International Association of Hydrogeologists Strategic Overview Series ECOSYSTEM CONSERVATION & GROUNDWATER KEY MESSAGES What are groundwater-dependent ecosystems and why are they important ? • groundwater-dependent ecosystems A groundwater-dependent ecosystem (GDE) is a community (GDEs) comprise a complex subset of micro-organisms, animals and plants, and associated of ecosystems of major significance substrates, whose functioning relies on the presence of in the conservation of biodiversity - water under the ground and/or its emergence to the surface. including many vital sites covered by the RAMSAR Convention and many Some GDEs are supported entirely by groundwater while others that remain unprotected others also receive water from different sources, but the groundwater contribution is critical as regards water • GDEs have direct value for the human chemistry to nourish certain species, and provide stable population from fish and plant water temperature and absence of sediment load. production, water storage and purification, and indirect value in terms of landscape and/or habitat GDEs are mainly land-surface features of various types : • aquatic – including springheads, and those wetlands, • there is need to identify GDEs under streams, rivers and lakes receiving groundwater three main types – aquatic, terrestrial, discharge (which are the main focus of attention here) subterranean – and improve • terrestrial – with phreatophyte vegetation, either shallow- understanding of their relationship rooted in alluvial settings (such as some lowland woods with the physical and chemical status and meadows) or deep-rooted in arid zones with much of groundwater deeper water-table. • degradation of GDEs can occur But they can also be subterranean – notably in limestone because of anthropogenic formations with karstic caverns and fissures inhabited by modifications to aquifer flow regimes small invertebrates and some specialised vertebrate species. and salinisation or pollution of their groundwater EL ROCIO WETLAND IN THE DOÑANA • potentially negative impacts on the NATIONAL PARK OF SOUTHERN SPAIN functioning of GDEs from groundwater withdrawals for irrigated agriculture or urban water-supply need to be assessed and managed • modest increases in groundwater salinity and/or pollution (with nutrients and pesticides) can drastically impact ecosystem structure and cause extermination of key species This Series is designed both to inform professionals in other sectors of key interactions with groundwater resources and hydrogeological science, and to guide IAH members in their outreach to related sectors. WETLAND ECOSYSTEM IN ARID REGION FROM RAMSAR SITES TO KNOWING YOUR WITH ONLY LIMITED CONTEMPORY GROUNDWATER LOCAL SPRINGS REPLENISHMENT AND FOSSIL AQUIFER FLOW The RAMSAR Convention (named after the town in Iran springs where it was signed in 1971) constitutes an agreement by and 169 countries to take action on the conservation of priority oasis wetlands (aquatic ecosystems many being GDEs), in the special interest of protecting wildfowl habitats. The agree- ment currently involves over 2,200 sites amounting to a land area in excess of 210,000 km2. At a very different scale, the ‘Conoce Tus Fuentes’ (‘Know Your Springs’) web-based AQUIFER initiative of the Andalucian Government of Spain has suc- ceeded in mobilising the general public, under academic coordination, in primary mapping of 10,100 springs across this relatively arid region. Both are excellent examples of approaches to raising political and public awareness of GDEs. AQUATIC STREAMBED ECOSYSTEM IN HUMID REGION ALONG UPPER REACHES OF RIVER FED BY PERENNIAL AND INTERMITTENT GROUNDWATER DISCHARGES GDEs are fundamental to the conservation of biodiversity – many being vital for survival of a intermittent wide variety of species and figuring prominently stream h perennial in sites covered by the RAMSAR Convention. ighest w stream ater- tabl zone of e Moreover, GDEs can be of significance as a fluctuation renewable source of human nutrition and as key lo west AQUIFER wate r-table features in the local landscape such as springs and lagoons. Some prefer to introduce the term ’aquifer- dependent ecosystem’ to emphasise that aquifers COASTAL LAGOON ECOSYSTEM DEPENDENT UPON SLIGHTLY BRACKISH WATER constrain the groundwater flow on which GENERATED BY MIXING OF FRESH GROUNDWATER AND ecosystems depend. It should also be noted that LIMITED SEAWATER INCURSION some aquatic ecosystems occur in aquifer recharge zones and represent a major source of groundwater system replenishment. lagoon sea AQUIFER How can degradation of groundwater- dependent ecosystems arise? saline/groundwater interface The degradation of GDEs occurs as a consequence of both modification of natural groundwater flow