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OSPAR eutrophication assessment

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Introduction

Coastal eutrophication is a growing marine environmental problem in Europe and the need for more effective monitoring and control measures is increasing. In 1997 the OSPAR Commission adopted the Common Procedure for the identification of the Eutrophication Status of the maritime area. OSPAR committed all members to reduce phosphorus and nitrogen inputs into the maritime areas and to combat eutrophication to achieve a healthy environment where eutrophication does not occur. The Common Procedure includes the main parameters involved in eutrophication processes which are differentiated in four categories of qualitative assessment criteria for application in the Comprehensive Procedure:

  • Category I: Nutrient enrichment
  • Category II: Direct effects of nutrient enrichment
  • Category III: Indirect effects of nutrient enrichment
  • Category IV: Other effects of nutrient enrichment

These assessment criteria can be different for the three maritime areas with regard to eutrophication (non-problem areas, potential problem areas and problem areas).

Ecological Quality Objectives (EcoQOs)

Ecological Quality Objectives are a tool to support the application of the ecosystem approach to the management of human activities affecting the marine environment and provide a means to define the desired quality of the marine environment. The specific EcoQOs correspond to a selection of assessment parameters and their assessment levels as applied under the Common Procedure. The specific EcoQOs for eutrophication agreed at the 5th North Sea Conference by Ministers and OSPAR 2002 are:

  1. Winter DIN and/or DIP should remain below elevated levels, defined as concentration > 50% above salinity related and / or region-specific natural background concentrations.
  2. Maximum and mean region-specific chlorophyll a concentrations during the growing season should remain below region-specific elevated levels, defined as concentrations > 50% above the spatial (offshore) and/or historical background concentration.
  3. Region/area-specific phytoplankton eutrophication indicator species should remain below respective nuisance and/or toxic elevated levels (and increased duration).
  4. Oxygen concentration, decreased as an indirect effect of nutrient enrichment, should remain above region-specific oxygen deficiency levels, ranging from 4-6 mg oxygen per liter.
  5. There should be no kills in benthic animal species as a result of oxygen deficiency and/or nuisance/toxic phytoplankton indicator species for eutrophication.

Category I: Nutrient enrichment

Introduction

The major causes of nutrient enrichment in coastal areas are associated with the need to satisfy human nutrition and diet by the use of fertilizers. Nutrients such as nitrates and phosphates are the most common single factor causing eutrophication. These nutrients are necessary for the growth of plants and biomass production of phytoplankton (microalgae) and macroalgae.

Nitrogen

Nitrogen is used by living organisms to produce a number of complex organic molecules such as amino acids, proteins and nucleic acids. The store of nitrogen found in the atmosphere (where it exists mainly as a gas (N2)) plays an important role for life. Other major sources include organic matter in soil and the oceans. Nitrogen is often the most limiting nutrient for plant growth. This occurs because most plants can only take up nitrogen in two solid forms: ammonium ion (NH4+) and the nitrate ion (NO3-). Most plants obtain the nitrogen they need as inorganic nitrate from the soil solution. Ammonium is used less by plants because it is extremely toxic in large concentrations. The stimulation of plant growth by nitrates may result in eutrophication, especially due to algae.

Phosphorus

The primary biological importance of phosphates is as a component of nucleotides which serve as energy storage (ATP) within cells or when linked together form the nucleic acids DNA and RNA. Most of world's phosphorus is locked up in rocks and can only be released weathering. A lot of the phosphorus that runs off into the ocean also gets buried into the ocean floor because it precipitates into a solid form and settles to the bottom as sediment. Phosphorus is only available to organisms in small quantities. For this reason, phosphorus is a limiting factor for plant growth. Their presence in water is due to detergents, fertilizers and biological processes. An excess of phosphate (PO43-) will stimulate the growth of plants and algae and is an important nutrient in eutrophication processes.

Silica

Diatoms are the predominant siliceous organisms in the marine environment and are a major component of the phytoplankton community. Diatoms accumulate silica (SiO2) as a structural element in their cell walls.

