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Defining Eutrophication

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Eutrophication: managing a growing problem in aquatic systems Laurence Mee Professor of Marine and Coastal Policy, Plymouth University. Defining Eutrophication. Most limnologists consider eutrophication as an increase in the rate of supply of organic matter to an ecosystem.

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Eutrophication:managing a growing problem in aquatic systemsLaurence MeeProfessor of Marine and Coastal Policy, Plymouth University
defining eutrophication
Defining Eutrophication

Most limnologists consider eutrophication as an increase in the rate of supply of organic matter to an ecosystem.

For marine scientists, eutrophication (GESAMP, 1990) is “used simply to mean ‘enhanced nourishment’ and refers to the stimulation of aquatic plant growth by mineral nutrients, particularly the combined forms of phosphorus or nitrogen”.

Link to lecture notes

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There are over 600 small lakes in Northern Ireland. Research on the sediments in six of these has reconstructed a remarkable record of changes in total phosphorus concentration over the past 150 years that appears to be typical of lakes in most developed countries. The data shown above is for three lakes that have no point sources (e.g. sewage) draining into them, only the inputs from surrounding agriculture. Each of the lakes shows an increase in phosphorus, initially as a result of land clearances (ploughing releases phosphorus) and then a more pronounced increase since the 1950s. This recent large change is due to land drainage, fertiliser use and the indirect impact of rural sanitation. Impacts of these activities are accelerating the demise of the lakes. Each of the lakes is affected in a slightly different manner according to the characteristics of the particular drainage basin. Recent decreases may reflect more prudent use of fertilisers.

  • (source: redrawn from Anderson, J. Freshwater. Biol. 38, 427-440, Fig. 9)
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How is eutrophication manifested in the sea?

Here are some of the impacts of eutrophication. The consequences of each of these impacts will be explained in the lecture:

  • Decrease in the transparency of water.
  • Decrease in the average size of phytoplankton cells.
  • Increased demand for oxygen below the photic zone.
  • Change in phytoplankton speciation.
  • Change in the aesthetic value of the water body.
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Case Study: The Black Sea

Link to lecture notes

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PRESSURE-STATE-RESPONSE MODEL FOR EUTROPHICATION

Environmental impacts

Eutrophication

Socio-economic impacts

Transboundary consequences

Response

Immediate causes

Secondary causes

Uncertainties

Barriers for overcoming the problem

Tertiary causes

Socio-economic root causes

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This figure is taken from Sala et al. ‘Global Biodiversity Scenarios for the year 2100’ to appear shortly in Science.

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Appendix:

Managing lakes to reduce eutrophication.

Follow the hyperlink to a draft World Bank Guideline. Please note that this document should not be cited - it is still a draft under review but gives a useful summary for those of you that are unfamiliar with limnology

Link

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Further reading:

Two key articles are priority reading:

Smil, Vaclav (1997) Global population and the nitrogen cycle. Scientific American, July 1997, 76-81

Vitousek, P. et al. (1997) Human alterations of the Global Nitrogen Cycle: sources and consequences. Ecological applications 7(3): 737-750

Get a subscription (free) to the web based peer reviewed Journal of Conservation Ecology (www.consecol.org)

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