Elevated sedimentation in lake records linked to agricultural activities in the Ishikari River floodplain,northern Japan |
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| Authors: | Young Sang Ahn Futoshi Nakamura Toshikazu Kizuka Yugo Nakamura |
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| Institution: | 1. Department of Forest Science, Graduate School of Agriculture, Hokkaido University, Sapporo, Japan;2. Division of Forest Soil Conservation, Department of Forest Environment, Korea Forest Research Institute, Seoul, Korea;3. Department of Agricultural Engineering, Graduate School of Agriculture, Hokkaido University, Sapporo, Japan;4. Institute of Seismology and Volcanology, Graduate School of Science, Hokkaido University, Sapporo, Japan |
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| Abstract: | The purpose of this study was to examine the historical change in sedimentation rates in lakes that have been impacted by river regulation and agricultural activities in the Ishikari River floodplain. We dated sediment cores using caesium‐137 (137Cs) dating and tephrochronology, and we estimated sediment sources from 137Cs concentrations in the topsoil of representative land covers. We found that, between 1739 and 1963, the distance between the lake and the main river channel and whether or not the lake was connected to the river affected the sedimentation rates. After 1963, agricultural drainage systems were established in the Ishikari River floodplain. The average sedimentation rate before and after the construction of drainage ditches varied between 1–66 and 87–301 mg cm–2 a–1, respectively. The increase in the sedimentation rate after 1963 was caused by the construction of a number of drainage networks, as well as extensive cultivation activity and/or fragmentation of the swamp buffers surrounding the lakes. The 137Cs activities at the surfaces of the lake as well as the catchment‐derived 137Cs contributions and 137Cs inventory in the lake profiles were used to examine the sediment influx from the various drainage areas after the establishment of the drainage system. Our results indicate that the majority of the lake sediments were derived from cultivated areas, and therefore the catchment‐derived 137Cs contribution in the lakes was strongly correlated with the sedimentation rate. The 137Cs inventory across all of the lake profiles was also significantly greater than the atmospheric fallout. We identified a negative correlation between the 137Cs lake profile inventory and the sedimentation rate. This is because the sediment originating from the drainage areas contained low 137Cs concentrations, which diluted the overall concentration of 137Cs in the lake sediment. Copyright © 2009 John Wiley & Sons, Ltd. |
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| Keywords: | agricultural runoff drainage ditch sedimentation rate catchment‐derived 137Cs contribution 137Cs inventory tephrochronology |
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