By Anna Sundberg. Weblog "El Agua"

Water is an essential human recourse, not only for consumption but also for sanitation, industry and food production. A large part of the available freshwater in the world comes from groundwater, making it one of the most important renewable resources on the planet ¹. Groundwater constitutes a water resource that is not only large but also of incomparable quality due to the purification services carried out by the groundwater biota². In addition, groundwater is important support for other ecosystems as it provides base flow in rivers and wetlands and therefore, disruption of the groundwater system might therefore lead to very large and widespread environmental impacts. Due to both over exploitation and contaminating groundwater is threatened, and thereby also the sustainability of human society³. The need for protection and sustainable usage is elevated in the case of groundwater since the known remedies are very few and in addition, climate change might also alter the weather patterns ultimately influencing the renewal of the water resources⁴.

Groundwater ecosystem services from groundwater organisms

Groundwater holds unique properties as it provides water of sufficient quality for drinking, to a high extent due to the ecosystem services provided by the groundwater organisms. The ecosystem services provided by organisms are for example purification of water by removal of contaminants, pathogens and virus whereas aquifers functions as water storage and contribute to base flow for rivers and wetlands ⁵. Groundwater also plays a significant part in the cycling of carbon and other nutrients, which is influenced by the regional climate.

A part of the water purification process is due to physiochemical processes of the soil and the geological formations, but the largest part is due to the complex connections of ecological community in the aquifers. Groundwater ecosystems are relying on energy from the surface, and are thereby allochthonous, because the lack of sunlight prohibits photosynthesis, and the capability of producing energy. Microbial functions performed by bacteria are breakdown of several contaminants infiltrating into the groundwater from the surface. The groundwater microbial community lives mainly in biofilm covering the surface of soil particles and, constitutes an important food source for larger invertebrates organisms, specially crustaceans, that forms the stygofauna⁶. These organisms live their whole life in groundwater, and are thereby also an important trophic link in subterranean ecosystems. Adversely, larger organisms support the microbial community by burrowing and turning the sediment and thus enhancing water flow in the aquifers, which further provides oxygen and available nutrients for the microbes. Furthermore, the grazing of stygofauna also provides available surface on the soil particles and provide a space and a food source of the microbes ⁷. Thus the groundwater fauna together with the microbes create an ecosystem that provide important functions for water purification water and makes the water suitable for human usage. It is therefore very important to develop sustainable management strategies as to not damage the groundwater fauna and their habitat in order to maintain and provide sustainable water resources for the future.

Major factors influencing the groundwater ecosystem

Groundwater ecosystems are viewed as a very stable environment with few environmental fluctuations due to the slow response to changes on the surface, however there are several factors affecting the groundwater⁸. The geological history plays a significant role in the shaping the groundwater communities, as it constitutes the soil and the bedrock, which in turn highly determine the chemical properties of the water but also the depth of the aquifer. The soil composition plays an important role in determining which species at what location and at what time, as the species live in the voids, spaces in between grains. The pore size in turn affects the flow of water within the aquifer that further alters the oxygen and organic content input from the surface which is transported with the water flow underground⁹.

Potential implications of agriculture on groundwater ecosystems

In the Mediterranean area, a large part of the available groundwater resources are used in agriculture, mainly for irrigation during summer. The aquifers are recharged during the rainy seasons in spring and autumn¹⁰. Agriculture has a wide range of impacts for the groundwater ecosystem communities; one of the most investigated is the water contamination due to intensive use of fertilizers and pesticides. Fertilizers are used for enhancing the growth of the crops while pesticides and insecticides are used to eliminate pathogens or insects that might attack the crop and thereby minimize the yield. These substances are later percolated down in the groundwater or during the artificially aquifer recharge by irrigation. In high concentrations these compounds might be toxic to organisms or in lower concentrations might case impact on the life history of the organisms by for example affecting the reproduction or feeding behaviors which in turn have negative effects on the survival of the populations and their resilience and resistance¹¹.

