Groundwater dependent ecosystems (GDEs) are defined as those ecosystems whose biological structure and ecological processes are directly or indirectly influenced by groundwater. Examples of GDEs are groundwater sensu strictu and springs (a transitional zone between ground and surface water), streams and their hyporheic zones (the latter defined as the water-saturated sediments below the stream bed), and seepage wetlands. Such surface-water ecosystems depend at least partially by groundwater seepage and the interchange of subterranean and surface fauna. Subterranean fauna sensu strictu is called stygofauna.
Groundwater hosts a high and valuable biodiversity, comprised of rare, often endemic, and particularly vulnerable species. GDE fauna includes a subterranean (the stygobites) and a surface-water component (surface-water species that actively or passively enter groundwater and/or GDEs). Ninety percent of stygobites are endemic and are a target group for the conservation of biodiversity: based on the Fauna Europaea (www.faunaeur.org) and BIOFRESH datasets, around 11–15% of the 17,000 freshwater animal species in Europe are stygobites. Some crustacean orders (Bathynellacea, Thermosbenacea) are entirely stygobiont.
A high number of aquatic species could be threatened by changes in groundwater quality. Among these are the crustaceans Proasellus, Microcharon (isopods), and Niphargus (amphipod) with their very limited distribution areas; many species of crustacean copepods, including some living fossils such as the genera Pseudectinosoma and Stygepactophanes (the latter currently monospecific); and the order Gelyelloida, restricted in groundwater in southern France. The latter remain a phylogenetic mystery, as their likely surface-water ancestors went extinct millions of years ago in the Tertiary era.
Many surface-water species depend on groundwater too. Among these are the salmonid fish Salmo macrostigma; and several benthic macroinvertebrates including especially limited-distribution plecopterans (such as Taeniopteryx mercuryi, found exclusively at the headwaters of the Vera creek in Abruzzo) and trichopterans (such as some spring-dwellers within the genus Beraea, which includes GDE-specific endemics like Beraea botosaneanui found only in Sardinia, Beraea crichtoni found only in a small area in southern Italy, and Beraea ilvae found only on Elba Island).
Only a few GDEs are Habitat Nature 2000 sites or Ramsar areas. Such ecosystems are cited in the Annex II, section 2. "Groundwater", pt. 2.2. of the Directive 2000/60/EC, and later in the so-called Groundwater Daughter Directive (Directive 2006/118/EC). A plethora of human activities have impacted or are impairing, sometimes severely, groundwater ecosystems and their ecology and biodiversity. Some of such damages are irreversible. Among the most damaging human activities are spring and headwater withdrawal, stream channelisation, in-stream excavation, spring and wetland filling, and wastewater discharge.
The impact of human activities on habitat and microhabitat structure and physico-chemistry in turn impacts the ecosystem biota, leading to severe declines in abundance or even the extinction of the most sensitive but otherwise common species. Species that depend on groundwater for only a part of their biological cycles (e.g., benthic invertebrates or fish that need the hyporheic zone for reproduction) also may be negatively affected, as may riparian plants that require a high water table to survive.
Many groundwater habitats and GDEs are excluded from any conservation plan unless located in protected areas. Unfortunately groundwater/GDE biodiversity is not well known to legislators and the public at large, and often to even to local conservation agencies. In fact, the groundwater portion of a GDE (which may comprise more than 90% of its extension) is often downplayed or even completely overlooked in management plans, whether nature-protection or development oriented.
The close relationship between the surface and the subterranean portion of GDEs, and how their conservation status affects surface biodiversity, are particularly poorly known. For example, physical modifications of the stream bed may decimate the hyporheic-obligate juveniles of fish and benthic macroinvertebrates, thus severely limiting recruitment and potentially leading to the local extinction of such organisms. Many current monitoring protocols for surface water bodies seem to ignore these aspects, despite what set forth in Directive 2000/60/EC. The result is a tendency to underestimate aquatic invertebrate biodiversity in absolute and relative terms with respect to terrestrial biodiversity.
