A Numerical index for evaluating phytoplankton response to changes in nutrient levels in deep Mediterranean reservoirs

This paper proposes a new ecological index based on phytoplankton (MedPTI) as suggested by the European Directive
2000/60/CE, Water Framework Directive (WFD). The index is a useful tool to verify the impacts of eutrophication in Mediterranean
reservoirs belonging to different categories of the WFD. Multiple data sets were employed to develop the MedPTI index. The
calibration data set included data collected from 30 Sardinian reservoirs in 1994. A list of 44 selected taxa was obtained and used
for index calculation. A second dataset including 48 averaged annual values from 10 reservoirs was used. Results showed good
correlation between MedPTI and concentration of total phosphorus, which was the limiting nutrient in these reservoirs. The trophic
classifications determined using the index agreed with the results from the OECD probabilistic model on the same series of data.
Finally, the index was included in an international exercise to compare the definition of reference conditions and quality class
boundaries against indices used in other Mediterranean countries.