MEDSAL - Salinization of critical groundwater reserves in coastal Mediterranean areas: Identification, Risk Assessment and Sustainable Management with the use of integrated modelling and smart ICT tools

The coastal Mediterranean regions suffer from water scarcity and over-exploitation of groundwater reserves to satisfy the increasing water demands. As a result, researchers report increasing groundwater depletion and progressive deterioration of groundwater quality in Mediterranean coastal aquifers. The GWS worsens the problem of water availability, which is further impacted by climate change effects. Because of the arid or semi-arid climate and the expected water scarcity stresses of variable severity, the availability of freshwater resources in the Mediterranean countries, especially in coastal areas, is becoming highly important. A potential “water crisis” due to lack of water availability is alarming and likely to occur. For the Mediterranean, GWS is a long-term and serious threat for maintaining sustainable access to fresh water, as: (a) it is a slow process taking many years to decades to develop and even longer to revert; restoration of freshwater quality may require three times longer than the residence time, with some effects even persisting after this timespan, (b) affects the most productive and vulnerable aquifers of the Mediterranean coastal areas and, (c) may impact significanlty the environment and socio-economic development. Coastal aquifers are dynamic and complex systems typified by transient water levels, variable 3D water density distributions, and heterogeneous/anisotropic hydraulic properties. Climate variations, groundwater pumping and fluctuating sea levels result in dynamic hydrologic conditions, where groundwater flow is density-dependent and GWS is mainly related to present seawater intrusion/saltwater up-coning; however, additional factors may be potential sources which despite causing similar adverse impacts are often underestimated or even non-identified, being obscured by the dominant concept of seawater intrusion. The lowering of groundwater levels in coastal aquifers can induce salinization by lateral seawater intrusion (GWS type Ia) or up-coning of saline waters from the freshwater-saltwater interface (GWS type Ib). Evaporation from water-logged soils through capillary rise can induce a hydrological salinization type (GWS type II). Once the natural subsurface outflow to the sea ceases due to over-exploitation, also solute transport to the sea is interrupted, causing internal salinization and “poisoning” of the system: coastal aquifers become solute traps (GWS type III). Applications of fertilizers, soil improving agents and irrigation water return flow or other pollution produce source-specific GWS (GWS type IV). Solution of entrapped salts or bedrock weathering (e.g. evaporites), release of brines from tectonic structures, or interconnection with deep aquifers holding synsedimentary saline waters/brines represent specific geogenic processes in some Mediterranean regions (GWS type V). Additional types and processes may occur or contribute. The contribution of salinization types may vary over time and in space and is related to changing land-use practice and external pressures such as climate change and resulting groundwater level or sea-level changes. As a result, it is very difficult to correctly identify causes of groundwater salinization and hence, to define remediation strategies and counter-measures. Because of the very slow response of hydrogeological systems to measures, inadequate management strategies are not detected and cannot be corrected directly. Apart from the reliable identification of GWS sources and processes, a decisive factor in the assessment of coastal aquifer status is the spatial and temporal availability of monitoring data. The lack of continuous records and measurements or their uneven distribution in space and time give ambiguous information and pose limitations for the reliable forecasting and the subsequent management of coastal aquifers. As a result, stakeholders are not able to conceive and apply appropriate management plans timely, and the decision-making procedure is jeopardized, thus having significant adverse impacts to the available freshwater resources and to the overall environment and socio-economic development of coastal Mediterranean areas.

