Marine Intrusion Research Articles

Development of a Macroinvertebrate Multimetric Index for the Evaluation of the Ecological Quality of Lake Nokoué

Nowadays, new tools for assessing the biotic integrity of aquatic environments are used. In Benin, the Macroinvertebrate MultiMetric Lake Index (M3LI) was designed to reveal the current state of Lake Nokoué. The inventory was carried out in eight seasonal data collection campaigns from 2019 to 2021 using an Eckman type grab and a trouble net. The composition, diversity and different metrics were calculated. Thirty-nine metrics grouped into five categories were defined and subjected to selection using a PCA in order to identify the relevant metrics for calculating the index. In the lake, 83 taxa divided into 25 orders and 54 families representing 32,770 specimens were determined. Insects, Molluscs, Crustaceans and Annelids constituted the essential macrofauna which was numerically dominated by Gastropods, Crustaceans, Bivalves and Insects. Of the 5 food functional groups obtained, crushers and collector-gatherers were dominant. Ten metrics relevant and well explained by environmental variables were used to calculate M3LI. The M3LI calculated varied from 6.44 at the station near Dantokpa to 3.38 at the Cotonou channel station with fluctuating water quality between poor quality and good quality. These results clearly explain the responses of the living communities of the lake faced with the various stresses due to daily marine intrusion, the role of receptacle of different continental waters and the various anthropogenic activities plunging the environment into a hypereutrophic state. It is therefore urgent to take measures to restoration of this environment to allow living species to regain their balance of life. This index is also a departure for the establishment of a biomonitoring program for the restoration of the lake.

Identification of hydrochemical processes of groundwater in Nekor-Ghiss plain (Morocco): using the application of multivariate statistics and Geographic Information Systems (GIS) to map groundwater

In arid and semiarid zones, groundwater is a vital and indispensable natural resource. Indeed, these water resources have become extremely limited due to several factors, including climate change, salinization, and overexploitation. This study covers the hydrochemical characterization of groundwater in the Nekor-Ghiss plain which is located in northern Morocco. To achieve this objective, a set of 79 water samples was analyzed, for various physical and chemical parameters of the samples, including E.C, pH, TDS, HCO3−, SO42−, Ca2+, Mg2+, Na+, K+, PO43−, NO3−, NO2− and NH4+. Several methods were used to interpret the hydrochemical data, namely graphical methods, principal component analysis (PCA), hierarchical ascending classification, and ion exchange indices. A detailed geochemical study of groundwater is described to identify the origin of the chemical composition of groundwater. The results show that the samples studied are characterized by very high mineralization (> 1500 mg/l), with the predominance of Na+, Cl− and SO42− ions. The interpretation of geochemical signatures of groundwater in the Nekor-Ghiss plain shows sulfate-sodium (Na–SO4) and chloride-sodium (Na–Cl) facies. Natural geochemical processes are responsible for water regulation, while human activities exert a limited influence on this control. Marine intrusion, evaporation, and the ion exchange process largely control the chemistry of the aquifer. Using PCA to confirm controlled water chemistry processes revealed three homogeneous groups. The study contributes to a better understanding of the quality and mineralization of groundwater in the Nekor-Ghiss plain, and it will serve as a reference for other plains with similar characteristics.

Seawater intrusion assessment in the Bir Guendouz-Boulanoire coastal transboundary aquifers of Morocco and Mauritania

The Bir Guendouz region, situated in Southern Morocco, is affected by saltwater intrusion. The transboundary aquifer is shared by Morocco and Mauritania, and it serves as the primary source of freshwater in this arid region. To differentiate between freshwater and saltwater areas, 750 non-invasive vertical electrical soundings (VES) were utilized along 42 perpendiculars to the coast. Dar-Zarrouk parameters—transverse resistance (Tr), longitudinal conductance (S), and longitudinal resistivity (ρl)— were determined using VES. These techniques remove uncertainties in resistivity interpretation that may arise due to the overlap between freshwater and saline aquifers during the process of suppression and equivalence. The results indicate a significant marine intrusion in the Bir Guendouz-Boulanoire aquifer, with varying degrees of salinization observed in different zones. Freshwater zones are identified by a transverse resistance of over 4450 Ω m2, a longitudinal conductance below 41.7 mho, and a longitudinal resistivity greater than 8.7 Ω m. These characteristics can be used to prevent saltwater intrusion and ensure the sustainable use of groundwater resources. Furthermore, they will aid in improving resource management between the two nations. The study's consequences also involve safeguarding the ecosystem and ensuring the longevity of these transboundary water resources. Therefore, for researchers, professionals, and decision-makers involved in sustainable management of transboundary groundwater, this study serves as a crucial reference.

