Developing Reference Conditions for Phytoplankton in the Baltic Coastal Waters Part II: Examples of Reference Conditions Developed for the Baltic Sea
For the implementation of the Water Framework Directive reference conditions have to
be established for the various quality element. In this report we outline a number of
approaches that can be pursued for establishing reference conditions for hytoplankton at a regional level and discuss the problems associated with their application. This report does not exhaust the topic of establishing reference conditions in the different coastal types of the Baltic Sea, while it should be digested as a source for inspiration when analyses are carried out at a regional level. Phytoplankton has been quantitatively analysed in the Baltic Sea since the 1970s with increasing frequency of sampling over the last decade. Prior to this only few qualitative studies have been carried out, providing insufficient material to estimate conditions from before the intensification of eutrophication in the Baltic Sea to be considered as reference conditions. In the Gulf of Bothnia, the outer coastal areas have not been substantially
impacted by anthropogenic nutrients inputs. Thus the distribution of phytoplankton data from these sites may therefore represent reference conditions. However, adopting this approach for all Finnish coastal waters, summer chlorophyll a reference conditions vary between 1.2 to 3.4 μg l-1. Paleoecological studies from the Laajalahti bay (which is a shallow bay in the south coast of Finland) suggest a reference value for annual summer chlorophyll a of 10 μg l-1. However, this value may not be representative for other shallow bays in southern Finland. In the Kattegat our investigations suggest reference values of approximately 2.1 μg l-1 for the mesohaline coastal waters, although this is only a rough estimate that needs to be supported by other studies.
Using relationships between secchi depths and phytoplankton biomass is a feasible approach to establish reference conditions, given that there are sufficiently longtime
series of historical secchi depth measurements and that other light attenuating
substances would have had trends comparable to that of phytoplankton. In Finnish coastal waters this approach suggests reference conditions from 1.6 to 2.0 μg l-1, i.e. a narrower span compared to the values established from reference sites. Consistent relationships between chlorophyll and secchi depths are found basin-wide in the Baltic Sea, and this approach is an option for establishing reference conditions provided that the underlying assumptions are carefully examined and their implications evaluated.
CARSTENSEN J.;
HEISKANEN Anna-Stiina;
KAUPPILA P.;
NEUMANN T.;
SCHERNEWSKI G.;
GROMISZ S.;
2006-04-20
JRC32856
EUR 21582 EN/2,
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