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Ecohydrology and hydrogeological processes: groundwater–ecosystem interactions with special emphasis on abiotic processes
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ECOHYD-103; No. of Pages 7 Ecohydrology & Hydrobiology xxx (2016) xxx–xxx
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Ecohydrology & Hydrobiology journal homepage: www.elsevier.com/locate/ecohyd
Original Research Article
Ecohydrology and hydrogeological processes: groundwater–ecosystem interactions with special emphasis on abiotic processes A`frica de la Hera a,*, Joe Gurrieri b, Shammy Puri c, Emilio Custodio d, Marisol Manzano e a
Geological and Mining Institute of Spain (IGME), Rı´os Rosas 23, 28003 Madrid, Spain US Forest Service, Golden, CO, USA International Association of Hydrogeologists, United Kingdom d Technical University of Catalonia (UPC), Spain e Technical University of Cartagena (UPCT), Spain b c
A R T I C L E I N F O
A B S T R A C T
Article history: Received 2 February 2015 Received in revised form 1 February 2016 Accepted 18 March 2016 Available online xxx
This paper presents a review on the integration of hydrological, ecological and hydrogeological processes into Integrated Water Resources Management (IWRM) practice. These processes, for example, interact and take part in the process of creation of groundwater-related wetlands, which are an important part of the Earth’s biodiversity. Tools for integrating water and ecosystems are presented, with emphasis on the hydrogeological aspects as often they are poorly considered. Recent pioneering projects (IGCP-604, UNESCO-IHP, GENESIS, and Groundwater Governance) developed models for the future integration of ecosystem health with groundwater exploitation. An IWRM approach where groundwater-related wetlands and the groundwater systems upon which they depend are included in conjunctive water management decisions can be an accepted and workable paradigm that will benefit present and future generations. ß 2016 European Regional Centre for Ecohydrology of the Polish Academy of Sciences. Published by Elsevier Sp. z o.o. All rights reserved.
Keywords: Conceptual models Groundwater-related wetland Groundwater depended ecosystems (GDE) Hydrogeology Integrated Water Resources Management Sustainability
1. Introduction and background Ecohydrology (EH) is conceived as a transdisciplinary paradigm, to deal with water-related problems in order to support sustainable development (Zalewski, 2015). There are several international projects that, since 2000, have developed this theme: Water Programme for Environmental Sustainability (WPA II, 2006–2009), European projects
* Corresponding author. Tel.: +34 91 349 59 67; fax: +34 91 349 59 50. E-mail addresses: [email protected] (A`. de la Hera), [email protected] (J. Gurrieri), [email protected] (S. Puri), [email protected] (E. Custodio), [email protected] (M. Manzano).
(GENESIS and INTERFACES) and GEF Projects, e.g. managing lakes and their basins for sustainable use (ILEC, 2005), IGCP604, UNESCO-IHP, GWG-2014, among others. This concept is related to Hydroecology (HE) which has been defined by Dunbar and Acreman (2001) as ‘‘the linkage of the knowledge from hydrological, hydraulic, geomorphological and biological/ecological sciences to predict the response of freshwater biota and ecosystems to variation of abiotic factors over a range of spatial and temporal scales’’. But EH and HE are different disciplines, concepts and ways of thinking, largely explained by Zalewski (2015). According to this author, the most important differences between EH and HE are in methodology, nevertheless as expressed by Petts (2007): ‘‘Ecology has created an environment of opportunity to embed hydrogeological perspectives within water
http://dx.doi.org/10.1016/j.ecohyd.2016.03.005 1642-3593/ß 2016 European Regional Centre for Ecohydrology of the Polish Academy of Sciences. Published by Elsevier Sp. z o.o. All rights reserved.
Please cite this article in press as: de la Hera, A`., et al., Ecohydrology and hydrogeological processes: groundwater– ecosystem interactions with special emphasis on abiotic processes. Ecohydrol. Hydrobiol. (2016), http://dx.doi.org/ 10.1016/j.ecohyd.2016.03.005
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resources management’’. This definition implies not just a comprehensive approach of the hydrological processes involved in the water cycle in its three dimensions, but also a real understanding of the quantitative and qualitative aspects of such processes in order to create a conceptual model, basic platform to later generate a hydrological model able to simulate future water management scenarios. In many parts of the world, groundwater is extensively exploited due to its temporal and spatial accessibility, which is also crucial for many ecosystems, thus jeopardizing base flows and ecosystem sustainability due to competition. Wetland behaviour is linked to groundwater and surface flow functioning, and to land use in the catchment. Thus, the protection of wetlands and of their services to human wellbeing is most effective when coordinated with other management programmes such as water and land management. Moreover, wetlands performance is controlled by factors that occur at different temporal and space scales and which maintain a hierarchical spatial organization: large scale factors are influenced by geographical, geological, climatic, economic and political aspects that do not act or are barely noticed at the local scale. The concept and consideration of what is currently called Integrated Water Resources Management (IWRM) addresses multifaceted water resources both from the technical and the governance points of view (Martı´nezSantos et al., 2014). This should consider the existence of wetlands and the services they provide, by carefully managing the available water resources, both natural (surface water, groundwater, imported water from other areas, rainfall harvesting, etc.) and industrial or artificial (seawater and brackish water desalination, water reclamation), and even the consideration of virtual water (hidden flow of water if food or other commodities are traded from one place to