Modelling marine and coastal eutrophication
Eutrophication has the growing attention of the regional and international community, and has been studied extensively during the past decades. The quality of marine waters is monitored continuously by means of water samples (in-situ data) and satellite observation. A remaining challenge is to improve the scientific guidance of management strategies to reduce eutrophication in the marine environment. Scientific simulation models of eutrophication processes are valuable tools used to aid scientific understanding in addition to field and satellite data and to guide management decisions. Models can be used to analyze the causes and consequences of eutrophication and predict bloom events. Integrated models are the first choice, because eutrophication is the result of complex interactions between human activities, hydrodynamics, and ecological processes.
Case study: modelling within the ISECA project
European countries have committed themselves to the OSPAR Convention of 1992, with the objective to reduce the input of nutrients coming from different sources such as agriculture, industry, waste water by 50% compared to the 1985 level. Another objective is to achieve a water quality which is not exceeding a level which is 50% above the minimum level corresponding to the pristine situation without human interference. Data models can be useful because they have the potential to enhance assessments of eutrophication and contribute in forecasting future impacts of different management strategies on marine water quality:
With models it is possible to find out which sectors contribute most to the loading of nutrients to the coastal waters under various scenarios (e.g. reductions in the size of the cattle stock, less use of fertilizers, or a combination,...). We can also compare the risk of a spring algal bloom, for example in the 2Seas marine waters, for 70% reduction in the nutrient loading by looking at the result on the eutrophication during the winter months:
The figure is a simulation of average winter values of dissolved inorganic nitrogen, an indicator for nutrient enrichment, in the Belgian Coastal Zone without (left) and with (right) 70% reduction nitrogen loading from the Scheldt catchment.
Some proportion of the nutrients responsible for the growth of algae in coastal waters are due to pollutants emitted from human activity in cities, land and sea transport networks and industry. Transported by the wind, they reach the coast where they may be deposited with the help of rain over several months preceding algal bloom events. To demonstrate the effect of atmospheric transport of algal nutrients to the coastal waters computer models can be used that are comprised of three elements: the physics of species transport and deposition, the sources responsible for the emissions and the weather data (wind speed and direction, rainfall, temperature, etc...). The picture below shows an interim simulation result from a combined model of the coarse weather data with the fine emissions set. Calculated quantities of nitrogen oxides deposited over the 2Seas region in April 2009 are shown as colour contours. It can be seen that most strongly affected by such atmospheric deposits are the coastal waters of the Netherlands (which also see the highest riverine input!) followed by the Eastern English Channel which receives input not only from the neighbouring land but also from shipping.
Emissions of nitrogen oxides, source EMEP:www.ceip.at
Contours of deposited nitrogen oxides in the 2Seas region. The circles represent urban centres
- Georgi Djambazov (2013). Atmospheric modelling for ISECA. Project communication doc.
- Jean-Luc de Kok (2013). Modelling marine and coastal eutrophication. Project communication doc.
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