Elevated sedimentation in lake records linked to agricultural activities in the Ishikari River floodplain, northern Japan

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 ( 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.

The significance of meandering channel to habitat diversity and fish assemblage: a case study in the Shibetsu River, northern Japan

“…However, the number and the amount of artificial oxbow lakes gradually decreased over time in the study segment. This might be caused by landfill for farmland development, sedimentation from surrounding areas, and drawdown of the groundwater level followed by channelization (Ahn et al 2009).…”

Differential effects of spatial network structure and scale on population size and genetic diversity of the ninespine stickleback in a remnant wetland system

“…Many freshwater organisms, such as fishes and amphibians, have adapted to such dynamic landscapes, often exhibiting high levels of species diversity and regional endemism (Tockner & Stanford, 2002;Zedler & Kercher, 2005). However, a number of wetlands have become isolated or have disappeared due to human alterations, such as levee construction associated with agricultural development and sedimentation from surrounding land-use practices (Galat et al, 1998;Ahn et al, 2009). Fragmented lotic patches are currently widespread, although artificial ditches and streams may still connect some habitat patches (Ishiyama, Akasaka & Nakamura, 2014).…”

Modeling suspended sediment sources and transport in the Ishikari River Basin, Japan using SPARROW

“…Wongsa and Shimizu (2004) indicated that land use change has a significant effect on soil eroded from hill slopes, but no significant effect on flooding for the Ishikari River basin. Ahn et al (2009) concluded that sedimentation rate increased in the Ishikari River floodplain because of agricultural development on the floodplains. However, detailed accounting of sediment sources (e.g., the type of land use) and transport in the Ishikari River basin remains poorly understood.…”