Aberturas de barra provocam mudanças de longa duração na dinâmica limnológica ao longo da coluna de água de uma lagoa costeira tropical

Abstract Aim In this study, we investigated the impact of an episodic marine intrusion on the water column characteristics of Jurubatiba lagoon, a tropical coastal ecosystem, for 12 months following a sandbar breaching event to elucidate the duration of its effects. Methods Monthly, we sampled the physical, chemical, and biological characteristics along the water column for one year after a sandbar breaching event and seawater inflow. We assessed the temporal (monthly) and spatial (along depth profiles) associations among these variables and the temporal correlation among vertical heterogeneities in these variables and environmental drivers of stratification. Results Marine intrusion resulted in salt wedges formation in the short-term, leading to stratification in dissolved oxygen, pH, salinity, and chlorophyll-a concentration along the water column for at least four months. However, temperature and solar incidence also emerged as crucial factors associated with vertical heterogeneity in limnological variables, influencing water density and pH throughout the study period. Precipitation and wind speed had only marginal effects on thermal and ectogenic stratifications, probably mediated by water colour, nutrient inputs, water column depth and lagoon’s orientation in the landscape. Conclusions Our data unveiled that, despite their shallowness and wind exposure, coastal lagoons can exhibit considerable vertical heterogeneities in limnological variables due to various climatic and hydrodynamic aspects. Notably, the effects of marine intrusions on salinity and ectogenic column stratification can persist for several months, affecting water quality and, probably, biotic communities and ecosystem functioning. Once human activities and climate change may intensify marine intrusions on coastal lagoons, understanding spatiotemporal dynamics and their drivers is fundamental to anticipating their effects and conserving such vulnerable ecosystems.

Assessment of the physicochemical and bacteriological quality of water source and a well in Bakoya aquifer, northern Morocco

This study aims to investigate the physical, chemical, and bacteriological quality of water derived from both a well and a spring across three distinct periods (2008, 2012, and 2021) in both summer and winter. These sampling points are situated within the urbanized area of Al Hoceima and serve as crucial sources of drinking water for a substantial portion of the city's population due to their proximity to the city center. The water hardness values observed at these natural points ranged from 5.9 to 82 (°F), categorizing the water from these sources as very hard. Furthermore, the Piper diagram revealed chemical facies characterized by chlorinated sodium and calcium magnesium sulfate. The elevated concentrations of sodium and chloride were attributed to the proximity of the Mediterranean Sea shoreline. Analysis of bacteriological parameters in these waters uncovered notable contamination by fecal germs. Principal Component Analysis (PCA) of the water samples identified two primary groups, elucidated by two factors that collectively account for 79.37% of the variance. The first factor (50.11%) is linked to gypsum dissolution and marine intrusion, while the second factor (29.26%) is associated with external contributions such as anthropogenic pollution.

Groundwater Quality Monitoring in Response to Marine Intrusion: A Case Study in Northern Morocco

Water stress, resulting from a demand for water exceeding the available quantity, is a major global challenge. Groundwater usage is a commonly adopted strategy to address this situation, but it often leads to marine intrusion, threatening the quality of water in coastal aquifers. This phenomenon typically stems from overexploitation of aquifers, declining water table levels, and rising sea levels due to climate change. Our study aims to monitor the quality of groundwater intended for human consumption and provide a detailed assessment of its current state. We identified several physicochemical parameters, such as temperature, pH, and bicarbonates, with maximum electrical conductivity values reaching 2810 µs/cm, a total hardness of 21 meq/L, sulfate levels of 689 mg/L, and chloride levels of 628 mg/L, from six boreholes and one well located along the coastal area of the Al Hoceima region. These samples were also subjected to Principal component analysis (PCA) of the chemical parameters, revealing two factors that represent approximately 62.15% of the total variance in the groundwater quality dataset. Simulation results indicate signs of seawater intrusion in several areas, particularly near the coast, emphasizing the urgency of protecting groundwater resources and developing sustainable management strategies to ensure a safe and reliable supply of drinking water in the region.

