Baltic Sea Environment Proceedings No. 115B Eutrophication in the Baltic Sea An integrated thematic assessment of the effects of nutrient enrichment in the Baltic Sea region Helsinki Commission Baltic Marine Environment Protection Commission Baltic Sea Environment Proceedings No. 115B Eutrophication in the Baltic Sea An integrated thematic assessment of the effects of nutrient enrichment in the Baltic Sea region Helsinki Commission Baltic Marine Environment Protection Commission Published by: Helsinki Commission Katajanokanlaituri 6 B FI-00160 Helsinki Finland http://www.helcom.fi Authors Jesper H. Andersen and Maria Laamanen (Eds.), Juris Aigars, Philip Axe, Mats Blomqvist, Jacob Carstensen, Ulrich Claussen, Alf B. Josefson, Vivi Fleming-Lehtinen, Marko Järvinen, Hermanni Kaartokallio, Seppo Kaitala, Pirkko Kauppila, Seppo Knuuttila, Leonid Korovin, Samuli Korpinen, Pekka Kotilainen, Aiste Kubiliute, Pirjo Kuuppo, Elżbieta Łysiak-Pastuszak, Georg Martin, Günther Nausch, Alf Norkko, Heikki Pitkänen, Tuija Ruoho-Airola, Roger Sedin, Norbert Wasmund and Anna Villnäs. For bibliographic purposes this document should be cited as: HELCOM, 2009 Eutrophication in the Baltic Sea – An integrated thematic assessment of the effects of nutrient enrichment and eutrophication in the Baltic Sea region. Balt. Sea Environ. Proc. No. 115B. Information included in this publication or extracts thereof are free for citing on the condition that the complete reference of the publication is given as stated above. Copyright 2009 by the Baltic Marine Environment Protection Commission – Helsinki Commission – Language revision: Janet F. Pawlak Design and layout: Bitdesign, Vantaa, Finland Photo credits: Front cover: Maija Huttunen, SYKE, Finland; SMHI, Sweden; Kristine Garde, DHI, Denmark; Bjarne Andresen, Fyn County, Denmark; Page 12: Samuli Korpinen, HELCOM; Page 16: Kristine Garde, DHI, Denmark; Page 17: Peter Bondo Christensen, NERI, Denmark; Christensen Jensen, MCA, Denmark; Page 18: Metsähallitus, Finland; Page 16: Page 28: Philip Axe, SMHI, Sweden; Page 31: Maria Laamanen, HELCOM; Page 35: Maija Huttunen, SYKE, Finland; Markku Viitasalo, SYKE, Finland; Page 37: Jouni Vainio, FMI, Finland; Metsähallitus, Finland; Page 50: Georg Martin, Estonian Marine Institute, Estonia; Page 59: Philip Axe, SMHI, Sweden; Søren Larsen, Fyn County, Denmark; Page 62: Jan-Erik Bruun, SYKE, Finland; Page 66; Maria Laamanen, HELCOM; Page 83: Seppo Knuuttila, SYKE, Finland; Page 84: Maija Huttunen, SYKE, Finland; Page 89: Elena Bulycheva; Page 93: Samuli Korpinen, HELCOM; Page 96; Maria Laamanen, HELCOM; Page 99; Minna Pyhälä, HELCOM; Page 100; Maria Laamanen, HELCOM; Page 104, 109: Samuli Korpinen, HELCOM; Page 113: SMHI, Sweden; Maria Laamanen, HELCOM; Tiina Paalme, Estonian Marine Institute, Estonia, Nanna Rask, Fyn County, Denmark; Christen Jensen, MCA, Denmark; Page 114: Samuli Korpinen, HELCOM; Page 118: Nikolay Vlasov, HELCOM; Page 120: Bjarne Andresen, Fyn County, Denmark. Number of pages: 148 Printed by: Erweko Painotuote Oy, Finland 2 ISSN 0357-2994 PREFACE The environment of the Baltic Sea is unique and This report describes and documents the degree fragile. Pollution, fi shing, physical modifi cations, and effects of nutrient enrichment and eutrophi- and other human activities exert pressure on a cation in the Baltic Sea including the Kattegat/ large variety of marine habitats and species. The Belt Sea area. The objectives of this eutrophication populations of the countries bordering the Baltic assessment are: Sea are concerned about its environmental status. • To defi ne the issue, by answering the questions: Because most of the threats are trans-boundary, ‘What is nutrient enrichment and eutrophica- solutions must be trans-national. Therefore, the tion?’ and ‘How are nutrient loads, nutrient con- Baltic Sea countries have joined forces in order centrations, biological quality elements and other to safeguard the Baltic Sea environment and to effects interlinked?’ coordinate mitigative efforts. The framework for • To document the eutrophication status of the this work is the ‘Convention on the Protection of Baltic Sea by focusing on the following chemical the Marine Environment of the Baltic Sea Area’ and biological quality elements: nutrients, phyto- – known as the Helsinki Convention. The govern- plankton, water transparency, submerged aquatic ing body is the Helsinki Commission, which is vegetation, oxygen concentrations, and benthic responsible for the coordination of activities and fauna. day-to-day work. • To document the causes of eutrophication by describing nutrient loads (waterborne and air- For more than three decades, the Helsinki Com- borne) to the Baltic Sea including their sources. mission (HELCOM) has coordinated monitoring and • To