Hydro-Saline Dynamics of a Shallow Mediterranean Coastal Lagoon: Complementary Information from Short and Long Term Monitoring

Abstract

The Vaccarès Lagoon System, located in the central part of the Rhône Delta (France), is a complex shallow coastal lagoon, exposed to a typical Mediterranean climate and a specific hydrological regime affected by man-controlled exchanges with the sea and agricultural drainage channels. In this article, we report the results obtained by a series of monitoring programs, with different spatial and temporal resolutions. Long-term datasets from 1999 to 2019 with data collected on a monthly basis and a high spatial resolution highlighted the significant spatial heterogeneity in salinity regimes, and helped to determine the long-term evolution of the total mass of dissolved salt. High-frequency surveys allowed to characterize the water levels and salinity dynamics seasonal response to (i) the exchanges with the Mediterranean Sea, (ii) the exchanges with agricultural drainage channels, and (iii) the rain and evaporation. In addition, wind effects on salinity variations are also explored. This work shows how different spatial and temporal monitoring strategies provide complementary information on the dynamic of such a complex system. Results will be useful and provide insight for the management of similar lagoon systems, accommodating for both human activities and ecological stakes in the context of global change.

An Integrated Approach for Evaluating the Restoration of the Salinity Gradient in Transitional Waters: Monitoring and Numerical Modeling in the Life Lagoon Refresh Case Study

“…Depending on the nature (hydraulic works, natural connection) and the characteristics of their connections with the sea, their watersheds or surrounding rivers, shallow coastal lagoons can exhibit very significant spatial and temporal heterogeneity in both salinity and water level. The importance of implementing different monitoring strategies to understand the hydrosaline functioning of these lagoons is reported in the recent literature [11].…”

“…An interesting aspect that emerged is the differentiation of the three probes with more defined conditions corresponding respectively to a stronger influence of fresh water input for the nearest position (P1) and a stronger influence of tide for the outermost position (P3), while more variable conditions were collected for the intermediate station (P2). Continuous measurements allow the acquisition of critical data for the development, calibration and validation of hydrodynamic models that can provide additional information on the hydro-saline functioning of lagoons [11,15,[45][46][47][48][49].…”

“…On the other hand, spatially-distributed profiles are also particularly useful for the validation of numerical modeling results in terms of spatial distribution of salinity patterns [11,15].…”

“…Salinity conditions are related to a complex interaction between different hydrological processes that involve discharge of fresh water, tidal regime and the exchanges with the sea, precipitation, interaction with the atmosphere (e.g., heat flux, evaporation rates) and wind-driven forces, which vary over a wide range of time-scales and that become relevant for really shallow waters, resulting in strong daily and seasonal variability [9,10]. All these drivers contribute to the high diversity in terms of salinity conditions between Mediterranean lagoons, ranging from oligohaline to hyperhaline waters [11].…”

“…During the different phases of this adaptive management approach, an intensive monitoring and modeling activity was carried out to support the assessment of the success of the implemented measures and of the identified mitigation actions. In microtidal lagoons, this monitoring activity needs to integrate different strategies able to capture, with the best resolution in time and space, variations of water levels, flows and salinity that are often encountered [11].…”