Significance of External Anthropogenic Nitrogen for Central Baltic Sea (N_CYCLING SIGNAL)

Project leader

Funding source

EU Fifth Framework Programme - Energy, environment and sustainable development

Project Details

Start date: 01/04/2000
End date: 31/03/2003
Funding: 821800 EUR


Problems to be solved The Baltic Sea ecosystem is eutrophied by inputs from the activities of 80 Million people living in its drainage area. Nitrate and ammonia, essential nutrients for plankton growth, are introduced mainly from the farmland along the rivers that drain into the Baltic Sea and via atmospheric deposition. The high nutrient concentrations are a problem for the coastal area as stated by the Helsinki Commission (HELCOM). Far-reaching effects of eutrophication like increased primary production, increased frequency of toxic phytoplankton blooms, oxygen depletion in sediments, and reduced fish stock recruitment (e.g. Baltic Cod) are problems, which demand international initiatives. The "Urban Waste Water Treatment Directive" (Directive 91/271/EEC) strives for better water quality, especially when other countries could be affected by wastewater discharges. The Baltic Sea area is regarded as a particularly sensitive environment in this respect, and the need to treat wastewaters in this region more stringently is evident. The purpose to decrease the input of nitrate, in particular from agricultural sources, is also pursued by the Nitrate Directive (91/676/EEC). Since the directive has failed to be implemented by the member states, it is of utmost importance to assess the impact of the nitrate load that has been dumped during the last years. In the central Baltic Sea nutrient concentrations have been roughly doubled during the last 30 years. Although concentration measurements have been carried out intensively over the last decades in rivers and the open Baltic Sea, it is still difficult to asses the effects of riverine nutrients within the marine environment. Also the establishment of a clear relationship between riverine and atmospheric nitrogen inputs and the increase of nutrients in the open Baltic Sea has so far failed. Scientific objectives and approach The project SIGNAL will develop and test a set of measurements that will enable us to better understand the sources of the riverine nitrogen input to the coastal areas, and the increase of nutrients in the Baltic Proper. A set of naturally occurring stable isotope signals studied here will be useful as a complement to quantitative measurements already carried out by HELCOM. The project will identify the riverine input sources (Objective 1). The isotope signals of N, C and O will be measured in dissolved compounds in the waters from some of the largest Baltic rivers. The atmospheric input representing the second largest nutrient source for the Baltic Sea contains nitrate, nitrous oxides and ammonia mainly originating from fossil fuel combustion and agricultural activities. This nitrogen deposition will also be studied (Objective 2). Expected changes in the river isotope signals after entering the Baltic Sea will be investigated by sampling along coast-open sea transects. The nitrogen input via N2-fixation by cyanobacteria (bluegreen algae) will be estimated too. During the last period of the project data from all rivers, transects and N2-fixation measurements, will be used to assess the role of the external input of nitrogen into the Baltic Proper. The isotopic data from SIGNAL can help to evaluate predictions from present ecosystem models and verify existing estimates of anthropogenic eutrophication effects in the central Baltic Sea. Expected impacts SIGNAL will identify and follow the signals of riverine and atmospheric nitrogen inputs and will thereby contribute to an improved nitrogen budget for the Baltic Proper. Understanding the effect of riverine inputs on the whole ecosystem is a clear improvement over only locally evaluated effects of eutrophication. Therefore, the scientific results of SIGNAL can facilitate decisions that address nutrient reduction of riverine inputs. Since also the atmospheric deposition is investigated, it might even be possible to distinguish between the inputs of nitrogen from sources that are not located within the drainage area of the Baltic Sea. Results of the SIGNAL project might generate a new tool for the evaluation of the environment and management decisions especially for the assessment of eutrophication. Stable isotope measurements are today mainly used for scientific purposes. However, they probably carry detailed information of human impacts and the analysis of isotope compositions might become an important tool to interpret changes within the marine and riverine ecosystems. Since the partners closely co-operate with the local monitoring authorities, the knowledge from the project is directly transferred to decision makers.

External Partners

Last updated on 2017-24-03 at 12:53