Check dams exacerbate the effects of high flow on aquatic insect communities in tropical stream of northern Thailand

Abstract

Check dams have been widely constructed in Thai streams and our study examined effects of dam-caused flow regime changes on aquatic insect communities. The flow regime of Huay Kaew Stream in Doi Suthep-Pui National Park, Chiang Mai, Thailand was separated into two periods: high flow and low flow periods, which characterize the natural flow dynamics in tropical streams. The sampling sites in three altitudes (1500, 900, and 500 m asl.) of the stream showed a similar trend in the effects of check dams during high flow. High discharge reduced the density of aquatic insects but this reduction was locally greater near check dams. Higher changes in water velocity at dammed sites caused greater decreases in aquatic insect community abundance because of alternating accumulation and dislodgement of fine sediment and leaf pack habitat below dams. An increase in cobble habitat because of dam erosion below a non-permanent check dam helped mitigate the effects of high flow and flow disturbance on aquatic insect density. A high density of check dams likely affects streambed structure and insect composition within the stream system.