Import–export balance of nitrogen and phosphorus in food, fodder and fertilizers in the Baltic Sea drainage area Eero Asmala a, ⁎, Laura Saikku b , Sanna Vienonen c a Finnish Environment Institute, Marine Research Centre, P.O. Box 140, FI-00251 Helsinki, Finland b University of Helsinki, Faculty of Biological and Environmental Sciences, P.O. Box 65, FI-00014 University of Helsinki, Finland c Finnish Environment Institute, Freshwater Centre, P.O. Box 140, FI-00251 Helsinki, Finland abstract article info Article history: Received 31 December 2010 Received in revised form 5 August 2011 Accepted 15 August 2011 Available online 9 September 2011 Keywords: Baltic Sea Eutrophication Phosphorus Nitrogen International trade Food production Nitrogen (N) and phosphorus (P) are essential elements for life, but in excess they contribute to aquatic eutro- phication. The Baltic Sea is a brackish semi-enclosed sea that is heavily influenced by anthropogenic loading of nutrients, resulting in a major environmental problem, eutrophication. In this study, the nutrient balance of the food production and consumption system in seven countries in the Baltic Sea drainage area was quantified for the period 2002–2005. The food production and consumption system accumulates nutrients in the Baltic Sea drainage area, due to extensive imports to the system. The average annual net surplus of nutrients was 1 800 000 tons N and 320 000 tons P in 2002–2005, or annually 28 kg N and 5 kg P per capita. The average total annual import was 2 100 000 tons N and 340 000 tons P during 2002–2005. The largest imports to the system were fertilizers, totaling 1 700 000 tons N and 290 000 tons P. Traded nutrients in food and fodder amounted to a net annual surplus of 180 000 tons N and 25 000 tons P. The nutrient load to the Baltic Sea due to the food consumption and production system was 21% N and 6% P of the respective annual net inputs to the region. This study shows that large amounts of nutrients to Baltic Sea drainage area are inputs from outside the region, eventually contributing to eutrophication. To reduce the nutrient imports, fertilizers should be used more effi- ciently, nutrients should be recycled more efficiently inside the region, and food system should be guided toward low-nutrient intensive diets. © 2011 Elsevier B.V. All rights reserved. 1. Introduction For life on Earth, nitrogen (N) and phosphorus (P) are indispensable elements. They are essential components of e.g. macromolecules aden- osine triphosphate and deoxyribonucleic acid (ATP and DNA), which carry energy and genetic information in living cells. Both nitrogen and phosphorus have been used in continuously increasing amounts as fer- tilizers in agricultural production, which in turn has been increasing the nutrient runoff to aquatic environments globally (Compton et al., 2000; Galloway et al., 2004). While their biogeochemistry differs greatly, N and P enrichment are the cause of eutrophication problems encoun- tered in many freshwater and estuarine and marine systems However, the biogeochemistry of nitrogen and phosphorus differs substantially (Vitousek et al., 2003; Filippelli, 2008). The Baltic Sea is a unique brackish water environment, with a salinity ranging from freshwater toward oceanic salinities (mean salinity 7 psu). The Baltic Sea is also a small water body due to its shallowness — its mean depth is only 54 m (Leppäranta and Myrberg, 2009). These physical properties combined with the influence of the about 90 million inhabitants of 14 countries in the 1720000 km 2 drainage basin result in high anthropogenic pressure on the environment and nonuniform eco- logical responses, e.g. to nutrient loading (Tamminen and Andersen, 2007). The interplay of the two elements examined in this study, nitro- gen and phosphorus, is highly pronounced in the Baltic Sea eutrophica- tion (Conley et al., 2009a). Eutrophication, i.e. the process of ecological response to the enrichment of growth-limiting nutrients (specifically ni- trogen and phosphorus) is considered to be the single greatest threat to the Baltic Sea environment (Elmgren, 2001; HELCOM, 2009). Nutrient enrichment leads to increased primary production, which in turn has consequences as alterations in species structure, biodiversity and recre- ational values (Rönnberg and Bonsdorff, 2004). The low-saline northernmost part of the Baltic Sea, Gulf of Bothnia exhibits strong phosphorus deficiency in primary production, while the almost oceanic saline waters of the Danish Straits are limited by the availability of nitrogen (HELCOM, 2009). Hence, current trends in combating eutrophication emphasize the need for reducing the load of both nitrogen and phosphorus (Howarth and Marino, 2006; Conley et al., 2009a; Paerl, 2009).In the Baltic Sea, there are also internal pro- cesses leading to changes in the budgets of bioavailable nutrients, such as binding of phosphorus to sediment particles and release of gas- eous nitrogen to the atmosphere via denitrification (Gunnars and Science of the Total Environment 409 (2011) 4917–4922 ⁎ Corresponding author at: Marine Research Centre, Finnish Environment Institute (SYKE), Erik Palménin aukio 1, P.O. Box 140, FI-00251 Helsinki, Finland. E-mail address: eero.asmala@ymparisto.fi (E. Asmala). 0048-9697/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.scitotenv.2011.08.030 Contents lists available at SciVerse ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv