Description of data and confidence


Data on air- and waterborne nutrient inputs from 1995 to 2012 are used in this indicator (although data on waterborne inputs is also available from 1994). Data reporting has not been perfect and gaps exist in the dataset. For waterborne inputs, the PLC-5.5 project corrected suspicious data and filled in data gaps to establish a complete and consistent dataset (HELCOM, 2013d). Gaps in time series of national air emissions have also been corrected by EMEP experts.​

Waterborne inputs

The dataset behind the present assessment was compiled by the PLC-5.5 project and updated by the Reduction Scheme Core Drafting Group, RedCore DG.

Data on waterborne inputs, water flow and retention are reported by Contracting Parties to the PLC Data Manager and maintained in a PLC-Water database. The database is presently being modernized and updated by the PLUS project to enhance quality assurance and improve the ease of reporting and accessing the data.

There are gaps in time series of national inputs in the PLC database. Therefore PLC experts have amended the dataset used in this assessment to fill in missing and suspicious data. The dataset has been checked and approved for use in this indicator by the Contracting Parties. A description of how data gaps have been filled is given in chapter 1.2 in BSEP 141 and documentation prepared by the PLC-5.5 project.

Data on waterborne inputs are available from 1994-2012 and cover inputs from the entire drainage basin of the Baltic Sea. This indicator, however, only includes data starting from 1995 since atmospheric input data is only available from 1995 onwards.

Inputs are calculated from measurements taken from monitored rivers and point sources as well as calculated estimates or modelled inputs from unmonitored areas. Quality assurance guidelines for sample analysis are described in the PLC guidelines and intercalibration activities are carried out periodically. The most recent intercalibration activity was carried out under the PLC-6 project.

No official information about the uncertainty of inputs of nutrients or organic matter or flow data have been reported to HELCOM yet, but uncertainty estimates are included as a request to be reported by the Contracting Parties in the PLC-6 guidelines. The PLC-5.5 project roughly estimates an uncertainty of 15-25% for annual total waterborne nitrogen and 20-30% on total phosphorus inputs to Kattegat, Western Baltic, the main part of Baltic Proper, Bothnian Bay and Bothnian Sea, and for the remaining parts of the Baltic Sea up to 50% uncertainty. The uncertainty for annual water flow to the above listed sub-basins is estimated to 5-10% for most sub-basins and 10-20% for the remaining ones. For more information see HELCOM 2015.

Further work on how to quantify input uncertainty is required. The QA/QC procedures related to data reporting are being developed in connection with modernizing the PLC database under the PLUS project

Airborne inputs

Atmospheric input data for all Baltic Sea sub-basins are available for the period 1995-2012. Atmospheric transport and deposition of nitrogen compounds are used for modelling atmospheric deposition to the Baltic Sea based on official emission data reported by EMEP Contracting Parties and expert estimates. Atmospheric input and source allocation budgets of nitrogen (oxidized, reduced and total) to the Baltic Sea basins and catchments were computed using the latest version of EMEP/MSC-W model. EMEP/MSC-W model is a multi-pollutant, three-dimensional Eulerian model. It takes into account processes of emission, advection, turbulent diffusion, chemical transformations, wet and dry depositions, and inflow of pollutants into the model domain. Further it includes a meteorological model. A comprehensive description of the model and its applications is available on the EMEP website.

Atmospheric deposition of oxidized and reduced nitrogen was computed for the entire EMEP domain, which includes the Baltic Sea basin and its catchment (Figure 7). Calculations are done annual on data from two years prior to the calculations. For further details see the annual report by EMEP to HELCOM Atmospheric Supply of Nitrogen, Lead, Cadmium, Mercury and Dioxins/Furanes to the Baltic Sea in 2011.

Data on air emissions and atmospheric deposition are maintained by EMEP and can be accessed via the EMEP website.

The results of the EMEP Unified model are routinely compared to available measurements at EMEP and HELCOM stations. The comparison of calculated versus measured data indicates that the model predicts the observed air concentrations of nitrogen within an accuracy of approximately 30%. Further work is required on reducing uncertainties in emission data and better parameterization of physical processes in the EMEP Unified model to increase the accuracy in future model estimates.

No official information about the uncertainty of provided nitrogen emission data have been sent to EMEP from neither EMEP nor HELCOM Contracting Parties, and consequently further work on emission uncertainty is essential. Submitted emissions data are passing through QA/QC procedures and stored in the EMEP Centre for Emission inventories and Projections CEIP in Vienna, Austria. Reviews about the consistency, comparability and trends of national inventories are available at  There are gaps in time series of national emissions that have to be corrected by experts to make the time series complete.

There are limited data on phosphorus deposition and no emission data for the modelling work has been available for evaluation. For most countries, measurements only covered wet deposition and there was a lack of data on particulate and dry deposition. A fixed deposition rate of 5 kg P per km2 to the Baltic Sea has been used in the PLC-5.5 assessment (HELCOM 2015), and the atmospheric phosphorus deposition data and the applied deposition rate is rather uncertain. As atmospheric deposition only constitutes 5-9% of total phosphorus inputs these uncertainties are less critical than in the case of atmospheric deposition of nitrogen, which constitutes 20-25% of total nitrogen inputs to the Baltic Sea. ​

Figure 8.jpg 

Figure 7. The EMEP model domain was used for computations on atmospheric deposition.

Data on actual (non-normalized) riverine flow as well as atmospheric and waterborne inputs of nitrogen and phosphorus are available in an Excel file.​

Confidence of indicator results

The confidence is affected by the certainty of the quality of the nutrient input data, the trend in the inputs and the uncertainty of MAI, in relation to how far the nutrient inputs are from MAI:

The confidence of the assessment is overall high, but can be further detailed as:

  • High for basins with nutrient reduction requirements: nitrogen in Kattegat, Gulf of Finland and Baltic Proper and for phosphorus to Baltic Proper, Gulf of Finland and Gulf of Riga.

  • Moderate for phosphorus to Bothnian Sea and nitrogen to Danish Straits due to limitations in the MAI calculation.

Arrangements for up-dating the indicator

Annual total waterborne inputs of nitrogen, phosphorus and their fractions are reported every year by the HELCOM Contracting Parties and compiled by the PLC Data Manager at the Marine Research Centre, Finnish Environment Institute (MK/SYKE). The data collection is based on a combination of monitored data (measurements at monitoring stations close to river mouth and at point sources) and estimates of inputs from unmonitored areas.

The HELCOM PLUS project is modernizing the PLC database and developing a web application to allow for improved access to the waterborne input data (to be completed in late 2016).

Data on air emissions are reported to EMEP, which subsequently models the atmospheric deposition to the Baltic Sea. EMEP host the emission and deposition data, which can be accessed via their website. EMEP is contracted by HELCOM to provide selected data products on an annual basis.

The Reduction Scheme Core Drafting Group, RedCore DG (and previously the LOAD core group) has in cooperation with Baltic Nest Institute (BNI), Sweden, and Danish Centre for Environment and Energy (DCE), Aarhus University, Denmark elaborated the present core pressure indicator on nutrient inputs. Although the modernized PLC database will improve the quality and access to waterborne input data, there is still no agreed operational procedure for filling in data gaps or carrying out the trend analyses and statistical tests.  ​