net input from a country to a basin comprises of the waterborne inputs
discharging from that country to the Baltic Sea plus the net nutrient transboundary
inputs to downstream countries and subtracted net nutrient inputs received from
upstream countries, plus, in case of nitrogen, the proportion of the airborne
inputs to Baltic Sea caused by emissions in the country.
EMEP models the atmospheric deposition attributed to emissions from Eurasian countries and some other sources. Thus, the contribution from each HELCOM country, international shipping on the Baltic Sea and other sources to the atmospheric deposition to each basin is readily obtained from the EMEP data. In addition, EMEP performs a normalization procedure so that natural variability that occurs due to interannual differences in wind and precipitation patterns is removed and thereby results of changes in nitrogen emissions can be identified with shorter time-series.
Annual inputs from rivers and coastal direct point sources are provided to the PLC database by the HELCOM countries based on monitoring and modelling. In addition to the reported data, corrections and filling of gaps due to missing data were performed within the PLC 5.5 project for data 1994-2010. Gaps in data for 2011 and 2012 were filled using the same methodology.
Some rivers are crossing country borders and therefore the nutrient inputs to the Baltic Sea from these rivers are originating also from these upstream countries. These contributions are denoted transboundary inputs. In the preparation of the country allocation calculations behind the 2013 Ministerial Declaration, data on inputs at the borders were collected and combined with estimates of the retention in the rivers downstream the borders to estimate the contributions of transboundary inputs. For the present follow-up it has not been possible to update this calculation in-depth, instead it has been assumed that the upstream transboundary inputs have had the same trend as the total waterborne inputs discharging from the downstream country. In
future, it will be important to use accurate time-series of measured
transboundary inputs at the border from
upstream countries where transboundary inputs constitute a major or perhaps
even the only contribution to a sub-basin for a Contracting Party e.g. as
Lithuania to Gulf of Riga. In such a case, if the upstream transboundary inputs
have a different trend than the total waterborne inputs discharging to a
downstream country, the evaluation of fulfilment of CART might possiblly have
been different compared with the result based on the assumption used in the
The riverine inputs are flow normalized according to generally accepted procedures (Larsen & Svendsen, 2013). The aim of the flow normalization is to remove interannual variations in nutrient inputs that are caused by natural variations in water flow.
In the 2013 Ministerial Declaration, the transboundary inputs from Germany via Odra through Poland and from Finland via Vuoksi and subsequently Neva through Russa are mentioned separately (Table 1). The trends in these inputs are not evaluated separately though because they are estimated in the quite crude manner described above. However, in Tables 7 and 8, the values used to calculate the national inputs are presented for the reference period and for the latest 3 years (column transboundary). These transboundary inputs are deducted from the inputs through Poland and Russia, respectively.