Hydrological behaviour of mediterranean salt marshes and implications for vegetal cover

International audience<p><span>Salinization is a worldwide issue particularly threatening arid and semi-arid soils. Primary salinization is due to unbalanced flows between upward water and solute flows leading to salts accumulation and downward flows which allow the leaching of salts. </span><span>S</span><span>oil salinity affects vegetation by causing osmotic and toxic stress. In return, soil water transfers are impacted since water extraction by plants is limited. </span><span>Salinity </span><span>leads </span><span>also </span><span>to a decrease of </span><span>soil hydraulic conductivity.</span></p><p>Salinisation is often described as a threat to agriculture, but less as a driver of specific ecosystem functioning, such as salt marshes. These interfaces between land and sea are very present in the Mediterranean deltas and lagoon complexes, and provide several ecosystem services, (e.g. being the natural areas among with the highest carbon storage rate). Salinity in these ecosystems is highly dependent on freshwater inputs from precipitation, natural or anthropic flooding, making them vulnerable to global changes. Nevertheless, the effects of flooding on hydrological dynamics and solute transfers in salt marshes are not well known.</p><p>We choose a study site in the lowlands of the Aude river (the Castelou site, Narbonne, France) to address the question of the hydrological behavior of a salt marsh managed by different flooding intensities in relation to plant communities. Soil moisture, saturated zone depth, and salinity dynamics are monitored by a set of continuous and point measurements at 12 sites distributed along a flood management gradient and a natural salt pressure gradient. Based on these observations, time continuous data series have been built by a physics-based modeling. The analysis provides a better understanding of the effects of flooding on soil water and solute stocks and fluxes, and relates them to the specific composition of plant communities.</p><p>We show that flooding has varying effects on water storage in unsaturated and saturated zones. Soil water recharge has a small effect on soil salt content on an annual scale but limits the level of osmotic stress. In the absence of flooding, osmotic stress is more pronounced, altering the specific composition of plant communities, suggesting changes in their functional properties.</p&gt

Participatory modeling to assess the impacts of climate change in a Mediterranean vineyard watershed

International audienceThe diversity of both pedoclimatic and socio-economic contexts in agricultural landscapes makes evaluating the impacts of climate change a challenge. Models are pertinent tools to quantitatively explore possible futures, and participatory approaches help account for local diversity. We developed a model through an approach that involves stakeholders in the model's construction and testing and in the discussion of results. We simulated spatially explicit impacts of climate change on water balance, grape phenology, and yield in a Mediterranean vineyard watershed for two climate scenarios. Results show a decrease in grape production of 7–14% by 2100. Yield decrease would be higher in irrigated high-yield areas despite a doubling of irrigation water supply. A forecasted 6 °C increase in temperature during berry ripening would threaten wine quality. The approach allows the communication of model results and limitations to stakeholders. It is a promising means of identifying potential local adaptations to climate change

Salinity Spatial Patterns in Mediterranean Coastal Landscape: The Legacy of the Historical Water Management and Land Planning

Mediterranean coastal areas have been occupied and developed intensively for a long time facing issues related to agricultural production, urbanization, tourism, preservation of natural resources often linked to salinity. This article explores the relationship between historical land planning and water management, and current soil and water salinity to gain insights into future projections.Soil samples (1185) were collected in a coastal plain of 114 km2 in the south of France and saturated paste extract Electrical Conductivity (ECsp) was deduced from 1:5 dilution. Soil salinity exhibits a wide range of variation (from 0.54 to 113.1 mS cm-1) and spatial patterns. ECsp is significantly different among soil types, higher at depth than at the surface (Kruskal Wallis and Wilcoxon tests) and influenced by the distance to ancient anthropogenic structures (Pettitt test). Surface water and shallow groundwater samples were collected for trace element concentrations and Oxygen (18O/16O) isotope ratio measurements. The geochemical signatures indicate a mixture between surface freshwater and seawater, with the presence of over-salted seawater and a stratification of salinity from the surface to the depth.Results suggest that groundwater is the source of soil salinity, and illustrate the long-term impact of water management and land planning. Less saline soils are found near the freshwater supply channel (constructed from 15th to 18th), while more saline soils are located near drainage channels. The presence of over-salted water reflects temporal evolution of the plain over the last few centuries (initially under seawater, gradually filled in, presence of ponds and salt works that have now disappeared). The current soil salinity patches continue to be a visible reminder of this evolution. The trend towards desalinization of the plain over the last few centuries has been made possible by massive freshwater inflows, which are now under threat due to the general decrease of water resources availability