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Defining Eutrophication

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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Defining Eutrophication

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  1. Eutrophication:managing a growing problem in aquatic systemsLaurence MeeProfessor of Marine and Coastal Policy, Plymouth University

  2. 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

  3. 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)

  4. 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.

  5. Case Study: The Black Sea Link to lecture notes

  6. Evolution of the NW Shelf ‘Dead Zone’ 1974 1973 1990 1978

  7. Decline in the Phyllophora beds on the NW Shelf 1980s 1970s 1950s 1960s

  8. Distribution and migration of Turbot prior to 1980 Spawning Feeding

  9. A causal chain for eutrophication

  10. 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

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

  12. 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

  13. 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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