Eutrophication: managing a growing problem in aquatic systems Laurence Mee Professor of Marine and...
19
Eutrophication: managing a growing problem in aquatic systems Laurence Mee Professor of Marine and Coastal Policy, Plymouth University
-
Upload
loraine-mclaughlin -
Category
Documents
-
view
216 -
download
1
Transcript of Eutrophication: managing a growing problem in aquatic systems Laurence Mee Professor of Marine and...
Eutrophication:managing a growing problem in
aquatic systems
Laurence MeeProfessor of Marine and Coastal Policy, Plymouth
University
The current lecture will: Describe the phenomenon Explain how it damages marine systems Examine a case study from the Black Sea Present a causal chain showing how
eutrophication is linked to social and economicdriving forces
Illustrate how our land-use practices areinfluencing nutrient discharge globally
Take a look at some of the uncertainties to bereduced through scientific research.
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
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)
How is eutrophication manifested in the sea?
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.
Here are some of the impacts of eutrophication. The consequences of each of these impacts will be explained in the lecture:
Case Study: The Black Sea
Link to lecture notes
Figure 2. Total N & P fertiliser application, Danube Basin
0
500000
1000000
1500000
2000000
2500000
3000000
3500000
19
62
19
64
19
66
19
68
19
70
19
72
19
74
19
76
19
78
19
80
19
82
19
84
19
86
19
88
19
90
19
92
19
94
19
96
Me
tric
to
ns
Total-P
Total-N
1973
1974
1978
1990
Evolution of the NW Shelf ‘Dead Zone’
1950s
1960s
1970s
1980s
Decline in the Phyllophora beds on the NW Shelf
Feeding
Spawning
Distribution and migration of Turbot prior to 1980
Figure 4. Normalised basin-wide fertiliser usage and N and P discharge to the Black Sea
0
20
40
60
80
100
120
19
86
19
87
19
88
19
89
19
90
19
91
19
92
19
93
19
94
19
95
19
96
19
97
% o
f m
axim
um
Total N discharge
N fertiliser
Total P discharge
P fertiliser
Figure 8a. Variation in observed area of NW shelf summer hypoxia with increasing loading of nitrogen fertiliser in the Danube basin
0
5
10
15
20
25
30
35
40
45
0 0.5 1 1.5 2 2.5 3 3.5
Nf, Nitrogen fertiliser, million tons/year, averaged over the 7 years prior to each data point
Th
ou
san
ds
of
squ
are
km
of
hyp
oxi
a
1961-1972
1973
1974-1991
1994-1996
A causal chain for eutrophication
A causal chain is a series of statementsthat demonstrate and summarize, in astepwise manner, the linkages betweenproblems and their underlying or 'root'causes. Uncertainties accompanying eachlinkage should be clearly stated. The analysisalso permits barriers to resolving theproblems to be investigated.
Eutrophication
Environmental impacts
Socio-economic impacts
Transboundary consequences
Immediate causes
Secondary causes
Tertiary causes
Socio-economic root causes
Barriers for overcoming the
problem
Response
Uncertainties
PRESSURE-STATE-RESPONSE MODEL FOR EUTROPHICATION
This figure is taken from Sala et al. ‘Global Biodiversity Scenarios for the year 2100’ to appear shortly in Science.
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
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)