another) (UNEP-MAP UNESCOIHP, 2011). IWRM was defined by the Global Water Partnership (GWP) as ‘‘a process which promotes the coordinated development and management of water, land and related resources, in order to maximize the resultant economic social welfare in an equitable manner without compromising the sustainability of vital ecosystems’’. IWRM, expressed through the conjunctive use of surface and groundwater, is a paradigm that incorporates technical, scientific, political, legislative, social and organizational aspects of a water system (Molina et al., 2009). Nevertheless and according to Zalewski (2015), to achieve sustainability, society needs to optimize water resources use instead of maximizing the benefits they can provide. In recent decades, an increase in the withdrawal of groundwater, mainly for human consumption and irrigation, has led to a reduction in its accessibility in many parts of the world with important consequences for aquatic environments (Acreman, 2000; Custodio, 2001, 2002; Llamas and Custodio, 2004; Vrba, 2004; Sophocleous, 2004). Some aquifers are not replenished at the time scale of human, society and ecosystem behaviour (GENESIS Project), i.e. their exploitation is not sustainable in terms of a steady state water balance. Pumping from aquifers readjusts the hydrological balance under natural conditions with
consequences on the relationships between its different components. Groundwater withdrawal leads to a reduction of natural aquifer discharge and under some circumstances increases recharge, which may affect the functioning of the natural environment (Dumont, 2015). When groundwater is pumped from an aquifer, the ‘‘groundwater head topography’’ is modified, creating drawdown. Once the perturbation reaches an area of interaction between the groundwater and land topographies or a groundwater divide, the rates of inflows into and outflows from the aquifer change (based on Theis, 1940). These changes may be observed in (a) areas of discharge, through flow or evapotranspiration, a lower groundwater table generates a decrease in the discharge rate, e.g., flows to springs and rivers decline or phreatophytes are no longer able to reach the groundwater table (Fig. 1), and (b) in areas of rejected recharge where the water table used to be close to the ground surface. Pumping results in an increase in recharge rate and less surface water flows are generated. The Upper Guadiana basin is a wellknown example of this phenomenon (Llamas, 1988; Martı´nezCortina et al., 2011; Martı´nez-Santos and Martı´nez-Alfaro, 2010; Martı´nez-Santos et al., 2008). Therefore, the aim of this paper is to characterize the hydrogeological processes occurring in the interaction between groundwater and wetlands within the framework of Integrated Water Resources Management (IWRM). 2. Groundwater related wetlands and IWRM While hydrologists, hydrogeologists and ecologists move forward on understanding the complex relationships between water and ecosystems, there are still many open questions, in particular concerning the relationship between groundwater and groundwater-related wetlands (GRW). Although IWRM is a mature and widely used concept, this does not imply that it does not need review and update, as shown in Table 1. Under an enlightened IWRM approach, the balance of positive and negative impacts associated with the intensive use of groundwater should be assessed as part of an integrated system, making it possible to formulate management scenarios on the basis of previously established goals and objectives. To achieve this goal, two complementary approaches are needed for both a scientific study and consequently a correct management framework: basin scale and wetland-bed scale. Both approaches are not new and have been largely explained by several authors (Sophocleous, 2002, 2004; Plan Andaluz de Humedales, 2002; Kløve et al., 2013). This corresponds to the fact that the key processes to maintain the ecological integrity of wetlands occur at two levels. Dumont (2015) provides a detailed description of alterations from withdrawals of water in a watershed. It mainly shows that pumping generates, on the one hand, aquifer stock consumption and, on the other hand, an increase in recharge and decrease in discharge, i.e. disruption of discharge to surface water bodies and ecosystems, with varying proportions through time. Therefore, the criteria used for decisions must reflect all
Please cite this article in press as: de la Hera, A`., et al., Ecohydrology and hydrogeological processes: groundwater– ecosystem interactions with special emphasis on abiotic processes. Ecohydrol. Hydrobiol. (2016), http://dx.doi.org/ 10.1016/j.ecohyd.2016.03.005
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Fig. 1. Simplified schematic diagrams of the changing relationships between some wetlands and the aquifer. (a) Dune slack wetland during wet season, or with aquifer under natural flow conditions: the main water source is groundwater discharge from the surrounding aquifer. (b) Same wetland during dry season, or with regional water table lowered by groundwater pumping: the only water source is precipitation on the wetland basin, which will generate small and temporal water bodies. (c) Wetland in small erosive depression and with layers of low-permeability materials underneath during wet season, or with aquifer under natural flow conditions: main water source is permanent groundwater discharge from a regional aquifer, but also temporal discharge from ephemeral perched water table formed after significant rainfall. (d) Same wetland during dry season, or with regional water table lowered by groundwater pumping: the wetland may get water from direct precipitation during heavy summer rainfall, but flooding is temporal and wetland dries because of evapotranspiration and ground infiltration. Modified from sources: Manzano et al. (2002), Foster et al. (2006), UNEP-MAP UNESCO-IHP (2015a).
Table 1 Analysis of IWRM concept showing its strengths and weaknesses. Strengths
Weaknesses
(a) It establishes defined objectives; (b) It makes ecosystem restoration possible; and (c) It uses decision support tools to define the best management option involving all affected parties.
