Revealing the impact of wildfires on groundwater quality: Insights from Sierra de la Culebra (Spain).

Wildfires induce changes in soil and vegetation composition, significantly impacting the hydrological cycle and altering future runoff and infiltration patterns. Ash residue on the ground can infiltrate the subsoil along with water, leading to modifications in groundwater hydrochemistry. Climate change and summer heatwaves can create favourable conditions for severe wildfires, such as the one that occurred in Zamora, Spain, in 2022. Fourteen simultaneous points of origin across various locations in Zamora triggered the worst environmental disaster in this province, as well as the largest fire recorded in the history of Spain. Following the severe wildfires in Sierra de la Culebra, Zamora, groundwater samples were obtained to compare the hydrochemistry with pre-fire background data spanning several years. A general decline in pH across all sampling points was observed, most notably at Z1, likely due to its very high permeability and leaching of organic acids from burned vegetation. Increases in major ions such as SO42- and NO3- were detected at Z1-2, while HCO3- levels decreased, indicating possible oxidation of soil organic matter and the introduction of wildfire-derived organic acids into the groundwater system. Elevated concentrations of Na+, K+, Mg2+, and Ca2+ were observed at Z3, suggesting possible ash residue infiltration. Despite the severity of the wildfires, the results indicate that there were no significant long-lasting impacts on groundwater quality overall. This finding suggests that the groundwater systems in the study area are resilient to such environmental catastrophes.

Guidelines for Managing Radon Hazards in Tourist Volcanic Caves in Spain.

Tourist volcanic caves are in high demand for ecotourism and geotourism lovers, as well as by sun and beach tourists as a complementary activity during their holidays. There are six tourist volcanic caves in the Canary Islands, all of them managed by the local administration of the island. The managers of these caves must ensure the safety of visitors and workers, who are exposed to natural hazards, such as radon, inherent to the environment in which the activity takes place. The methodology for analyzing natural radon radiation is based on the latest studies published by experts in this field and on previous experiences in tourist caves. This article proposes a protocol for the correct management of radon in tourist caves in the Canary Islands, adapted to current regulations, to mitigate effects on the health of visitors and workers.

Presence of microplastics in the groundwater of volcanic islands, El Hierro and La Palma (Canary Islands).

The increasing amount of plastic litter worldwide is a serious problem for the environment and its biodiversity, ecosystems, animal and human welfare and the economy. The degradation of these plastics leads to microplastics (MPs), which have been reported for the first time in groundwater in the Canary archipelago. This research investigates the presence of MPs at nine different points on La Palma and El Hierro, where samples were collected in galleries, wells and springs during the month of December 2022. Six different polymers were found with Fourier transform infrared spectroscopy (FTIR) - polypropylene (PP), polyethylene (PE), cellulose (CEL), polyethylene terephthalate (PET), polystyrene (PS) and polymethyl methacrylate (PMMA). The particle concentrations found ranged from 1 to 23 n/L, with a maximum particle size of 1900 µm, the smallest being 35 µm. PP and PE were the most common polymers found in the analysis, associated with the use of packaging, disposable products, textiles and water pipes, related to poorly maintained sewerage networks where leaks occur, allowing these MPs to escape into the environment and end up in groundwater. The detection of microplastic pollution in groundwater emphasises environmental hazards, including biodiversity disruption and water source contamination. Additionally, it presents potential risks to human health by transferring contaminants into the food chain and through respiratory exposure.

Effects of the 2021 La Palma volcanic eruption on groundwater hydrochemistry: Geochemical modelling of endogenous CO2 release to surface reservoirs, water-rock interaction and influence of thermal and seawater.

Volcanic islands face unique challenges in protecting and managing their water resources due to their small size, limited freshwater availability, and vulnerability to natural hazards. The recent 2021 eruption of the Tajogaite volcano on La Palma Island in the Canary Islands, Spain, raised concerns regarding the potential impact on groundwater hydrochemistry. This work aimed to characterize and model the processes that lead to the measured hydrochemical impacts in the groundwater of La Palma as a consequence of the volcanic eruption. The study involved conducting three groundwater sampling campaigns during the eruption, and six after the eruption ceased. A total of 15 monitored points, including piezometers, wells, water galleries, and the main gully collector of the island, all relatively close (2 to15 km) to the erupted volcano, were sampled for the analysis of major solutes and SiO2. Unpublished hydrochemical data previous to the eruption were provided by the local water management authorities of La Palma (CIALP) and the Geological Survey of Spain (IGME). Statistical analyses were performed to assess the differences in groundwater composition before, during, and after the eruption, and a Principal Component Analysis (PCA) mixing model was calculated. Three compositional extreme waters were defined as end members in the system: (1) a high SiO2 computed thermal end member; (2) a low salinity computed fresh groundwater; (3) and seawater. The results of the mixing model showed two main events of maximum mixing ratios in the fresh groundwater reservoirs of La Palma after the eruption; the first one of seawater in July 2022, and the next one of thermal fluids in December 2022. This water mixing during and after the eruption, together with a volcanic CO2 input to the reservoirs, led to significant increases in the concentrations of Na, Ca, SiO2 and SO4 in fresh groundwater, as well as a drop in pH. The significance of these findings relies in improving our understanding of the effects of volcanic eruptions on groundwater, emphasizing the necessity for frequent monitoring and evaluation, given the scarcity and vulnerability of groundwater resources in volcanic islands.