As a result, nothing has been done so far to define for practical and methodological purposes an analysis and assessment protocol concerning GDE biodiversity, even though such protocols may easily focus only on invertebrate fauna. The scientific background and basic know-how about stygobiont occurrence and diversity as bioindicators of the conservation status of groundwater have been developed with the EU project PASCALIS (Protocols for the Assessment and Conservation of Aquatic Life in the Subsurface, PF7, EVK2-CT-2001-00121), with the University of L'Aquila as a partner and coordinator of two workpackages. The PASCALIS' main objective was the establishment of a rigorous protocol for the quantification of groundwater biodiversity and the development of tools for its conservation on a European scale. The University of L'Aquila then was an active external participant to the EU project BIOFRESH (Biodiversity of Freshwater Ecosystems: Status, Trends, Pressures, and Conservation Priorities. FP7, 226874), contributing to the development of a detailed pan-European database on subterranean biodiversity. The GENESIS project (Groundwater and Dependent Ecosystems: New Scientific and Technological Basis for Assessing Climate Change and Land-use Impacts on Groundwater. VII FP7 226536) integrated the up-to-date knowledge about methods, concepts and tools to support a revision of the Water Framework Directive (WFD) and the Groundwater Daughter Directive to include the comprehensive management of groundwater ecosystems. The GENESIS project identified the pressures and impacts on GDE physico-chemistry — described and utilized within Action A3 of the AQUALIFE project — but the quantitative effects on GDE biodiversity in particular remain unknown.
Therefore, a void must be filled to allow environmental monitoring agencies and other stakeholders to quantify groundwater and GDE biodiversity and correlate it to surface human activities. Only when such a step has been taken can effective, all-encompassing conservation and protection management plans be developed that also include the groundwater/GDE component.
Groundwater and the ecosystems that depend on them are running into a serious global threat, linked to human activities that take place on the surface. Groundwater is the main source of drinking water in the European scale, and in other regions of the planet; and, for this reason substantial, but at the same time anthropocentric, they are monitored from the point of view of physico-chemical and quantity. Although scientific research has finally recognized the ecological dimension of groundwater, there is no legislation at both Community and national level which provide for monitoring the state of biological quality of subterranean ecosystems and those who depend on them. There is a further regulatory gap, largely related to the legal vacuum in the field of bio-monitoring of the quality of the GDE, which concerns the conservation of their biodiversity. Despite this state of affairs, the preservation of the GDE and biodiversity hosting plays a crucial aspect in view of the conservation of habitats and species with high intrinsic value of conservation.
Why is the GDE-dependent fauna so important for the conservation of biodiversity at a global, EU and national level?
The reasons are many:
- the subterranean fauna, which is given to strictly dependent GDE, is characterized by a high rate of endemism (up to 90% of the subterranean fauna = stygobitic), is endemic to restricted areas or obvious a point endemism (single known species of a single-site collection of a single area);
- the subterranean fauna is often made up of true living fossils, only evidence of life forms more or less widely distributed in surface water in the geological past (at the scale of tens of thousands to millions of years ago) and whose descendants are today the 'only evidence of an extinct fauna in the area now confined to groundwater;
- the subterranean fauna plays numerous ecosystem services in the recycling of nutrients and oxygenation of the sediment in which they live.
But what are the main threats which alter the structure and function of the GDE?
Human activities that insist on the surface of the aquifers, springs, river environments are putting at serious risk the survival of the species that make up the biodiversity of the GDE, and because some determinants are generating pressures corresponding to a significant impact on the GDE, resulting in the extinction of species rare both in terms of abundance of geographical distribution, and because the disappearance of the communities who live and make the GDE determines the decline of ecosystem services associated with the presence of diverse animal communities.
Main determinants (D) and related pressures (P) affecting groundwater. The status (S) and impacts (I) concerns both the groundwater resources, both aquatic and terrestrial ecosystems and associated employees. The responses (R) are the action programs of relevant EU rules (primarily the program of measures set out in the Water Framework Directive) (from: Protection of groundwater in Europe. The new Groundwater Directive - Consolidating the framework EU regulatory. 2008. DOI 10.2779 / 86124).
