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No. 37: Danish contribution to the EU Water Framework Directive intercalibration phase 2

Henriksen, P., Josefson, A., Hansen, J.W., Krause-Jensen, D., Dahl, K. & Dromph, K. 2014. Danish contribution to the EU Water Framework Directive intercalibration phase 2. Aarhus University, DCE – Danish Centre for Environment and Energy, 36 pp. Technical Report from DCE – Danish Centre for Environment and Energy No. 37 dce2.au.dk/pub/TR37.pdf

Summary

This report presents the Danish contributions to the European Water Framework Directive intercalibration phase 2. The project was initiated and financed by the Danish Nature Agency and focused on development of phytoplankton indicators based on biovolume and carbon biomass, further development and adjustment of the Danish benthic fauna index, and evaluating the possibilities of intercalibrating indicators of benthic vegetation. The results of this project have been included in the Baltic GIG and NEA GIG Milestone 6 reports.

Phytoplankton indicators were established for total phytoplankton biovolume and carbon biomass. The indicators were derived from relationships between concentrations of total nitrogen (TN) and biovolume or carbon biomass of the phytoplankton community. For each indicator site-specific ecological status class boundaries were determined.

The sub-elements ‘blooms’ and ‘abundance’ are not included in the Danish assessment systems. Blooms due to requirement of generally large data sets with high sampling frequency compared to the available data, and abundance due to the lack of indicator species which can be expected to correlate with the predominant pressure ‘nutrients’.

The Danish benthic fauna index was modified to be useful at low salinities also, and methods for establishing ecological status classes and assessment of ecological status were described. For the intercalibration of type NEA8b 35 Danish stations were chosen and 11 of these were defined as benchmark stations.

Relationship between the Danish indicator ‘depth limit of eelgrass’ (or calculated EQRs for this indicator) and environmental parameters like TN and Secchi depht were demonstrated.

There is no joint Danish assessment tool combining depth distribution of eelgrass, cover of macrophytes, and number of perannual species. However each of those single elements has been tested against nitrogen concentration or nitrogen load which is regarded as the most important anthropogenic pressure in inner Danish waters.

It was not possible to find a common metric for intercalibration between Denmark and Sweden.