Climate change decreases aquatic ecosystem productivity of Lake Tanganyika, Africa

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Climate change decreases aquatic ecosystem
productivity of Lake Tanganyika, Africa

• OReilly et al., 2003 Nature 424 766-768

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Burundi
Lake Tanganyika -Longest lake in the world
(650km) -Rift valley lake -Oligotrophic -Permanent
ly stratified, anoxic hypolimnion -Important
source of income and nutrition for neighbouring
countries
U.R. of Tanzania
D. R. Congo
Zambia
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Cool Windy Season
Warm Calm Season
May-Septermber
October-April
Southerly Winds
Cool Air
Warm Air
CoolerWater
Warmer Water
New 1º Production More Fish!
Lower 1º Production Dominated by Nutrient
Recycling
POM and DOM
Highly Stratified Thermocline
Weakly Stratified
Less Thermal Resistance
More Thermal Resistance
PSi
High Inorganic Nutrients
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Global Warming
Lake Physical Structure
R20.76
R20.90
R20.44
Figure 1 Air temperature (a), and wind speed (b)
during the windy season over the past 50 years.
Figure 2 Surface water temperature (a), deep
water temperature (b) , and oxycline depth (c)
during the windy season over the past 80 years.
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Phytoplankton 1º Production
A Note on Stable C Isotopes
Phytoplankton preferentially take up lighter
(12C) isotopes When a nutrient becomes
limiting, they take anything they can get
0 ?13C () -30
Figure 3 Sediment ?13C () over the past 200
years.
Increased C consumption
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(Not as) Cool (Less) Windy Season
Old Cool Windy Season
Southerly Winds
Southerly Winds
Warmer Air
Cool Air
WarmerWater
CoolerWater
20 Less New 1º Production 30 Less Fish!
New 1º Production More Fish!
More Stratified
Weakly Stratified
More Thermal Resistance
Less Thermal Resistance
PSi
PSi
High Inorganic Nutrients
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Lake Fisheries
Recent decline in fisheries -Fishing catch has
remained the same Results explain recent
decline in fisheries Evidence for bottom-up
control of a lake
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Sunset over the lake