(a) How and who decides on the acceptability of management decisions for society (e.g. changes in groundwater abstraction rates); (b) Establishing the priority of human demands versus nature needs is often politically controversial; (c) There is often a lack of alternative sources of water to satisfy human demand, thus leaving ecosystems degraded in perpetuity; and (d) There is frequently a lack of centralized control over water use.
relevant implications, in terms of both value generated by withdrawals and disruption of natural water flows, thus highlighting the trade-offs. Most groundwater-related wetlands occur in discharge areas. Those located in recharge areas are limited
depending on size, hydraulic transmitivity and recharge (Sophocleous, 2002, 2004). They are frequently shallow water table areas, but some are linked to deep groundwater flows intersecting the land surface, in both the coastal and in inland areas. The various types of discharge springs
Please cite this article in press as: de la Hera, A`., et al., Ecohydrology and hydrogeological processes: groundwater– ecosystem interactions with special emphasis on abiotic processes. Ecohydrol. Hydrobiol. (2016), http://dx.doi.org/ 10.1016/j.ecohyd.2016.03.005
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is presented by Springer and Stevens (2008). In groundwater-related wetlands many ecosystem services are derived from or supported by the presence of groundwater inflow because of its role in regulating the hydrology of the wetland (UNEP-MAP UNESCO-IHP, 2015a,b; UNEP-MAP UNESCO-IHP, IGME, 2015). Discharge occurs when the groundwater level (or the piezometric head) is above the ground surface. Processes related to groundwater inflow to wetlands are: groundwater supply, provision of nutrients, oxygen, organic matter, and attenuation of pollutants. Discharge dynamics also affect the substrate composition, which influences the diversity and nature of macrozoobenthic communities (ecologic, phenotypic and genotypic adaptations, Bertrand et al., 2011). 2.1. Tools for practitioners Most wetland managers are familiar with geographical analysis of wetlands, however, understanding interactions with groundwater requires a geological view in a third dimension, i.e., looking at vertical sections through the soils and rocks that lie beneath the wetland (Miller and Acreman, 2006) and also potential contributions from adjacent aquifers. Groundwater-dependent wetlands are the ecological outcome of groundwater (GW)–surface water (SW) interactions. A variety of methods to study GW/SW interactions have been developed. Field methods include stream-flow measurements, water quality sampling in streams and wells, mini piezometers, dye and isotopic tracers, habitat surveys, and repeated visual observations with infrared cameras or other temperature based methods. Office methods include satellite image analysis, baseflow hydrograph separation, water balance analyses and numerical modelling, to name a few (Rosenberry and LaBaugh, 2008; GENESIS Project). Tracer methods have proven their usefulness in groundwater management, although their usefulness is not always sufficiently recognized by groundwater managers (GENESIS Project). Also the analysis of aquatic ecology (depth to water table requirements for obligate wetland plants) and soils (peat development, redoximorphic features) provide valuable information that can be used to plan groundwater usage. Water balance modelling can assist in the determination of vegetation water requirements by providing an understanding of the balance between rainfall, evapotranspiration and available soil moisture within the rooting zone. Knowledge of the rooting depth and water table requirements for different wetland or riparian species contributes to the understanding of the potential reliance of the ecosystem on groundwater. The potential reliance of aquatic or terrestrial ecosystems on groundwater can be understood by establishing whether groundwater maintains low flows or the presence of water in dry periods and whether groundwater provides a particular temperature or water quality benefit (Richardson et al., 2011). Approaches involve physical measurements (e.g. hydraulic gradients), flux calculations, geochemical approaches using environmental or introduced tracers, as well as biological approaches such as vegetation mapping and soil profiles.
A number of different types of remotely sensed datasets are available, each suitable for certain applications pertaining to groundwater, with none being applicable in all situations. Data from the visible and near-infrared spectrum have most commonly been used to inventory and monitor groundwater in the past (Meijerink et al., 2007), but other types of data are rapidly being accepted as significantly enhancing the quality of hydrogeological information derived from remotely sensed imagery. Each data type has distinct advantages and disadvantages, with each being sensitive to unique landscape components and processes. These components (e.g., soil moisture and type, inundation, evapotranspiration, elevation, vegetation biomass and type, and more) can be synthesized to provide enhanced information on groundwater distribution, abundance, and hydrogeochemical evolution. Water table and surface water level elevation should be accurate enough and be able to consider the variation in gradient between surface water and the aquifer over time (Richardson et al., 2011). Once a conceptual hydrogeological, biogeochemical and ecological conceptual model of the wetland functioning exists, it is possible to simulate future scenarios. Modelling approaches use available data to create an empirically or physically-based model that describes system response to drivers. The advantage of modelling is that temporal effects, such as changes over time and lags in response can be evaluated. Modelling approaches can be used to predict or to retrospectively determine the effects of multiple drivers on groundwater flow dynamics and levels that support a particular groundwater related wetland. It is critical that the scale of groundwater modelling is commensurate with the temporal and spatial scale of occurrence of the GRW, as the analysis often requires greater resolution than is available from many groundwater modelling approaches used to support regional management of groundwater systems. Because many GRWs are small in comparison to their associated groundwater flow systems, multiple scales of models may be required to increase confidence (Richardson et al., 2011). 3. Opportunities and challenges For many years there has been a general consensus on the need to consider surface and groundwater together in order to achieve the more logical and comprehensive paradigm for Integrated Water Resources Management. Nevertheless, in many countries this goal is far from being achieved. In Spain, for example, groundwater is in the public domain, but due to some legal transitory dispositions, in reality most of it remains in private hands making comprehensive water management efforts complex (Llamas et al., 2014). In the western US, some state water rights laws continue to ignore the connection between surface water and groundwater. In India, groundwater resources are still treated as private goods associated with land ownership, though legislation to declare them as common pool resources are on the statute. Groundwater is one of the components of the water cycle and linked to the other
