This work presents an integrated methodology that comprises the first and the last metrics indicated above, analyzed during the growing season (February-October). Significant (p < 0.01) direct relationships between pressures (nutrient concentrations) and the biomass metric (90th percentile of chlorophyll a) were found, which allow confidence in the assessment. Afterwards, reference conditions and the boundaries of a five-class classification were set using phytoplankton biomass. These boundaries were further tested against the results of a risk assessment, carried out on the basis of primary (e.g. high chlorophyll concentrations) and secondary symptoms (e.g. oxygen depletion) of eutrophication, as well as nutrient loads and the susceptibility of systems. Significant (p < 0.01) direct relationships were also found between biomass and the scale of risk. Phytoplankton bloom intensity and frequency data were also used in the analysis although data were too scarce for a detailed evaluation of all water bodies (WBs). The worst ecological status (moderate to poor) were found in only few water bodies in the Ria de Aveiro, Mondego, Sado and Guadiana estuaries. Further research is needed for testing and improving the tool, especially for the phytoplankton bloom intensity and frequency metric.
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