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Algal forecast: considerable risk of blue-green algal blooms in some of Finland's sea areas

Press release 2015-06-05 at 10:00

According to the algal forecast from the Finnish Environment Institute’s (SYKE) Marine Research Centre for the current year, the risk of blue-green algal blooms is considerable in the entire western Gulf of Finland, the southern areas of the Finnish Archipelago Sea and the northern part of the Baltic Sea's main basin. In the southern parts of the Bothnian Sea and the eastern Gulf of Finland the risk is moderate. Meanwhile in the Bothnian Bay, the northern parts of the Bothnian Sea and in the easternmost part of the Gulf of Finland the risk of blue-green algal blooms is low.

Map of algal forecast for 2015
 

Forecast for the Gulf of Finland worse than the previous year

The probability of extensive blue-green algal blooms is higher than it was last year particularly in the Gulf of Finland and the southern Bothnian Sea. The reason behind this is the fact that the phosphate phosphorus concentrations of the surface layer have risen compared to the situation in winter last year. Poor oxygen conditions have increased phosphate release from the sea floor in the main basin. This deep water mass has flown to the Gulf of Finland, where it has mixed with the upper water layers as a result of winter storms. The nutrient situation will enable heavier algal blooms in the Gulf of Finland over the coming summer, provided that the weather conditions are favourable.

Compared to last winter, phosphorus concentrations have also increased in the Åland Sea and the Bothnian Sea. The reason behind this is the flow of phosphorous-rich water from the Baltic Sea's main basin into the Gulf of Bothnia. Phosphorous concentrations in the Baltic Sea's main basin remain considerably high as they have in previous years.

Blue-green algae may form various toxins and substances that cause skin irritation, so heavy algal blooms should always be treated with caution. The bloom period of blue-green algae in Finland's sea areas usually peaks in late July and early August, though in some areas blooms may continue well into autumn. The formation of algal blooms is facilitated by calm and warm weather.

Basis for the risk assessment

The blue-green algal bloom forecast is based on estimates performed using the ecosystem model in use at the Finnish Environment Institute (SYKE). The model's source data consists of nutrient concentrations measured during monitoring cruises carried out during the previous winter. Since it is impossible to reliably predict the weather conditions of the coming summer, the assessments are based on known sea current, wind and temperature conditions over five selected years, as well as changes in nutrient concentrations during the spring.

The expert assessment also considers the uncertainty issues of the model and draws on the experience of former forecasts and accumulated observational data from previous years. The forecast is most reliable at predicting the risk of algal blooms in open sea areas. The drift of algal blooms formed on the open seas to coastal areas is largely dependent on the prevailing winds and sea currents. In the coastal areas of the Gulf of Finland and the Bothnian Sea, and in the Finnish Archipelago Sea, the risk of algal blooms varies based on local sources of nutrient load, sea currents and depth ratios.

Major Baltic inflow not yet affecting the prognosis

The major Baltic saline water inflow arriving from the North Sea at the beginning of the year was evident in the winter in the deeps of the southern Baltic Sea. In the Arkona and Bornholm Basins, the salinity of water near the seabed is at present close to 25‰ in parts, whereas the level last winter was approximately 15‰ or less. The oxygen levels of water near the seabed have improved in these deeps as a result of oxygen-rich water brought in by the inflow. According to the results of the Swedish Meteorological and Hydrological Institute (SMHI), the major Baltic inflow had reached the Gotland basin during the spring. As it proceeds to the deeper parts of the Baltic Sea, the inflow displaces the old, low-oxygen and nutrient-rich deep water. However, the potential effects of this mixing of water masses on the algal situation will not become evident in the Finnish sea areas until after the following winter.

Regular monitoring on algal blooms starting

Starting this week and continuing until the end of August, the Marine Research Centre of the Finnish Environment Institute (SYKE) will provide weekly updates on Thursdays on the algal situation in Finland's sea areas. Should it be necessary, the monitoring will take place more frequently.

More information

Algal prognosis
Leading Researcher Harri Kuosa, Finnish Environment Institute SYKE, tel. +358 295 251 106, firstname.lastname@ymparisto.fi

The state of the Gulf of Finland and the Baltic Sea
Senior Research Scientist Mika Raateoja, Finnish Environment Institute SYKE, tel. +358 295 251 536, firstname.lastname@ymparisto.fi
Senior Research Scientist Seppo Knuuttila, Finnish Environment Institute SYKE, tel. +358 295 251 286 firstname.lastname@ymparisto.fi


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