Please cite this article in press as: de la Hera, A`., et al., Ecohydrology and hydrogeological processes: groundwater– ecosystem interactions with special emphasis on abiotic processes. Ecohydrol. Hydrobiol. (2016), http://dx.doi.org/ 10.1016/j.ecohyd.2016.03.005
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ones, so the right consideration of groundwater has to be done within good understanding of the whole from the hydrological, hydrochemical, and environmental points of view. A significant challenge in the management of GRWs is the determination of environmental water requirements (EWR). Zalewski (2011) suggests the concept of an ecohydrology sustainability threshold for the European WFD implementation. Others, such as Aldous and Bach (2014), support this idea through developing quantitative, measurable thresholds that are sensitive to changes in groundwater quantity. Complications for EWR determinations exist for systems that are in a state of rapid change of a kind different to what has been historically experienced and/or otherwise substantial (Richardson et al., 2011). Key questions that need to be answered in a EWR framework are: (a) What are the threats to the groundwater system and wetland ecosystem? (b) How might the current wetland ecosystem change if the groundwater system changes? (c) What is the long-term wetland ecosystem state due to the change? and (d) What constitutes an acceptable change that leaves the wetland ecosystem intact and functioning? As a general rule, low storage-to-recharge ratio local groundwater flow systems are typically less robust aquifers and, hydrogeologically more susceptible to climatic variability or longer-term climatic shifts, than high-storage, regional groundwater systems. Biotic components of the hydrogeologically less robust systems will more likely have adaptive strategies to deal with the naturally variable conditions (Shafroth et al., 2000). Conversely, species evolving in more stable regional groundwater systems are less resistant to change, particularly from aquifer pumping stresses. Muller et al. (2014) identified other key challenges, including developing innovative interdisciplinary analysis methods, developing dynamically coupled model systems, integrated monitoring techniques for coupled processes at the water/biota interface, and transitioning from basic to applied ecohydrological science to develop sustainable water and land resource management strategies under regional and global change. Changes in future climate and land use will alter the hydrologic cycle and impact the quantity and quality of regional water systems. Rising groundwater temperatures and lowering of groundwater levels are already observed in many groundwater systems (Bloomfield et al., 2013; Kumar, 2012; Menberg et al., 2014; Nyenje and Batelaan, 2009). Groundwater resources are related to climate change through the direct interaction with surface water resources but also indirectly through the recharge process. Expected consequences of climate change include higher groundwater temperature, lower water tables, and decreased groundwater discharge, which may in turn reduce stream base flows and lake levels, and decrease groundwater discharge to GRWs. These effects will be intensified if water abstractions are increased to meet a growing water demand. Predicting the behaviour of recharge and discharge conditions under the future climatic and land use changes is essential for Integrated Water Resources Management (GENESIS Project; Cap-Net,
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2010). Understanding of how rising groundwater temperatures will affect the biota of many GRWs is still pending. 4. Conclusions – integrating groundwater resources, ecosystems, and IWRM for a sustainable future A workable balance between groundwater use and natural flows can be obtained through the application of conjunctive groundwater–surface water management in IWRM. However, the right application of this concept implies that ecologists, hydrogeologists, water managers and stakeholders work together in order to balance the trade-offs in water management decision-making. Although the scientific community required to solve these problems is divided into multiple disciplines, each with its own parochial biases, interdisciplinary cooperation is crucial to the success of this important effort. Hydrological processes involved in the water cycle are associated with both biotic and abiotic components of the Earth system, particularly in the sphere of surface– groundwater interactions. Any alteration in the quality or quantity of water will affect these biotic and abiotic components and therefore should be assessed and analyzed within an integrated management structure. An IWRM approach where GRWs and the groundwater systems upon which they depend are included in water management decision-making can become an accepted and workable paradigm that benefits present and future generations. There are a set of ecohydrological concepts and tools useful in determining the amount of withdrawal that can be obtained from an aquifer. They are rooted in hydrogeologic science but are dependent on the biological and social sciences as well and rely on social and political decisions. The authors recognize that, in many cases, the mechanics of managing ecological systems is still in its infancy and not well defined. However, the integration of hydrogeologic processes and ecohydrologic concepts into the IWRM process is possible today and will result in more holistic and sustainable outcomes that will benefit human populations as well as the ecosystems upon which societies depend. The authors call upon the hydrogeological and ecological community to develop educational syllabi for education of a new cadre of experts that can implement ecohydrogeology in the field. They are of the opinion that field application of ecohydrology must include the behaviour and the dynamics of aquifers that contribute to aquatic ecosystems. With these analyses and improved conceptualisations, there is a strong promise of improving the resilience of groundwater related wetlands, especially in the face of climate and global change, drawing on the fact that aquifers will provide the essential buffer to droughts in the coming decades. Conflict of interest We certify that we have no affiliation or financial involvement with any organization or entity with a direct
Please cite this article in press as: de la Hera, A`., et al., Ecohydrology and hydrogeological processes: groundwater– ecosystem interactions with special emphasis on abiotic processes. Ecohydrol. Hydrobiol. (2016), http://dx.doi.org/ 10.1016/j.ecohyd.2016.03.005
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financial or any other interest in the subject matter or materials discussed in the manuscript. Acknowledgements The authors wish to thank to the Editors-in-Chief, Professor Maciej Zalewski and Professor Michael McClain their invitation to present a paper in this Special Issue under the initiative of the Scientific Advisory Committee (SAC) of UNESCO-IHP’s Ecohydrology Programme. The authors cordially thank the reviewers for their remarks and advices that have helped to highly improve the paper content. Funding body None declared.
