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Groundwater — a global focus on the ‘local resource’
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ScienceDirect Groundwater — a global focus on the ‘local resource’ Stephen Foster1,2, John Chilton3, Geert-Jan Nijsten4 and Andrea Richts5 Groundwater is a key natural resource supporting socioeconomic development, but still quite widely misunderstood, undervalued, poorly managed and inadequately protected. Anthropogenic perturbation of groundwater systems accelerated markedly during the 20th century, as a result of massive exploitation for urban watersupply and irrigated agriculture, and radical land-use changes in many aquifer recharge zones. Increasing concerns about resource sustainability, quality degradation and dependentecosystem impacts have arisen, but despite notable technological advances it is not straightforward to provide a quantitative global assessment of groundwater status, given its widespread distribution, difficulty of aggregation and inadequate investment in monitoring. The challenge of identifying appropriate governance provisions and of translating these into effective institutional arrangements for local resource administration and quality protection is also considerable, but some successes have been recently achieved. An overview of resource assessment and management trends is presented in a form accessible to the broader environmental sector. Addresses 1 Global Water Partnership, c/o Osberton Road, Summertown, Oxford OX2-7NU, UK 2 University College London, Gower Street, London WC1, UK 3 International Association of Hydrogeologists, PO Box 4130, Goring on Thames, Reading RG8 6BJ, UK 4 IGRAC – International Groundwater Centre, Westvest 7, 2611AX Delft, The Netherlands 5 Federal Institute for Geosciences and Natural Resources (BGR), Stilleweg 2, 30655 Hannover, Germany Corresponding author: Foster, Stephen ([email protected])
Current Opinion in Environmental Sustainability 2013, 5:685–695 This review comes from a themed issue on Aquatic and marine systems Edited by Charles J Vo¨ro¨smarty, Claudia Pahl-Wostl and Anik Bhaduri For a complete overview see the Issue and the Editorial
Springs, the surface manifestation of underground water, played a key role in human settlement and social development. However, until the industrial revolution, human capability to abstract and pollute groundwater was tiny in comparison to the available resource. Intensive groundwater exploitation followed major advances in geological knowledge, well drilling, pump technology and rural electrification, with rapid expansion occurring during 1950–1970 in many industrialised nations and during 1970–1990 in parts of the developing world [1,2]. Comprehensive, reliable statistics on abstraction and use are not available, but global groundwater withdrawals are increasing and are estimated to have reached 900 km3/a in 2010 [2]. Groundwater has been calculated to provide 36% of potable water-supply, 42% of water for irrigated agriculture and 24% of direct industrial water-supply [3] — although the proportions vary widely from country to country and across larger countries. Groundwater withdrawal intensity varies widely, with the highest levels occurring over large parts of China, India, Pakistan, Bangladesh and Iran, and more patchily in the US, Mexico, EU, North Africa and Middle East [4]. The social value of groundwater should not be gauged solely by volumetric withdrawals. Compared to surface water, its use often brings greater economic benefits per unit volume, because of ready local availability, scaling to demand, high drought reliability and generally good quality requiring minimal treatment [5]. The dependence of cities and innumerable medium-sized towns on groundwater is intensifying, and the contribution of groundwater to irrigated agriculture is high in terms of crop yield and economic productivity [6,7]. Groundwater has been a cornerstone of the ‘green revolution’ of Asian agriculture, provides public water-supply for 310 and 105 million respectively in the EU and US, and supports rural livelihoods extensively in Sub-Saharan Africa [1].
Received 17 May 2013; Accepted 17 October 2013 Available online 21st November 2013 1877-3435/$ – see front matter, # 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cosust.2013.10.010
The context — groundwater system characteristics Significance for human survival and development
Since the earliest times much of humankind has met its needs for good quality water from subterranean sources. www.sciencedirect.com
Vast reservoirs of freshwater reserves
Groundwater systems constitute the planet’s predominant reservoir and strategic reserve of freshwater storage, but calculating this huge volume is not straightforward. The precision and usefulness of such calculations will inevitably be open to question, since all are subject to major assumptions about the effective depth and porosity of the freshwater zone [1]. Certain aquifers (Figure 1) extend uniformly over large land areas and have much more water in storage than all of the world’s surface Current Opinion in Environmental Sustainability 2013, 5:685–695
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Figure 1
North America High Plains Aquifer
North Africa Nubian Sandstone Aquifer
North China Plain Quaternary Aquifer
Gangetic Plain Quaternary Aquifer
South America Guarani Sandstone Aquifer Legend groundwater basins region with complex aquifers region with little or no groundwater Aquifer systems with non-renewable resources
Australia Great Artesian Basin
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Global distribution of groundwater resources. Simplified map (by the BGR-Germany/IAH/UNESCO WHYMAP Project) showing the widespread occurrence of useful groundwater and location of the world’s largest aquifers with vast storage reserves in part of palaeo-groundwater.
reservoirs and lakes, and moreover lose very little of it by direct evaporation. Aquifers have two fundamental characteristics — a capacity for groundwater storage and for groundwater flow. However, different geological formations vary greatly in: aquifer unit storage capacity between unconsolidated granular sediments and highly consolidated fractured rocks; aquifer saturated thickness and pore-space connectivity between different geological formations, resulting in a wide range of groundwater flow potential. and their areal extent can also vary from a few km2 to many thousands of km2 [1]. This synopsis must focus on the so-called major aquifers with large storage reserves and high waterwell yields, capable of playing a strategic role in climate-change Current Opinion in Environmental Sustainability 2013, 5:685–695
adaptation. However, lower-yielding minor aquifers should not be overlooked — since their large geographical extension allows them to meet widely distributed watersupply demands on an economical and secure basis. Aquifer flow regimes — from recharge to discharge
Groundwater moves slowly, at velocities between 0.01 and 10 m/d for most aquifer types and settings. It flows from areas of aquifer recharge by infiltration of excess rainfall and/or surface run-off to areas of aquifer discharge as springs and seepages to watercourses, wetlands and lagoons which sustain vital ecosystems. Aquifer storage helps buffer inputs and transforms highly variable recharge into more constant discharge regimes maintaining baseflow in rivers. Groundwater residence times are usually counted in decades, centuries or millennia (Figure 2), with groundwater in deeper, more confined aquifers having been recharged at earlier, wetter periods of Quaternary history. Shallow groundwater flow systems often conform in geometry with surface watersheds and river basins, but flow www.sciencedirect.com
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Figure 2 intermittent discharge area
(b) humid regions
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major perennial discharge area
unsaturated zone
artesian discharge area
minor perennial discharge area
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Typical groundwater systems in (a) semi-arid and (b) humid regions. Residence periods are order-of-magnitude values from the location of recharge to the point of discharge.
in deeper sedimentary formations is dictated by geological structure and in many cases cuts across surface-water divides. In the most arid regions underlain by major aquifers, it is groundwater flow that represents the main active drainage, making the geological basin hydrologically dominant rather than surface topography. Replenishment processes and uncertainties
The estimation of contemporary recharge rates to aquifers is of fundamental significance when considering the sustainability of groundwater resource development. With increasing aridity, direct rainfall recharge generally becomes progressively less significant than indirect recharge from surface runoff and incidental artificial recharge from human activity [8]. However, there is often substantial scientific uncertainty in quantifying individual recharge components due to the inherent geo-complexity of natural systems (resulting in considerable variation in vegetation cover, soil types and hydrogeological conditions), and wide spatial and temporal variability of rainfall and runoff events. These considerations, www.sciencedirect.com
coupled with limited monitoring data, mean that recharge estimates should always be treated with caution [1]. Understanding the intimate linkages between land-use and groundwater recharge is an essential basis for integrated water resources management, not just for quantifying recharge but also in relation to pollution risks. The common paradigm of ‘constant average rates of presentday recharge’ is false and can lead to serious ‘double resource accounting’, especially in the more arid regions [1]. The contemporary rate of aquifer recharge varies considerably with: changes in land use and vegetation cover, notably the introduction of irrigated agriculture, but also vegetation clearance and soil compaction; urbanisation processes; in particular the level of watermains leakage, the proportion of unsewered (in situ) sanitation and the degree to which construction makes the land-surface impermeable; Current Opinion in Environmental Sustainability 2013, 5:685–695
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Table 1 Benefits and problems of groundwater development. (Specific problems are not directly correlated with specific benefits and do not occur in all aquifers and areas.) Socio-economic benefits
Economical provision of good-quality urban water-supplies Low-cost development of drought-reliable rural water-supplies Accessible and reliable water-supply for irrigated crop cultivation Improved drainage and salinity alleviation in some areas
widespread water-table lowering by groundwater abstraction and/or land drainage, which leads to increased areas and/or rates of infiltration in some aquifer systems; changes in surface water regime, especially diversion or canalization of river flow. Response to climate variability
There remains uncertainty over the impact of the current global warming trend on groundwater recharge [9]. However, the long-term response of groundwater systems to climate variability independent of human activity can be identified from palaeo-hydrological evidence in many large aquifer systems of what are today the more arid parts of the world (Figure 1). Here isotopic techniques reveal that most groundwater stored (and sometimes still flowing) in large sedimentary formations was recharged more than 5000 years ago by late Pleistocene and early Holocene rainfall (Figure 2), when the climate in these areas was cooler and wetter. It is thus commonly referred to as ‘fossil groundwater’. Accumulations of chloride and isotopic evidence in the vadose zone profiles of such areas indicate that little rainfall recharge (<5 mm/a) has taken place since. As current groundwater recharge is responsible for at very most only a tiny fraction of groundwater stored in such aquifer systems, these resources can be considered as ‘non-renewable’ [10].
Resource sustainability problems
Inefficient resource utilisation on a widespread basis Growing social inequity in access to groundwater Physically unsustainable abstraction rates in more arid regions Localised land subsidence due to aquitard compaction Irreversible aquifer damage locally due to saline intrusion/upconing Damage to some groundwater-dependent ecosystems Reduction in dry weather baseflow in upper reaches of many groundwater-fed watercourses
water-dependent economy, large overdrafts can have a series of consequences whose implications need to be weighed against the socio-economic benefits of resource development [1]. There are examples of major aquifer depletion resulting from groundwater abstraction for agricultural irrigation with lowering of the water-table over extensive areas, and more localised depletion around some major urban conurbations. Cumulative net groundwater resource depletion from 1900 to 2008 (and mainly since 1950) has been estimated to be at least 4500 km3, mainly from major aquifer systems in India, USA, Saudi Arabia and China [11] (Figure 3), and more by others [12], although all estimates are debatable because of uncertainty about the average specific yield of the strata dewatered. In major urban centres the overall urbanisation process generally increases infiltration rates [13], and this tends to counteract the effect of intensive groundwater withdrawals where the main underlying aquifer system is unconfined and allows free vertical recharge. Cities underlain by semi-confined aquifers tend to exhibit more serious depletion — for example piezometric surface decline of 30–50 m in Bangkok, Jakarta, Manila, Mexico City, Sana’a, Shanghai, Tianjin and Tokyo. Utilisation of non-renewable groundwater reserves
Groundwater — assessing the main sustainability issues Consequences of intensive and uncontrolled exploitation
Rapid and often uncontrolled expansion in groundwater exploitation has generated major socioeconomic benefits, but increasingly encounters significant problems (Table 1). In many cases current abstraction rates are not physically sustainable in the long-term and some are associated with aquifer degradation and/or environmental impact. Whilst it is accepted that over-drafting aquifer storage and exploitation of non-renewable resources can be a legitimate strategy of managed development or during planned social transformation to a less Current Opinion in Environmental Sustainability 2013, 5:685–695
The large non-renewable groundwater resources of some major aquifer systems can provide very reliable sources of water-supply, which are completely resilient to current climate variability. However, in the end their use will be time-dependent and as such deserves careful consideration in terms of efficient utilisation, ecological impacts and intergenerational equity. It should always be considered a strategic development subject to special investigation, monitoring and management [10]. At present the countries most dependent on non-renewable groundwater resources are Saudi Arabia, Libya and Algeria (Figure 1), but significant use also occurs in Australia, China, Iran, Egypt, Tunisia, Botswana, Mauritania and Peru [2]. www.sciencedirect.com
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Figure 3 6000
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Global groundwater resource depletion. A widespread and accelerating phenomena.
Local impacts of aquifer depletion
All groundwater exploitation by waterwells results in a decline in water-table or piezometric surface over a certain area. Some decline may be desirable, since it can improve land drainage and maximise groundwater recharge rates by providing additional storage space for excess wet-season rainfall. However, if overall abstraction from part or all of an aquifer system exceeds the long-term average replenishment, a continuous decline in waterlevel will occur. Since a significant fraction of total groundwater flow is required to maintain dry-weather river flows and/or to sustain dependent ecosystems, abstraction reduces natural aquifer discharge, in some
cases seriously. Other severe, and essentially irreversible, side-effects can also occur (Table 2), most notably the encroachment of saline water (laterally or from depth or above). Contribution to sea-level rise
Groundwater resource depletion also contributes indirectly to sea-level rise by creating a transfer of water from long-term terrestrial storage to active circulation in the surface hydrosphere, leading eventually to a net water transfer to the oceans. However, the scale and significance of this process is subject to considerable uncertainty. A volume-based assessment focusing primarily on
Table 2 Classification of groundwater quality problems. (Based upon the genesis and processes of quality deterioration.) Type of problem Salinisation processes
Anthropogenic pollution
Wellhead contamination Mobilisation of naturally occurring contamination
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Underlying causes
Parameters of concern
Mobilisation/fractionation from inadequate management of irrigated cropping; mine drainage or petroleum exploitation; or surface-water irrigation without adequate drainage Inadequate protection of vulnerable aquifers against man-made discharges/leachates from urban and industrial activities, and intensification of agricultural cultivation and livestock husbandry Inadequate well construction and completion, allowing direct ingress of polluted water Related to pH-Eh evolution of groundwater and dissolution of minerals from aquifer matrix — and can be seriously aggravated by anthropogenic factors, especially mine-water drainage and water-table rebound in disused mines
Na, Cl and sometimes F, Br, SO4
Pathogens, NO3, NH4, Cl, SO4, B, heavy metals, DOC, aromatic/halogenated hydrocarbons, some pesticides and their metabolites Mainly pathogens, NO3, NH4, Cl Mainly Fe, F and As — also I, Mn, Al, Mg, SO4, Se, and NO3 (from palaeo-recharge)
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Figure 4
OIL WELL FORMATION WATER separation and discharge of brines HISTORIC ARID ZONE + SOIL ACCUMULATION leaching from the vadose zone
CURRENT IRRIGATED SOIL FRACTIONATION+ leaching from the vadose zone
PHREATIC EVAPORATION / SALT FRACTIONATION+
SEA-WATER INTRUSION*
rising water table due to excessive irrigation/inadequate drainage
landward hydraulic gradient due to excessive pumping (sometimes layering occurs)
WATER TABLE INFLOW OF SALINE GROUNDWATER* from adjacent formations following heavy pumping
INTRUSION OF PALEO-SALINE GROUNDWATER* up-coning from depth due to excessive pumping
brackish and saline water fresh water
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Principal processes causing aquifer salinisation. Normally no more than two or three mechanisms are active in any specific case. (* direct consequence of locally excessive groundwater abstraction and associated with soil concentration).
major aquifer systems that have been subject to long-term storage depletion during 2000–2008 [11] gives a minimum estimate of 106 km3/a (equivalent to 0.3 mm/a or 18% of current sea-level rise; Figure 3). This and other methods indicate that the figure could perhaps increase to 0.5 mm/ a or more (30+% of current sea-level rise) [9]. Processes of quality deterioration
Sustainable groundwater development is not only constrained by resource availability but also by quality deterioration, and a generic classification of groundwater quality problems is given in Table 2. Since this synopsis aims to assess emerging quality concerns resulting from inadequate resource management and protection it focuses mainly on the first two categories. There have been many significant advances in groundwater investigation technology during the last decade — including improved linking of numerical modelling of groundwater flow and pollutant transport with external processes, new isotopic and chemical age dating techniques that can be applied to ‘younger’ groundwater flow regimes, new geophysical techniques such as transient electro-magnetic surveys and magnetic resonance sounding, new remote sensing techniques and much greater use of GIS to display and compare large spatial datasets. However, application to practical groundwater assessCurrent Opinion in Environmental Sustainability 2013, 5:685–695
ment at global level is still patchy, due to the high cost and/or technical capacity requirement, and to deficiencies in groundwater monitoring networks. Widespread continuing dependence on deep municipal boreholes and/or shallow domestic waterwells for quality monitoring is a particular impediment, since the former can be tardy indicators of groundwater pollution due to dilution with older recharge and the latter are often subject to direct wellhead contamination. The sparseness of reliable data reduces ability to present a comprehensive and wellsubstantiated statement on the global status of groundwater quality. Data on groundwater quality are rather scant, highly dispersed and often incomplete for many of the determinands mentioned in Table 2 as indicative of deterioration. Moreover, some data are of questionable reliability because of inappropriate sampling techniques, poor sample transport and storage, and the use of inadequate analytical protocols. This applies particularly to certain organic parameters, which are the least stable and must be analysed to low detection limits. Aquifer salinisation mechanisms
Globally, significant areas are suffering serious groundwater and soil salinisation [1] as a result of various processes (Figure 4) including: www.sciencedirect.com
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excess infiltration causing rising groundwater tables, which is usually associated with inefficient irrigation using imported surface water in areas of inadequate natural drainage; natural salinity being mobilised from the landscape, consequent upon natural vegetation clearing for farming development with increased rates of groundwater recharge; excessive disturbance of natural groundwater salinity stratification in the ground through uncontrolled waterwell construction and pumping. Groundwater salinisation is very costly to remediate and often quasi-irreversible, since the saline water which invades macropores and fissures diffuses rapidly into the matrix of porous aquifers, and then can take decades to be flushed out even after flow of freshwater has been re-established. The classic ‘groundwater salinity-depth profile’ has freshwater overlying denser saline water, but over-deepening of irrigation waterwells to maintain or increase yield often leads to up-coning and pumping of some saline groundwater, which then infiltrates through over-irrigation to impact shallow aquifers. Natural inversion of the ‘classic profile’ can occur as a result of a number of processes in certain hydrogeological settings. Such situations are especially susceptible to hydraulic disturbance during groundwater abstraction and require careful diagnosis and management. Aquifer vulnerability to anthropogenic pollution
Groundwater pollution arising from human activity at the land surface has been reported with increasing frequency for more than 40 years in industrialised countries and for up to 25 years in more rapidly developing nations, due to absence of proactive aquifer protection policies [1]. Many more pollution incidents are likely to be occurring unobserved because of inadequate groundwater quality monitoring. While aquifers are much less vulnerable to anthropogenic pollution than surface water bodies, when they become polluted contamination is very persistent and difficult to remediate as a result of their physical inaccessibility and porous structure. An important characteristic of porous media and soils is their potential for natural contaminant attenuation. Aquifer pollution vulnerability is a helpful, widely used, but simplified concept — best expressed as a function of the intrinsic characteristics of the subsoil profile and vadose zone (or confining beds) separating the saturated aquifer from the overlying land surface. However, although not all soil profiles are equally effective in contaminant attenuation, deeper aquifers are only likely to be affected by persistent contaminants (nitrate, salinity and certain synthetic organics). An important factor, especially in consolidated strata, is the possibility of downward conwww.sciencedirect.com
taminant transport via preferential pathways. This greatly increases aquifer vulnerability to pollutants that would otherwise be retarded by adsorption and/or eliminated by biodegradation [1]. Spectacular groundwater pollution incidents with large plumes can be associated with industrial point sources from major spillage or casual discharge in vulnerable areas. But much more insidious and widespread problems arise from some urban sanitation and agricultural practices. If sanitation is achieved by on-site arrangements (soakaways, septic tanks, cesspools and latrines) it can lead to major increase in overall groundwater recharge rates to unconfined aquifers but significant deterioration of groundwater quality (from nitrate, organic carbon, and the possibility of toxic synthetic compounds) [13]. In urban areas where wastewater disposal is via mains sewerage, large volumes of minimally treated wastewater are often used for flood irrigation of agricultural crops, which incidentally results in the augmentation and contamination of local groundwater. Moreover, in many urban areas there are numerous small-scale industries (notably textile manufacture, leather processing, garment cleaning and vehicle maintenance), which generate liquid effluents (including spent oils and solvents) that are often disposed of to the ground. Intensification of agricultural cultivation is often sustained by ever-increasing quantities of inorganic fertilizers and a wide spectrum of synthetic pesticides [14]. Close correlation between high nitrate in shallow groundwater and intensive agricultural cultivation has been widely reported (with apparent absence of denitrification in permeable soil profiles), together with soluble and mobile pesticide residues whose degradability can decrease very markedly once leached below the base of the soil zone. This pollution arises from both rainfed and irrigated agriculture — and although precision irrigation techniques offer the theoretical possibility of reducing leaching losses they will also result in increasing salinity of irrigation returns to groundwater.
Groundwater — facing the governance challenge Strengthening basic governance provisions
Groundwater governance is interpreted as the exercise of appropriate authority to promote responsible collective action for sustainable and efficient resource utilisation and protection in the interest of humankind and dependent ecosystems. The major GW-MATE Programme (of the World Bank in association with the Global Water Partnership during 2001–2011) reached the opinion that groundwater management failures result more from inadequate governance provisions than insufficient resource understanding. Current Opinion in Environmental Sustainability 2013, 5:685–695
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Most (but not all) countries have adequate legal provisions for resource use management, but many have inadequate institutional arrangements and operational capacity for implementing these provisions [15,16]. There is a widespread need to address agency weaknesses, personnel shortages, insufficient stakeholder engagement and lack of acceptance of responsibility. Moreover, groundwater pollution protection poses special additional challenges technically in terms of adequate investigation and monitoring, and institutionally at the interface between water resource agencies and land-use administrations. Geographic scale — a key consideration
Groundwater is a widely distributed but for the most part essentially local resource. Thus resource management and pollution protection must be carried out close to groundwater users and potential polluters, and be directed at coherent groundwater management units and/or special protection zones, with clearly defined, scientifically sound boundaries. While the river basin is the fundamental spatial unit for application of IWRM, this has to be reconciled with the fact that coherent groundwater units defined by hydrogeological criteria are the appropriate spatial framework within which to manage and protect groundwater. Moreover, while river systems are flow-dominated, the behaviour of most aquifers is determined by their large groundwater storage. Thus for some hydrogeological settings a modified spatial approach will be required [17,18]. Appropriate role for national governments
The GW-MATE Programme worked on a widespread geographical basis with public administrations and private stakeholders on groundwater management and protection [19] and concluded that the key roles of national government were: to ensure a specific national agency with district/ catchment offices (or provincial government agencies) is mandated for groundwater governance (with clear responsibility, authority, finance, capacity and accountability) and working closely with surface-water management; to provide a framework for groundwater management planning, involving identification of priority aquifers by socioeconomic and ecological importance, assessment of resource and quality status/risks, definition of management measures and review of their effectiveness — thereby ensuring ‘vertical integration’ between national and local level (Figure 5); to promote policy integration through effective dialogue on groundwater sustainability considerations in agricultural production, urban water-supply, energy pricing and land use. Current Opinion in Environmental Sustainability 2013, 5:685–695
The political economy of governance reform
Whilst the cost–benefit case for groundwater governance reform may be sufficient to gain political credibility, other local considerations often exert a major influence on whether reforms actually happen. Indeed, the status quo tends to benefit the vested interests of some ‘wellestablished constituencies’ [15], and even with negative groundwater outcomes for many there will still normally be some ‘winners’ around! A ‘fine line’ may divide limited awareness of risks to groundwater and genuine defence of related interests, from outright corruption with total disregard for known negative consequences. The most effective way of counteracting corrupt practice will be to promote enhanced understanding of groundwater constraints and vulnerabilities amongst all stakeholders, and information transparency through open access to data on waterwell abstraction licenses, waste-disposal permits and groundwater resource and quality status. In areas of intensive water demand for irrigated agriculture, the hydrogeologic and socioeconomic setting of a given aquifer usually both defines the management problem itself, and constrains the management solution. Thus a ‘one-size-fits-all’ approach to groundwater resource management is simply inadequate. Moreover, since groundwater systems are subject to continuous evolution, significant uncertainty and sometimes rapid change, an adaptive approach to resource management is far preferable to embarking on ‘serious management’ in crisis mode later. A very different management approach will also be required between areas whose water resource use is essentially ‘groundwater only’ from those with significant surface-water and groundwater resources in close juxtaposition. Moreover, it is wise to pursue managed development of groundwater resources from the outset in regions which for the most part currently have a low-intensity of groundwater withdrawals, such as SubSaharan Africa [16]. Approaches to managing irrigation waterwell use ‘Groundwater-only’ areas
The first reaction of public administrations to groundwater depletion in ‘groundwater-only’ areas is to propose major stand-alone investments in aquifer recharge enhancement and/or ‘efficient’ irrigation technology. Whilst both these measures will make a contribution, they have significant limitations in absolute terms and in field practice. In reality the requirement (if physical sustainability is being sought) must be to focus on reducing consumptive water-use whilst raising water-use productivity to maintain farmer incomes [7]. This should lead to a ‘package’ of demand-side and supply-side measures as part of a balanced aquifer management plan. It will then be critical to identify an appropriate blend of management instruments (stakeholder/user www.sciencedirect.com
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Figure 5
Water Resources & Environment GROUNDWATER MANAGEMENT AGRICULTURE & FOOD
WATER SUPPLY & ENERGY
NATIONAL LEVEL legal provisions financing measures vertical policy integration horizontal policy harmonisation resource status reporting
SYNTHESIS OF MANAGEMENT PROGRESS/PROBLEMS
MAJOR URBAN INFRASTRUCTURE
FRAMEWORK POLICY & FINANCIAL FACILITIES
PROVINCIAL/BASIN LEVEL
ECONOMIC DEVELOPMENT
resource allocation detailed planning monitoring strategy /data management
GW BODY MANAGEMENT PLANS & MONITORING
PLANNING FRAMEWORK FINANCIAL ALLOCATIONS
LOCAL LEVEL (DISTRICT/CATCHMENT)
MUNICIPAL AUTHORITIES
plan elaboration/implementation resource administration/regulations demand/supply-side measures resource/source protection use/resource monitoring
GROUNDWATER USERS & LAND OWNERS
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A general scheme of groundwater resource management planning. Indicating the process of ‘vertical integration’ between national and local government usually required groundwater management initiatives and the parallel need for ‘horizontal policy integration’ to harmonise management plans.
engagement and regulatory provisions with some financial incentive) to enable plan refinement and implementation. In many instances existing national policy as regards crop guarantee prices and perverse electricity subsidies is acting as a strong disincentive for stakeholders to cooperate with long-term sustainable groundwater use plans and to confront the harsh reality of weakly recharged aquifers trying to support inappropriate agricultural economies. In these instances, improved ‘horizontal policy coordination’ will be essential [7] before embarking on cooperative groundwater resource management plans (Figure 5). ‘Conjunctive use’ areas
Groundwater irrigation has developed widely in many alluvial irrigation-canal commands, usually on a sponwww.sciencedirect.com
taneous basis but sometimes encouraged by government subsidy. It is now not unusual to find that 30-60% of irrigation water-supply in such settings is derived from waterwells, albeit that a proportion of the groundwater resource itself originates as irrigation-canal seepage [20]. Spontaneous conjunctive use arises where inadequate canal-water service levels cause private waterwell drilling to proliferate. This essentially unplanned, unregulated and unmanaged groundwater use can result in aquifer depletion to depths impacting village waterwells, interfering with low-cost ground-level irrigation pumps and inducing saline groundwater encroachment. Meanwhile, some irrigation-canal commands still experience excessive surface-water use and losses, causing water-logging of crop lands, soil salinisation and depressed agricultural productivity. Current Opinion in Environmental Sustainability 2013, 5:685–695
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Many benefits can potentially accrue when moving from spontaneous conjunctive use to planned conjunctive management of water resources. A balance has to be sought which avoids long-term water-table decline whilst countering rising water-table and reducing soil waterlogging and salinisation. Decisions, based on sound understanding of surface water-groundwater interactions, need to be made on which sections of primary and secondary irrigation canals should be lined. Planned management should allow agricultural production to be increased through improvements in cropping intensity and water productivity without compromising groundwater use sustainability. However, impediments to conjunctive management in established irrigation-canal commands (through canal modification, rural electrification, and waterwell construction) can be considerable and include socio-political resistance, split institutional responsibility and negative inertia. Fostering land-use stewardship
Groundwater recharge and quality considerations need to be integrated with the environmental stewardship of agricultural land. BMPs (Best Management Practices) for agricultural cropping (including control of organic and inorganic fertilizer and pesticide applications, choice of main crop and use of cover crops to take up nutrients, collection and disposal of livestock manure and conversion of arable land to less intensive uses) have proved useful in this respect, although the time-scale for beneficial impacts is substantial in many groundwater systems [21]. More recently such measures have been combined to establish whole-farm or groundwater-body nutrient balance management. However, even this cannot everywhere achieve the required improvement of groundwater recharge quality [14] and in some cases more drastic land-use controls need to be taken. For example, recharge zones close to public-supply waterwells can be taken out of intensive agricultural use and converted to woodland [22] or grassland, often with improved amenity value for local communities. All such measures need wide stakeholder involvement and usually some financial compensation to farmers of the designated land. A governance and institutional framework which encourages local participation and consultation, accountability and acceptance of responsibility is thus required. Groundwater in urban infrastructure and environmental management
The dynamics of urban development are intimately intertwined with the underlying groundwater — and this means that groundwater considerations should be fully integrated into urban infrastructure and environmental management. Groundwater planning is a basic management need in urban areas, especially (but not exclusively) where waterwell extraction is intensive or large-scale water transfers are being introduced into areas heavily dependent on local groundwater. There are numerous Current Opinion in Environmental Sustainability 2013, 5:685–695
examples from around the world of very costly problems arising in the absence of such planning, and some of the key issues to be addressed [23] include: protection and sustainable deployment of water utility groundwater sources; promoting conjunctive management of water utility groundwater sources; regularising private groundwater use in urban areas; taking an integrated approach to urban water-supply and sanitation; defining pragmatic ways of reducing industrial pollution threats to urban groundwater; considering urban wastewater as a valuable resource. Urban groundwater management plans should relate consistently with other sectors, including consideration of the sanitation/drainage interface and of infrastructure stability. This requires effective coordination of numerous authorities and agencies, and (very importantly) with metropolitan and municipal land-use administration. Plan implementation must be staged, with structured stakeholder interaction through some form of ‘permanent consultation mechanism’. Implementation may require strengthening institutional arrangements and linkages, raising substantial capital investment, improving groundwater use and aquifer response monitoring, an effective public information campaign, and promoting capacitybuilding programmes.
References and recommended reading Papers of particular interest, published within the period of review, have been highlighted as: of special interest of outstanding interest 1.
Foster SSD, Chilton PJ: Groundwater: the processes and global significance of aquifer degradation. Philos Trans R Soc London B 2003, 358:1957-1972.
2. Margat J, van der Gun J: Groundwater around the world: a geographical synopsis. London: Taylor and Francis; 2013, . This book provides an exceptionally extensive compendium of groundwater occurrence, use and resource condition around the world — it is authoritatively written and well illustrated. 3.
Doell P et al.: Impact of water withdrawals from groundwater and surface water on continental water storage variations. J Geodyn 2012, 59/60:143-156.
4.
Wada YL et al.: Global depletion of groundwater resources. Geophys Res Lett 2010, 37:L20402 http://dx.doi.org/10.1029/ 2010GL044571.
5.
Burke JJ, Moench MH: Groundwater and society: resources, tensions and opportunities. New York: United Nations Publication ST/ESA/205; 2000, .
6.
Llamas MR, Custodio E: Intensive use of groundwater: a new situation which demands proactive action. Intensive use of groundwater’ Balkema (Lisse). 2003:13-31.
Gardun˜o H, Foster S: Sustainable groundwater irrigation — approaches to reconciling demand with resources. GWMATE strategic overview series 4. Washington, DC: World Bank; 2010, www.worldbank.org/gwmate. A substantial policy paper based on the practical experience of attempting to manage groundwater resource use for agricultural irrigation in a
7.
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series of pilot studies in Latin America, North Africa, Southern & Eastern Asia.
groundwater use, conservation and protection, and the impediments to governance reform.
8.
16. Tuinhof A et al.: Appropriate groundwater management for Sub-Saharan Africa — in face of demographic pressure and climatic variability. GW-MATE strategic overview series 5. Washington, DC: World Bank; 2011, www.worldbank.org/ gwmate.
Scanlon BR et al.: Choosing appropriate techniques for quantifying groundwater recharge. Hydrogeol J 2002, 10:18-39.
9.
Taylor RG et al.: Groundwater and climate change. Nature Climate Change 2012 http://dx.doi.org/10.1038/NCLIMATE1744 www.nature.com/natureclimatechange. A highly authoritative multi-authored paper systematically assessing the relation between past and future climate change, and groundwater resources. 10. Foster S, Loucks DP: Non-renewable groundwater resources — a guidebook on socially-sustainable management for water-policy makers. UNESCO IHP-VI Series on Groundwater 10; Paris: 2006. 11. Konikow LF: Contribution of global groundwater depletion since 1900 to sea-level rise. Geophys Res Lett 2011, 38:1-17401. 12. Rost et al.: Agricultural green and blue water consumption and its influence on the global water system. Water Resour Res 2008, 44 http://dx.doi.org/10.1029/2007WR006331.
13. Howard KWF: Urban groundwater — meeting the challenge. IAH selected paper series 8. London, UK: Taylor and Francis; 2007, . 14. Foster S, Candela L: Diffuse groundwater quality impacts from agricultural land-use; management and policy implications of scientific realities. RSC publication ‘groundwater science & policy — an international overview’. London: RSC Publishing; 2008, 454-470. 15. Foster S et al.: Groundwater governance — conceptual framework for assessment of provisions and needs. GWMATE strategic overview series 1. Washington, DC: World Bank; 2009, www.worldbank.org/gwmate. The first paper to deal specifically with the issue of the governance of
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17. Foster S, Ait-Kadi M: Integrated Water Resources Management (IWRM): how does groundwater fit in? Hydrogeol J 2012, 20:414-418. 18. Richts A: River and groundwater basins of the world. Hannover, Germany: BGR-WHYMAP Publication; 2012, www.whymap.org. 19. Foster S, Gardun˜o: Groundwater-resource governance: are governments and stakeholders responding to the challenge? Hydrogeol J 2013, 21:317-320. 20. Foster S, Van Steenbergen F: Conjunctive use of groundwater and surface water — a ‘lost opportunity’ for water management in the developing world? Hydrogeol J 2011, 19:959-962. 21. Meals DW: Lag time in water quality responses to best management practices: a review. J Environ Qual 2010, 39:85-96. 22. Zhang H, Hiscock KM: Modelling the effect of forest cover in mitigating nitrate contamination of groundwater: a case study from the Sherwood Sandstone aquifer in the East Midlands, UK. J Hydrol 2011, 399:212-225. 23. Foster S, Hirata R: Groundwater use for urban development: enhancing benefits and reducing risks. On the water front-2011. Sweden: Stockholm International Water Institute; 2011, 21-33. A very detailed and systematic review of policy issues and management approaches for urban groundwater use, which is a rapidly increasing phenomena in the developing world.
Current Opinion in Environmental Sustainability 2013, 5:685–695
ScienceDirect Groundwater — a global focus on the ‘local resource’ Stephen Foster1,2, John Chilton3, Geert-Jan Nijsten4 and Andrea Richts5 Groundwater is a key natural resource supporting socioeconomic development, but still quite widely misunderstood, undervalued, poorly managed and inadequately protected. Anthropogenic perturbation of groundwater systems accelerated markedly during the 20th century, as a result of massive exploitation for urban watersupply and irrigated agriculture, and radical land-use changes in many aquifer recharge zones. Increasing concerns about resource sustainability, quality degradation and dependentecosystem impacts have arisen, but despite notable technological advances it is not straightforward to provide a quantitative global assessment of groundwater status, given its widespread distribution, difficulty of aggregation and inadequate investment in monitoring. The challenge of identifying appropriate governance provisions and of translating these into effective institutional arrangements for local resource administration and quality protection is also considerable, but some successes have been recently achieved. An overview of resource assessment and management trends is presented in a form accessible to the broader environmental sector. Addresses 1 Global Water Partnership, c/o Osberton Road, Summertown, Oxford OX2-7NU, UK 2 University College London, Gower Street, London WC1, UK 3 International Association of Hydrogeologists, PO Box 4130, Goring on Thames, Reading RG8 6BJ, UK 4 IGRAC – International Groundwater Centre, Westvest 7, 2611AX Delft, The Netherlands 5 Federal Institute for Geosciences and Natural Resources (BGR), Stilleweg 2, 30655 Hannover, Germany Corresponding author: Foster, Stephen ([email protected])
Current Opinion in Environmental Sustainability 2013, 5:685–695 This review comes from a themed issue on Aquatic and marine systems Edited by Charles J Vo¨ro¨smarty, Claudia Pahl-Wostl and Anik Bhaduri For a complete overview see the Issue and the Editorial
Springs, the surface manifestation of underground water, played a key role in human settlement and social development. However, until the industrial revolution, human capability to abstract and pollute groundwater was tiny in comparison to the available resource. Intensive groundwater exploitation followed major advances in geological knowledge, well drilling, pump technology and rural electrification, with rapid expansion occurring during 1950–1970 in many industrialised nations and during 1970–1990 in parts of the developing world [1,2]. Comprehensive, reliable statistics on abstraction and use are not available, but global groundwater withdrawals are increasing and are estimated to have reached 900 km3/a in 2010 [2]. Groundwater has been calculated to provide 36% of potable water-supply, 42% of water for irrigated agriculture and 24% of direct industrial water-supply [3] — although the proportions vary widely from country to country and across larger countries. Groundwater withdrawal intensity varies widely, with the highest levels occurring over large parts of China, India, Pakistan, Bangladesh and Iran, and more patchily in the US, Mexico, EU, North Africa and Middle East [4]. The social value of groundwater should not be gauged solely by volumetric withdrawals. Compared to surface water, its use often brings greater economic benefits per unit volume, because of ready local availability, scaling to demand, high drought reliability and generally good quality requiring minimal treatment [5]. The dependence of cities and innumerable medium-sized towns on groundwater is intensifying, and the contribution of groundwater to irrigated agriculture is high in terms of crop yield and economic productivity [6,7]. Groundwater has been a cornerstone of the ‘green revolution’ of Asian agriculture, provides public water-supply for 310 and 105 million respectively in the EU and US, and supports rural livelihoods extensively in Sub-Saharan Africa [1].
Received 17 May 2013; Accepted 17 October 2013 Available online 21st November 2013 1877-3435/$ – see front matter, # 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cosust.2013.10.010
The context — groundwater system characteristics Significance for human survival and development
Since the earliest times much of humankind has met its needs for good quality water from subterranean sources. www.sciencedirect.com
Vast reservoirs of freshwater reserves
Groundwater systems constitute the planet’s predominant reservoir and strategic reserve of freshwater storage, but calculating this huge volume is not straightforward. The precision and usefulness of such calculations will inevitably be open to question, since all are subject to major assumptions about the effective depth and porosity of the freshwater zone [1]. Certain aquifers (Figure 1) extend uniformly over large land areas and have much more water in storage than all of the world’s surface Current Opinion in Environmental Sustainability 2013, 5:685–695
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Figure 1
North America High Plains Aquifer
North Africa Nubian Sandstone Aquifer
North China Plain Quaternary Aquifer
Gangetic Plain Quaternary Aquifer
South America Guarani Sandstone Aquifer Legend groundwater basins region with complex aquifers region with little or no groundwater Aquifer systems with non-renewable resources
Australia Great Artesian Basin
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Global distribution of groundwater resources. Simplified map (by the BGR-Germany/IAH/UNESCO WHYMAP Project) showing the widespread occurrence of useful groundwater and location of the world’s largest aquifers with vast storage reserves in part of palaeo-groundwater.
reservoirs and lakes, and moreover lose very little of it by direct evaporation. Aquifers have two fundamental characteristics — a capacity for groundwater storage and for groundwater flow. However, different geological formations vary greatly in: aquifer unit storage capacity between unconsolidated granular sediments and highly consolidated fractured rocks; aquifer saturated thickness and pore-space connectivity between different geological formations, resulting in a wide range of groundwater flow potential. and their areal extent can also vary from a few km2 to many thousands of km2 [1]. This synopsis must focus on the so-called major aquifers with large storage reserves and high waterwell yields, capable of playing a strategic role in climate-change Current Opinion in Environmental Sustainability 2013, 5:685–695
adaptation. However, lower-yielding minor aquifers should not be overlooked — since their large geographical extension allows them to meet widely distributed watersupply demands on an economical and secure basis. Aquifer flow regimes — from recharge to discharge
Groundwater moves slowly, at velocities between 0.01 and 10 m/d for most aquifer types and settings. It flows from areas of aquifer recharge by infiltration of excess rainfall and/or surface run-off to areas of aquifer discharge as springs and seepages to watercourses, wetlands and lagoons which sustain vital ecosystems. Aquifer storage helps buffer inputs and transforms highly variable recharge into more constant discharge regimes maintaining baseflow in rivers. Groundwater residence times are usually counted in decades, centuries or millennia (Figure 2), with groundwater in deeper, more confined aquifers having been recharged at earlier, wetter periods of Quaternary history. Shallow groundwater flow systems often conform in geometry with surface watersheds and river basins, but flow www.sciencedirect.com
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Figure 2 intermittent discharge area
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major perennial discharge area
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Typical groundwater systems in (a) semi-arid and (b) humid regions. Residence periods are order-of-magnitude values from the location of recharge to the point of discharge.
in deeper sedimentary formations is dictated by geological structure and in many cases cuts across surface-water divides. In the most arid regions underlain by major aquifers, it is groundwater flow that represents the main active drainage, making the geological basin hydrologically dominant rather than surface topography. Replenishment processes and uncertainties
The estimation of contemporary recharge rates to aquifers is of fundamental significance when considering the sustainability of groundwater resource development. With increasing aridity, direct rainfall recharge generally becomes progressively less significant than indirect recharge from surface runoff and incidental artificial recharge from human activity [8]. However, there is often substantial scientific uncertainty in quantifying individual recharge components due to the inherent geo-complexity of natural systems (resulting in considerable variation in vegetation cover, soil types and hydrogeological conditions), and wide spatial and temporal variability of rainfall and runoff events. These considerations, www.sciencedirect.com
coupled with limited monitoring data, mean that recharge estimates should always be treated with caution [1]. Understanding the intimate linkages between land-use and groundwater recharge is an essential basis for integrated water resources management, not just for quantifying recharge but also in relation to pollution risks. The common paradigm of ‘constant average rates of presentday recharge’ is false and can lead to serious ‘double resource accounting’, especially in the more arid regions [1]. The contemporary rate of aquifer recharge varies considerably with: changes in land use and vegetation cover, notably the introduction of irrigated agriculture, but also vegetation clearance and soil compaction; urbanisation processes; in particular the level of watermains leakage, the proportion of unsewered (in situ) sanitation and the degree to which construction makes the land-surface impermeable; Current Opinion in Environmental Sustainability 2013, 5:685–695
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Table 1 Benefits and problems of groundwater development. (Specific problems are not directly correlated with specific benefits and do not occur in all aquifers and areas.) Socio-economic benefits
Economical provision of good-quality urban water-supplies Low-cost development of drought-reliable rural water-supplies Accessible and reliable water-supply for irrigated crop cultivation Improved drainage and salinity alleviation in some areas
widespread water-table lowering by groundwater abstraction and/or land drainage, which leads to increased areas and/or rates of infiltration in some aquifer systems; changes in surface water regime, especially diversion or canalization of river flow. Response to climate variability
There remains uncertainty over the impact of the current global warming trend on groundwater recharge [9]. However, the long-term response of groundwater systems to climate variability independent of human activity can be identified from palaeo-hydrological evidence in many large aquifer systems of what are today the more arid parts of the world (Figure 1). Here isotopic techniques reveal that most groundwater stored (and sometimes still flowing) in large sedimentary formations was recharged more than 5000 years ago by late Pleistocene and early Holocene rainfall (Figure 2), when the climate in these areas was cooler and wetter. It is thus commonly referred to as ‘fossil groundwater’. Accumulations of chloride and isotopic evidence in the vadose zone profiles of such areas indicate that little rainfall recharge (<5 mm/a) has taken place since. As current groundwater recharge is responsible for at very most only a tiny fraction of groundwater stored in such aquifer systems, these resources can be considered as ‘non-renewable’ [10].
