water pumped must come from some change in flow rates and the withdrawal of water stored in the system prior to development, when the aquifer was in a state of equilibrium.
It is important to note that the relative contributions of changes in storage, changes in recharge and changes in discharge evolve over time. Equally certain is that, if the system can reach a new equilibrium, changes in storage will stop and inflows to the aquifer will again balance with discharges.
Accordingly, the long-term source of water for wells is associated with changes in the amount of water entering or leaving the aquifer.
Climate change and aquifer sustainability
Considering the dynamics of a developing aquifer previously analized, when can an aquifer be considered sustainable?
The first factor to consider regarding the sustainability of aquifers is that the amount of groundwater available for use depends on how changes in recharge and discharge flows affect the surrounding environment.
The second factor to consider is the development of sustainable management strategies that take into account two very important components:
- The differentiation between the amount of water pumped (i.e., extracted from the aquifer) and the amount of water actually consumed (i.e., not returned to the aquifer) when estimating water availability.
- The effects of climate change on the surrounding environment.
Taking this last component into account, the question arises as to how climate change may affect the sustainability of aquifers. The answer is not simple, of course, but some effects of climate change on aquifers can be mentioned, which may significantly alter their balance:
- Changes in groundwater recharge as a result of changes in mean precipitation and temperature, or in the seasonal distribution of precipitation
- More severe and long-lasting droughts.
- Changes in evapotranspiration as a consequence of changes in vegetation.
- Possible increased demand for groundwater as a source of backup water supply.
In addition, it should be noted that surficial aquifers, which supply much of the flow to streams, lakes, wetlands, and springs, are probably the part of the groundwater system most sensitive to climate change.
Figure 3 Illustration of the effects of climate change (Source: available at https://www.pcimag.com/articles/107133-climate-change-and-the-future-of-coatings-businesses).
According to the above, the consideration of climate can be a key factor, although undervalued, to ensure the sustainability and proper management of groundwater resources.
Therefore, it is imperative to work to achieve sustainable development, not only of aquifers, but of all aspects that are part of our civilization.
References
- Alley, W.; Reilly, T.; Franke, O. (1999) “Sustainability of Groundwater Resources”. U.S. Geological Survey Circular 1186. Denver, Colorado. USA.
- Smith, M., Cross, K., Paden, M. y lavan, P. (2020) “Acuíferos: Gestión Sostenible de las Aguas Subterráneas”. UICN ORMACC. San José, Costa Rica.
