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.