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Location Assessment of anthropogenic activities on the Biodiversity of Lake Tana at the side of Bahir Dar City

  • Student: Getachew Fentew
  • Institution: Bahir Dar University
  • Degree: M.Sc.
  • Posted on: August 02, 2012

Thesis Abstract

The survival of humankind and most of the biodiversity depend on the inland freshwaters which constitute less than 0.01% of the earth’s total water resources. And, the inland aquatic ecosystems are the most fragile and threatened ecosystems on the earth as they bear the impact of all human activities – both on land and in water. Water resources and aquatic biodiversity are intimately interrelated and interdependent. Both provide a wide range of functions and have intrinsic value as well as provide for the sustenance of human populations. Degradation of water quality, depletion of water resources and loss of aquatic biodiversity are prominent features of the environmental landscape requiring urgent attention at global and national scales. Lake Tana, which is emerged as one of the global top 250 lake regions most important for biological diversity (LakeNet,1999) is threatened by a number of anthropogenic activities carried out in and around Bahir Dar town including agricultural activities ( like farming, livestock grazing, fish processing); development activities like construction and settlement; discharge of untreated domestic, municipal and industrial wastes; and the urban runoffs end up to the lake.Which all results increased nutrient load of the ecosystem-eutrophication, which results to changes in species composition, especially cyanobacteria, and biomass. This in turn results to fish kill caused by decreased biochemical oxygen demand and other interrelated consequences. Resulting in turbid water and loss of biodiversity. Cultural eutrophication, the process by which anthropogenic addition of nutrients to water bodies accelerates eutrophication, the natural aging process for aquatic system. The impact of anthropogenic activities on the biodiversity of Lake Tana is shown by the reduction in papyrus abundance and replacement by other rooted vegetations and weeds. The dominance of aquatic ecosystems by blue greens, especially the genus Microcystis is considered as an indication of the changing of aquatic ecosystems by human interventions. The phytoplankton biomass estimated as chlorophyll-a is 9.64mg/m3 which indicate that the lake trophic status to be mesotrophic. The lower concentration of DO (1.63mg/l) is mainly due to the urban runoffs that end up to the lake which collects oxygen-demanding wastes. The southern gulf of lake Tana which receives many contaminant inflows from nearby farmlands with intensive fertilizers (non-point source), and untreated industrial, municipal swage, as well as leaching from pit latrines and septic tankers and fish processing activities remains the most important sources of pollution. The remarkably high concentration of nitrate and phosphate (0.33mg/l which is above the back ground level) seem to be associated with the intensive human activities carried out in and around Bahir Dar city