Premium
Elevated sedimentation in lake records linked to agricultural activities in the Ishikari River floodplain, northern Japan
Author(s) -
Ahn Young Sang,
Nakamura Futoshi,
Kizuka Toshikazu,
Nakamura Yugo
Publication year - 2009
Publication title -
earth surface processes and landforms
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.294
H-Index - 127
eISSN - 1096-9837
pISSN - 0197-9337
DOI - 10.1002/esp.1854
Subject(s) - sedimentation , floodplain , drainage basin , hydrology (agriculture) , sediment , drainage , geology , environmental science , geomorphology , geography , ecology , cartography , geotechnical engineering , biology
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 ( 137 Cs) dating and tephrochronology, and we estimated sediment sources from 137 Cs 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 137 Cs activities at the surfaces of the lake as well as the catchment‐derived 137 Cs contributions and 137 Cs 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 137 Cs contribution in the lakes was strongly correlated with the sedimentation rate. The 137 Cs inventory across all of the lake profiles was also significantly greater than the atmospheric fallout. We identified a negative correlation between the 137 Cs lake profile inventory and the sedimentation rate. This is because the sediment originating from the drainage areas contained low 137 Cs concentrations, which diluted the overall concentration of 137 Cs in the lake sediment. Copyright © 2009 John Wiley & Sons, Ltd.