discuss solutions to the eutrophication prob- assessment activities in the Baltic Sea region. In lems in the Baltic Sea, e.g. by assessing existing 2005, the Commission adopted a new Monitoring national and Baltic-wide strategies, actions and and Assessment Strategy. As a result, focus of the measures to combat eutrophication, and by assessment activities shifted towards integrated outlining supplementary measures required to thematic assessments, which concentrate on reduce eutrophication to acceptable levels also specifi c issues and are more detailed and solution- taking into account future challenges related to oriented than the previous, broad Periodic Assess- changing environmental conditions and human ments of the State of the Marine Environment in pressures. the Baltic Sea Area published in 1980, 1987, 1990, 1996, 2002 and 2003. This report is directly linked to the HELCOM Baltic Sea Action Plan, which identifi ed eutrophication The effects of nutrient enrichment, also known as one of the four main issues to address in order as eutrophication, are perhaps the single greatest to improve the environmental health of the Baltic threat to the Baltic Sea environment. Understand- Sea. The Action Plan sets a strategic goal related to ing of eutrophication becomes clearer when one eutrophication, namely, ‘Baltic Sea unaffected by considers the origin of the word, which has its root eutrophication’, and identifi ed a set of Ecological in two Greek words: ‘eu’ which means ‘good’ or Objectives which corresponds to good ecologi- ‘well’, and ‘trope’ which mean ‘nourishment’. Con- cal/environmental status. This thematic assess- sequently, a translation would be ‘well nourished’, ment addresses each of the Ecological Objectives but the modern use of the word eutrophication is for eutrophication and enables an evaluation of related to excess loads of nutrients, nutrient enrich- progress towards the Ecological Objectives. ment, and adverse effects in aquatic ecosystems. Nutrient enrichment results in an increase in pro- In the Baltic Sea Action Plan, the Contracting ductivity and undesirable changes in ecosystem Parties acknowledged that a harmonized approach structure and functioning. Marine systems such as to assessing the eutrophication status of the Baltic the Baltic Sea can cope with the increases to some Sea is required. Therefore, the Contracting Parties extent. When the limits of ‘normal’ ecosystem agreed to further develop a common HELCOM structure and functioning are exceeded, however, assessment tool for use in a Baltic-wide thematic the ecosystem as a whole is confronted with the assessment of eutrophication in coastal as well as problem of eutrophication. open sea waters. 3 Ecological objectives related to eutrophication scaling, as well as the use of parameters that are were adopted in the HELCOM Baltic Sea Action considered supporting in WFD. Plan. They are: concentrations of nutrients close to natural levels, clear water, natural level of algal This thematic eutrophication assessment is aimed blooms, natural distribution and occurrence of at decision-makers, managers, scientists, educators plants and animals, and natural oxygen levels. and others interested in the health status of the Baltic Sea; it includes a glossary in order to support In some coastal areas, the classifi cation presented readers without a professional background in in the Baltic Sea-wide eutrophication assessment marine ecology or oceanography. The assessment cannot be directly compared to the results of is supplemented by a technical Background Report national assessments and the Baltic Sea intercali- as well as an Executive Summary which are avail- bration exercise sensu the Water Framework Direc- able via http://www.helcom.fi . tive owing to differences in spatial and temporal 4 TABLE OF CONTENTS PREFACE . .3 TABLE OF CONTENTS . .5 1 INTRODUCTION . .7 1.1 What is nutrient enrichment and eutrophication? . .7 1.2 Why is the Baltic Sea sensitive to eutrophication? . .8 1.3 How are loads, nutrient concentrations and eutrophication effects coupled? . 11 1.4 Assessment principles and data sources . 12 2 WHAT ARE THE EUTROPHICATION SIGNALS? . .14 2.1 Eutrophication signals in focus . .14 2.1.1 Nutrients . .15 2.1.2 Phytoplankton and water transparency . .16 2.1.3 Submerged aquatic vegetation . .16 2.1.4 Oxygen . 17 2.1.5 Benthic invertebrate communities . .18 2.2 Nutrients . .19 2.2.1 Status 2001–2006 . .20 2.2.2 Temporal trends . .20 2.3 Phytoplankton . .28 2.3.1 Status 2001–2006. .30 2.3.2 Temporal trends . .33 2.4 Water transparency . .36 2.4.1 Status 2001-2006 . .39 2.4.2 Temporal trends . .43 2.5 Submerged aquatic vegetation . .45 2.5.1 Current status . .47 2.5.2 Temporal trends . .51 2.6 Oxygen . .52 2.6.1 Status 2001–2006 . .56 2.6.2 Temporal