Modeling the salinity fluctuations in salt marsh lagoons

Abstract

Coastal wetlands are among the most productive and fluctuating ecosystems of the world. These ecosystems, however, are affected by human activities that may change their nutrient dynamics and water regime, causing the degradation of water quality, the disappearance of lagoons and wetlands, or the establishment of invasive species. In this context, the La Pletera salt marsh is composed of several coastal lagoons and wetlands that were affected by the incomplete construction of an urban development in 1987. This area has been the focus of two LIFE restoration projects aimed at recovering its ecological functionality, and protecting a threatened endemic fish species (Aphanius iberus). Thanks to these projects, a new lagoon was created in 2002 simply by excavating below sea level, which ensured water permanency all year round. Between 2014 and 2017, samples were regularly taken to measure temperature, salinity and water levels in the lagoons of the La Pletera salt marsh. In this study we focus on two natural lagoons (Life A and Life B), and the one created in 2002 (Life C). Using the one-dimensional General Lake Model (GLM), we evaluated water inflows and outflows and evaporation fluxes, since water circulation determines the resultant salinity in these lagoons. This model is an open source model that, to our knowledge, is being used for the first time in such small lagoons. The study focuses mainly on dry periods, when the lagoon inflow is low and evaporation is high. Results show that Life A and Life B are more affected by evaporation and that lagoon water circulation was higher in Life-C. From a management point of view, the maintenance of salinity conditions is fundamental for the protection of Aphanius iberus, a species adapted to high salinity fluctuations but strongly affected by competition from the invasive Eastern mosquitofish (Gambusia holbrooki) when water salinity is not high enough or variable. Between 2014 and 2018, additional lagoons were created in the La Pletera salt marsh as part of a new LIFE project. Knowledge of the hydrology and the resultant water salinity in the new lagoons are essential to ensure the continued survival of Aphanius iberus in the area.