Comparative study of emerging pollutants of interest in the groundwater of the volcanic islands of La Palma and El Hierro (Canary Islands).

Emerging pollutants (EPs) include a wide array of chemical compounds, as well as some microorganisms, which presence was unknown or unmeasurable until recently, or have recently started to be considered a threat towards the environment or animal and human health. No clear or homogeneous regulations exist for their measurement or control, and efforts should be made to assess their presence and offer solutions for their safe management, as well as to achieve an optimal protection of water resources. A previous study performed by our research group thoroughly studied a wide profile of EPs in El Hierro Island (Canary Islands) for the first time. Now, we present the study of the same panel of 70 EPs in La Palma Island (Canary Islands). 14 samples were collected in 2021, at different locations in La Palma island, representing seven municipalities (Los Llanos de Aridane, Santa Cruz de la Palma, El Paso, Breña Baja, Tazacorte, Barlovento and Fuencaliente) and four installation types (Piezometers/Wells, Wastewater Treatment Plant (WWTP), Water Gallery and Water Springs). High performance liquid chromatography-mass spectrometry (HPLC-MS) was performed to analyse the EP array, which included five chemical families: UV filters, UV blockers/stabilizers, parabens, Pharmaceutical Active Compounds (PhACs) and pesticides. Subsequently, a comprehensive descriptive and statistical analysis, including different tests was performed on the data obtained. Heterogeneous concentration levels of the EPs studied were found based on municipality and installation type among the island, with some of the PhACs and UV blockers/stabilizers showing very high levels, especially at Breña Baja and wastewater treatment plants (WWTPs). It is worth noting that some of the samples comprised within the WWTPs category were collected outside the treatment plant, after water has been treated, so they should not bear dangerous concentrations of any hazardous compound. The high presence of two pesticides, imidacloprid (ranging from 68.7 to 24,896.5 ng⋅L-1) and acetamiprid (ranging from 1010.7 to 5168.1 ng⋅L-1) was worth highlighting too. In addition, three EP concentration clusters were found to virtually divide the island based on mathematical percentiles of EP mean concentrations, which can help gain more insight into the contamination status of the island and measures that could be taken for their management. Finally, a comparison between La Palma results and the profile observed at El Hierro by our research group was presented. Altogether, the study performed calls for a need to take actions towards avoiding entrance of EPs in the water cycle, and not just focusing on remediation strategies once they have reached the groundwater, freshwater or soil.

Effect of tourist activity on wastewater quality in selected wastewater treatment plants in the Balearic Islands (Spain).

Unregulated sewage discharge into the sea poses a considerable danger to marine ecosystems, with coastal regions being particularly vulnerable to this because of the impact of tourism. This issue is amplified during the summer season, as the Balearic Islands are a heavily frequented destination. This study aims to determine the water quality in five different wastewater treatment plants (WWTPs) representative on the islands. For this purpose, we analysed several parameters, including biochemical oxygen demand (BOD), chemical oxygen demand (COD), treated water flow, suspended solids (SS), nitrates (N) and phosphorus (P), at the inlet and outlet of the WWTPs for 5 years. We set particular thresholds for each parameter and documented any breach by comparing the findings with the existing regulations. The least favourable results indicate non-compliance regarding N and P levels throughout the entire study period, as well as a lack of reduction percentage. Furthermore, flow analysis reflects the significant influence of tourism on water quality, with notable increases in both population and treated water volume during the peak tourist season. Overall, the investigation offers a robust foundation for comprehending water quality in relation to coastal landscape in the Balearic Islands. It pinpoints significant worry spots and underscores tourism's immediate impact on this ecological feature.

The genesis of an extremely acidic perched aquifer within roasted pyrite waste in a fully urbanized area (Zaragoza, Spain).

