We present data of major and noble gas composition from mainly newly reported, natural springs - related gas seeps across Grande Terre, the main island of New Caledonia (NC). Two types of springs are investigated: (1) Ophiolitic Springs which emerge from the NC Ophiolite, recognised as the youngest large and well-preserved ophiolite, including seven sites in the Massif du Sud and one site in a chromite mine tunnel located in the Ti & eacute;baghi Massif in the north of Grande Terre; (2) Four Basement Springs which emerge from the pre-Late Cretaceous basement in the eastern central part of Grande Terre. Our results reveal that both seep types are dominated by air-like N-2 (60-95%; delta N-15 = -0.2 to + 0.1 parts per thousand vs Air), and contain CH4 (up to 23%) whose delta C-13 generally range from -40 parts per thousand to -20 parts per thousand VPDB in the Ophiolitic Springs and is lighter in the Basement Springs (delta C-13(CH4) = -70 to -35 parts per thousand VPDB). Ophiolitic Sites also show elevated H-2 content reaching 35%, with delta D values ranging from -740 to -710 parts per thousand VSMOW, whereas Basement Sites display very low levels of H-2 (<300 ppm). The gas composition and isotopic signatures at Ophiolitic Sites are characteristic of serpentinization environments, suggesting that this process is the primary pathway for H-2 generation; consistent with previous studies. This is confirmed by the elevated dissolved OH- which results in elevated pH (up to 11.83), among other factors. Isotopic data for CH4 and CO2 indicate that CH4 in the Ophiolitic Sites likely originates from both biogenic and abiotic processes, while microbial methanogenesis is the major source of CH4 in the Basement Springs and at the Ti & eacute;baghi Tunnel. The H-2-CH4-H2O isotopic fractionation factors suggest equilibration at approximately 50-100 degrees C, indicating a low-temperature serpentinization system within the New Caledonia Ophiolite, which aligns with previous studies. Consistent with the regional geology and tectonics, helium isotopic data (He-3/He-4) reveal a predominantly radiogenic signature (similar to 0.3 Ra) at the Basement Sites where the crust is thicker, and a significant mantle-derived component (similar to 13-37% mantle helium) in the southernmost coastal Prony region. For the central part of the Massif du Sud peridotite nappe where crustal and mantle-derived contributions are absent, we propose that the air-like signatures revealed by He-3/He-4, He-4/Ne-20, Ar-36/N-2 and Kr-84/N-2 ratios reflect atmospheric entrainment and the degassing of air-saturated groundwater during water table fluctuation, which also accounts for the predominance of the air-like N-2 in the gas emissions.
Understanding how anthropogenic pressures and environmental gradients shape coastal fish communities is a central question in biogeography and marine conservation. Yet, the set of species expected to occur at a site given ecological conditions but being absent – the so‐called dark diversity – has received far less attention than observed species, even if they hold key information about local extirpations and conservation effectiveness. Quantifying dark diversity in the sea is particularly challenging because many species are rare, cryptobenthic or mobile, while sampling effort is rarely standardized. Here we combined 930 environmental DNA (eDNA) samples collected at 401 sites along 2000 km of the French Mediterranean coast with fine‐scale mapping of habitats, anthropogenic pressures and protection levels. Using a Bayesian model of dark diversity affinity (DDA) that explicitly controls for sampling effort, we decomposed the correlates of species absences into site characteristics and species traits, separating dispersal‐related from sensitivity‐related signals. At the site level, fishing effort, marine traffic, and artificial habitats were associated with greater DDA, so a deficit of species, whereas protected areas and diverse natural habitats were associated with lower DDA, increasing the likelihood of observing more complete fish communities. At the species level, demersal and predator species, together with those bearing their eggs (e.g. many elasmobranchs) compared to species with demersal or pelagic eggs, exhibited the highest DDA, suggesting local extirpations linked to a combination of limited dispersal and higher sensitivity to cumulative pressures. Beyond the creation of marine protected areas, preserving habitat heterogeneity and mitigating coastal pressures therefore emerge as essential levers to limit the local erosion of fish biodiversity. More broadly, coupling eDNA with a sampling‐effort‐corrected DDA framework offers a transferable benchmark to evaluate where, and for which species, conservation efforts are most needed.