Effects of global and climate change on the freshwater-seawater interface movement in a Mediterranean karst aquifer of Mallorca Island

Karst aquifers are globally prized freshwater sources, posing a significant preservation challenge. These aquifers typically exhibit dual or even triple porosities, encompassing matrix, fractures-fissures and conduits, rendering them highly responsive to variations in chemical characteristics and hydraulic head. In coastal regions, these aquifers often possess extensive subsurface conduit networks intricately linked to the rock matrix, facilitating groundwater discharge into the sea. Therefore, they display acute sensitivity to seawater intrusion, swiftly reacting to changes in precipitation and pumping regimes. This makes them exceptionally vulnerable to short-term meteorological fluctuations and long-term climate change. Their high heterogeneity leads to uneven penetration of the freshwater-seawater interface, causing rapid seawater intrusion inland over significant distances. The Mediterranean region, characterized by water deficit and water stress, faces strong impacts from climate change, featuring a warming atmospheric trend exceeding the global average, along with diminished rainfall exacerbating water scarcity. Increasing water demands for agriculture, urban development, and the growing tourism industry, because of global change, are worsening water stress. Our primary research objectives were analyzing the environmental consequences of global and climate change on seawater intrusion in Mediterranean coastal karst aquifers, with a focus on the role of the double-flow model, thus contributing to the understanding of the processes involved. To achieve this, we selected a study region on Mallorca Island in the western Mediterranean, where a karst aquifer system discharges into the sea. We employed various study methods, notably hydrochemical techniques and multi-isotopic analysis, encompassing the examination of 2H and 18O isotopes in water, 87Sr/86Sr ratio, Sr and B concentrations, and δ11B in water. A key finding is the rebound effect, wherein aquifers recontaminate due to solute molecular back-diffusion following cessation of extractions and the retreat of marine intrusion, providing insight into the impact of climate and global change on Mediterranean karst aquifers.

Using sedimentary prokaryotic communities to assess historical changes in the Gippsland Lakes

Abstract The Gippsland Lakes is the largest estuarine system in Australia. Over the last 2 centuries, this unique aquatic ecosystem has suffered substantial modifications mostly associated with anthropogenic impacts, including the creation in 1889 of an artificial channel to the ocean after European arrival, creating chronic salinisation in the system. However, the biological impacts of this historic shift are unclear. Here, we use shotgun metagenomics of environmental DNA from historical sediments of Lake King and Lake Victoria to detect ancient microbial DNA and track past ecological changes in prokaryotic communities. Sedimentary prokaryotic communities changed with core depth, organic matter levels and European arrival. Specifically, we observed an increase in sulfate‐reducing bacteria (e.g., Desulfobacterales) and organic matter enrichment in the upper layers of the sediment cores of the Gippsland Lakes, which could reflect a period of eutrophication caused by higher rates of organic deposition and marine intrusion post‐European arrival. However, while some species presented authentic ancient DNA signals, the shifts in community composition probably reflect changes in indigenous sediment‐dwelling microorganisms in response to geochemical changes of the sediment. Overall, these observations suggest that historic waterway management practices may influence microbial systems today and that sedimentary microbial communities can change in response to both natural biogeochemical dynamics along the depth profile and past environmental conditions.

At the edge of the desert: The evolution of the Holocene environment in Lake Rkiz, Senegal River valley