Nutrient assessment table

Nutrient concentration (µmol/l) Assessment
Ammonium1 (NH4+) Throughout the year
Nitrate2 (NO3-) Throughout the year
Nitrite3 (NO2-) Throughout the year
Phosphate (PO43-) Throughout the year
Silicate (SiO44-) Throughout the year
Dissolved Inorganic Nitrogen (DIN)(1+2+3) Winter*
Dissolved Inorganic Phosphate (DIP) Winter*
Total Nitrogen (includes all forms of nitrogen compounds) Calculated from all seasons
Total Phosphor (includes all forms of phosphor compounds) Calculated from all seasons
Winter N/P, N/Si and P/Si ratios Winter**
*During phytoplankton blooms, inorganic nutrients in surface layers may be almost completely consumed, leading to nutrient limitation. This results in a large seasonable variability of nutrient concentrations. For this reason DIN and DIP are usually measured and assessed during winter, when biological activity is lowest (highest nutrient concentrations and algal growth at minium).**Increased winter nutrient ratios, and in particular, increased N/P ratios (compared to Redfield Ratio = 16), when coupled with absolute excess of nitrate, may cause shifts in species composition, from diatoms to flagellates, some of which are toxic. Since such increased N/P ratios increase the risk of nuisance and toxic algal species, increased winter N/P ratios are used in the common assessment.

For all these nutrients action is required in potential problem areas and problem areas except the assessment of silicate (SiO44-) in non-problem areas (action discretionary).

Category II: Direct effects of nutrient enrichment

Phytoplankton chlorophyll a (µg/l)

Chlorophyll is bound with the living cells of plants, algae and other phytoplankton. It is a key biochemical component in the molecular apparatus that is responsible for photosynthesis, the critical processes in which the energy from sunlight is used to produce oxygen. Chlorophyll a is the most abundant form of chlorophyll within photosynthetic organisms and gives plants their green color. Chlorophyll a is an indicator for algal biomass and its spatial and temporal varieties. Monitoring chlorophyll levels is a direct way of tracking algal growth. Surface waters that have high chlorophyll conditions are typically high in nutrients (generally phosphorus and nitrogen). These nutrients cause the algae to grow or bloom. Thus, chlorophyll measurements can be utilized as an indirect indicator of nutrient levels. Action is required in potential problem areas and problem areas but discretionary in non-problem areas.

Phytoplankton indicator species (abundance (cells/l) and species composition))

Two types of area-specific phytoplankton indicator species can be distinguished: nuisance and toxic species. The table gives an overview of the most important phytoplankton indicator species.

Species Type Occurrence/period of bloom
Phaeocystis spp. Nuisance Spring-summer
Noctiluca scintillans Nuisance Spring
Chrysochromulina polylepis Toxic for fish and benthos Spring
Gymnodinium mikimotoi Toxic, Paralytic shellfish poisoning (PSP)(mussels) Late summer-autumn
Alexandrium spp. Toxic, Paralytic shellfish poisoning (PSP)(mussels) May-June
Dinophysis spp. Toxic, Diarrhoeic shellfish poisoning (DSP)(mussels) Late summer-autumn
Fibrocapsa japonica Toxic for fish and marine mammals
Prorocentrum spp. Toxic, Diarrhoeic shellfish poisoning (DSP)(mussels)
Chattonella spp. Toxic for fish

Assessment action is required in potential problem areas and problem areas but discretionary in non-problem areas.

Macrophytes including macroalgae (biomass and species composition)

Shifts in species form an important area-specific assessment/indicator parameter in shallow waters, estuaries and embayments. Assessment action is required in potential problem areas and problem areas but discretionary in non-problem areas.

Category III: Indirect effects of nutrient enrichment

Oxygen deficiency: O2 concentration (mg/l)

Decaying algal blooms and long-term nutrients and associated organic matter enrichment can lead to oxygen deficiency and the degree is widely used as an indirect effect for nutrient enrichment. Oxygen depletion may result in hypoxia (low oxygen) or even in anoxia (absence of oxygen). Assessment action is required in potential problem areas and problem areas but discretionary in non-problem areas. Table below gives an overview of the assessment levels of the various degrees of oxygen deficiency.

