Trophic state evaluation after urban loads diversion in a eutrophic coastal lagoon (Óbidos Lagoon, Portugal): a modeling approach

Abstract

Ó bidos Lagoon is classified as a sensible system according to the eutrophication criteria in the Portuguese Decree-Law 149/2004, which transpose the standards of Urban Waste Water Treatment Directive (Council Directive 91/271/EEC) concerning urban waste water treatment. From September 2005 onwards, the urban loads of five Waste Water Treatment Plant (WWTP) were deviated to a submarine outfall to prevent water degradation and improve the lagoon trophic state (LTS). This paper evaluated the LTS after urban loads diversion, testing the hypothesis behind the management decision. First, the loads reaching the lagoon were determined with the Harp-Nut guidelines and watershed modeling. Then, the water quality in the lagoon was simulated with a hydro-ecological model and compared with measured data. Finally, management scenarios corresponding to nutrient loads reduction were tested to determine hypothesis-driven LTS. Results showed that the loads from pig farms should be diverted instead of the WWTP, to improve the LTS and achieve a ''Good/Bad'' status. The proposed method stresses the importance of integrated modeling tools in the Water Framework Directive, given their skill in testing various hypothesis, and ultimately ruling out inadequate management decisions before implementation.

Ecological modeling and eutrophication—A review

“…It also provides the ability of one or two groups of phytoplankton (i.e., flagellates and diatoms) and/or zooplankton (i.e., micro‐ and mesozooplankton) simulation. It has the capability of coupling a hydrodynamic model with an ecological model enabling a flexible and comprehensive analysis of the model's result, either the ecological or hydrodynamic features (Malhadas et al., ; Zouiten, ).…”

“…The ecological model is coupled to the hydrodynamic using Euler forward scheme (explicit method) (Malhadas, Mateus, Brito, & Neves, 2014). The parameters of the ecological processes in water column follow a Nutrient-Phytoplankton-Zooplankton-Detritus philosophy (EPA, 1985;Malhadas et al, 2014).…”

“…The ecological model is coupled to the hydrodynamic using Euler forward scheme (explicit method) (Malhadas, Mateus, Brito, & Neves, 2014). The parameters of the ecological processes in water column follow a Nutrient-Phytoplankton-Zooplankton-Detritus philosophy (EPA, 1985;Malhadas et al, 2014). MOHID Water is set in order to simulate water column physical characteristics such as salinity and temperature, phytoplankton and zooplankton growth and decay, nutrients and metals cycling, as well as water sediments interactions.…”

“…It also provides the ability of one or two groups of phytoplankton (i.e., flagellates and diatoms) and/or zooplankton (i.e., micro-and mesozooplankton) simulation. It has the capability of coupling a hydrodynamic model with an ecological model enabling a flexible and comprehensive analysis of the model's result, either the ecological or hydrodynamic features (Malhadas et al, 2014;Zouiten, 2012). Trancoso et al (2005) used MOHID for the better understanding of the ecological dynamics in the Portuguese Ria de Aveiro lagoon and to create a useful tool to outline the management practices.…”

Phytoplankton community dynamics in an intermittently open hypereutrophic coastal lagoon in southern Portugal

“…However, management measures must take into account the multiple sources of stress and the complex mechanisms that determine the functioning of the different coastal lagoons. In Óbidos lagoon(Malhadas et al, 2014), diversion of urban loads of waste water treatment plants to reduce nutrient loads might not have been as effective as intended to mitigate eutrophication because fuzzy inputs and contribution of the lagoon sediment itself can play a main role. In addition, reducing freshwater inputs could have drastic consequences in the particular case of Salgados lagoon due to its effect on depth.…”