Resource sustainability problems
Inefficient resource utilisation on a widespread basis Growing social inequity in access to groundwater Physically unsustainable abstraction rates in more arid regions Localised land subsidence due to aquitard compaction Irreversible aquifer damage locally due to saline intrusion/upconing Damage to some groundwater-dependent ecosystems Reduction in dry weather baseflow in upper reaches of many groundwater-fed watercourses
water-dependent economy, large overdrafts can have a series of consequences whose implications need to be weighed against the socio-economic benefits of resource development [1]. There are examples of major aquifer depletion resulting from groundwater abstraction for agricultural irrigation with lowering of the water-table over extensive areas, and more localised depletion around some major urban conurbations. Cumulative net groundwater resource depletion from 1900 to 2008 (and mainly since 1950) has been estimated to be at least 4500 km3, mainly from major aquifer systems in India, USA, Saudi Arabia and China [11] (Figure 3), and more by others [12], although all estimates are debatable because of uncertainty about the average specific yield of the strata dewatered. In major urban centres the overall urbanisation process generally increases infiltration rates [13], and this tends to counteract the effect of intensive groundwater withdrawals where the main underlying aquifer system is unconfined and allows free vertical recharge. Cities underlain by semi-confined aquifers tend to exhibit more serious depletion — for example piezometric surface decline of 30–50 m in Bangkok, Jakarta, Manila, Mexico City, Sana’a, Shanghai, Tianjin and Tokyo. Utilisation of non-renewable groundwater reserves
Groundwater — assessing the main sustainability issues Consequences of intensive and uncontrolled exploitation
Rapid and often uncontrolled expansion in groundwater exploitation has generated major socioeconomic benefits, but increasingly encounters significant problems (Table 1). In many cases current abstraction rates are not physically sustainable in the long-term and some are associated with aquifer degradation and/or environmental impact. Whilst it is accepted that over-drafting aquifer storage and exploitation of non-renewable resources can be a legitimate strategy of managed development or during planned social transformation to a less Current Opinion in Environmental Sustainability 2013, 5:685–695
The large non-renewable groundwater resources of some major aquifer systems can provide very reliable sources of water-supply, which are completely resilient to current climate variability. However, in the end their use will be time-dependent and as such deserves careful consideration in terms of efficient utilisation, ecological impacts and intergenerational equity. It should always be considered a strategic development subject to special investigation, monitoring and management [10]. At present the countries most dependent on non-renewable groundwater resources are Saudi Arabia, Libya and Algeria (Figure 1), but significant use also occurs in Australia, China, Iran, Egypt, Tunisia, Botswana, Mauritania and Peru [2]. www.sciencedirect.com
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Figure 3 6000
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Global groundwater resource depletion. A widespread and accelerating phenomena.
Local impacts of aquifer depletion
All groundwater exploitation by waterwells results in a decline in water-table or piezometric surface over a certain area. Some decline may be desirable, since it can improve land drainage and maximise groundwater recharge rates by providing additional storage space for excess wet-season rainfall. However, if overall abstraction from part or all of an aquifer system exceeds the long-term average replenishment, a continuous decline in waterlevel will occur. Since a significant fraction of total groundwater flow is required to maintain dry-weather river flows and/or to sustain dependent ecosystems, abstraction reduces natural aquifer discharge, in some
cases seriously. Other severe, and essentially irreversible, side-effects can also occur (Table 2), most notably the encroachment of saline water (laterally or from depth or above). Contribution to sea-level rise
Groundwater resource depletion also contributes indirectly to sea-level rise by creating a transfer of water from long-term terrestrial storage to active circulation in the surface hydrosphere, leading eventually to a net water transfer to the oceans. However, the scale and significance of this process is subject to considerable uncertainty. A volume-based assessment focusing primarily on
Table 2 Classification of groundwater quality problems. (Based upon the genesis and processes of quality deterioration.) Type of problem Salinisation processes
Anthropogenic pollution
Wellhead contamination Mobilisation of naturally occurring contamination
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Underlying causes
Parameters of concern
Mobilisation/fractionation from inadequate management of irrigated cropping; mine drainage or petroleum exploitation; or surface-water irrigation without adequate drainage Inadequate protection of vulnerable aquifers against man-made discharges/leachates from urban and industrial activities, and intensification of agricultural cultivation and livestock husbandry Inadequate well construction and completion, allowing direct ingress of polluted water Related to pH-Eh evolution of groundwater and dissolution of minerals from aquifer matrix — and can be seriously aggravated by anthropogenic factors, especially mine-water drainage and water-table rebound in disused mines
Na, Cl and sometimes F, Br, SO4
Pathogens, NO3, NH4, Cl, SO4, B, heavy metals, DOC, aromatic/halogenated hydrocarbons, some pesticides and their metabolites Mainly pathogens, NO3, NH4, Cl Mainly Fe, F and As — also I, Mn, Al, Mg, SO4, Se, and NO3 (from palaeo-recharge)
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Figure 4
OIL WELL FORMATION WATER separation and discharge of brines HISTORIC ARID ZONE + SOIL ACCUMULATION leaching from the vadose zone
CURRENT IRRIGATED SOIL FRACTIONATION+ leaching from the vadose zone
PHREATIC EVAPORATION / SALT FRACTIONATION+
SEA-WATER INTRUSION*
rising water table due to excessive irrigation/inadequate drainage
landward hydraulic gradient due to excessive pumping (sometimes layering occurs)
WATER TABLE INFLOW OF SALINE GROUNDWATER* from adjacent formations following heavy pumping
INTRUSION OF PALEO-SALINE GROUNDWATER* up-coning from depth due to excessive pumping
brackish and saline water fresh water
Current Opinion in Environmental Sustainability
Principal processes causing aquifer salinisation. Normally no more than two or three mechanisms are active in any specific case. (* direct consequence of locally excessive groundwater abstraction and associated with soil concentration).
major aquifer systems that have been subject to long-term storage depletion during 2000–2008 [11] gives a minimum estimate of 106 km3/a (equivalent to 0.3 mm/a or 18% of current sea-level rise; Figure 3). This and other methods indicate that the figure could perhaps increase to 0.5 mm/ a or more (30+% of current sea-level rise) [9]. Processes of quality deterioration
Sustainable groundwater development is not only constrained by resource availability but also by quality deterioration, and a generic classification of groundwater quality problems is given in Table 2. Since this synopsis aims to assess emerging quality concerns resulting from inadequate resource management and protection it focuses mainly on the first two categories. There have been many significant advances in groundwater investigation technology during the last decade — including improved linking of numerical modelling of groundwater flow and pollutant transport with external processes, new isotopic and chemical age dating techniques that can be applied to ‘younger’ groundwater flow regimes, new geophysical techniques such as transient electro-magnetic surveys and magnetic resonance sounding, new remote sensing techniques and much greater use of GIS to display and compare large spatial datasets. However, application to practical groundwater assessCurrent Opinion in Environmental Sustainability 2013, 5:685–695
ment at global level is still patchy, due to the high cost and/or technical capacity requirement, and to deficiencies in groundwater monitoring networks. Widespread continuing dependence on deep municipal boreholes and/or shallow domestic waterwells for quality monitoring is a particular impediment, since the former can be tardy indicators of groundwater pollution due to dilution with older recharge and the latter are often subject to direct wellhead contamination. The sparseness of reliable data reduces ability to present a comprehensive and wellsubstantiated statement on the global status of groundwater quality. Data on groundwater quality are rather scant, highly dispersed and often incomplete for many of the determinands mentioned in Table 2 as indicative of deterioration. Moreover, some data are of questionable reliability because of inappropriate sampling techniques, poor sample transport and storage, and the use of inadequate analytical protocols. This applies particularly to certain organic parameters, which are the least stable and must be analysed to low detection limits. Aquifer salinisation mechanisms
Globally, significant areas are suffering serious groundwater and soil salinisation [1] as a result of various processes (Figure 4) including: www.sciencedirect.com
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excess infiltration causing rising groundwater tables, which is usually associated with inefficient irrigation using imported surface water in areas of inadequate natural drainage; natural salinity being mobilised from the landscape, consequent upon natural vegetation clearing for farming development with increased rates of groundwater recharge; excessive disturbance of natural groundwater salinity stratification in the ground through uncontrolled waterwell construction and pumping. Groundwater salinisation is very costly to remediate and often quasi-irreversible, since the saline water which invades macropores and fissures diffuses rapidly into the matrix of porous aquifers, and then can take decades to be flushed out even after flow of freshwater has been re-established. The classic ‘groundwater salinity-depth profile’ has freshwater overlying denser saline water, but over-deepening of irrigation waterwells to maintain or increase yield often leads to up-coning and pumping of some saline groundwater, which then infiltrates through over-irrigation to impact shallow aquifers. Natural inversion of the ‘classic profile’ can occur as a result of a number of processes in certain hydrogeological settings. Such situations are especially susceptible to hydraulic disturbance during groundwater abstraction and require careful diagnosis and management. Aquifer vulnerability to anthropogenic pollution
