Anthropogenic impacts recorded in the sediments of Lunawa, a small tropical estuary, Sri Lanka |
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| Authors: | N P Ratnayake Y Sampei T Tokuoka N Suzuki H Ishida |
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| Institution: | (1) Division of Earth and Planetary Science, Graduate School of Science, Hokkaido University, N 10, W 8, Kita-Ku, Sapporo 060-0810, Japan;(2) Present address: Department of Earth Resources Engineering, Faculty of Engineering, University of Moratuwa, Moratuwa, Sri Lanka;(3) Department of Geosciences, Shimane University, Matsue 690-8504, Japan;(4) Present address: The Tokuoka Laboratory for Study of Brackish Water Environments, Hikino-Build, Hizuicho 34-1, Matsue 690-0863, Japan;(5) Japan National Oil Corporation, Fukoku Seimei Bldg, 2-2-2 Uchisaiwaicho Chiyoda-ku, Tokyo 100, Japan |
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| Abstract: | The Lunawa Estuary has been selected as a model for studying the long-term diagnoss of tropical estuarine pollution and its impact on ecosystems. Surface and short-core sediments from the Lunawa Estuary were collected, and analyzed for total organic carbon (TOC), nitrogen, sulfur and hydrocarbon contents, hydrogen index and other related sediment properties. Water quality and surface sediment data indicate that the Lunawa Estuary is presently an anoxic water body. The upper part of the sediment cores, characterized by very high TOC values of more than 10%, and absence of bioturbation along with strong laminations indicate anoxic water since 1970 AD, determined by 14 C dating. However, before 1970 AD, lower TOC content and presence of bioturbation and homogenous sediments with animal traces suggest the presence of oxic bottom water and thus a much better physicochemical condition. The lower part of the cores may also suggest the influence of gradual global warming. Regular laminations in the upper portions of the cores probably resulted from monsoon pulses with material preserved under anoxic condition. |
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| Keywords: | Sri Lanka Lunawa Estuary Anoxia Organic matter TOC |
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