1) Climate change alters the hydrological cycle thereby resulting in alternating periods of drought and periods of extremely high rainfall, triggering a cascade phenomenon that is leading to drastic reduction of capacity of the aquifers and the ecosystems that depend on it: once perennial rivers in ' Mediterranean area are becoming intermittent, with periods of extreme dry that lasts for more than three months (July-September); sources diminish their scope; sectors river fed directly from groundwater are gradually disconnecting dall'acquifero below, resulting in a lower scope concomitant to the depletion of the aquifer. By contrast, the disastrous floods in other periods of the hydrological year, leading to sharp rises in river flows, with increase in the rate of erosion of the riverbed and instability of the river corridor hyporheic with consequent alteration of its biodiversity.
The rivers in Abruzzo at risk: perennial rivers that become intermittent (courtesy of Dr. A. Di Sabatino, University of L'Aquila)
Pumping from river and repercussions on the regime of river discharge (from The Nature Conservancy).
2) Changes in land use
Changes in land use have profound effects on the quality and quantity of underground water and the ecosystems that depend on them. The main determinants in the land-use change are farming, animal husbandry, industrial settlements, particularly concentrated along the coastlines of the Abruzzo region, the presence of urban centers of varying size and Disruptive connectivity environmental presence of purifiers, Imhoff tanks, etc .. Changes are associated with more action to contain the flood risk along the river courses, which lead to the total eradication of riparian strips with the loss of the potential to reduce nitrogen load and increase of 'soil erosion. Changes in land use are also associated with climate warming on a local scale, a situation that underlies water demand accessory for the maintenance of all field activities. The agricultural activity first generates an increase of pollutants in both surface and groundwater, where are found at increasing concentrations nitrogenous compounds, mainly in the oxidized form of nitrogen (nitrate), as the nitrogen-based fertilizers are often used in excess from farms. In recent years it also assists to an alarming increase in the concentration of ammonium in groundwater under hypoxic conditions and in the absence or marked decrease of nitrification processes both physical and biological. The European Union has set the threshold range of concentrations in groundwater but each member state has established its own limits (for Italy: from 0.084 to 52 mg / l of ammonium; European Commission, 2010), although it has been observed that concentrations greater than 0.084 mg / l are lethal for many species of invertebrates and species groundwater threshold value down to 0.035 mg / l. These contaminants are added to pesticides, although in Abruzzo their concentration in groundwater has not yet reached levels of alert.
3) Over-exploitation of water resources
The uncontrolled use of groundwater resources for agricultural and industrial is leading rapidly to a severe depletion of aquifers. In the coastal floodplains, islands and in many countries bordering the Mediterranean, this phenomenon is leading to the well known phenomenon of salt intrusion resulting salinization of coastal groundwater leaking in this way every potential use.
The saltwater intrusion from overexploitation of coastal alluvial aquifers leads to desertification and soil salinization.
4) Pollution of groundwater
The pollution of groundwater is becoming one of the most pressing threats not only to the quality status of the resource (referred to Legislative Decree 152/2006, as amended) as well as the below-ground biodiversity and ecosystem services. Nitrate pollution is widespread, mainly in agricultural areas, but also in the vicinity of urban settlements provided purifiers undersized or obsolete. Is the increase in ammonium concentration in groundwater that reaches higher concentrations of 0.080 mg / l in the groundwater is proper, both in the environment hyporheic river. The presence of organochlorine compounds are common in coastal and inland alluvial aquifers in the vicinity of industrial sites, together with PAHs (polycyclic aromatic hydrocarbons). Heavy metals are found mainly in shallow alluvial aquifers and the environment hyporheic river where are chelated, remaining in situ for a long time.
Diagram taken from Millennium EcosystemAssessment (MA, 2005): for inland waters in general shows the most significant determinants.
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