22
2.1 Introduction
Anthropogenic nutrient over-enrichment is one of the oldest environmental problems . It has escalated during the last century with the exponential increase of human
population and consumption, and today eutrophication is a global problem (Díaz
and Rosenberg 2011 ; Rockström et al. 2009 ; Wassmann and Olli 2006 ).
Eutrophication in marine systems is well described, both for the global and the
regional level (Boesch 2002 ; Jørgensen and Richardson 1996 ; Wassmann and Olli
2006 ).
Eutrophication can be defi ned as an increased input of nutrients or organic matter
into an ecosystem, resulting in an increase in primary production (Nixon 1995 ,
2009 ). Key indicators of aquatic eutrophication include increases in the total amount
of phosphorus and nitrogen , chlorophyll and decreased water transparency. The
primary effects are increased production of fi lamentous algae, changed species
composition of microalgae and an increased probability for harmful, and potentially
toxic , algal blooms. A complex array of secondary effects may also occur, for
example, oxygen defi ciency and poorer living conditions for perennial underwater
vegetation, immobile zoobenthos living in bottom sediments and certain fi sh species (Fig. 2.1 ). These may in turn amplify ecological and associated socio-economic
impacts, potentially impeding recovery processes (Lundberg 2005 ). Extended
hypoxic (low oxygen saturation) or anoxic (complete oxygen defi ciency) bottom
areas (so-called dead zones) are key resultant stressors in marine ecosystems , and
the Baltic Sea is the largest stressed ecosystem in the world in this respect
(Carstensen et al. 2014 ; Díaz and Rosenberg 2008 ).
The fi rst signs of eutrophication on a larger scale in the Baltic Sea became apparent in the 1960s, when oxygen defi ciency in the central area was linked to human
activities (Elmgren 2001 ; Fonselius 1969 ; Jansson 1997 ; Lundberg 2014 ). The
main anthropogenic sources of eutrophication are agriculture (including crop cultivation and animal husbandry), industries, municipal sewage water and atmospheric
deposition (Elmgren and Larsson 2001 ; HELCOM 2009a , 2013 ; Wassmann and
Olli 2006 ). However, there was a time lag of two decades after the initial fi ndings
in the 1960s, before the issue generated broader public awareness. Today, though,
the network of organisations working for the protection and restoration of the
marine environment is well developed in the countries surrounding the Baltic Sea
(Kern and Löffelsend 2004 ; Lundberg 2013 ).
2.1.1 Governance of Baltic Sea Eutrophication and the Aims
of the Study
Eutrophication, along with overfi shing and the presence of hazardous chemicals ,
constitutes the most serious environmental problems and risks in the Baltic Sea,
posing severe threats to biodiversity as well as to other ecosystem services such as
M. Karlsson et al.
2.1 Introduction
Anthropogenic nutrient over-enrichment is one of the oldest environmental problems . It has escalated during the last century with the exponential increase of human
population and consumption, and today eutrophication is a global problem (Díaz
and Rosenberg 2011 ; Rockström et al. 2009 ; Wassmann and Olli 2006 ).
Eutrophication in marine systems is well described, both for the global and the
regional level (Boesch 2002 ; Jørgensen and Richardson 1996 ; Wassmann and Olli
2006 ).
Eutrophication can be defi ned as an increased input of nutrients or organic matter
into an ecosystem, resulting in an increase in primary production (Nixon 1995 ,
2009 ). Key indicators of aquatic eutrophication include increases in the total amount
of phosphorus and nitrogen , chlorophyll and decreased water transparency. The
primary effects are increased production of fi lamentous algae, changed species
composition of microalgae and an increased probability for harmful, and potentially
toxic , algal blooms. A complex array of secondary effects may also occur, for
example, oxygen defi ciency and poorer living conditions for perennial underwater
vegetation, immobile zoobenthos living in bottom sediments and certain fi sh species (Fig. 2.1 ). These may in turn amplify ecological and associated socio-economic
impacts, potentially impeding recovery processes (Lundberg 2005 ). Extended
hypoxic (low oxygen saturation) or anoxic (complete oxygen defi ciency) bottom
areas (so-called dead zones) are key resultant stressors in marine ecosystems , and
the Baltic Sea is the largest stressed ecosystem in the world in this respect
(Carstensen et al. 2014 ; Díaz and Rosenberg 2008 ).
The fi rst signs of eutrophication on a larger scale in the Baltic Sea became apparent in the 1960s, when oxygen defi ciency in the central area was linked to human
activities (Elmgren 2001 ; Fonselius 1969 ; Jansson 1997 ; Lundberg 2014 ). The
main anthropogenic sources of eutrophication are agriculture (including crop cultivation and animal husbandry), industries, municipal sewage water and atmospheric
deposition (Elmgren and Larsson 2001 ; HELCOM 2009a , 2013 ; Wassmann and
Olli 2006 ). However, there was a time lag of two decades after the initial fi ndings
in the 1960s, before the issue generated broader public awareness. Today, though,
the network of organisations working for the protection and restoration of the
marine environment is well developed in the countries surrounding the Baltic Sea
(Kern and Löffelsend 2004 ; Lundberg 2013 ).
2.1.1 Governance of Baltic Sea Eutrophication and the Aims
of the Study
Eutrophication, along with overfi shing and the presence of hazardous chemicals ,
constitutes the most serious environmental problems and risks in the Baltic Sea,
posing severe threats to biodiversity as well as to other ecosystem services such as
M. Karlsson et al.