Ecological Modelling 265 (2013) 99–113 Contents lists available at SciVerse ScienceDirect Ecological Modelling jo ur nal ho me page: www.elsevier.com/locate/ecolmodel An advanced tool for eutrophication modeling in coastal lagoons: Application to the Victoria lagoon in the north of Spain Hala Zouiten a,∗ , César Álvarez Díaz a,b , Andrés García Gómez a,b , José Antonio Revilla Cortezón a , Javier García Alba b a University of Cantabria, E.T.S.I. Caminos Canales y Puertos, Avda. de los Castros s/n, 39005 Santander, Spain b Environmental Hydraulics Institute “IH Cantabria”, C/Isabel Torres n ◦ 15, Parque Científico y Tecnológico de Cantabria, 39011 Santander, Spain a r t i c l e i n f o Article history: Received 21 November 2012 Received in revised form 31 May 2013 Accepted 4 June 2013 Keywords: Eutrophication Numerical model Kinetics of phytoplankton Kinetics of nutrients Coastal lagoons a b s t r a c t A mathematical eutrophication model, EnvHydrEM (Environmental Hydraulics Institute Eutrophication Model), was developed to be applied specifically to coastal lagoons. This model takes into consider- ation 19 state variables, including phytoplankton, carbon (total inorganic carbon and sediment carbon), phosphorus (organic phosphorus and phosphate), nitrogen (organic nitrogen, ammonia and nitrate), sil- ica (available dissolved and particulate biogenic silica), dissolved oxygen, carbonaceous organic matter, zooplankton, bacterioplankton, detritus, iron (total and ferrous iron) and manganese (total manganese and manganous ion). EnvHydrEM also describes all possible interactions between the considered vari- ables, showing biological and physicochemical processes that can occur in this type of aquatic systems. These are usually characterized by a series of peculiar aspects which result mainly from the complex interaction between inland and marine waters, as well as from a low hydrodynamic renewal rate. To provide an example, the EnvHydrEM model was applied to the study of the eutrophication process in the Victoria lagoon, in northern Spain. In this case study, the proposed model has proved its ability to reproduce the chlorophyll-a concentration trends in the water body. The study also concluded that the Victoria lagoon is a mesotrophic aquatic media in which silica is the most critical factor for the analysis of its eutrophication state, due mainly to the presence of diatoms. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Population growth and economic development, observed in recent decades throughout the world, are the main factors respon- sible for many of the environmental changes currently taking place. These pressures greatly influence aquatic systems and are the result of multiple human factors (urban, agricultural and industrial dis- charges, sediment accumulation, modification of aquatic system characteristics, etc.) which can cause a marked increase in the nutri- ent inputs to the aquatic system. In several parts of the world, this forced enrichment of nitrates (mainly from the agricultural land washing), ammonia and phosphates (abundant in urban dis- charges) has created an imbalance in aquatic systems known as “cultural eutrophication”, manifested by a large algal production and often followed by a decrease in dissolved oxygen, both of which are harmful to wildlife (Carlson and Simpson, 1996; Rivera, 2002). ∗ Corresponding author. Tel.: +34 942201616x1144; fax: +34 942266361. E-mail addresses: zouitenh@unican.es, h.zouiten@yahoo.fr (H. Zouiten), alvarezc@unican.es (C.Á. Díaz), garciagan@unican.es (A.G. Gómez), revillaj@unican.es (J.A.R. Cortezón), garciajav@unican.es (J.G. Alba). Eutrophication can also have a natural origin, especially in sys- tems with low hydrodynamic renewal. Traditionally the field of limnology has used the terms eutrophic and oligotrophic environ- ments to designate abundance or deficiency of organisms, organic matter or nutrients. In this regard, eutrophic systems are those in which the nutrient availability is able sustain a high biomass and, conversely, pristine oligotrophic systems are those in which the low availability of these substances limits the development of biological activity. Originally, the terms eutrophic and oligotrophic were used to describe the type of environments from a qualitative point of view. Subsequently, other scales were developed based on phytoplankton abundance in the system, in order to assess this phenomenon from a quantitative approach. The scientific commu- nity has since been accepted that the “eutrophic degree” of a water body is quantified as the average annual concentration of chloro- phyll in that environment (OCDE, 1982; Ryding and Rast, 1992). Vollenweider (1976) was the first author who proposed measuring the eutrophic degree of an ecosystem by means of the chlorophyll concentration, a parameter which, in itself, is associated to the increase in the water nutrient concentration. Therefore, the evaluation of the trophic state of a water body expresses the relationship between nutrient availability and 0304-3800/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ecolmodel.2013.06.009