In foreland fold-thrust belts, tectonically deformed aquifers remain underexplored, largely due to the complex architecture of their hydrogeological reservoirs. This limited understanding prevents the development of sustainable management policies to face the current decline in groundwater availability. In the southwestern Subalpine Chains, we characterised the structure of the folded Senonian karst aquifer of the Devoluy Massif, which is transected by the Median Devoluy Thrust. Using surface structural data, we performed an original 3D structural model of the massif. Quantitative analyses of this model indicate a total Senonian package volume of 114 km(3), of which 25 km(3) lie below the elevation of Gillardes Spring, the main karst discharge. A structural restoration of the base of the Senonian indicates Alpine shortening of similar to 4.4 km in the southern part of the massif and similar to 1.2 km in the northern part. The deformation of the karst reservoir into two N-trending synclines, separated by the Median Devoluy Thrust, is identified as a key control on the northward groundwater drainage pattern, culminating at Gillardes Spring. This 3D structural modelling approach also allowed for identification of suitable areas for the exploration of new deeper resources. Finally, this study highlights the potential of a hydrostructural approach and 3D structural modelling for assessing the hydrogeology in tectonically deformed karst reservoirs.
Riverscapes are the integration of terrestrial and aquatic systems from headwaters to estuaries that provide habitat and ecosystem benefits when in good health. However, current riverscape degradation is pervasive, impairing the function and resulting benefits of these systems. Healthy riverscapes are adaptive and some can 'heal' after disturbance with minimal to no human assistance. As riverscape health is threatened, a need exists to address current degradation and understand the potential for riverscape restoration-concisely communicating what comprises healthy riverscapes is essential to direct limited resources and increase efficacy of restoration and conservation efforts. Healthy riverscapes have (i) space to interact within their valley bottom; (ii) natural flow, sediment, and vegetation regimes appropriate to the biophysical setting and river type; and (iii) structural forcing to support diversity and that creates varied residence times for water, sediment, and vegetation. These three principles are grounded in interdisciplinary science and lessons from riverscape scientists and restoration practitioners across the world. Understanding the context, anthropogenic influences, boundary conditions, and legacy effects influencing riverscapes is essential for the appropriate application of these principles in pursuit of achieving riverscape health. Emphasizing a holistic, biogeomorphic view of riverscapes through these principles can guide policies, restoration actions, and monitoring frameworks that ensure that riverscapes remain capable of accommodating and adjusting to disturbances while continuing to support biodiversity and human benefits.This article is categorized under: Water and Life > Conservation, Management, and Awareness
Macroalgal forests characterised by species of the genus Cystoseira sensu lato form important shallow coastal rocky habitats in the Mediterranean Sea. These forests support a high biodiversity and provide important ecosystem services and societal benefits. Currently these habitats are often in a poor condition in many areas, due to loss and degradation from both anthropogenic and climate stressors. Restoration has recently moved to the forefront of the United Nations and European Union agendas to reverse this trend, particularly in the last decade with the implementation of various international policies. However, this has been in the form of generic targets (e.g., restoration of 30% of degraded habitats by 2030) and has not been linked to specifically what habitat or species to restore, where and how. Initial targets have been missed, new targets are expected through the proposed EU Nature Restoration Law, but overall guidance is still lacking. There are few specific guides to marine habitat restoration limited to mostly seagrass, corals and shellfish. As a priority action for the recovery of coastal marine ecosystems a decision-support framework has been developed for the restoration of Mediterranean macroalgal forests, comprising a stepwise decision tree with additional descriptions of key elements to be considered for a restoration action. The decision tree includes steps concerning current and historical forest presence, site local condition assessment and choice of actions. Key considerations include restoration implementation (competence, society and support, finance and governance), success evaluation (at the target species and the ecosystem level) and long-term management. The framework builds on existing work on Cystoseira s.l. restoration, the work carried out in the EU AFRIMED project, but also on principles and guidelines in place for both generic and specific marine habitats. The work reported here has involved the expertise of scientists and information from stakeholders. Gaps were identified and recommendations were made, dealing with stressors, coordinating and networking stakeholders, integrating top down policy and bottom up initiatives, funding of restoration actions, establishing synergies between restoration, conservation and marine spatial planning and finally communication and publicity.
