Groundwater ecology literature review

Groundwater ecology is the study of ecosystems that occur in the subsurface within groundwater. Groundwater often contains a diverse range of organisms, and those that live in groundwater and generally do not live above the ground surface are called Stygobites. Stygobites species come from several different taxonomic groups of animals. Many animals found in groundwater are Crustaceans (Copepoda, Ostracoda, Amphipoda, Isopoda, Syncarida, Cladocera) but species of Oligocheata and Hirundinea from the phyla Anelida (worms), Mollusca (snails and slugs) and Nematoda (roundworms) also live in groundwater. Groundwater Ecology is important because stygobites provide a unique contribution to global biodiversity. Stygobites have unusual adaptations to their subsurface environment and there is a high degree of endemism therefore they provide insight into fundamental questions of evolution, ecology and biodiversity. Stygobite studies can also be used to investigate past changes in geomorphology and climate, and the distribution of stygobites can inform aquifer characterisation. Groundwater ecosystems also provide important “ecosystem services” due to their role in biogeochemical cycling, and they can enhance contaminant attenuation. Groundwater fauna can also be useful indicators of the environmental health of aquifers. There are however many threats to groundwater ecosystems including habitat removal by opencast quarrying, groundwater abstraction which removes organisms and causes physical and chemical changes to the habitat, and aquifer contamination. Most records of stygobites in the UK are from caves in the Carboniferous Limestone and boreholes in the Chalk. Ten species of stygobite are known in the UK and Ireland but groundwater organisms have not been well studied, and there may be undiscovered species. The groundwater fauna of many areas of the UK, and many rock types has not yet been investigated. More comprehensive studies have been carried out in other countries and this has lead to insight into the best methods of sampling stygobites, and some understanding of their diversity and distribution in groundwater. Sampling should be designed to take into account variability in geology and hydrogeology as well as regional variations. The best sampling methods in boreholes are net hauling and pumping, and repeated sampling generally increases the number of species found. Determining the factors controlling the distribution of species in groundwater is difficult because there are many factors which interact in a complex way. Sophisticated computational data analysis techniques are needed to unravel these complexities. Some of the most important regional scale factors thought to determine stygobite distributions are glacial history and geology. The composition of groundwater ecosystems also depends upon the type of aquifer (karstic, porous, fracture, compact), and in karst aquifers whether the ecosystem is in the vadose or phreatic zone. It is believed that local effects, (e.g. aquifer heterogeneity, water chemistry, and the location of the water table), also affects species diversity and abundance in groundwaters. Future work might include a survey of the groundwater fauna in the UK to assess groundwater biodiversity and investigate the distribution of stygobites in different geologies. Future hydrogeological research areas might include studies of the physical hydrogeological controls on stygobite diversity such as targeted sampling of inflows into boreholes to determine where in the aquifer stygobites live, and the frequency that stygobites enter boreholes. Hydrochemistry research might focus on assessing the “ecosystem services” provided by groundwater ecosystems such as their role in biogeochemical cycling, contaminant attenuation processes, and sustaining surface groundwater dependent ecosystems. Multi-disciplinary studies involving collaboration between hydrogeologists and biologists and ecologists would be particularly beneficial.