This summer we have again had to state the weak situation of the Baltic Sea. Blue-green algae blooms have taken over the beaches. As we know, blue-green algae blooms are caused by the fact that the nutrients they need, especially nitrogen and phosphorus, have flowed into the Baltic Sea too much for decades.
To our delight, the nutrient load flowing into the Baltic Sea has been halved in the last 40 years. However, the seabed still has nutrients for the growth of algae for decades. In addition to blue-green algae, the nutrients cause oxygen loss to the seabed, which then kills fish and other bottom animals.
Nutrients still end up in considerable quantities in the sea. By far the biggest polluter is agriculture, which produces 70-90 percent of nitrogen and 60-80 percent of phosphorus emissions (source 2). Other significant sources of emissions are housing and industry, forestry and fish farming, and nitrogen from car traffic. Marine traffic also causes nitrogen and phosphorus emissions along with gray and black waters and food waste. In addition, nutrients are washed into the sea during the loading and unloading of fertilizers in ports.
Figure 1. Emissions of nitrogen and phosphorus into the Baltic Sea have already decreased over the last 40 years (source 1)
Passenger car ferries operating in Finland have been leaving their gray and black water ashore for years. In addition, according to the regulations, all other passenger ships, such as cruise ships, must nowadays treat their toilet waste water or leave it in reception facilities in ports. However, cargo ships are allowed to release their black and gray water into the sea – some cargo ships even leave it ashore.
In recent years, we have studied how much cargo ships release nutrients into the Baltic Sea. It was a case study, that is, we carefully studied one port and its surroundings, in this case Port of HaminaKotka.
We noticed that the share of emissions from the black and gray waters of cargo ships arriving at that port is only a small fraction of the total nutrient load in the area. Cargo ships produced 781 kg of nitrogen and 134 kg of phosphorus in their waste water during their journeys to the port, which corresponds to only 0.06% phosphorus and 0.01% nitrogen of the total load in the area. (source 3)
In another study, we also found out what part of the fertilizers from ships visiting HaminaKotka ended up in the sea during loading or unloading. Compared to the total nutrient emissions in the area, mainly the agricultural emissions coming along the river, the nutrient emissions from loading and unloading in the port were about 4 percent for nitrogen and 0.1 percent for phosphorus of the total emissions. (source 4)
According to the study, the effect of waste water from cargo ships on the eutrophication of the Baltic Sea is therefore smaller than previously thought – mainly because the emissions caused by agriculture are so large. It must be remembered that these results only apply to the port of HaminaKotka. But of course they give some sort of picture of the general nutrient load caused by sea transport. Nutrients from ships’ black and gray waters are spread around the Baltic Sea, but nutrients from fertilizer loading end up in one place.
Although the share of nutrients ending up in the Baltic Sea from cargo ships and port operations is small, it is still too much. It is important that the loading and unloading of ships in ports is developed so that as little as possible ends up in the sea. In addition, cargo ships’ black and gray waters must be treated either with systems on board or on land.
Regarding waste water, what makes it interesting is that according to our research, only 0.5% of cargo ships left their waste water in the port, even though there is not even an additional bill for waste water. Is it just a matter of indifference or is their reception at the ports deficient? Is wastewater mainly treated in ships and therefore leaving it in the harbor is considered pointless? On the other hand, we know that ships’ water treatement systems have a large variety and their efficiency varies greatly.
A law is currently being prepared that prohibits all ships from discharging waste water, even treated water, into Finnish territorial waters. However, before enacting the law, it would be good to conduct more research in order to evaluate the efficiency of the ships’ wastewater treatment systems in reducing nitrogen and phosphorus emissions into the sea, and to specify the amount of treated and untreated wastewater. Are ships’ water treatement systems really all so ineffective that all ships must leave their waste water ashore? In addition, the composition and environmental effects of other pollutants in wastewater, such as bacteria and pharmaceutical residues, require further research.
This blog has been written together with Suvi-Tuuli Lappalainen, PhD student at the Estonian Maritime Academy.
The article was previously published in Finnish in Navigator Magazine, an online magazine for maritime professionals, on August 19, 2024.
Sources:
- HELCOM Thematic assessment of eutrophication 2016-2021. Baltic Sea Environment Proceedings 192. https://helcom.fi/post_type_publ/holas3_eut/
- Raudsepp, U.; Maljutenko, I.; Kõuts, M.; Granhag, L.; Wilewska-Bien, M.; Hassellöv, I.-M.; Eriksson, K.M.; Johansson, L.; Jalkanen, J.-P.; Karl, M.; et al. Shipborne nutrient dynamics and impact on the eutrophication in the Baltic Sea. Sci. Total Environ. 2019, 671, 189–207. https://doi.org/10.1016/j.scitotenv.2019.03.264.
- Lappalainen, S.-T.; Tapaninen, U.; Kotta, J. Nitrogen and Phosphorus Discharges from Cargo Ships’ Black and Grey Waters—A Case Study of a Baltic Sea Port. Oceans 2024, 5, 560-570. https://doi.org/10.3390/oceans5030032
- Lappalainen, S-T.; Kotta, J.; Tombak, M-L.; Tapaninen, U. Using Machine Learning Methodology to Model Nutrient Discharges from Ports: A Case Study of a Fertilizer Terminal. J. Mar. Sci. Eng. 2024, 12, 143. https://doi.org/10.3390/jmse12010143.
Tales of Talsinki 