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UNEP-MAP UNESCO-IHP, 2015a. Management and protection of Mediterranean groundwater-related coastal wetlands and their services. Regional Report. Strategic Partnership for the Mediterranean Sea Large Marine Ecosystem. Paris. UNEP-MAP UNESCO-IHP, 2015b. Main hydro(geo)logical characteristics, ecosystem services, and drivers of change of 26 representative Mediterranean groundwater-related coastal wetlands. Technical Report. Paris. UNEP-MAP UNESCO-IHP, IGME, 2015. Map of selected coastal Mediterranean wetlands. Strategic Partnership for the Mediterranean Sea Large Marine Ecosystem (MedPartnership). Madrid. Vrba, J., 2004. The impact of aquifer intensive use on groundwater quality. In: Llamas, M.R., Custodio, E. (Eds.), Intensive use of Groundwater, Challenges and Opportunities. Balkema, pp. 113–132. WPA II. Water Programme for Environmental Sustainability WPA II (Second Phase). https://sustainabledevelopment.un.org/index.php?page= view&type=1006&menu=1348&nr=1662 (consulted 07.09.15). Zalewski, M., 2011. Ecohydrology for implementation of the water framework directive. Water Manag. 164, 375–385. Zalewski, M., 2015. Ecohydrology and hydrologic engineering: regulation of hydrology-biota interactions for sustainability. J. Hydrol. Eng. 20, A4014012, Special issue. Grand challenges in hydrology.
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Contents lists available at ScienceDirect
Ecohydrology & Hydrobiology journal homepage: www.elsevier.com/locate/ecohyd
Original Research Article
Ecohydrology and hydrogeological processes: groundwater–ecosystem interactions with special emphasis on abiotic processes A`frica de la Hera a,*, Joe Gurrieri b, Shammy Puri c, Emilio Custodio d, Marisol Manzano e a
Geological and Mining Institute of Spain (IGME), Rı´os Rosas 23, 28003 Madrid, Spain US Forest Service, Golden, CO, USA International Association of Hydrogeologists, United Kingdom d Technical University of Catalonia (UPC), Spain e Technical University of Cartagena (UPCT), Spain b c
A R T I C L E I N F O
A B S T R A C T
Article history: Received 2 February 2015 Received in revised form 1 February 2016 Accepted 18 March 2016 Available online xxx
This paper presents a review on the integration of hydrological, ecological and hydrogeological processes into Integrated Water Resources Management (IWRM) practice. These processes, for example, interact and take part in the process of creation of groundwater-related wetlands, which are an important part of the Earth’s biodiversity. Tools for integrating water and ecosystems are presented, with emphasis on the hydrogeological aspects as often they are poorly considered. Recent pioneering projects (IGCP-604, UNESCO-IHP, GENESIS, and Groundwater Governance) developed models for the future integration of ecosystem health with groundwater exploitation. An IWRM approach where groundwater-related wetlands and the groundwater systems upon which they depend are included in conjunctive water management decisions can be an accepted and workable paradigm that will benefit present and future generations. ß 2016 European Regional Centre for Ecohydrology of the Polish Academy of Sciences. Published by Elsevier Sp. z o.o. All rights reserved.
Keywords: Conceptual models Groundwater-related wetland Groundwater depended ecosystems (GDE) Hydrogeology Integrated Water Resources Management Sustainability
1. Introduction and background Ecohydrology (EH) is conceived as a transdisciplinary paradigm, to deal with water-related problems in order to support sustainable development (Zalewski, 2015). There are several international projects that, since 2000, have developed this theme: Water Programme for Environmental Sustainability (WPA II, 2006–2009), European projects
* Corresponding author. Tel.: +34 91 349 59 67; fax: +34 91 349 59 50. E-mail addresses: [email protected] (A`. de la Hera), [email protected] (J. Gurrieri), [email protected] (S. Puri), [email protected] (E. Custodio), [email protected] (M. Manzano).
(GENESIS and INTERFACES) and GEF Projects, e.g. managing lakes and their basins for sustainable use (ILEC, 2005), IGCP604, UNESCO-IHP, GWG-2014, among others. This concept is related to Hydroecology (HE) which has been defined by Dunbar and Acreman (2001) as ‘‘the linkage of the knowledge from hydrological, hydraulic, geomorphological and biological/ecological sciences to predict the response of freshwater biota and ecosystems to variation of abiotic factors over a range of spatial and temporal scales’’. But EH and HE are different disciplines, concepts and ways of thinking, largely explained by Zalewski (2015). According to this author, the most important differences between EH and HE are in methodology, nevertheless as expressed by Petts (2007): ‘‘Ecology has created an environment of opportunity to embed hydrogeological perspectives within water
http://dx.doi.org/10.1016/j.ecohyd.2016.03.005 1642-3593/ß 2016 European Regional Centre for Ecohydrology of the Polish Academy of Sciences. Published by Elsevier Sp. z o.o. All rights reserved.
