Transcript Lake Malawi - Department of Environmental Sciences

Lake Malawi
Craig Krajeski
Lake Malawi
• Tectonic lake located
at the southern end of
the East African Rift
• Between the
countries of Malawi,
Mozambique, and
Tanzania
Munthali, S.M. (2011)
Lake Malawi
• Maximum depth of
700 m
• 580 km long, and up
to 80 km wide
• Surface area of
29,400 km2
• Warm, monomitic lake
and permantley
anoxic below 250 m
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Lake Inputs
• 70% of the lake’s
annual inflow comes
from rainfall during
the wet season (800
to 2400 mm/yr)
• Wet season
November-April
• other 30% of inflow
comes from the lake’s
drainage basin
Lyons, R.P., et al. (2011)
Lake Outflow
• The Shire River is
Lake Malawi’s only
outlet with a relatively
small annual outflow
• Annual evaporation
rates vary between
1000 to 1400 mm/yr
Lyons, R.P., et al. (2011)
Lake Malawi Cichlids
• 500 species of cichlid
fish have evolved in
Lake Malawi in the
last million years
• 90% of these cichlids
are endemic to the
lake
• Most diverse
community of
freshwater fish
species in the world
Science.kennesaw.edu
Cichlid Diversity
• Due to intense
competition for food
cichlid species have
evolved to exploit an
array of diets
• These include
piscivores, scale
eaters, crevice
feeders, algae eaters,
and egg eaters
Malawicichlids.com
Organic geochemical records from Lake Malawi (East
Africa) of the last 700 years,
part II: Biomarker evidence for recent changes in primary
productivity (Castaneda, I.S., et al., 2011)
• Research Objective: extend the existing records of changes in the
algal community structure of Lake Malawi and gain a better
understanding of the environmental factors influencing primary
productivity within the lake
• Examined two varved sediment cores from Lake Malawi, which
together provided a continuous record of environmental variability in
East Africa of the last 730 years
•Varve: annual coupling of a light layer of
sediment representing the windy season
and a dark layer representing the rainy
season
Castaneda, I.S., et al. (2011)
Methods
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Analyzed sediment cores for
biomarkers using a gas
chromatograph and mass
spectrometer
Diatoms are dominant algal group in
Lake Malawi and identified by the lipid
loliolide/isololiolide
Dinoflagellates – dinosterol
Cyanobacteria - docosanyl 3-Omethylxylopyranoside
Bacterivorous ciliates - tetrahymanol
Green algae is present in Lake Malawi
but presently lacks sedimentary
biomarkers
Lake Malawi sediments were found to
contain biomarkers of eustigmatophyte
algae, a yellow-green algae, but they
have not been identified in the lake
climategeology.ethz
Results
• The most notable
changes in the
biomarker records are
the increase in
dinoflagellate and
bacterivorous ciliate
biomarkers over the
past few centuries,
accompanied by a
decrease in diatom
lipids
Castaneda, I.S., et al. (2011)
Results
• A number of changes are observed the Lake Malawi algal biomarker
record since ~1900 AD. It is likely that a number of factors are
responsible for these changes including increased temperature,
watershed deforestation, nutrient loading, and possibly, changes in
wind strength and direction.
• During the past century, an increase in the abundance of the
compound retene is noted and can likely be attributed to increased
soil erosion due to deforestation, or from an increase in wood
burning in the Lake Malawi basin.
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Management Problem
• Overfishing and increased economic activity are depleting the fish
stock in Lake Malawi.
• High population growth rate contributes to overfishing, species loss,
and pollution of the lake.
• The rising population along the lake shore, has led to more efficient
fishing methods and to the fishing of previously unexploited fish
species to keep up with growing demand.
• High population growth has increased land cultivation in the lake's
drainage basin and contributed to the pollution of the lake through
the use of fertilizers and deforestation.
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Management Problem
• Sixty years ago the main commercial fisheries in Lake Malawi were
supported by cichlid tilapia.
• Since then the endemic tilapia species have become so scarce that
the main commercial fisheries have resorted to fish farms stocking
Oreochromis shiranus (an endemic tilapia) in large enclosures in
open water.
• Currently, cichlid species are commercially fished from the lake.
• The Malawi Fisheries Department reports total fish catches between
26,000 to 47,000 tons annually with 60% to 70% of this being small
cichlid species.
malawicichlids.com
agfax.net
Management Solutions
• Education of the population is necessary to protect the natural
resources of Lake Malawi.
• The government must intensify its family planning program to reduce
the current rapid population growth. It is important to understand that
the population problem in Malawi is compounded by poverty.
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Management Solutions
• Economic development should be part of any efforts to reduce
overfishing and loss of species. It is not enough to discourage small
fishers from catching fish when they are forced to do so in order to
survive. The government must find alternative ways for these people
to earn an income other than by fishing.
• An ongoing Poverty Alleviation Program aims to address the wide
income disparity between rural and urban areas, and between rich
and poor. Rural people must be rewarded for their efforts to
conserve the fish species.
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Questions?