Mineral magnetic analyses of sediment cores recording recent soil erosion history in central Tanzania

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• 作者：Eriksson ; M.G. ; Sandgren ; P.
• 关键词：soil erosion ; mineral magnetism ; lake sediments ; sedimentation rate ; landscape history ; Tanzania
• 刊名：Palaeogeography, Palaeoclimatology, Palaeoecology
• 出版年：1999
• 出版时间：September 1, 1999
• 年：1999
• 卷：152
• 期：3-4
• 页码：365-383
• 全文大小：948 K

文摘

Sediment cores, covering the period from ca. 1835 to 1988 AD, were retrieved from Lake Haubi, located in a severely eroded area in the Kondoa District, central Tanzania. The results of mineral magnetic analyses undertaken on the sediment cores reflect two distinctly different depositional environments. Before ca. 1902 AD the basin formed a seasonally inundated swamp, which subsequently turned into a lake. The swamp sediment is black, uniform, and extremely clay-rich. It contains antiferromagnetic minerals (e.g. haematite) but lacks ferrimagnetic minerals (e.g. magnetite) due to post-depositional dissolution. The lake sediment is also very clay-rich but laminated. Here ferrimagnetic minerals (magnetite) dominate the magnetic assemblage. The soil erosion history of the catchment has been reconstructed using results based on the mineral magnetic analyses and on the sedimentation rates obtained from ²¹⁰Pb datings, whereby variations in magnetic concentrations and ratios, attributed to variations in sediment influx, are assumed to reflect soil erosion within the catchment. The results from the magnetic analyses are in general agreement with the sedimentation rates. High sediment accumulation occurred around the turn of the century, and increased generally since 1935, with particularly high rates between ca. 1945 and 1950, and from ca. 1955 to the present. The reconstructed soil erosion history has been compared to both historical records of anthropogenic activity in the Kondoa District and to rainfall data. From this comparison we infer that effects on soil erosion from variations in rainfall are subordinate to those induced by man.