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resources management’’. This definition implies not just a comprehensive approach of the hydrological processes involved in the water cycle in its three dimensions, but also a real understanding of the quantitative and qualitative aspects of such processes in order to create a conceptual model, basic platform to later generate a hydrological model able to simulate future water management scenarios. In many parts of the world, groundwater is extensively exploited due to its temporal and spatial accessibility, which is also crucial for many ecosystems, thus jeopardizing base flows and ecosystem sustainability due to competition. Wetland behaviour is linked to groundwater and surface flow functioning, and to land use in the catchment. Thus, the protection of wetlands and of their services to human wellbeing is most effective when coordinated with other management programmes such as water and land management. Moreover, wetlands performance is controlled by factors that occur at different temporal and space scales and which maintain a hierarchical spatial organization: large scale factors are influenced by geographical, geological, climatic, economic and political aspects that do not act or are barely noticed at the local scale. The concept and consideration of what is currently called Integrated Water Resources Management (IWRM) addresses multifaceted water resources both from the technical and the governance points of view (Martı´nezSantos et al., 2014). This should consider the existence of wetlands and the services they provide, by carefully managing the available water resources, both natural (surface water, groundwater, imported water from other areas, rainfall harvesting, etc.) and industrial or artificial (seawater and brackish water desalination, water reclamation), and even the consideration of virtual water (hidden flow of water if food or other commodities are traded from one place to another) (UNEP-MAP UNESCOIHP, 2011). IWRM was defined by the Global Water Partnership (GWP) as ‘‘a process which promotes the coordinated development and management of water, land and related resources, in order to maximize the resultant economic social welfare in an equitable manner without compromising the sustainability of vital ecosystems’’. IWRM, expressed through the conjunctive use of surface and groundwater, is a paradigm that incorporates technical, scientific, political, legislative, social and organizational aspects of a water system (Molina et al., 2009). Nevertheless and according to Zalewski (2015), to achieve sustainability, society needs to optimize water resources use instead of maximizing the benefits they can provide. In recent decades, an increase in the withdrawal of groundwater, mainly for human consumption and irrigation, has led to a reduction in its accessibility in many parts of the world with important consequences for aquatic environments (Acreman, 2000; Custodio, 2001, 2002; Llamas and Custodio, 2004; Vrba, 2004; Sophocleous, 2004). Some aquifers are not replenished at the time scale of human, society and ecosystem behaviour (GENESIS Project), i.e. their exploitation is not sustainable in terms of a steady state water balance. Pumping from aquifers readjusts the hydrological balance under natural conditions with
consequences on the relationships between its different components. Groundwater withdrawal leads to a reduction of natural aquifer discharge and under some circumstances increases recharge, which may affect the functioning of the natural environment (Dumont, 2015). When groundwater is pumped from an aquifer, the ‘‘groundwater head topography’’ is modified, creating drawdown. Once the perturbation reaches an area of interaction between the groundwater and land topographies or a groundwater divide, the rates of inflows into and outflows from the aquifer change (based on Theis, 1940). These changes may be observed in (a) areas of discharge, through flow or evapotranspiration, a lower groundwater table generates a decrease in the discharge rate, e.g., flows to springs and rivers decline or phreatophytes are no longer able to reach the groundwater table (Fig. 1), and (b) in areas of rejected recharge where the water table used to be close to the ground surface. Pumping results in an increase in recharge rate and less surface water flows are generated. The Upper Guadiana basin is a wellknown example of this phenomenon (Llamas, 1988; Martı´nezCortina et al., 2011; Martı´nez-Santos and Martı´nez-Alfaro, 2010; Martı´nez-Santos et al., 2008). Therefore, the aim of this paper is to characterize the hydrogeological processes occurring in the interaction between groundwater and wetlands within the framework of Integrated Water Resources Management (IWRM). 2. Groundwater related wetlands and IWRM While hydrologists, hydrogeologists and ecologists move forward on understanding the complex relationships between water and ecosystems, there are still many open questions, in particular concerning the relationship between groundwater and groundwater-related wetlands (GRW). Although IWRM is a mature and widely used concept, this does not imply that it does not need review and update, as shown in Table 1. Under an enlightened IWRM approach, the balance of positive and negative impacts associated with the intensive use of groundwater should be assessed as part of an integrated system, making it possible to formulate management scenarios on the basis of previously established goals and objectives. To achieve this goal, two complementary approaches are needed for both a scientific study and consequently a correct management framework: basin scale and wetland-bed scale. Both approaches are not new and have been largely explained by several authors (Sophocleous, 2002, 2004; Plan Andaluz de Humedales, 2002; Kløve et al., 2013). This corresponds to the fact that the key processes to maintain the ecological integrity of wetlands occur at two levels. Dumont (2015) provides a detailed description of alterations from withdrawals of water in a watershed. It mainly shows that pumping generates, on the one hand, aquifer stock consumption and, on the other hand, an increase in recharge and decrease in discharge, i.e. disruption of discharge to surface water bodies and ecosystems, with varying proportions through time. Therefore, the criteria used for decisions must reflect all
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Fig. 1. Simplified schematic diagrams of the changing relationships between some wetlands and the aquifer. (a) Dune slack wetland during wet season, or with aquifer under natural flow conditions: the main water source is groundwater discharge from the surrounding aquifer. (b) Same wetland during dry season, or with regional water table lowered by groundwater pumping: the only water source is precipitation on the wetland basin, which will generate small and temporal water bodies. (c) Wetland in small erosive depression and with layers of low-permeability materials underneath during wet season, or with aquifer under natural flow conditions: main water source is permanent groundwater discharge from a regional aquifer, but also temporal discharge from ephemeral perched water table formed after significant rainfall. (d) Same wetland during dry season, or with regional water table lowered by groundwater pumping: the wetland may get water from direct precipitation during heavy summer rainfall, but flooding is temporal and wetland dries because of evapotranspiration and ground infiltration. Modified from sources: Manzano et al. (2002), Foster et al. (2006), UNEP-MAP UNESCO-IHP (2015a).