The analysis of faunal remains, pollen grains and other palynomorphs from a 4 m long core recovered at Lake Rkiz, Mauritania (16.911420 N, −15.172668 W, 0 m asl) documents the major phases of marine intrusion in the Senegal River system during the Holocene. Lake Rkiz was exposed to marine waters from 10 to 4 ka: a brackish lagoon developed at 10 ka, followed by a mangrove between 8.7 and 7 ka both in a calm environment. Rhizophora populations were never developed, however, either because they did not reach the core site at the northern extremity of the lake, or because they were restricted to the Senegal River bed. After 7 ka, the environment became increasingly unstable and the mangrove was replaced by a more clearly marine environment. During the last two millennia, a new, discrete phase of marine intrusion is recorded at Lake Rkiz. Contemporary to that already noted in the Ferlo River valley which feeds the Senegal River through Lake Guiers to the south, it also testifies to a positive oscillation of the sea level. The evolution of the regional vegetation of Lake Rkiz follows that of North tropical Africa with the expansion of a gallery forest of tropical humid affinity dominated by Celtis during the AHP. As elsewhere in the Sahara and Sahel, tropical plant types co-occurred with Saharan ones attesting to a mosaic-like landscape.

Impact of Releases from the Kef Eddir Dam on the Recharge of the Oued Damous Aquifer

Artificial recharge is a good way to mobilize water in aquifers and recharge groundwater. Dam release is one of the techniques used for groundwater recharge. The periodic releases programmed by the Kef Eddir dam make it possible to recharge the Damous wadi aquifer located in the coastal wilaya of Tipaza in Algeria, whose overexploitation lowers the level of its water and causes a marine intrusion that pollutes it. In this work, to estimate the impact of these releases on aquifer recharge, we followed the releases of March 2020 and May 2021. The piezometric levels of groundwater were measured before the releases, during flow caused by them, and after them. These measures concern 13 wells located along the Damous wadi watercourse for the first year and 18 wells for the second year. These two years have seven wells in common. It allowed us to compare piezometric levels and recharges between 2020 and 2021. In the absence of releases on our return in May and June 2022, we measured the depth of water presence and took samples from 6 wells to measure the water conductivity. These measurements allow us to evaluate the piezometry of the water table over these three years, and the conductivity will indicate the degree of salinity of its water. Keywords: Artificial recharge; Kef Eddir dam; Oued Damous aquifer; Piezometric level; Releases.

High-resolution calcareous nannofossil biostratigraphy and facies of Nimar Sandstone Formation (Bagh Group), central India and its bearing on Oceanic Anoxic Event 2

It is proposed to consider Narmada Valley Late Cretaceous sequences in three sectors with proper selection of stratotype in each sector: Eastern Sector: comprising of Lameta group of rocks with type area in Jabalpur area, essentially laid down in lacustrine-paedogenic milieu and containing a variety of fossils including dinosaur remains of Late Maastrichtian age. No evidence of sea incursion is available in the Eastern Sector either via the Narmada lineament or the K-G Basin. Central Sector: comprising of the Bagh Group in ascending order of: Nimar Sandstone Formation–Nodular Limestone Formation–Coralline-Bryozoan Limestone Formation, laid down in estuarine complex entirely within Turonian without any evidence of Cenomanian and Coniacian age calcareous nannofossils or other fossils being present. In the western part of Central Sector: Siliciclastic rocks and limestones referred to as Nimar Sandstone Formation curiously lack Late Cenomanian marker species, hence could be of Early Turonian age. Western Sector: comprises of Lacustrine sediments associated with Deccan Flood Basalt. The absence of the Cenomanian/Turonian Boundary and Black shales negates the presence of global OAE2 events in the Narmada lineament, but several OAE events are recognised in the Cauvery Basin, southeastern India. Uranium- and Thorium-rich Lower and Upper Nimar Sandstone Formation overlying crystalline basement are interpreted to have been essentially laid down in a fully marine estuarine milieu with reworked plant, and palynofossils including dinosaur remains. Calcareous nannofossils recovered from Upper Nimar Sandstone Formation over four decades ago and assigned Late Turonian age is revised based on modern data incorporating calcareous nannofossil and planktonic foraminifera datum and now suggest an older age of Early Turonian matching a zone with FAD of Quadrum gartneri at the base and FAD of H. helvetica at the top. It must be emphasised that except for the solitary and unique incursion of Early Turonian (ca. 93.9 Ma) sea along the Narmada lineament reaching eastward (>300 km) up to the present town of Indore, no other marine intrusion ever took place on Indian shield except along collision facing Subathu–Dogadda lineament during Late Maastrichtian. It would be erroneous to suggest that the global eustatic rise of sea level caused the entry of the Turonian sea along the Narmada lineament; instead, it was earlier speculated by me that Large Igneous Province activity of Mahajanga Flood Basalt of Madagascar (ca. 93.9 Ma) could have most probably caused a short-lived Turonian sea to enter Narmada lineament from the west around C/T boundary.