Groundwater pollution arising from human activity at the land surface has been reported with increasing frequency for more than 40 years in industrialised countries and for up to 25 years in more rapidly developing nations, due to absence of proactive aquifer protection policies [1]. Many more pollution incidents are likely to be occurring unobserved because of inadequate groundwater quality monitoring. While aquifers are much less vulnerable to anthropogenic pollution than surface water bodies, when they become polluted contamination is very persistent and difficult to remediate as a result of their physical inaccessibility and porous structure. An important characteristic of porous media and soils is their potential for natural contaminant attenuation. Aquifer pollution vulnerability is a helpful, widely used, but simplified concept — best expressed as a function of the intrinsic characteristics of the subsoil profile and vadose zone (or confining beds) separating the saturated aquifer from the overlying land surface. However, although not all soil profiles are equally effective in contaminant attenuation, deeper aquifers are only likely to be affected by persistent contaminants (nitrate, salinity and certain synthetic organics). An important factor, especially in consolidated strata, is the possibility of downward conwww.sciencedirect.com
taminant transport via preferential pathways. This greatly increases aquifer vulnerability to pollutants that would otherwise be retarded by adsorption and/or eliminated by biodegradation [1]. Spectacular groundwater pollution incidents with large plumes can be associated with industrial point sources from major spillage or casual discharge in vulnerable areas. But much more insidious and widespread problems arise from some urban sanitation and agricultural practices. If sanitation is achieved by on-site arrangements (soakaways, septic tanks, cesspools and latrines) it can lead to major increase in overall groundwater recharge rates to unconfined aquifers but significant deterioration of groundwater quality (from nitrate, organic carbon, and the possibility of toxic synthetic compounds) [13]. In urban areas where wastewater disposal is via mains sewerage, large volumes of minimally treated wastewater are often used for flood irrigation of agricultural crops, which incidentally results in the augmentation and contamination of local groundwater. Moreover, in many urban areas there are numerous small-scale industries (notably textile manufacture, leather processing, garment cleaning and vehicle maintenance), which generate liquid effluents (including spent oils and solvents) that are often disposed of to the ground. Intensification of agricultural cultivation is often sustained by ever-increasing quantities of inorganic fertilizers and a wide spectrum of synthetic pesticides [14]. Close correlation between high nitrate in shallow groundwater and intensive agricultural cultivation has been widely reported (with apparent absence of denitrification in permeable soil profiles), together with soluble and mobile pesticide residues whose degradability can decrease very markedly once leached below the base of the soil zone. This pollution arises from both rainfed and irrigated agriculture — and although precision irrigation techniques offer the theoretical possibility of reducing leaching losses they will also result in increasing salinity of irrigation returns to groundwater.
Groundwater — facing the governance challenge Strengthening basic governance provisions
Groundwater governance is interpreted as the exercise of appropriate authority to promote responsible collective action for sustainable and efficient resource utilisation and protection in the interest of humankind and dependent ecosystems. The major GW-MATE Programme (of the World Bank in association with the Global Water Partnership during 2001–2011) reached the opinion that groundwater management failures result more from inadequate governance provisions than insufficient resource understanding. Current Opinion in Environmental Sustainability 2013, 5:685–695
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Most (but not all) countries have adequate legal provisions for resource use management, but many have inadequate institutional arrangements and operational capacity for implementing these provisions [15,16]. There is a widespread need to address agency weaknesses, personnel shortages, insufficient stakeholder engagement and lack of acceptance of responsibility. Moreover, groundwater pollution protection poses special additional challenges technically in terms of adequate investigation and monitoring, and institutionally at the interface between water resource agencies and land-use administrations. Geographic scale — a key consideration
Groundwater is a widely distributed but for the most part essentially local resource. Thus resource management and pollution protection must be carried out close to groundwater users and potential polluters, and be directed at coherent groundwater management units and/or special protection zones, with clearly defined, scientifically sound boundaries. While the river basin is the fundamental spatial unit for application of IWRM, this has to be reconciled with the fact that coherent groundwater units defined by hydrogeological criteria are the appropriate spatial framework within which to manage and protect groundwater. Moreover, while river systems are flow-dominated, the behaviour of most aquifers is determined by their large groundwater storage. Thus for some hydrogeological settings a modified spatial approach will be required [17,18]. Appropriate role for national governments
The GW-MATE Programme worked on a widespread geographical basis with public administrations and private stakeholders on groundwater management and protection [19] and concluded that the key roles of national government were: to ensure a specific national agency with district/ catchment offices (or provincial government agencies) is mandated for groundwater governance (with clear responsibility, authority, finance, capacity and accountability) and working closely with surface-water management; to provide a framework for groundwater management planning, involving identification of priority aquifers by socioeconomic and ecological importance, assessment of resource and quality status/risks, definition of management measures and review of their effectiveness — thereby ensuring ‘vertical integration’ between national and local level (Figure 5); to promote policy integration through effective dialogue on groundwater sustainability considerations in agricultural production, urban water-supply, energy pricing and land use. Current Opinion in Environmental Sustainability 2013, 5:685–695
The political economy of governance reform
Whilst the cost–benefit case for groundwater governance reform may be sufficient to gain political credibility, other local considerations often exert a major influence on whether reforms actually happen. Indeed, the status quo tends to benefit the vested interests of some ‘wellestablished constituencies’ [15], and even with negative groundwater outcomes for many there will still normally be some ‘winners’ around! A ‘fine line’ may divide limited awareness of risks to groundwater and genuine defence of related interests, from outright corruption with total disregard for known negative consequences. The most effective way of counteracting corrupt practice will be to promote enhanced understanding of groundwater constraints and vulnerabilities amongst all stakeholders, and information transparency through open access to data on waterwell abstraction licenses, waste-disposal permits and groundwater resource and quality status. In areas of intensive water demand for irrigated agriculture, the hydrogeologic and socioeconomic setting of a given aquifer usually both defines the management problem itself, and constrains the management solution. Thus a ‘one-size-fits-all’ approach to groundwater resource management is simply inadequate. Moreover, since groundwater systems are subject to continuous evolution, significant uncertainty and sometimes rapid change, an adaptive approach to resource management is far preferable to embarking on ‘serious management’ in crisis mode later. A very different management approach will also be required between areas whose water resource use is essentially ‘groundwater only’ from those with significant surface-water and groundwater resources in close juxtaposition. Moreover, it is wise to pursue managed development of groundwater resources from the outset in regions which for the most part currently have a low-intensity of groundwater withdrawals, such as SubSaharan Africa [16]. Approaches to managing irrigation waterwell use ‘Groundwater-only’ areas
The first reaction of public administrations to groundwater depletion in ‘groundwater-only’ areas is to propose major stand-alone investments in aquifer recharge enhancement and/or ‘efficient’ irrigation technology. Whilst both these measures will make a contribution, they have significant limitations in absolute terms and in field practice. In reality the requirement (if physical sustainability is being sought) must be to focus on reducing consumptive water-use whilst raising water-use productivity to maintain farmer incomes [7]. This should lead to a ‘package’ of demand-side and supply-side measures as part of a balanced aquifer management plan. It will then be critical to identify an appropriate blend of management instruments (stakeholder/user www.sciencedirect.com
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Figure 5
Water Resources & Environment GROUNDWATER MANAGEMENT AGRICULTURE & FOOD
WATER SUPPLY & ENERGY
NATIONAL LEVEL legal provisions financing measures vertical policy integration horizontal policy harmonisation resource status reporting
SYNTHESIS OF MANAGEMENT PROGRESS/PROBLEMS
MAJOR URBAN INFRASTRUCTURE
FRAMEWORK POLICY & FINANCIAL FACILITIES
PROVINCIAL/BASIN LEVEL
ECONOMIC DEVELOPMENT
resource allocation detailed planning monitoring strategy /data management
GW BODY MANAGEMENT PLANS & MONITORING
PLANNING FRAMEWORK FINANCIAL ALLOCATIONS
LOCAL LEVEL (DISTRICT/CATCHMENT)
MUNICIPAL AUTHORITIES
plan elaboration/implementation resource administration/regulations demand/supply-side measures resource/source protection use/resource monitoring
GROUNDWATER USERS & LAND OWNERS
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A general scheme of groundwater resource management planning. Indicating the process of ‘vertical integration’ between national and local government usually required groundwater management initiatives and the parallel need for ‘horizontal policy integration’ to harmonise management plans.
