Summary
Based on analyses of the biological quality elements; phytoplankton, macroalgae and macrobenthos this report seeks to establish a scientific foundation to the development of tools that can be applied to assess the five classes of ecological status of the Water Frame Work Directive (WFD) in coastal waters.
The first part of this report has its focus on establishing preliminary reference conditions for phytoplankton biomass, expressed as chlorophyll a , using secchi depth data from the early 1900s and Secchi depth and Chl a obtained from recent monitoring data. The recent data were used to establish Secchi depth–Chl a relationships and correlations between Secchi depth and Chl a (90th percentiles of Chl a concentrations).
For all investigated areas a significant correlation was found between the Secchi depth and the Chl a concentrations and calculated 90th percentiles of historical Chl a concentrations were lower than recent ones. The outcome of these analyses was a first step in establishing reference conditions for phytoplankton in Danish waters.
The focus on macroalgae was the identification of useful indicators. The study was based on hypotheses that cover of the algal community in deeper water increases and composition of the algal community changes towards reduced cover of opportunistic species when water quality improves and that macroalgal cover on unstable substratum is lower than on firm substratum. Algal variables were analysed with reference to substratum and physiochemical variables along with descriptive analyses of algal communities. Coupling algal variables to water quality demonstrated significant relationships between several algal variables and water quality. In conclusion total cover and cumulated cover of coastal macroalgal communities was found to be suitable indicators of water quality if appropriate reference levels for these indicators are defined. Furthermore, there were indications that focus on algae from deeper, light-limited waters renders algal indicators sensitive to changes in water quality.
A somewhat different approach in the study on macrobenthos was to evaluate earlier proposed indices on Danish data along the environmental gradient of oxygen deficiency to arrive at useful indices applicable on Danish conditions. Macrobenthic data from the period 1999-2003 from 11 areas monitored in the Danish National Monitoring and Assessment Programme were analysed. The areas ranged from those hit by severe seasonal hypoxia nearly each year to those who never experience hypoxia. The work was the first test of the AMBI index on Danish monitoring data and both diversity measures and AMBI where significantly correlated with rank numbers based on hypoxic conditions. Overall, the results indicated that both diversity-based indices and the sensitivity based index AMBI can be used to evaluate quality status of benthic communities in Danish waters with respect to bottoms in the salinity regime > 18 psu.
Full report in pdf format (1,721 kB)
