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Lake Malawi

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 km 2

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Lake Malawi

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  1. Lake Malawi Craig Krajeski

  2. 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)

  3. 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 Livescience.com

  4. 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)

  5. 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)

  6. 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

  7. 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

  8. 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)

  9. Methods • 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-O-methylxylopyranoside • 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

  10. 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)

  11. 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. homeschoolersresources.blogspot.com kentsimmons.uwinnipeg.ca

  12. 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. flickr.com sciencecentric.com

  13. 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

  14. 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. fotopedia.com traveljournals.net

  15. 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. imagineafrica.co.uk travelpp.com

  16. Questions?

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