A model for describing the eutrophication in a heavily regulated coastal lagoon. Application to the Albufera of Valencia (Spain) Pilar del Barrio Fernández a, * , Andrés García Gómez a , Javier García Alba a , César Álvarez Díaz a , José Antonio Revilla Cortezón b a Environmental Hydraulics Institute “IH Cantabria”, C/Isabel Torres n  15, Parque Científico y Tecnológico de Cantabria, 39011 Santander, Spain b Universidad de Cantabria, E.T.S.I. Caminos Canales y Puertos, Avda. de los Castros s/n, 39005 Santander, Spain article info Article history: Received 29 June 2011 Received in revised form 9 August 2012 Accepted 11 August 2012 Available online Keywords: Eutrophication Modelling Coastal lagoon Phytoplankton Albufera of Valencia abstract A simplified two-dimensional eutrophication model was developed to simulate temporal and spatial variations of chlorophyll-a in heavily regulated coastal lagoons. This model considers the hydrodynamics of the whole study area, the regulated connexion of the lagoon with the sea, the variability of the input and output nutrient loads, the flux from the sediments to the water column, the phytoplankton growth and mortality kinetics, and the zooplankton grazing. The model was calibrated and validated by applying it to the Albufera of Valencia, a hypertrophic system whose connection to the sea is strongly regulated by a system of sluice-gates. The calibration and validation results presented a significant agreement between the model and the data obtained in several surveys. The accuracy was evaluated using a quantitative analysis, in which the average uncertainty of the model prediction was less than 6%. The results confirmed an expected phytoplankton bloom in April and October, achieving mean maximum values around 250 mgl 1 of chlorophyll-a. A mass balance revealed that the eutrophication process is magnified by the input loads of nutrients, mainly from the sediments, as well as by the limited connection of the lagoon with the sea. This study has shown that the developed model is an efficient tool to manage the eutrophication problem in heavily regulated coastal lagoons. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Eutrophication is a widespread phenomenon in inhabited areas of the planet, being considered one of the major threats to the health of marine and coastal ecosystems (Nixon, 1995). This phenomenon produces a very large increase of biomass in the system, a serious impoverishment of the diversity, and a decline in the quality of the affected water body (Chau and Haisheng, 1998). Due to the importance, complexity, and variability of eutrophicated systems, mathematical models are essential tools to represent the degree of eutrophication of natural water bodies (Chao et al., 2010; Fan et al., 2009). The complexity of the models that describe eutrophication in aquatic systems ranges from simple NPZ (Denman and Gargett, 1995; McClain et al., 1996), or NPDZ (Hood et al., 2003; Oschlies and Garcon, 1999), to multi-nutrient, multi- species and size-structured ecosystem models (Lima and Doney, 2004; Lopes et al., 2009; Sundarambal et al., 2010). In fact, most of the available models assessing water quality in variable and high productive environments like coastal lagoons (Everett et al., 2007; Ferrarin and Umgiesser, 2005; Ohno and Nakata, 2008); are complex. Moreover, large data requirements and high computa- tional costs make them time consuming and expensive to develop (Lawrie and Hearne, 2007). In addition, more complexity in an ecosystem model does not necessarily improve model performance (Friedrichs et al., 2006; Hood et al., 2003). On the contrary, models that use simpler formulations have lower computational demands and can be easier to parameterize and interpret (Fulton, 2001). These mathematical tools are usually coupled to physical models that range from 1-box models (Li et al., 1999; Usaquen Perilla et al., 2012), which do not represent the heterogeneity of the entire system, to full models (Lima and Doney, 2004; Skogen et al., 1995), which usually have fine resolution grids and sophisticated numerical schemes to describe the system hydrodynamics. However, in spite of the fact that spatial resolution and heteroge- neity are crucial characteristics in model performance (Fulton, 2001) the significant increase of the use of low spatial resolution models (Baird et al., 2003; Everett et al., 2007) is common in order to avoid high time consumption and computational demands. Hence, the combination of a fine resolution grid, a sophisticated numerical scheme, and a simple ecological model, could give a reasonable description of the observed phenomena in complex * Corresponding author. Tel.: þ34 942201616; fax: þ34 942266361. E-mail addresses: delbarriop@unican.es (P. del Barrio Fernández), garciagan@ unican.es (A.G. Gómez), garciajav@unican.es (J.G. Alba), alvarezc@unican.es (C.Á. Díaz), revillaj@unican.es (J.A. Revilla Cortezón). Contents lists available at SciVerse ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman 0301-4797/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jenvman.2012.08.019 Journal of Environmental Management 112 (2012) 340e352