Table 1 Analysis of IWRM concept showing its strengths and weaknesses. Strengths
Weaknesses
(a) It establishes defined objectives; (b) It makes ecosystem restoration possible; and (c) It uses decision support tools to define the best management option involving all affected parties.
(a) How and who decides on the acceptability of management decisions for society (e.g. changes in groundwater abstraction rates); (b) Establishing the priority of human demands versus nature needs is often politically controversial; (c) There is often a lack of alternative sources of water to satisfy human demand, thus leaving ecosystems degraded in perpetuity; and (d) There is frequently a lack of centralized control over water use.
relevant implications, in terms of both value generated by withdrawals and disruption of natural water flows, thus highlighting the trade-offs. Most groundwater-related wetlands occur in discharge areas. Those located in recharge areas are limited
depending on size, hydraulic transmitivity and recharge (Sophocleous, 2002, 2004). They are frequently shallow water table areas, but some are linked to deep groundwater flows intersecting the land surface, in both the coastal and in inland areas. The various types of discharge springs
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is presented by Springer and Stevens (2008). In groundwater-related wetlands many ecosystem services are derived from or supported by the presence of groundwater inflow because of its role in regulating the hydrology of the wetland (UNEP-MAP UNESCO-IHP, 2015a,b; UNEP-MAP UNESCO-IHP, IGME, 2015). Discharge occurs when the groundwater level (or the piezometric head) is above the ground surface. Processes related to groundwater inflow to wetlands are: groundwater supply, provision of nutrients, oxygen, organic matter, and attenuation of pollutants. Discharge dynamics also affect the substrate composition, which influences the diversity and nature of macrozoobenthic communities (ecologic, phenotypic and genotypic adaptations, Bertrand et al., 2011). 2.1. Tools for practitioners Most wetland managers are familiar with geographical analysis of wetlands, however, understanding interactions with groundwater requires a geological view in a third dimension, i.e., looking at vertical sections through the soils and rocks that lie beneath the wetland (Miller and Acreman, 2006) and also potential contributions from adjacent aquifers. Groundwater-dependent wetlands are the ecological outcome of groundwater (GW)–surface water (SW) interactions. A variety of methods to study GW/SW interactions have been developed. Field methods include stream-flow measurements, water quality sampling in streams and wells, mini piezometers, dye and isotopic tracers, habitat surveys, and repeated visual observations with infrared cameras or other temperature based methods. Office methods include satellite image analysis, baseflow hydrograph separation, water balance analyses and numerical modelling, to name a few (Rosenberry and LaBaugh, 2008; GENESIS Project). Tracer methods have proven their usefulness in groundwater management, although their usefulness is not always sufficiently recognized by groundwater managers (GENESIS Project). Also the analysis of aquatic ecology (depth to water table requirements for obligate wetland plants) and soils (peat development, redoximorphic features) provide valuable information that can be used to plan groundwater usage. Water balance modelling can assist in the determination of vegetation water requirements by providing an understanding of the balance between rainfall, evapotranspiration and available soil moisture within the rooting zone. Knowledge of the rooting depth and water table requirements for different wetland or riparian species contributes to the understanding of the potential reliance of the ecosystem on groundwater. The potential reliance of aquatic or terrestrial ecosystems on groundwater can be understood by establishing whether groundwater maintains low flows or the presence of water in dry periods and whether groundwater provides a particular temperature or water quality benefit (Richardson et al., 2011). Approaches involve physical measurements (e.g. hydraulic gradients), flux calculations, geochemical approaches using environmental or introduced tracers, as well as biological approaches such as vegetation mapping and soil profiles.
A number of different types of remotely sensed datasets are available, each suitable for certain applications pertaining to groundwater, with none being applicable in all situations. Data from the visible and near-infrared spectrum have most commonly been used to inventory and monitor groundwater in the past (Meijerink et al., 2007), but other types of data are rapidly being accepted as significantly enhancing the quality of hydrogeological information derived from remotely sensed imagery. Each data type has distinct advantages and disadvantages, with each being sensitive to unique landscape components and processes. These components (e.g., soil moisture and type, inundation, evapotranspiration, elevation, vegetation biomass and type, and more) can be synthesized to provide enhanced information on groundwater distribution, abundance, and hydrogeochemical evolution. Water table and surface water level elevation should be accurate enough and be able to consider the variation in gradient between surface water and the aquifer over time (Richardson et al., 2011). Once a conceptual hydrogeological, biogeochemical and ecological conceptual model of the wetland functioning exists, it is possible to simulate future scenarios. Modelling approaches use available data to create an empirically or physically-based model that describes system response to drivers. The advantage of modelling is that temporal effects, such as changes over time and lags in response can be evaluated. Modelling approaches can be used to predict or to retrospectively determine the effects of multiple drivers on groundwater flow dynamics and levels that support a particular groundwater related wetland. It is critical that the scale of groundwater modelling is commensurate with the temporal and spatial scale of occurrence of the GRW, as the analysis often requires greater resolution than is available from many groundwater modelling approaches used to support regional management of groundwater systems. Because many GRWs are small in comparison to their associated groundwater flow systems, multiple scales of models may be required to increase confidence (Richardson et al., 2011). 3. Opportunities and challenges For many years there has been a general consensus on the need to consider surface and groundwater together in order to achieve the more logical and comprehensive paradigm for Integrated Water Resources Management. Nevertheless, in many countries this goal is far from being achieved. In Spain, for example, groundwater is in the public domain, but due to some legal transitory dispositions, in reality most of it remains in private hands making comprehensive water management efforts complex (Llamas et al., 2014). In the western US, some state water rights laws continue to ignore the connection between surface water and groundwater. In India, groundwater resources are still treated as private goods associated with land ownership, though legislation to declare them as common pool resources are on the statute. Groundwater is one of the components of the water cycle and linked to the other
