Aarhus University Seal / Aarhus Universitets segl

No. 93: Development and testing of tools for intercalibration of phytoplankton, macrovegetation and benthic fauna in Danish coastal areas

Carstensen, J., Krause-Jensen, D., Josefson, A. 2014. Development and testing of tools for intercalibration of phytoplankton, macrovegetation and benthic fauna in Danish coastal areas. Aarhus University, DCE – Danish Centre for Environment and Energy, 85 pp. Scientific Report from DCE – Danish Centre for Environment and Energy No. 93.

Summary

This report describes the development of indicators and assessment tools for the Water Framework Directive’s (WFD) marine biological quality elements: phytoplankton, macroalgae and benthic macrofauna. It also addresses intercalibration of these with Sweden and Germany.

Phytoplankton biomass, which is quantified as the summer chlorophyll a concentration, increases with nutrient levels, most significantly with the total nitrogen concentration. The suggested reference conditions in Danish and Swedish coastal waters, sharing the same typology, are similar, but Denmark has suggested a stricter boundary setting than Sweden, and these differences must be clarified.

Phytoplankton composition across coastal water bodies is mainly governed by differences in salinity, but increasing levels of total nitrogen also suggested a shift from dinoflagellates and other species to increasing dominance of diatoms. This shift is not perceived as a degradation of ecological status and the analyses of phytoplankton communities did not result in meaningful indicators sensitive to changes in nutrient levels. The scientific understanding of phytoplankton community responses to nutrient enrichment is not yet ripe for operational implementation in the WFD, and the implementation must await scientific advances in this field.

Macroalgae cover and composition have been described by six different indicators, which are not biased by differences in depth and substrate of the monitoring observations. Three of these indicators, selected according to their sensitivity to total nitrogen and the uncertainty involved in their estimation, are proposed as the basis for assessing the ecological status of this biological quality element.

An assessment tool is proposed for macroalgae, but the approach can be applied more generally to other biological quality elements. The idea is to transform all indicators to a common EQR-scale, where status classes are equidistantly distributed. Indicators for the same biological quality element can be combined by weighted average, once transformed to the common EQR-scale. A quality of the proposed tool is its transparency from the indicator level to the overall assessment.

The quality of soft sediment macrobenthic fauna may be measured by an index integrating diversity and sensitivity components of species, the Danish quality index DKI, albeit with restricted applicability.

An investigation was undertaken to identify important natural factors influencing local richness diversity (alpha) and consequently the Shannon diversity (H), one major component in the DKI index, to make the DKI operational in a wider context including Danish shallow coastal areas and estuaries. For this purpose, fauna data were used from an open sea area fringed by 17 estuaries. Both dispersal and environmental filtering were important in regulating alpha diversity in the estuaries, where salinity filtered primarily dispersive species. So although dispersal limitation may determine the species composition of alpha, the level of alpha is determined by salinity. Thus, for the purpose of normalizing, DKI correction for salinity makes sense.

It is concluded that the original relationships between salinity and DKI components could be kept in the ‘new’ general version of DKIver2, re-described in this report with two minor amendments and more detailed suggestions of status determination procedure. It is recommended to use the salinity normalized DKIver2 index in general, and to use the 20th percentile of index data when evaluating status against a common set of boundaries for all types.