Contents lists available at ScienceDirect Journal of Hydrology journal homepage: www.elsevier.com/locate/jhydrol Research papers Modeling the salinity fluctuations in salt marsh lagoons Xavier Casamitjana a , Anna Menció b , Xavier D. Quintana c , David Soler b , Jordi Compte c , Mònica Martinoy d , Josep Pascual e a Department of Physics, University of Girona, 17003 Girona, Spain b Grup de Geologia Ambiental i Aplicada (GAiA), Department of Environmental Sciences, University of Girona, 17003 Girona, Spain c GRECO, Institute of Aquatic Ecology, University of Girona, 17003 Girona, Spain d Servei de Control de Mosquits de la Badia de Roses i del Baix Ter, Spain e Ajuntament de Torroella de Montgrí, Girona, Spain ARTICLE INFO This manuscript was handled by C. Corradini, Editor-in-Chief, with the assistance of Subashisa Dutta, Associate Editor Keywords: Coastal lagoons Salt marsh hydrology General Lake Model Salinity fluctuations Hydrological regime of the La Pletera lagoons Lake modelling 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 reg- ularly 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. 1. Introduction Coastal wetlands have usually been described as the confluence of inland and marine water. These ecosystems are considered among the most fluctuating and productive in the world, performing a wide range of services, including shoreline stabilization, sediment and nutrient retention, and coastal water quality buffering (Mitsch and Gosselink, 2000; Costanza et al., 1997; Gedan et al., 2011; Beer and Joyce, 2013). Depending on their connection to the sea, coastal lagoons are ca- tegorized as open or closed lagoons. This second group includes lagoons that have no sea connection or only a short period of connection (Kjerfve and Magill, 1989; Félix et al., 2015). Intermittently closed and open lagoons are characterized by their shallowness (less than 5 m deep, approximately), which results in a high ratio of sediment surface area to water volume, thereby increasing the relative importance of sediment–water column interactions (Tyler et al., 2001). In these sys- tems, salinity can vary significantly (from fresh to brackish or hy- persaline), depending on the amount of freshwater input, the climate, and the frequency and duration of the opening (Ridden and Adams, 2008). These lagoons have often been perceived as a surface expression of shallow aquifers and are thought to be fed by groundwater inputs during most of the year. As a result, they are vulnerable to minor changes in catchment and groundwater hydrology (Chikita et al., 2015; Sadat-Noori et al., 2016; Menció et al., 2017; Rodellas, et al., 2018). https://doi.org/10.1016/j.jhydrol.2019.06.018 Received 23 January 2019; Received in revised form 2 April 2019; Accepted 8 June 2019 E-mail addresses: xavier.casamitjana@udg.edu (X. Casamitjana), anna.mencio@udg.edu (A. Menció), xavier.quintana@udg.edu (X.D. Quintana), david.soler@udg.edu (D. Soler), jcomptec@gmail.com (J. Compte), monicmartinoy@gmail.com (M. Martinoy), jpascual@meteolestartit.cat (J. Pascual). Journal of Hydrology 575 (2019) 1178–1187 Available online 11 June 2019 0022-1694/ © 2019 Elsevier B.V. All rights reserved. T