engagement and regulatory provisions with some financial incentive) to enable plan refinement and implementation. In many instances existing national policy as regards crop guarantee prices and perverse electricity subsidies is acting as a strong disincentive for stakeholders to cooperate with long-term sustainable groundwater use plans and to confront the harsh reality of weakly recharged aquifers trying to support inappropriate agricultural economies. In these instances, improved ‘horizontal policy coordination’ will be essential [7] before embarking on cooperative groundwater resource management plans (Figure 5). ‘Conjunctive use’ areas
Groundwater irrigation has developed widely in many alluvial irrigation-canal commands, usually on a sponwww.sciencedirect.com
taneous basis but sometimes encouraged by government subsidy. It is now not unusual to find that 30-60% of irrigation water-supply in such settings is derived from waterwells, albeit that a proportion of the groundwater resource itself originates as irrigation-canal seepage [20]. Spontaneous conjunctive use arises where inadequate canal-water service levels cause private waterwell drilling to proliferate. This essentially unplanned, unregulated and unmanaged groundwater use can result in aquifer depletion to depths impacting village waterwells, interfering with low-cost ground-level irrigation pumps and inducing saline groundwater encroachment. Meanwhile, some irrigation-canal commands still experience excessive surface-water use and losses, causing water-logging of crop lands, soil salinisation and depressed agricultural productivity. Current Opinion in Environmental Sustainability 2013, 5:685–695
694 Aquatic and marine systems
Many benefits can potentially accrue when moving from spontaneous conjunctive use to planned conjunctive management of water resources. A balance has to be sought which avoids long-term water-table decline whilst countering rising water-table and reducing soil waterlogging and salinisation. Decisions, based on sound understanding of surface water-groundwater interactions, need to be made on which sections of primary and secondary irrigation canals should be lined. Planned management should allow agricultural production to be increased through improvements in cropping intensity and water productivity without compromising groundwater use sustainability. However, impediments to conjunctive management in established irrigation-canal commands (through canal modification, rural electrification, and waterwell construction) can be considerable and include socio-political resistance, split institutional responsibility and negative inertia. Fostering land-use stewardship
Groundwater recharge and quality considerations need to be integrated with the environmental stewardship of agricultural land. BMPs (Best Management Practices) for agricultural cropping (including control of organic and inorganic fertilizer and pesticide applications, choice of main crop and use of cover crops to take up nutrients, collection and disposal of livestock manure and conversion of arable land to less intensive uses) have proved useful in this respect, although the time-scale for beneficial impacts is substantial in many groundwater systems [21]. More recently such measures have been combined to establish whole-farm or groundwater-body nutrient balance management. However, even this cannot everywhere achieve the required improvement of groundwater recharge quality [14] and in some cases more drastic land-use controls need to be taken. For example, recharge zones close to public-supply waterwells can be taken out of intensive agricultural use and converted to woodland [22] or grassland, often with improved amenity value for local communities. All such measures need wide stakeholder involvement and usually some financial compensation to farmers of the designated land. A governance and institutional framework which encourages local participation and consultation, accountability and acceptance of responsibility is thus required. Groundwater in urban infrastructure and environmental management
The dynamics of urban development are intimately intertwined with the underlying groundwater — and this means that groundwater considerations should be fully integrated into urban infrastructure and environmental management. Groundwater planning is a basic management need in urban areas, especially (but not exclusively) where waterwell extraction is intensive or large-scale water transfers are being introduced into areas heavily dependent on local groundwater. There are numerous Current Opinion in Environmental Sustainability 2013, 5:685–695
examples from around the world of very costly problems arising in the absence of such planning, and some of the key issues to be addressed [23] include: protection and sustainable deployment of water utility groundwater sources; promoting conjunctive management of water utility groundwater sources; regularising private groundwater use in urban areas; taking an integrated approach to urban water-supply and sanitation; defining pragmatic ways of reducing industrial pollution threats to urban groundwater; considering urban wastewater as a valuable resource. Urban groundwater management plans should relate consistently with other sectors, including consideration of the sanitation/drainage interface and of infrastructure stability. This requires effective coordination of numerous authorities and agencies, and (very importantly) with metropolitan and municipal land-use administration. Plan implementation must be staged, with structured stakeholder interaction through some form of ‘permanent consultation mechanism’. Implementation may require strengthening institutional arrangements and linkages, raising substantial capital investment, improving groundwater use and aquifer response monitoring, an effective public information campaign, and promoting capacitybuilding programmes.
References and recommended reading Papers of particular interest, published within the period of review, have been highlighted as: of special interest of outstanding interest 1.
Foster SSD, Chilton PJ: Groundwater: the processes and global significance of aquifer degradation. Philos Trans R Soc London B 2003, 358:1957-1972.
2. Margat J, van der Gun J: Groundwater around the world: a geographical synopsis. London: Taylor and Francis; 2013, . This book provides an exceptionally extensive compendium of groundwater occurrence, use and resource condition around the world — it is authoritatively written and well illustrated. 3.
Doell P et al.: Impact of water withdrawals from groundwater and surface water on continental water storage variations. J Geodyn 2012, 59/60:143-156.
4.
Wada YL et al.: Global depletion of groundwater resources. Geophys Res Lett 2010, 37:L20402 http://dx.doi.org/10.1029/ 2010GL044571.
5.
Burke JJ, Moench MH: Groundwater and society: resources, tensions and opportunities. New York: United Nations Publication ST/ESA/205; 2000, .
6.
Llamas MR, Custodio E: Intensive use of groundwater: a new situation which demands proactive action. Intensive use of groundwater’ Balkema (Lisse). 2003:13-31.
Gardun˜o H, Foster S: Sustainable groundwater irrigation — approaches to reconciling demand with resources. GWMATE strategic overview series 4. Washington, DC: World Bank; 2010, www.worldbank.org/gwmate. A substantial policy paper based on the practical experience of attempting to manage groundwater resource use for agricultural irrigation in a
7.
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Groundwater — a global focus on the ‘local resource’ Foster et al. 695
series of pilot studies in Latin America, North Africa, Southern & Eastern Asia.
groundwater use, conservation and protection, and the impediments to governance reform.
8.
16. Tuinhof A et al.: Appropriate groundwater management for Sub-Saharan Africa — in face of demographic pressure and climatic variability. GW-MATE strategic overview series 5. Washington, DC: World Bank; 2011, www.worldbank.org/ gwmate.
Scanlon BR et al.: Choosing appropriate techniques for quantifying groundwater recharge. Hydrogeol J 2002, 10:18-39.
9.
Taylor RG et al.: Groundwater and climate change. Nature Climate Change 2012 http://dx.doi.org/10.1038/NCLIMATE1744 www.nature.com/natureclimatechange. A highly authoritative multi-authored paper systematically assessing the relation between past and future climate change, and groundwater resources. 10. Foster S, Loucks DP: Non-renewable groundwater resources — a guidebook on socially-sustainable management for water-policy makers. UNESCO IHP-VI Series on Groundwater 10; Paris: 2006. 11. Konikow LF: Contribution of global groundwater depletion since 1900 to sea-level rise. Geophys Res Lett 2011, 38:1-17401. 12. Rost et al.: Agricultural green and blue water consumption and its influence on the global water system. Water Resour Res 2008, 44 http://dx.doi.org/10.1029/2007WR006331.
13. Howard KWF: Urban groundwater — meeting the challenge. IAH selected paper series 8. London, UK: Taylor and Francis; 2007, . 14. Foster S, Candela L: Diffuse groundwater quality impacts from agricultural land-use; management and policy implications of scientific realities. RSC publication ‘groundwater science & policy — an international overview’. London: RSC Publishing; 2008, 454-470. 15. Foster S et al.: Groundwater governance — conceptual framework for assessment of provisions and needs. GWMATE strategic overview series 1. Washington, DC: World Bank; 2009, www.worldbank.org/gwmate. The first paper to deal specifically with the issue of the governance of
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17. Foster S, Ait-Kadi M: Integrated Water Resources Management (IWRM): how does groundwater fit in? Hydrogeol J 2012, 20:414-418. 18. Richts A: River and groundwater basins of the world. Hannover, Germany: BGR-WHYMAP Publication; 2012, www.whymap.org. 19. Foster S, Gardun˜o: Groundwater-resource governance: are governments and stakeholders responding to the challenge? Hydrogeol J 2013, 21:317-320. 20. Foster S, Van Steenbergen F: Conjunctive use of groundwater and surface water — a ‘lost opportunity’ for water management in the developing world? Hydrogeol J 2011, 19:959-962. 21. Meals DW: Lag time in water quality responses to best management practices: a review. J Environ Qual 2010, 39:85-96. 22. Zhang H, Hiscock KM: Modelling the effect of forest cover in mitigating nitrate contamination of groundwater: a case study from the Sherwood Sandstone aquifer in the East Midlands, UK. J Hydrol 2011, 399:212-225. 23. Foster S, Hirata R: Groundwater use for urban development: enhancing benefits and reducing risks. On the water front-2011. Sweden: Stockholm International Water Institute; 2011, 21-33. A very detailed and systematic review of policy issues and management approaches for urban groundwater use, which is a rapidly increasing phenomena in the developing world.
Current Opinion in Environmental Sustainability 2013, 5:685–695