Indicator 14.1.a Nitrogen input via the inflows into the North and Baltic Seas

Text from the Indicator Report 2022 

One of the main causes of nitrogen inputs reaching the North and Baltic Seas via inflows is nitrogen surplus in agriculture, which is measured in indicator 2.1.a. Like nitrogen, phosphorus also leads to eutrophication. Phosphorus pollution in rivers is examined separately in indicator 6.1.a.

The calculations for this indicator use monitoring data on nitrogen concentrations and on the discharge volumes of small and major rivers flowing into the North and Baltic Seas, which the German Environment Agency collates as reported by the Länder and by river basin commissions. Data is also included for smaller rivers which do not flow directly into the North or Baltic Sea but are tributaries to larger rivers. In these cases, the data for each river are taken from its last monitoring site before the confluence. The Rhine is also included in the figures, even though its estuary is not in Germany. The data for the Rhine were recorded at the point where it leaves Germany (monitoring site at Bimmen, Kleve).

The nitrogen concentrations for each river are weighted for discharge volume, so that major rivers which discharge large qualities of water have a greater influence on the average that smaller ones. To prevent the graph being distorted by single extreme events like floods or droughts, which can result in anomalously very high or very low nitrogen inputs, the values are depicted as a five-year moving average.

The average nitrogen concentration for all North and Baltic Sea inflows, weighted for discharge volume, has followed a downward trend since the beginning of the time series, with the reduction in concentration more marked for the North Sea than the Baltic. The 2016-2020 average for the North Sea inflows was a concentration of 2.8 mg/l and reached jointly the target value for the first time. For rivers flowing into the Baltic Sea, the average concentration was 3.1 mg/l for the same period and, thus, exceeded the upper limit of 2.6 mg/l.

In contrast to the aggregated indicator 14.1.a “Nitrogen inputs via the inflows into the North and Baltic Seas”, each river by itself has to meet the management target to achieve good quality, as defined by the Ordinance on the Protection of Surface Waters. The target is neither achieved for the North Sea nor the Baltic Sea.

Of the three major inflows into the Baltic Sea, the Peene, the Trave and the Warnow, only the latter had already reached the management target by 2016-2020. Nevertheless, Peene and Trave showed a small reduction in concentration across the five-year averages by 0.1 mg/l. In some of the smaller Baltic Sea inflows, concentrations of nitrogen are still several times higher than the management target, with values of up to 5.9 mg/l, and the target was only reached by a quarter of the smaller Baltic Sea inflows.

Of the North Sea inflows, only the Rhine met the management target in the period 2016 to 2020, and, hence, was mainly responsible for the joint achievement of the weighted for discharge volume target value. The five-year averages of nitrogen concentrations decreased for all major North Sea inflows (Ems, Weser, Rhein and Eider) by 0.1 to 0.2 mg/l, except for the Elbe. A slight decline was also measured by the five-year averages of nitrogen concentrations for the small North Sea inflows. Accordingly, the values were between 2.6 mg/l and 3.5 mg/l in the period from 2016-2020.

The synoptic table provides information about the evaluation of the indicator in previous years. It shows if the weather symbol assigned to an indicator was rather stable or volatile in the past years. (Evaluation of the Indicator Report 2022 )

Indicator	14.1.aa Nitrogen input via the inflows into the Baltic Sea
Target	Adherence to good quality in accordance with the Ordinance on the Protection of Surface Waters (Oberflächengewässerver-ordnung) (annual averages for total nitro-gen in rivers flowing into the Baltic may not exceed 2.6 mg/l)
Year	2017	2018	2019	2020
Evaluation

Indicator	14.1.ab Nitrogen input via the inflows into the North Sea
Target	Adherence to good quality in accordance with the Ordinance on the Protection of Surface Waters (annual averages for total nitrogen in rivers flowing into the North Sea may not exceed 2.8 mg/l)
Year	2017	2018	2019	2020
Evaluation