Technical data

Data source: Most of the monitoring data representing the status for the period 2001-2006 originate from the HELCOM Cooperative Monitoring in the Baltic Marine Environment Programme (HELCOM COMBINE), and partly also from national monitoring and assessment activities. They were summarized during the preparation of the thematic assessment “Eutrophication in the Baltic Sea – an integrated thematic assessment of the effects of nutrient enrichment in the Baltic Sea region” (HELCOM, 2009).

Background values and acceptable deviation (normally 50%) used for the description of Ecological Quality Status are also taken from HELCOM (2009).

Data used for the temporal trend assessment of nutrient concentrations are from the Baltic Environmental Database (BED), which includes both HELCOM COMBINE monitoring data and historical measurements (http://nest.su.se/Models/bed.htm) as well as from the IOW data base.

Description of data: The unit of the measurements is µmol/l. Nutrient measurements are one of the key eutrophication parameters since the beginning of the HELCOM monitoring programme.

Geographic coverage: All regions of the Baltic Sea. All in all 189 stations/regions were used, c.f. HELCOM (2009).

Temporal coverage: Most of the available data are covering the period 1970 or later to date. Several measurements are available for the 1950s and 1960s.

Methodology and frequency of data collection: Data were mainly collected by HELCOM’s and national monitoring programmes.

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 nutrient concentration assessments were first defined by a group of national experts from the HELCOM Contracting Parties for the HELCOM thematic assessment on eutrophication (HELCOM 2009a). 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).

For the description of nutrient trends in the surface layer normally the winter period is used. Whereas for the long-term trends (Figs. 2 and 4) uniformly the period December-March was used, the winter period describing the period 2001-2006 differs regionally.

Reference conditions can be derived from: i) reference sites, ii) historical data, iii) modelling and iv) expert judgement. However, they are mostly based on historical data and modelling, since reference sites no longer exist in the Baltic Sea and the use of expert judgement is always dubious and less transparent (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: Nutrient measurements are performed over several decades by internationally well accepted standard methods which are documented in HELCOM’s COMBINE manual. The comparability is secured by numerous international intercomparison exercises (f.e. Quasimeme during recent times).

For the purpose of the eutrophication assessment any suitable parameter could be used aiming to have an assured evaluation. For the Nutrient Indicator Fact Sheet this is a disadvantage. Mostly, DIN was reported, in some cases also nitrate or nitrate+nitrite, which of course form the largest part of DIN. For some locations only TP and TN were reported. These location could not be included in the report.

Further work required: The indicator will be updated annually. Therefore, the continuation of data collection is mandatory for as many temporal and spatial points as possible in all sub-regions.

References

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.

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Last updated: 4 May 2010