Work due 01 Jan 2013

Medium - term work: 

It is necessary to get access to more data, in terms of better spatial coverage and longer time series, in order to improve the assessment. In order to obtain longer time series it is also important that data is associated with unique station identifiers such that observations within a specific area can be merged. Indicators could make use of salinity data at stations as co-variate in order to compensate for inter-annual variations in salinity.
Other methodological aspects that require improvement are: a) analytical methods to determine chlorophyll b) definition of the growing season, c) classification and geographical aggregation.

a) Analytical methods:
For the assessment of chlorophyll-a concentrations, different analytical methods are generally used. Although these different analytical methods generally give comparable results with reasonable to good correlations between methods, simple fluorometric and photometric methods are less accurate and therefore may be a source of uncertainty. It is recommended to include a description of analytical methods to determine chlorophyll and to account for different analytical methods in the trend analysis.

b) Definition of the growing season:
In the current application, two growing seasons are distinguished, one for the northern part of the Baltic Sea (June-September) and one for the southern part of the Baltic Sea, the North Sea, NE Atlantic waters, Mediterranean and Black Sea (May-September). It is questionable whether using one growing season for all waters that range geographically from the Mediterranean, the Black Sea to the North Sea and Baltic Sea, is appropriate. Moreover, currently only surface concentrations are considered. However, in the Black Sea, not only do the chlorophyll concentrations show peaks in late winter, late spring and autumn, these peaks do not only occur at the surface but also in subsurface layer (BS SoE, 2008). It is therefore recommended to revise the definition of the summer period to a definition of the phytoplankton growing season that takes into account the differences between regional seas, for instance by applying the seasonal periods that were defined for the WFD.

c) Classification and geographical aggregation:
In the current trend analysis stations are aggregated per country, and there is no distinction between sampling stations that are strongly influenced by anthropogenic eutrophication (e.g. transitional and coastal waters) and sampling stations that are not or only to a minor extent influenced by eutrophication. It is therefore recommended to replace the classification system per regional sea by a classification system that accounts for the geographical differences within the seas. As the implementation of the MSFD is still in progress, a future option might be to apply the environmental targets that are being developed under the MSFD.

• Access to more data in terms of spatial coverage and time series
• Data associated with unique station identifiers

• Documentation of the analytical method used in the analyses
• Reassess definition of growing season in different geographical areas
• Streamlining class boundaries with boundaries defined as part of European water policies