Contaminated groundwater is a serious problem in developed countries. The abandonment of industrial waste may lead to acid drainage affecting groundwater and severely impacting the environment and urban infrastructure. We examined the hydrogeology and hydrochemistry of an urban area in Almozara (Zaragoza, Spain); built over an old industrial zone, with pyrite roasting waste deposits, there were acid drainage problems in underground car parks. Drilling and piezometer construction, and groundwater samples revealed the existence of a perched aquifer within old sulfide mill tailings, where the building basements interrupted groundwater flow, leading to a water stagnation zone that reached extreme acidity values (pH < 2). A groundwater flow reactive transport model was developed using PHAST to reproduce flow and groundwater chemistry, in order to be used as a predictive tool for guiding remediation actions. The model reproduced the measured groundwater chemistry by simulating the kinetically controlled pyrite and portlandite dissolution. The model predicts that an extreme acidity front (pH < 2), coincident with the Fe (III) pyrite oxidation mechanism taking dominance, is propagating by 30 m/year if constant flow is assumed. The incomplete dissolution of residual pyrite (up to 18 % dissolved) predicted by the model indicates that the acid drainage is limited by the flow regime rather than sulfide availability. The installation of additional water collectors between the recharge source and the stagnation zone has been proposed, together with periodic pumping of the stagnation zone. The study findings are expected to serve as a useful background for the assessment of acid drainage in urban areas, since urbanization of old industrial land is rapidly increasing worldwide.

First emerging pollutants profile in groundwater of the volcanic active island of El Hierro (Canary Islands).

Emerging pollutants (EPs) are substances present in wastewater that have not been studied, previously, leading to ambiguity in regulations for their presence in water resources. Territories that are highly dependent on groundwater resources are at a high risk of suffering the consequences of EP contamination due to their dependence on good quality groundwater for agriculture, drinking, and other uses. A relevant example is El Hierro (Canary Islands), which was declared a biosphere reserve by the UNESCO in 2000 and is almost completely powered by renewable energies. Using high performance liquid chromatography-mass spectrometry, the concentrations of 70 EPs were assessed at 19 sampling points on El Hierro. The results indicated that no pesticides were present in groundwater; however, varied concentration levels of ultraviolet (UV) filters, UV stabilizers/blockers and pharmaceutically active compounds (PhACs) were found, with La Frontera being the most contaminated municipality. With regard to the different installation types, piezometers and wells were the ones showing the highest concentrations for most EPs. Interestingly, the depth of sampling correlated positively with EP concentration, and four different clusters virtually dividing the island into two areas could be identified based on the presence of each EP. More studies should be performed to ascertain why a few of the EPs showed considerably high concentrations at different depths. The results obtained highlight the need to, not only implement remediation measures once EPs have reached the soil and aquifers, but also to avoid their incorporation into the water cycle via homes, animal husbandry, agriculture, industry, and wastewater treatment plants (WWTPs).

Heterogeneity-Driven Hydrodynamics Conditions the Hydrochemistry of Spring Water in Volcanic Islands.

Perched aquifers represent significant unexploited groundwater reserves in volcanic islands and contain valuable freshwater resources. These water reserves provide critical resources to indigenous populations suffering water scarcity. Groundwater discharged from a perched aquifer into two adjacent (14 m) springs in the volcanic summits constituted by basaltic and pyroclastic deposits of Gran Canaria Island (Spain) was examined. Based on springs discharge data, a three-dimensional groundwater flow and solute transport model of the investigated perched aquifer was calibrated to reproduce its hydraulic regime, as well as to explain the hydrochemical and isotopic composition of its main discharge systems, the studied springs. Groundwater flow simulations effectively replicated flow paths of the two springs affected by the existing geological heterogeneities, with differential travel times of 246 and 130 years, respectively, and with a convergent flow toward them partially explaining the averaged differences in electrical conductivity, δ18 O, and tritium observed between the springs. It can be concluded that, although water quality in both springs is similar and homogenous, as they come from the same aquifer system, geological heterogeneities in the upper elevation volcanic areas is likely the cause for the differences in the residence times of the two springs, which suggests that the flow regimes for the two springs are independent. The chemistry of the two springs, however, is essentially the same, with the exception of tritium, which is used to ascertain residence time.

Net carbon balance study for selected roads in Tenerife, Canary Islands.

Carbon dioxide emissions linked to the transport sector are particularly relevant to islands. The Canary Islands have high level of tourism, with tourists who generally travel in rented vehicles on arrival in the archipelago. In addition, mobility of the local population in the islands is also always growing. Thus, transport is one of the sectors that emits the greatest amount of greenhouse gases. In this sense, the net carbon balance becomes a pioneering study in the framework of management of high-capacity road transport routes and will help plan new strategies, which pursue the neutrality and climate resilience of the road network. It will therefore be possible to design different future scenarios, according to traffic intensities detected, to mitigate their local effects by increasing green areas, which will contribute to greater absorption. This study calculated the carbon footprint linked to vehicles on the three high-capacity roads on the island of Tenerife, as well as the carbon footprint of the public lighting attached to these roads. The absorption of carbon by vegetation planted by the Road Service and the soil located on the margins of the road have also been calculated to explore the possibility of modifying the vegetation, using other types of local shrubs and trees that have a higher absorption factor. The results demonstrate that conifers have the highest absorption factor, the Canary Island pine being the best option in this case. However, it is not always possible to place trees on the roadside, and it is necessary to resort to smaller species. This study concludes that better mobility planning, an increase in electric vehicles, improved energy production from renewable sources, and the promotion and enhancement of absorption capacity of carbon sinks are key in the face of climate change. Integr Environ Assess Manag 2023;19:1023-1030. © 2022 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

A comparison between carbon footprint of water production facilities in the Canary Islands: groundwater resources vs. seawater desalination.

