Applicability of ecological assessment tools for management decision-making: A case study from the Lima estuary (NW Portugal)

Abstract

The Water Framework Directive (WFD) aims to achieve and conserve a good ecological status of all surface waters, including estuarine environments, which should be assessed considering several biological elements, together with physical, chemical and pollution elements.In this study, we investigated the applicability of ecological indicators for a practical management issue: selection of the most suitable location for a marina in a salt-marsh temperate estuary (River Lima, NW Portugal). Considering the WFD principles, we assumed that the most suitable location for the implementation of a marina should be the one with the least ecological value, considering that it could be an opportunity for ecological rehabilitation. In order to attain this purpose, the ecological quality status of five potential locations in the navigable lower stretch of the Lima estuary was assessed following an ecosystem-based approach. Several key ecological quality elements such as physical and chemical parameters of water and sediment, phytoplankton biomass, as well as macroinvertebrate and fish communities were surveyed. In addition, heavy-metal analyses, fecal indicator evaluation and “first-screening” toxicity tests were also performed. All collected information was integrated using a scaled value approach, in order to rank the five locations. Furthermore, for the assessment of the ecological quality status of the potential sites, a macroinvertebrate (M-AMBI) and a demersal community based (EDI-Estuarine Demersal Indicators) indices were used. Different human pressures were detected, being the uppermost site more susceptible to urban wastewater discharge, whereas the location downstream the commercial seaport was more prone to accumulate contaminants in the sediments. The scaled values approach allowed the ranking of the potential sites, where the uppermost location ranked last. M-AMBI and EDI also classified that location with the lower ecological quality status. Both biological indices were in agreement concerning the discrimination of the location with the lowest ecological quality status, which coincided with the one ranked last by the scaled values approach. The selected biological indices proved to be useful tools for decision-making support in an environmental management context.