MEDSAL aims to develop an integrated Framework for monitoring, protection and management of coastal groundwater reserves subject to increased salinization risks, due to overexploitation and rapid changes occurring from relevant climatic/non-climatic drivers. This new integrated approach not only targets to detect and identify GWS in a fast and more effective way, but also proposes a solid and novel methodology for identifying type or combination of types of GWS (I-V) in coastal aquifers for facilitating reliable GWS forecasting, risk assessment and management. The envisaged framework also endeavors to propose adequate measures based on a process and cause analysis and schedules, targets and indicators for the restoration of groundwater quality based on new approaches. The proposed MEDSAL Framework is envisaged to integrate and fuse different tools, models and methods in order to: • Identify GWS sources (single or multi-sourced) and decipher their governing processes; • Assess the potential interactions with other compartments (small scale) and with other water systems at catchment (large) scale; • Forecast the spatiotemporal evolution of primary (salinization) and secondary (e.g. induced post-contamination due to geochemical and/or other interactions) cascading effects and impacts; • Perform a risk assessment under variable climatic projections and stresses; • Develop a public web-GIS Observatory to support monitoring, alerintg, management, decision making and increase of resilience to GWS risk. The described Framework will be developed along three inter-related and multi-disciplinary pillars, namely: i) Field studies, data collection and innovative application of environmental isotopes; ii) Coupling of advanced hydrogeological (e.g. FEFLOW, SEAWAT) and hydrogeochemical modelling (e.g. PHREEQC, compartment modelling) to decipher and simulate flow and transport processes along with the potential cascading interactions within involved aquifer systems; iii) Application of advanced geostatistical and machine learning techniques for the optimization of data processing and modelling outcomes, also accounting for the inherent uncertainty of each model and reduction of the overall computational burden and time. The vision of MEDSAL Framework is to provide novel integrated approaches (e.g. tools, proxy indicators, models) for the accurate swift assessment and more efficient management of GWS risk in Mediterranean coastal aquifers, having as key priority the transferability of the envisaged methodological results to regions of limited resources (technical, funding, personnel), in order to increase the capacity building and efficacy of coastal groundwater management plans. An innovative element is the use of environmental isotopes for fast detection of GWS origin and processes, applicable in data-scarce coastal environments. The better integration of methods based on environmental tracers (hydrogeochemistry, environmental isotopes) such as compartment modelling and physical-based groundwater flow and transport modelling will provide more versatility and improved performance of prediction tools by better cross-validation and calibration. The use of artificial intelligence and deep learning algorithms will improve parameter estimation, pattern recognition in time series and spatial data and calibration. The overall MEDSAL's concept has a clear interdisciplinary approach. It engages the in-depth knowledge of the physical environment (driving sources and processes that control GWS) with diverse state-of-the-art tools and techniques (e.g. environmental isotopes, physical models, geostatistics, machine learning) applied jointly for the first time, towards GWS simulation and forecasting. Results are considered along with future projections of climate changes to deliver tailor-made management plans for Project’s test sites, considering their diverse physical and socio-economic characteristics, legislative frameworks and regulatory issues.

The MEDSAL project is expected to have significant environmental and socio-economic impact to water availability in coastal regions of the Mediterranean. First, a sustainable, measurable, attributable impact will be attained in the case study areas. In all case studies, salinization processes will be identified, attributed to activities and, measures will be proposed with timed outcomes. In all case study areas, the quality and availability of groundwater for drinking water supply and agriculture will be improved because of MEDSAL. Second, it will have impact beyond the case study regions through the transferability of the overall Framework and its tools/methods, MEDSAL aspires to progressively affect the wider coastal Mediterranean region, North and South, East and West and islands in the Mediterranean. The approach of MEDSAL will produce faster detection, better identification, and attribution, scaling to larger areas and improvement of remedation strategies and measures in the partner countries. The impacts will directly affect critical socio-economic domains, such as agriculture and tourism, which are among the principal water-users for most Mediterranean countries, especially in coastal areas. Water availability in coastal areas will be improved through a more accurate and reliable management of GWS; resilience/adaptation to potential adverse impacts due to climate change will be enhanced and the harmonization of policies and regulatory frameworks will create common grounds for extensive cooperation between the involved parties. Specifically: • Detecting groundwater salinization will be improved also for less experienced stakeholders; • the proposed system of types of groundwater salinization (intrusion, up-coning, solute traps, pollution, hydrological feedbacks by evaporation) will become known, documented and visible in case study sites (observatory, internet database), helping stakeholders to apply these cases to other aquifers and react in an adequate way; • modelling of groundwater salinization in coastal aquifers will be streamlined and improved by multi-model ensembles also for data-scarce regions and karstic aquifers; • high-risk areas can be identified and prioritized better and faster, e.g. for climate change impacts; • MEDSAL can be the prototype and create a framework for a coastal protection program against salinization including short-, mid- and long-term quality targets. MEDSAL is also expected to set the basis for new modelling routines of improved efficacy for GWS forecasting: (i) by introducing a new adaptive approach to modelling GWS covering a broad spectrum of coastal aquifers (porous, fractured and karstic) with various degrees of data scarcity and uncertainty by defining a progressive strategy from conceptual and analytical models, to increasingly compartmental models and finally physically-based and numerical process models for flow and transport. (ii) by enhancing physical-based models for flow and transport with hydrogeochemical processes in coastal aquifers, and (iii) by incorporating advanced geostatistics and machine learning techniques in groundwater flow and transport modelling.