TERRESTRIAL SAVANNA ECOSYSTEM regimes and salinisation or pollution of groundwater. DEPENDENT UPON EXCEPTIONALLY DEEP-ROOTED TREES AND BUSHES TAPPING THE WATER TABLE IN ARID REGION All groundwater pumping has some effect on deep-rooted savanna trees water-table levels – but in terms of ecosystem calcrete lenses impact the main concern is where the cumulative vadose zone effect of major extraction (for agricultural irrigation AQUIFER or urban water-supply) causes substantial and per- very limited lateral groundwater flo sistent water-table lowering. This can also sometimes w arise in the absence of intensive groundwater use: 2 POTENTIAL INTERFERENCE WITH GDEs OF GROUND- WATER PUMPING FROM A MULTI-LAYERED AQUIFER deep waterwells mainly shallow waterwells with potential impact on with probable impact on wetland ecosystem 2 wetland ecosystems 1a/1b 1a 1b 2 clay lens AQUIFER 1a 1b 2 wetland ecosystems • if recharge zones experience major changes from depth in aquifers (or contained in aquitards), that increase consumptive water-use (eg : low- which are then further concentrated in irrigated land afforestation) or riverbed modifications soils before leaching to shallow groundwater. that decrease aquifer replenishment (eg : impermeabilisation or diversion) Groundwater pollution can have a similar impact • where dewatering for tunnel construction – and the most widespread cause is agrochemical or mining operations seriously impacts the leaching from land-use practices. Pesticides and groundwater flow regime. nutrients that are leached from soils eventually The resulting reduction in groundwater discharge reach the water-table, and can migrate to GDEs can trigger a change in ecosystem functioning in natural discharge zones. The effect of ground- and in turn ecosystem structure, and in extreme water quality deterioration, notably increases of cases cause its complete elimination. nitrate, ammonium or phosphate (even at low concentrations) and/or trace pesticide contamina- There is often uncertainty about the reaction of tion, may lead to greater ecosystem impacts than individual species to hydrological change and groundwater flow diminution. Elevated nitrate species interdependence within a GDE. More- and phosphate concentrations can cause over, the way that groundwater discharges into, ecosystem eutrophication, eliminating oxygen and interacts with, the surface environment and killing fish and small aquatic animals. (in the transitional hyporheic zone) can be critical to aquatic life (not just the presence of water). Whilst certain irreversible changes can What can be done to protect groundwater- occur in relatively short periods (such as dependent ecosystems? oxidation of wetland or streambed sediments), some species are well adapted to survive hydro- Two main lines of action are required for protect- logic extremes, and those naturally exposed to ion of GDEs and have been strongly advocated for variations in groundwater behaviour (for example all sites covered by the RAMSAR Convention: in ephemeral streams) are more resilient. • increasing knowledge of their hydrogeo- logical and ecological condition, and the Modest increases in groundwater salinity can economic consequences of degradation for change ecosystem structure dramatically, and human well-being cause extermination of some species. This can • integrating their protection into basin/aquifer occur where irrigation waterwells mobilise salts water-resource and land-use management. 3 Systematic assessment is required for each GDE to groundwater system. Economic assessment of understand its evolving relationship with underly- GDEs will require clear definition of the benefits ing aquifers, to evaluate groundwater quality and of these ecosystem services including : define chemical baseline, to identify anthropo- • direct values to the human population in genic pressure trends, and to determine the terms of fish and plant production, and socioeconomic contribution of ecosystem services. providing water storage and purification The end product should be a conceptual model of • indirect values from sustaining biodiversity, GDE functioning, using GIS and other data habitat and landscape for social, cultural, management systems to display results clearly. aesthetic and ethical reasons. But in the developing nation context it is recog- All measures that strengthen the governance and nised that direct use values from harvested plants practical management of groundwater can con- and animals, and from landscapes or habitats for tribute, or be adapted, to the cause of protecting tourism are likely to be more important. If the GDEs – by including criteria to maintain ground- livelihoods of poor and vulnerable people depend water levels and conserve groundwater qual- directly