Reclamation and Land Consolidation Effects on Organic Matter Sedimentation in Lake Kiba-Gata, Japan

Abstract

The effects of reclamation and land consolidation on organic matter sedimentation were studied in a small lagoon, Kiba-gata, which is one of the three Kaga lagoons (Shibayama-gata, Imae-gata, and Kiba-gata) located in central Japan. Reclamation work was conducted during 1954–1969 to increase the paddy field area and to improve the drainage system. Lake Kiba-gata was affected by changes in the drainage system and land consolidation around the lagoon. A sediment core was obtained in the central part of Lake Kiba-gata in June 2012. The organic matter flux recorded in the sediment core increased from 1.1 to 2.3 and from 3.9 to 7.5 g cm−2 year−1, respectively, during 1903–1974 and 1989–2012, although it was similar to the flux recorded for 1974–1989 following reclamation. The C/N ratio, δ13C, and δ15N values also changed during these time intervals. These results indicate that the primary productivity in the lagoon is increasing with time and that the recent contribution of phytoplankton to productivity has exceeded the level of past contributions because of changes in drainage and increase in human activity around the lake due to the reclamation and land consolidation