Assessment level Deficiency
< 2 mg/l ca. 75% deficiency (acute toxic)
4-5 mg/l ca. 50% deficiency
<5-6 mg/l Deficient
>6 mg/l No problems

Changes/ kills in zoobenthos and fish

Both assessment parameters are 'yes-or-no' parameters, indirectly related to nutrient enrichment and conclusions should be based on additional information on the occurrence of toxic phytoplankton species and oxygen levels. A distinction can be made between acute toxicity kills and long-term changes in zoobenthos species composition. Assessment action is required in potential problem areas and problem areas but discretionary in non-problem areas.

Category IV: Other effects of nutrient enrichment

Some phytoplankton species produce toxins. Diarrhoeic and paralytic shellfish poisoning mussel infections events are a relevant assessment parameter in relation to potential toxic algal species in areas where cultivated or wild shellfish stocks are harvested for human consumption. This parameter should be based on coherent monitoring on phytoplankton indicator species.

See also

References

  1. OSPAR Commission, Background Document: Ecological Quality Objectives for the Greater North Sea with Regard to Nutrients and Eutrophication Effects [1]
  2. Guiry, Michael D. (2013). Phaeocystis Lagerheim, 1893. In: Guiry, M.D. & Guiry, G.M. (2013). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=115088 on 2013-04-23.
  3. Guiry, Michael D. (2013). Noctiluca scintillans (Macartney) Kofoid & Swezy, 1921. In: Guiry, M.D. & Guiry, G.M. (2013). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=109921 on 2013-04-23.
  4. Guiry, Michael D. (2013). Chrysochromulina polylepis Manton & Parke, 1962. In: Guiry, M.D. & Guiry, G.M. (2013). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=115127 on 2013-04-23.
  5. Guiry, Michael D.; Moestrup, Ø. (2013). Gymnodinium mikimotoi Miyake & Kominami ex Oda, 1935. In: Guiry, M.D. & Guiry, G.M. (2013). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=109813 on 2013-04-23.
  6. Guiry, Michael D.; Moestrup, Ø. (2013). Alexandrium Halim, 1960. In: Guiry, M.D. & Guiry, G.M. (2013). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=109470 on 2013-04-23.
  7. WoRMS (2013). Dinophysis Ehrenberg, 1839. In: Guiry, M.D. & Guiry, G.M. (2013). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=109462 on 2013-04-23.
  8. Guiry, Michael D.; Moestrup, Ø. (2013). Fibrocapsa japonica S.Toriumi & H.Takano, 1973. In: Guiry, M.D. & Guiry, G.M. (2013). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=233761 on 2013-04-23.
  9. Guiry, Michael D. (2013). Prorocentrum Ehrenberg, 1834. In: Guiry, M.D. & Guiry, G.M. (2013). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=109566 on 2013-04-23.
  10. Guiry, Michael D. (2013). Chattonella B.Biecheler, 1936. In: Guiry, M.D. & Guiry, G.M. (2013). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=233776 on 2013-04-23.
  11. OSPAR Commission, 2008: Second Integrated Report on the Eutrophication Status of the OSPAR Maritime Area [2]
  12. OSPAR Commission (2005), Common Procedure for the Identification of the Eutrophication Status of the OSPAR Maritime Area (Reference number: 2005-3)[3]
  13. OSPAR Commission (2005), Agreement on the Eutrophication Monitoring Programme (Reference Number: 2005-4) [4]
  14. 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.
  15. Overview of eutrophication indicators to assess environmental status within the European Marine Strategy Framework Directive. Ferreira, J.G.; Andersen, J.H.; Borja, A.; Bricker, S.B.; Camp, J.; Cardoso da Silva, M.; Garcés, E.; Heiskanen, A.-S.; Humborg, C.; Ignatiades, L.; Lancelot, C.; Menesguen, A.; Tett, P.; Hoepffner, N.; Claussen, U. (2011). Estuarine, Coastal and Shelf Science 93(2): 117-131.
  16. Coastal eutrophication: recent developments in definitions and implications for monitoring strategies. Andersen, J.H.; Schlüter, L.; Ærtebjerg, G. (2006).Journal of Plankton Research 28(7): 621-628.
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The main author of this article is Knockaert, Carolien
Please note that others may also have edited the contents of this article.