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ones, so the right consideration of groundwater has to be done within good understanding of the whole from the hydrological, hydrochemical, and environmental points of view. A significant challenge in the management of GRWs is the determination of environmental water requirements (EWR). Zalewski (2011) suggests the concept of an ecohydrology sustainability threshold for the European WFD implementation. Others, such as Aldous and Bach (2014), support this idea through developing quantitative, measurable thresholds that are sensitive to changes in groundwater quantity. Complications for EWR determinations exist for systems that are in a state of rapid change of a kind different to what has been historically experienced and/or otherwise substantial (Richardson et al., 2011). Key questions that need to be answered in a EWR framework are: (a) What are the threats to the groundwater system and wetland ecosystem? (b) How might the current wetland ecosystem change if the groundwater system changes? (c) What is the long-term wetland ecosystem state due to the change? and (d) What constitutes an acceptable change that leaves the wetland ecosystem intact and functioning? As a general rule, low storage-to-recharge ratio local groundwater flow systems are typically less robust aquifers and, hydrogeologically more susceptible to climatic variability or longer-term climatic shifts, than high-storage, regional groundwater systems. Biotic components of the hydrogeologically less robust systems will more likely have adaptive strategies to deal with the naturally variable conditions (Shafroth et al., 2000). Conversely, species evolving in more stable regional groundwater systems are less resistant to change, particularly from aquifer pumping stresses. Muller et al. (2014) identified other key challenges, including developing innovative interdisciplinary analysis methods, developing dynamically coupled model systems, integrated monitoring techniques for coupled processes at the water/biota interface, and transitioning from basic to applied ecohydrological science to develop sustainable water and land resource management strategies under regional and global change. Changes in future climate and land use will alter the hydrologic cycle and impact the quantity and quality of regional water systems. Rising groundwater temperatures and lowering of groundwater levels are already observed in many groundwater systems (Bloomfield et al., 2013; Kumar, 2012; Menberg et al., 2014; Nyenje and Batelaan, 2009). Groundwater resources are related to climate change through the direct interaction with surface water resources but also indirectly through the recharge process. Expected consequences of climate change include higher groundwater temperature, lower water tables, and decreased groundwater discharge, which may in turn reduce stream base flows and lake levels, and decrease groundwater discharge to GRWs. These effects will be intensified if water abstractions are increased to meet a growing water demand. Predicting the behaviour of recharge and discharge conditions under the future climatic and land use changes is essential for Integrated Water Resources Management (GENESIS Project; Cap-Net,
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2010). Understanding of how rising groundwater temperatures will affect the biota of many GRWs is still pending. 4. Conclusions – integrating groundwater resources, ecosystems, and IWRM for a sustainable future A workable balance between groundwater use and natural flows can be obtained through the application of conjunctive groundwater–surface water management in IWRM. However, the right application of this concept implies that ecologists, hydrogeologists, water managers and stakeholders work together in order to balance the trade-offs in water management decision-making. Although the scientific community required to solve these problems is divided into multiple disciplines, each with its own parochial biases, interdisciplinary cooperation is crucial to the success of this important effort. Hydrological processes involved in the water cycle are associated with both biotic and abiotic components of the Earth system, particularly in the sphere of surface– groundwater interactions. Any alteration in the quality or quantity of water will affect these biotic and abiotic components and therefore should be assessed and analyzed within an integrated management structure. An IWRM approach where GRWs and the groundwater systems upon which they depend are included in water management decision-making can become an accepted and workable paradigm that benefits present and future generations. There are a set of ecohydrological concepts and tools useful in determining the amount of withdrawal that can be obtained from an aquifer. They are rooted in hydrogeologic science but are dependent on the biological and social sciences as well and rely on social and political decisions. The authors recognize that, in many cases, the mechanics of managing ecological systems is still in its infancy and not well defined. However, the integration of hydrogeologic processes and ecohydrologic concepts into the IWRM process is possible today and will result in more holistic and sustainable outcomes that will benefit human populations as well as the ecosystems upon which societies depend. The authors call upon the hydrogeological and ecological community to develop educational syllabi for education of a new cadre of experts that can implement ecohydrogeology in the field. They are of the opinion that field application of ecohydrology must include the behaviour and the dynamics of aquifers that contribute to aquatic ecosystems. With these analyses and improved conceptualisations, there is a strong promise of improving the resilience of groundwater related wetlands, especially in the face of climate and global change, drawing on the fact that aquifers will provide the essential buffer to droughts in the coming decades. Conflict of interest We certify that we have no affiliation or financial involvement with any organization or entity with a direct
Please cite this article in press as: de la Hera, A`., et al., Ecohydrology and hydrogeological processes: groundwater– ecosystem interactions with special emphasis on abiotic processes. Ecohydrol. Hydrobiol. (2016), http://dx.doi.org/ 10.1016/j.ecohyd.2016.03.005
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financial or any other interest in the subject matter or materials discussed in the manuscript. Acknowledgements The authors wish to thank to the Editors-in-Chief, Professor Maciej Zalewski and Professor Michael McClain their invitation to present a paper in this Special Issue under the initiative of the Scientific Advisory Committee (SAC) of UNESCO-IHP’s Ecohydrology Programme. The authors cordially thank the reviewers for their remarks and advices that have helped to highly improve the paper content. Funding body None declared.
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