Eutrophication Assessment of Coastal Waters Based on Indicators: a Literature Review

Numerous methods have been developed for the quantitative assessment of eutrophication: statistical techniques, simulation models and water quality indicators are the most widely used techniques to assess trophic levels. All these methods share a common goal: to evaluate the environmental impact due to high nutrient concentrations / phytoplankton biomass and classify the waters into oligotrophic, mesotrophic and eutrophic water types. This classification provides a useful tool for assessing environmental quality and help coastal managers and planners in the decision making. In the present work the indicators used for eutrophication assessment are reviewed. They provide useful information because voluminous amounts of data can be expressed through a single number. Variable indices such as chlorophyll and nutrient concentrations, phytoplankton biomass and water transparency are examined and ranges defining levels of eutrophication are proposed. Among the flux measurements, primary productivity has also been considered as an indicator useful in assessing trophic levels and a productivity scaling is also given. Community indices and their application in eutrophication studies are overviewed and their effectiveness in describing eutrophic trends is evaluated; their assumptions, advantages and shortcomings are also discussed. Among the twelve community indices evaluated for assessing eutrophication, only four were found to respond to eutrophic conditions; in nutrient and phytoplankton variables used as indicators, their frequency distribution showed overlapping between water types; this seems to be a problem in defining boundary values discriminating trophic levels. As the indices express ecosystem status and conditions, if they are going to be used under the Water Framework Directive, special consideration is needed since different scales seem to apply at regional level rather than forming a universal tool applicable to all European coastal waters.