Data source: The HELCOM countries have provided average status concentrations for 2003-2007. The open sea chlorophyll-a concentration measurements were made during research and monitoring cruises of the HELCOM contracting parties. The data is kept at the database of the Finnish Environment Insitute SYKE, where the contact person is Vivi Fleming-Lehtinen.
Description of data: The unit of the measurements is µg/l (microgrammes per liter).
Geographical coverage: All regions of the Baltic Sea.
Temporal coverage: From 1979 to 2007.
Methodology and frequency of data collection: Measurements have been made on irregular research cruises and during monitoring cruises.
Methodology of data analyses: The status of the Baltic Sea according to the described indicator has been classified using the multi-metric indicator-based HELCOM Eutrophication Assessment Tool (HEAT). Each area was assessed using information on reference conditions (RefCon) and acceptable deviation from reference condition (AcDev) combined with national monitoring data from the period 2003–2007. The basic assessment principle is RefCon ± AcDev = EutroQO, where the latter is a "eutrophication quality objective" (or target) corresponding to the boundary between good and moderate ecological status. When the actual status data (average for 2003-2007) exceeds the EutroQO or target, the areas in question is regarded as affected by eutrophication.
The Ecological Quality Ratio (EQR) is a dimensionless measure of the observed value (AcStat) of an indicator compared with the reference value (RefCon). The ratio is equal to 1.00 if actual status is better than or equal to reference conditions and approaches 0.00 as deviation from reference conditions becomes large. The value of EQR is used to assign a quality class to the observed status. The classes in descending order of quality are RefCon, High, Good, Moderate, Poor, Bad. The central definition of the quality classes is given by the value of acceptable deviation (AcDev).
The RefCons and AcDev values for the chlorophyll-a concentration assessment were first defined by a group of national experts from the HELCOM Contracting Parties for the HELCOM thematic assessment on eutrophication (HELCOM 2009). The first assessment was based on identifying the status for the period 2001-2006, including data from coastal areas. This assessment covers the period 2003-2007.
For a complete explanation of the methodology used, please see Andersen et al (2010) and thematic integrated assessment on eutrophication of the Baltic Sea (HELCOM 2009).
The months of June, July, August and September were chosen to represent the period of abundant occurrence of cyanobacteria.
Reference conditions for the open Baltic sub regions were determined by combining information obtained from the means of the data collected between 1979 and 1980, through modeling work (Schernewsky & Neumann) and using scientific judgement. In coastal and transitional sights also other statistical methods were used. The target value was set at a 50% deviation from the reference conditions as calculated for the HELCOM integrated thematic assessment on eutrophication of the Baltic Sea (HELCOM 2009).
The eutrophication status maps were produced by spatially interpolating the values for the areas listed in the data table. ArcGIS 9.3.1 was used to interpolate the open and coastal areas. The coastal areas interpolation was delimited by a 6 nautical miles buffer along the coastline. The result was then joined to the open sea areas and the final map was processed to add a smoother transition between coast and open sea areas.
Strength and weaknesses of data: Practically the method is unchanged, although the reliability of the laboratory analyses may vary over time. The temporal and spatial coverage of the data is not even. In addition, timing of the measurements in relation to the cyanobacterial biomass maximum may have an effect on the results, especially if the amount of data is low.
Reliability, accuracy, robustness, uncertainty (at data level): Interpretation of the data ought to be done over long time periods (minimum of five years).
Further work required (for data level and indicator level): The indicator will be updated annually with data collected from as many temporal and spatial points as possible in each of the sub-areas.
Andersen, J.H., P. Axe, H. Backer, J. Carstensen, U. Claussen, V. Fleming-Lehtinen, M. Järvinen, H. Kaartokallio, S. Knuuttila, S. Korpinen, M. Laamanen, E. Lysiak-Pastuszak, G. Martin, F. Møhlenberg, C. Murray, G. Nausch, A. Norkko, & A. Villnäs. 2010. Getting the measure of eutrophication in the Baltic Sea: towards improved assessment principles and methods. Biogeochemistry. DOI: 10.1007/s10533-010-9508-4.
HELCOM 2009. Eutrophication in the Baltic Sea – An integrated thematic assessment of the effects of nutrient enrichment in the Baltic Sea region. Helsinki Commission. Baltic Sea Environment Proceeding No. 115B.
Schernewski, G. and Neumann, T. 2005. The trophic state of the Baltic Sea a century ago: a model simulation study. Journal of Marine Systems 53:109-124.
Last updated: 26 May 2010