Study of the quality index of groundwater (GWQI) and its use for irrigation purposes using the techniques of the geographic information system (GIS) of the plain Nekor-Ghiss (Morocco)

Groundwater is an indispensable source of water for drinking water supply, agriculture and industry worldwide. In arid and semi-arid regions, groundwater has seriously deteriorated in recent decades due to environmental changes, anthropogenic activities and marine intrusion. A total of 79 groundwater samples from the Nekor-Ghiss plain were sampled for major chemical ion analysis. These analyzes showed that the water samples were highly mineralized (>1,500 mg/L), with hardness (83.5% of the samples were very hard) and high concentrations of chemical elements, such as Cl−, Mg2+, Na+ and SO42-. To assess the quality of water in the study area for irrigation and consumption purposes, we used the quality index (GWQI) as well as a multi-criteria analysis based on “geographic information system” by assigning a weight to the different water quality parameters. Also, Piper and Durov diagram was investigated. The results of the study were focused on the water quality parameters of the collected groundwater samples, such as the sodium adsorption rate (SAR), the percentage of soluble sodium (Na%), the Residual Sodium Carbonate (RSC) and Permeability Index (PI) Majority of water samples in the study area are suitable to be used for irrigation. Magnesium Risk (MH) and Kelley’s Ratio Kelly ratio. 51.9% unsuitable samples to 59.49% good samples for irrigation purposes. Monitoring the quality and quantity of groundwater is crucial for the effective and sustainable management of this valuable resource. According to the results obtained, it appears that 92% of all the samples are located in the domain of frequent recharge waters of limestone and dolomitic aquifers, namely, Ca-Mg-HCO3. About 8% of the samples measured have a composition of the Ca-Na-Mg-HCO3 type.

Hydrogeophysical investigation of aquifer parameters and seawater intrusion: a case study from Eastern Mitidja plain, Algeria

The rapid depletion of surface water due to climate change increases the world's water demand. As a result, groundwater resources are rapidly emerging as the primary source of freshwater supply for various needs. However, overexploitation and inadequate management of these resources can lead to irreversible contamination of freshwater reservoirs. Effective groundwater resource management depends on a detailed understanding of hydrogeological parameters that control the complex functioning of aquifers. However, these data are often scarce due to their expensive acquisition process. The present study assesses the use of geophysical methods for the estimation of hydrogeological parameters namely hydraulic conductivity and transmissivity. Moreover, the study evaluates the marine intrusion in the coastal aquifer of one of the most important plains of Algeria. The approach suggested is based on a combination of cost-effective geophysical techniques (geoelectrical surveys) and precise hydrogeological data. The results identified aquifer parameters relevant to the location of new water wells and allowed delineation of the seawater/freshwater interface.

First insight into microplastic groundwater pollution in Latin America: the case of a coastal aquifer in Northwest Mexico

Microplastics have been studied on biota and other environmental domains, such as soils. Despite the importance of groundwater as a resource for millions of people worldwide as drinking water and personal hygiene, domestic, agricultural, mining, and industrial purposes, there are very few studies concerning microplastics in this domain around the world. We present the first study in Latin America addressing this topic. Six capped boreholes were analyzed in terms of abundance, concentration, and chemical characterization, at three different depths, from a coastal aquifer in Northwest Mexico. This aquifer is highly permeable and affected by anthropogenic activities. A total of 330 microplastics were found in the eighteen samples. In terms of concentration, the interval ranged from 10 to 34 particles/L, with an average of 18.3 particles/L. Four synthetic polymers were identified: isotactic polypropylene (iPP), hydroxyethylcellulose (HEC), carboxylated polyvinyl chloride (PVC), and low-density polyethylene (LDPE); with iPP being the most abundant (55.8%) in each borehole. Agriculture activities and septic outflows are considered the potential regional sources of these contaminants into the aquifer. Three possible transport pathways to the aquifer are suggested: (1) marine intrusion, (2) marsh intrusion, and (3) infiltration through the soil. More research about the occurrence, concentration, and distribution of the different kinds of microplastics in groundwater is needed to have a better understanding of the behavior and health risks to organisms, including human beings.

