Nutrient pollution from ships remains small but not negligible

Helsinki, 27 February (HELCOM Information Service) – The nutrient pollution load originating from the ship borne waste water discharges to the Baltic Sea remains rather small, but not negligible due to the high sensitivity of the marine environment, according to a major new study prepared by Finnish researchers from VTT for the Helsinki Commission. This nutrient load which is concentrated along the shipping routes is immediately available for uptake by the plankton algae adding to the severe eutrophication of the Baltic Sea. 

The results of the study clearly indicate that the main nutrient load to the Baltic Sea derives from waterborne inputs and atmospheric deposition. The ship borne discharges of nitrogen represent approximately 0.05% (469 tonnes) of the total waterborne nitrogen load (744,900 tonnes), and phosphorus load represents approximately 0.5% (156 tonnes) of the total phosphorus load (34,500 tonnes) into the Baltic Sea. In addition, the nutrient load from ships’ exhaust gases corresponds to 6% (16,760 tonnes) of the total annual atmospheric deposition of nitrogen (264,100 tonnes) to the Baltic Sea.

Excessive loads of phosphorus and nitrogen have a detrimental impact on the marine environment. Phosphorus is directly responsible for the mass occurrences of the blue-green algae blooms which form foul-smelling masses and make the water unfit for swimming. In the Gulf of Finland, where although the major phosphorus load comes from land-based sources, as a result of the sharp increase in maritime traffic the annual phosphorus load from ships is currently almost the same as from four Finnish coastal cities - Espoo, Hamina, Kotka, and Porvoo.

Due to the low response rate in port and ship owners’ inquiries, the estimated nutrient load from ship generated sewage was calculated assuming that there is no waste water treatment onboard and all waste waters are discharged into the sea, i.e. theoretical worst case scenario. The calculation included cargo ships (estimated discharge of up to 225 tonnes of nitrogen and 75 tonnes of phosphorus), cruise ships (113 tonnes of nitrogen and 38 tonnes of phosphorus) and passenger/car ferries (131 tonnes of nitrogen and 44 tonnes of phosphorus).

The theoretical worst case scenario mostly applies to cargo vessels and cruise ships. For instance, cruise trips last typically seven days and during that time waste has to be processed. The cruisers can discharge treated sewage directly into the sea, when it is possible according to international regulations. On the other hand, during their short trips major ferries usually collect all waste waters in holding tanks and later utilise the reception facilities provided by ports. Currently most of the passenger ship companies have started to discharge sewage ashore to the municipal sewer network.

The pleasure crafts were not included in the calculations, since no updated information concerning their nutrient load was available. Waste water discharges from pleasure crafts may have local effect on archipelago areas and near coastlines. But the effect of their nutrient load should also be estimated, if the total nutrient load from maritime transport is to be defined. Current HELCOM regulation requires pleasure crafts fitted with toilets to have a toilet retention system in order to be able to deliver sewage to the reception facilities in ports.

According to international regulations (Annex IV of the MARPOL 73/78 Convention), the discharge of sewage into the sea is allowed if the ship is discharging comminuted and disinfected sewage using at a distance of more than 3 nautical miles from the nearest land, or sewage which is not comminuted or disinfected at a distance of more than 12 nautical miles from the nearest land, provided that in any case, the sewage that has been stored in holding tanks shall not be discharged instantaneously but at a moderate rate when the ship is en route and proceeding at not less than 4 knots.

But the nutrient load caused by nitrogen and phosphorus from ships treated sewage is currently not regulated. The standards for ships originated waste water quality concern only Biochemical Oxygen Demand (BOD), total suspended solids and faecal coliforms. Hence, the treated sewage containing some nitrogen and phosphorus that is discharged into the sea increases the nutrient load in the receiving Baltic marine environment.

To eliminate illegal discharges and encourage delivery of ship-generated waste ashore, including oily waste, and as of 1 January 2006 also sewage and garbage, HELCOM has established a “no-special-fee” system for use of port reception facilities. Under this system, ships are not charged for using such reception facilities, costs are instead recovered from general harbour fees or general environmental fees, for instance. Most of the Baltic Sea countries have reported that the coverage of the "no-special-fee" system has already been duly extended in their ports. The increased amounts of wastes now being delivered to the Baltic Sea ports illustrate that more and more ships are delivering their oil wastes to port reception facilities rather than illegally discharging them into the Baltic Sea.

Currently, HELCOM is considering new regulations on wastewater discharges from ships in the Baltic Sea. Among possible additional measures are restrictions for the discharge of sewage from passenger ships into the Baltic Sea, as well as a joint proposal of the Baltic Sea countries to be submitted to the International Maritime Organization (IMO) to amend the existing sewage treatment regulations (Annex IV to the MARPOL 73/78) to cover also nutrients. Future regulations will most likely set new discharge criteria for onboard sewage treatment plants concerning the nutrient concentration in discharged effluent, since the total prohibition to discharge sewage, either treated or untreated, to the Baltic Sea might be difficult to reach. However, a lot of research and development of waste water purification system onboard ship is needed, before the system’s ability to remove nutrients corresponds to the requirements of municipal treatment plants.

Note to Editors: 

The Baltic Marine Environment Protection Commission, more usually known as the Helsinki Commission, or HELCOM, is an intergovernmental organisation of all the nine Baltic Sea countries and the EU which works to protect the marine environment of the Baltic Sea from all sources of pollution. HELCOM is the governing body of the "Convention on the Protection of the Marine Environment of the Baltic Sea Area," known as the Helsinki Convention.

For more information, please contact:

Mr. Nikolay Vlasov

Information Secretary

HELCOM

Tel: +358 (0)207 412 635

Fax: +358 (0)207 412 639

E-mail: nikolay.vlasov@helcom.fi