Irrigation is important for effective agriculture, as water in many cases is the limiting factor for growth in warmer climates regions. In Spain, 75 % of the abstracted groundwater is used in agriculture, which means that the impact on the groundwater ecosystems in the region is severe. During irrigation a large amount of water are pumped from the aquifer during a relatively short time frame resulting in large quantities of water removals and high fluctuations of the water table in the aquifer. Some organisms will probably be pumped up immediately, but due to the change and rapid fluctuations in water level some organisms might also be stranded in the voids, if they cannot move fast enough to avoid the disturbance¹². Even if not all species disappear it might case major disturbances for the whole community, it also has a negative impact on the ability of the populations and lately of the whole ecosystem to recover from disturbances. There is evidence that with water level fluctuations the groundwater habitats suffer from a long term disruption resulting in species loss due to loss of habitat, both for the microbial community and the stygofauna, which means that they cannot carry out their functions of water purification¹¹. Consequently the intensive usage of water in agriculture or for drinking and sanitation is compromised both on short and mid-term time frames.

IMDEA Agua is involved in a number of projects among to secure the groundwater resources for the future and to apply the groundwater ecological assessments in aquifers management. Groundwater Ecology group is investigating the groundwater biotic community’s ecological properties to gain more knowledge in the ecosystem services they provide for groundwater and/or groundwater dependent ecosystems (i.e. hyporheic zone of rivers, wetlands). Within the Smart-Hydro project (RTC-2014-2367-5) the IMDEA Agua Groundwater Ecology group is developing management practices to help farmers to achieve an optimized use of aquifers but also to safeguard the equilibrium among the water use, mainly abstraction for irrigation, and environmental stability for the groundwater biota while securing groundwater resources for the future. We specifically aim to assess the ecosystem services provided by the groundwater invertebrate communities, mainly crustaceans, to detect the impacts of overexploitation and artificial alluvial aquifer recharge on the groundwater ecosystem integrity.

Anna Sundberg, researcher at the IMDEA Water Institute.

References and further reading

1          Wada, Y. et al. Global depletion of groundwater resources. Geophysical Research Letters 37, n/a-n/a, doi:10.1029/2010gl044571 (2010).

2          Griebler, C. & Avramov, M. Groundwater ecosystem services: a review. Freshwater Science 34, 355-367, doi:10.1086/679903 (2015).

3          Changming, L., Jingjie, Y. & Kendy, E. Groundwater Exploitation and Its Impact on the Environment in the North China Plain. Water International 26, 265-272, doi:10.1080/02508060108686913 (2001).

4          Kløve, B. et al. Climate change impacts on groundwater and dependent ecosystems. Journal of Hydrology 518, 250-266, doi:10.1016/j.jhydrol.2013.06.037 (2014).

5          Schmidt, S. I. & Hahn, H. J. What is groundwater and what does this mean to fauna? – An opinion. Limnologica – Ecology and Management of Inland Waters 42, 1-6, doi:10.1016/j.limno.2011.08.002 (2012).

6          Hancock, P. J., Boulton, A. J. & Humphreys, W. F. Aquifers and hyporheic zones: Towards an ecological understanding of groundwater. Hydrogeology Journal 13, 98-111, doi:10.1007/s10040-004-0421-6 (2005).

7          Boulton, A. J., Fenwick, G. D., Hancock, P. J. & Harvey, M. S. Biodiversity, functional roles and ecosystem services of groundwater invertebrates. Invertebr Syst 22, 103-116, doi:10.1071/Is07024 (2008).

8          Korbel, K. L. & Hose, G. C. Habitat, water quality, seasonality, or site? Identifying environmental correlates of the distribution of groundwater biota. Freshwater Science 34, 329-343, doi:10.1086/680038 (2015).

9          Dole-Olivier, M.-J., Malard, F., Martin, D., LefÉBure, T. & Gibert, J. Relationships between environmental variables and groundwater biodiversity at the regional scale. Freshwater Biology 54, 797-813, doi:10.1111/j.1365-2427.2009.02184.x (2009).

10        Molina, J. L. et al. Aquifers Overexploitation in SE Spain: A Proposal for the Integrated Analysis of Water Management. Water Resources Management 23, 2737-2760, doi:10.1007/s11269-009-9406-5 (2009).

11        Di Lorenzo, T. & Galassi, D. M. P. Agricultural impact on Mediterranean alluvial aquifers: do groundwater communities respond? Fundamental and Applied Limnology / Archiv für Hydrobiologie 182, 271-282, doi:10.1127/1863-9135/2013/0398 (2013).

12        Stumpp, C. & Hose, G. C. The impact of water table drawdown and drying on subterranean aquatic fauna in in-vitro experiments. PLoS One 8, e78502, doi:10.1371/journal.pone.0078502 (2013).