Sun Jingrui, Du Weilong, Lucas Martyn C, Ding Chengzhi, Chen Jinnan, Tao Juan, He Daming
Yunnan Key Laboratory of International Rivers and Transboundary Eco-security, Yunnan University, Kunming, 650091, China; Institute of International Rivers and Eco-security, Yunnan University, Kunming, 650091, China.
Department of Biosciences, University of Durham, Durham DH1 3LE, UK.
J Environ Manage. 2023 Feb 1;327:116817. doi: 10.1016/j.jenvman.2022.116817. Epub 2022 Nov 29.
River barriers reduce river connectivity and lead to fragmentation of fish habitats, which can result in decline or even extinction of aquatic biota, including fish populations. In the Mekong basin, previous studies have mainly focused on the impacts of large dams but ignored the impacts of small-scale barriers, or drew conclusions from incomplete barrier databases, potentially leading to research biases. To test the completeness of existing databases and to evaluate the catchment-scale fragmentation level, a detailed investigation of river barriers for the whole Upper Mekong (Lancang catchment) was performed, by conducting visual interpretation of high-resolution remotely sensed images. Then, a complete catchment-scale barrier database was created for the first time. By comparing our barrier database with existing databases, this study indicates that 93.7% of river barriers were absent from the existing database, including 75% of dams and 99.5% of small barriers. Barrier density and dendritic connectivity index (DCI and DCI) were used to measure channel fragmentation within the catchment. Overall, 50.5% of sub-catchments contained river barriers. The Middle region is the most fragmented area within the Lancang catchment, with a median [quartiles] barrier density of 5.34 [0.70-9.67] per 100 km, DCI value of 49.50 [21.50-90.00] and DCI value of 38.50 [9.00-92.25]. Furthermore, since 2010, distribution ranges of two representative fish species Schizothorax lissolabiatus (a rheophilic cyprinid) and Bagarius yarrelli (a large catfish) have reduced by 19.2% and 32.8% respectively, probably due in part to the construction of river barriers. Our findings indicate that small-scale barriers, in particular weirs and also small dams are the main reason for habitat fragmentation in the Lancang and must be considered alongside large dams in water management and biodiversity conservation within the Mekong.
河流屏障会降低河流连通性，导致鱼类栖息地破碎化，进而可能致使包括鱼类种群在内的水生生物群落数量减少甚至灭绝。在湄公河流域，以往的研究主要聚焦于大型水坝的影响，却忽视了小型屏障的影响，或者从不完整的屏障数据库得出结论，这可能导致研究存在偏差。为检验现有数据库的完整性并评估流域尺度的破碎化程度，通过对高分辨率遥感影像进行目视解译，对湄公河上游（澜沧江流域）的河流屏障展开了详细调查。随后，首次创建了完整的流域尺度屏障数据库。通过将我们的屏障数据库与现有数据库进行对比，本研究表明现有数据库中缺失93.7%的河流屏障，其中包括75%的水坝和99.5%的小型屏障。采用屏障密度和枝状连通性指数（DCI和DCI）来衡量流域内河道的破碎化程度。总体而言，50.5%的子流域存在河流屏障。中部地区是澜沧江流域内破碎化程度最高的区域，每100公里的中位数[四分位数]屏障密度为5.34[0.70 - 9.67]，DCI值为49.50[21.50 - 90.00]，DCI值为38.50[9.00 - 92.25]。此外，自2010年以来，两种具有代表性的鱼类——软唇裂腹鱼（一种喜流水的鲤科鱼类）和巨魾（一种大型鲶鱼）的分布范围分别缩小了19.2%和32.8%，部分原因可能是河流屏障的修建。我们的研究结果表明，小型屏障，尤其是堰闸以及小型水坝是澜沧江栖息地破碎化的主要原因，在湄公河的水资源管理和生物多样性保护中，必须将其与大型水坝一同加以考虑。