The Canary Islands have a water culture tied to the exploitation of their groundwater by means of wells and water galleries. However, the growth of tourism, the increase in the local population and the development of agriculture have led to the emergence of new ways of obtaining water, such as the desalination of seawater. The presence of these desalination plants covers the entire archipelago except for the island of La Palma, and sometimes they function as a complement to water needs, while in other cases they are the only source of drinking water available. To study the environmental impact of the production of drinking water through the exploitation of the aquifer and the desalination of seawater, the carbon footprint methodology was used following the guidelines of the GHG Protocol. The result has shown that seawater installations have the largest carbon footprint, mainly due to the high electricity consumption in the islands and the electricity mix of the archipelago which, as it does not rely entirely on renewable energy sources, increases CO2 emissions into the atmosphere due to the production of drinking water in the islands.

Groundwater conditions the effectiveness of surface water diversion in the remediation of the eutrophicated volcanic lake of Furnas, Azores archipelago.

Volcanic lakes in oceanic islands represent extremely important areas for biodiversity and offer exceptional conditions for nature-based tourism as one of the main pillars of economic growth in these regions. Nitrogen and phosphorus fertilizers are being used extensively at the Azores archipelago, similarly to other places in the world, to increase agricultural production and is causing severe pollution and eutrophication of surface freshwater reservoirs. This work concentrates on the evaluation of the efficiency of surface water diversion as a remediation measure to reduce nutrient loading and reverse eutrophication of Furnas crater lake on the island of São Miguel. Nutrient loading was monitored using an extensive water quality monitoring program in the main watershed of the eutrophicated lake that, together with watershed-scale mass balance methods and groundwater and solute transport models, allowed us to identify an average 98% efficiency in the reduction of nitrate loading. However, phosphorus total load in the discharged water to Furnas lake was observed to only be decreased by 33% due to the groundwater origin of phosphorus. Results from modelling suggested that nutrients were emitted from both point (nitrates) and diffuse (phosphorus) sources as surface runoff and as groundwater seepage, respectively. The results obtained recognized a partially successful surface water diversion, since groundwater path was not initially identified, thus highlighting the importance of groundwater flow regime in the design of such remediation measures. This work also provides a perspective on surface water diversion to revert eutrophication under a volcanic formation, where lakes can be naturally more nutrient rich.

Stormwater management in urban areas using dry gallery infiltration systems.

The increase in the frequency of extreme precipitation events due to climate change, together with the continuous development of cities and surface sealing that hinder water infiltration into the subsoil, is accelerating the search for new facilities to manage stormwater. The Canary Islands (Spain) are taking advantage of the knowledge acquired in the construction of water mines to exploit a novel stormwater management facility, which we have defined as a dry gallery. Dry galleries are constituted by a vertical well connected to a horizontal gallery dug into highly permeable volcanic layers of the vadose zone, from where infiltration takes place. However, the lack of scientific knowledge about these facilities prevents them from being properly dimensioned and managed. In this work, we simulate for the first time the infiltration process and the wetting front propagation from dry galleries based on a 3D unsaturated flow model and provide some recommendations for the installation and sizing of these facilities. The fastest advance of the wetting front takes place during the earliest times of infiltration (<2 h), with plausible propagation velocities and infiltration rates higher than 1000 m∙d-1 and 2 m3∙s-1. As time progresses, the propagation velocity and infiltration rate decrease as a consequence of the hydraulic gradient attenuation between the gallery and the aquifer. Therefore, stormwater infiltration is a highly transient process in which a sizing underestimation of 100% may be committed if unsaturated conditions or geological configuration are neglected.

Comparative study of the environmental footprints of marinas on European Islands.

Ports have been key elements in Europe's economic development. This situation is even more relevant on islands, which are highly dependent on the maritime sector. Consequently, over the years, ports with diverse functionalities have been established both in mainland Europe and on its outlying islands. This article discusses the environmental impact of leisure marinas on European islands, especially as they are closely linked to economic development through tourism. The aim is to study the environmental impact of these infrastructures by determining the carbon and water footprints of marinas on European islands in the Atlantic and the Mediterranean. The results obtained enable the authors to make recommendations in order to reduce the overall environmental footprint of marinas on islands, considering that these territories are much more vulnerable to climate change than mainland locations in Europe.