Wednesday, May 28, 2008 - 4:00 PM
495

Effects of diversion dams on organic matter dynamics: A large-scale experiment with decommissioning of a hydroelectric dam

Junjiro Negishi, Izumi Katano, Tomoko Minagawa, Shiro Sagawa, and Yuichi Kayaba. Aqua Restoration Research Center, Public Works Research Institute, Mubanchi, Kanyuuchi, Kawashima-kasada-cho, Kakamigahara, Gifu, 501-6021, Japan

Although adverse effects of dams are well recognized, little is known about how dams affect stream organic matter dynamics. This study examined how diversion dams alter organic matter dynamics by measuring litter fall and very coarse organic matter (VCPOM, > 1cm) along a river prior to and following decommissioning of a hydroelectric diversion dam. Field experiment was conducted within 8-km stretch of third-order Yunishi-gawa River, central Japan in the fall of 2006 and 2007. Yunishi-gawa Dam, which was completed in 1960, was decommissioned with its gates left fully open on September 29, 2006. One control and three treatment sites were located in upstream and downstream of the dam, respectively. The amount of leaf litter fall and drifting VCPOM, transport distance of VCPOM, and standing crop of benthic VCPOM were estimated in each site. Flow regimes in treatment sites were fully restored in 2007. With litter fall being similar across two years in all sites, drifting mass, transport distance, and standing crops of VCPOM in treatment sites significantly increased and became similar to the level in the control site. Our findings indicated that diversion dams could severely alter organic matter dynamics largely by disconnecting upstream source areas and decreasing transport distance.


Web Page: dam decommissioning, organic matter, restoration