Abstract
Transport behavior of riverine suspended solids plays an important role in understanding biogeochemical cycles and carbon dynamics of river systems. The dynamics of particulate organic matter (POM) are susceptible to changing watershed environments in river systems. This study focuses on the relationship between riverine organic matter properties and land use in watersheds. The study was conducted in the Kumaki River system on the Noto Peninsula, in central Japan. The system consists of a forested headwater and upstream river area and of paddy fields along the midstream and downstream portions of the Kumaki River. The Nishiyachi River, which is one of main tributaries of the Kumaki River, has a paddy field located in the downstream watershed. River bottom sediment sampling was performed between June 2009 and April 2011 at four sites in the Kumaki River and one site in the Nishiyachi River. The C/N ratio andΔ14C of organic matter decreased along the river line, but the δ13C of organic matter and δ15N of total nitrogen increased. These results suggest that the distribution of forest and paddy fields in the watershed is reflected in the organic matter properties of river bottom sediments in each river watershed. Variation in the parameters at each sampling site appears to be affected by suspension, transport, and sedimentation of river suspended solids to different degrees as a result of rainfall events.