Proposed recharge of island aquifer by deep wells with regenerated water in Gran Canaria (Spain)

Managed aquifer recharge (MAR) and, in particular, recharge by direct injection into the aquifer through wells or boreholes allows for a series of very interesting solutions to solve various technical and environmental problems related to management of the urban water cycle. These problems include the overexploitation of water resources, marine intrusion or contamination of groundwater by irrigation returns. The island of Gran Canaria presents several of these problems; thus, the feasibility of implementing a recharge system has been studied to provide a solution to some of them, using a resource of great potential such as reclaimed water. A detailed characterization of groundwater quality in the study area was carried out, complemented by a field campaign with water sampling from the surrounding catchments, in situ analysis and subsequent laboratory analysis. Specifically, an MBR treatment with disinfection is proposed, where the final conclusions indicate that this is a technically and economically viable project, innovative in its application on islands, a priori with an acceptable productive recharge capacity, possibly scalable after the experimental phase and extrapolable to other locations with similar conditions. In addition, it presents a set of important environmental benefits with respect to conservation of and improvement of the state of the groundwater bodies in the studied area, as well contributing to knowledge of and research into water management in volcanic lands and islands.

The benthic food web connects the estuarine habitat mosaic to adjacent ecosystems

Energy flows from land to sea and between pelagic and benthic environments have the potential to increase the connectivity between estuaries and adjacent ecosystems as well as among estuarine habitats. To identify such energy flows and the main trophic pathways of energy transfer in the Minho River estuary, we investigated the spatial and temporal fluctuations of carbon and nitrogen stable isotope ratios in benthic (and their potential food sources) and epibenthic consumers. Sampling was conducted along the estuarine salinity gradient from winter to summer of 2011. We found that the carbon (δ13C = 13C/12C) and nitrogen (δ15N = 15N/14N) stable isotope ratios of the most abundant benthic and epibenthic consumers varied along the salinity gradient. The δ13C values increased seaward, whereas the opposite pattern was found for the δ15N, especially during the summer. The stable isotope ratios revealed two trophic pathways in the Minho estuary food web. The first pathway is supported by phytoplankton and represented by filter feeders such as zooplankton and some deposit feeders, particularly amphipods and polychaetes. The second pathway is supported by detritus and composed essentially of deposit feeders, which by being consumed, allow detritus to be incorporated into higher trophic levels. Spatial and temporal feeding variations in the estuarine benthic food web are driven by hydrology and proximity to adjacent ecosystems (terrestrial, marine). During high river discharge periods, the δ13CPOC (ca. -28‰) and C:NPOM (>10) values suggested an increase of terrestrial-derived OM to the particulate OM pool, which was then used by suspension feeders. During low river discharge periods, marine intrusion increased upriver, which was reflected in benthic consumers' 13C-enriched stable isotope values. No relationship was found between food quality (phytoplankton vs. detritus) and food chain length because the lowest and highest values were associated with freshwater and saltmarsh areas, respectively, both dominated by the detrital pathway. This study demonstrates that benthic consumers enhance the connectivity between estuaries and its adjacent ecosystems by utilizing subsidies of terrestrial and marine origin and that benthic-pelagic coupling is an important energy transfer mechanism to the benthic food web.

Assessment of groundwater hydrogeochemical characteristics and salinization intrusion in coastal arid area (South Gabes, South-East Tunisia)

In the southern region of Gabes, groundwater is experiencing a quality deterioration in relation to the increase in demand to meet the various sectors of economic and agricultural activities. Indeed, the degradation of quality generally results in high concentrations of total dissolved solids, ranging from 2.44 to 13.68 g/L, and waters contamination by nitrates. The determination of the groundwater salinity origin from Gabes, largely influenced by tectonics, was approached from the study of the evolution in the space of major chemical elements and by statistical treatment. Based on these methods, this work aims to demonstrate that the high waters’ salinity in this aquifer is explained by an interaction between its waters and the evaporitic levels of the aquifer formation, by the marine intrusion around the El Hajel Wadi, and by the return of irrigation water to the Mareth-Arram region. The hypothesis of marine intrusion is justified by the high chloride content due to the presence of reverse reactions of cation exchange. Geochemical interactions (reverse basic exchanges and precipitation/dissolution phenomena of minerals from the aquifer formation) show that these waters have poor to bad quality.

Delineation of seawater intrusion and groundwater quality assessment in coastal aquifers: The Korba coastal aquifer (Northeastern Tunisia)

The aim of this study is to determine the general state of the Korba aquifer (northwestern Tunisia) with respect to seawater intrusion and to assess the suitability of groundwater for drinking and irrigation purposes. A total of 60 groundwater samples were collected and analysed for physicochemical parameters (pH, EC, TDS, Na+, K+, Ca2+, Mg2+, HCO3−, Cl−, NO3−, SO42− and Br−). Major ionic ratios highlighted the dominance of the reverse ion exchange process triggered by the marine intrusion. Br−/Cl− ratio suggested that the irrigation with saline water and wastewater were potential additional sources of salinization. Hydrochemical Facies Evolution Diagram coupled with a GIS-based framework revealed that most of samples are located beneath the mixing line, showing dominant marine intrusion process. Based on the water quality index, most of groundwater samples were unsuitable for drinking. In addition, according to high sodium adsorption ratio, the groundwater quality was limited for irrigation purposes.

Combined geophysical methods to investigate seawater intrusion in the Souss-Massa coastal area, Morocco

Groundwater are strategic water resources for irrigation and drinking purposes in the Souss-Massa semi-arid region (Morocco). These resources have been threatened during the last decades by different factors such as drought, over-pumping and marine intrusion. The latter is responsible for the degradation of the groundwater quality along the coastal area, which is reducing its usability. Therefore, the localisation of the freshwater/saline water interface is essential for better sustainable management of groundwater resources in the area. The objective of the present study is to assess the temporal changes, the extent, and the depth of the seawater intrusion in the Souss-Massa coastal area. To fulfil this objective, two monitoring sites were equipped with water conductivity measurement devices (Subsurface Monitoring Device – SMD) to observe the temporal changes of the salinity at a local scale, as well as to support the interpretation of a transient electromagnetic (TEM) survey. This survey consisted of 83 TEM soundings, along thirteen profiles located perpendicularly to the ocean and the two rivers delineating the study area. The data from the SMD stations highlight the temporal changes of electrical conductivity (EC) with depth, clearly illustrating the freshwater/saltwater interface location in the central part of the study area (−35.55 m NGM at the Tifnit location, ca. 1 km from the coast). In addition, the results of the TEM measurements show that the marine intrusion is already advanced towards the land, over a maximum distance of 2500 m. Finally, some new monitoring sites have been proposed to improve the current monitoring network for seawater intrusion and assess whether mitigation solutions lead to a slower progression of the seawater intrusion. Decision-makers can use these results as a basis for the development and implementation of effective policies to ensure a sustainable and integrated water resources management in this region.

A Different Processing of Time-Domain Induced Polarisation: Application for Investigating the Marine Intrusion in a Coastal Aquifer in the SE Iberian Peninsula.

This study presents the developments regarding the time-domain induced polarisation method as a supporting tool for resistivity soundings during investigations of coastal detrital aquifers that are salinized by marine intrusion. The interpretation of resistivity measurements in such aquifers, which have variable hydrochemistry and lithology, involves uncertainties owing to the presence of low-resistivity lithologies, such as clays. To reduce these uncertainties, the use of other geophysical parameters is necessary; hence, this study focuses on induced polarisation since it can be measured simultaneously with resistivity. In detail, we propose the determination of induced polarisation using 1D techniques while developing a different algorithm for processing the induced polarisation data. The aim is to extend the results of this phenomenon, using, instead of chargeability, the concepts of polarisability and decay time, which are extracted from the decay curve, given that they represent more intrinsic properties of the various analyzed subsurface media. Results were obtained by applying this methodology to a Quaternary aquifer of the Costa del Sol in the SE Iberian Peninsula (in the province of Almería) during two different campaigns, one in mid-autumn and one late winter (i.e., in October and February, respectively) are presented. The results reveal the position of the saline front during each campaign while reflecting the seasonal movement of the marine intrusion.