Barrier database (AMBER-GB) for: A Global Assessment of Stream Fragmentation in Great Britain

Artificial barriers are one of the main threats to river ecosystems, resulting in habitat fragmentation and loss of connectivity. Yet, the abundance and distribution of most artificial barriers, excluding high head dams, is poorly documented. We provide a global assessment of the distribution and typology of artificial barriers in Great Britain, and estimate for the first time the extent of river fragmentation. To this end, barrier data were compiled from existing databases and were ground truthed by field surveys in England, Scotland and Wales to derive a correction factor for barrier density across Great Britain. Field surveys indicate that existing barrier databases underestimate barrier density by 68%, particularly in the case of low-head structures (<1 m) which are often missing from current records. Field-corrected barrier density estimates ranged from 0.48 barriers/km in Scotland to 0.63 barriers/km in Wales, and 0.75 barriers/km in England. Corresponding estimates of stream fragmentation, measured as mean barrier-free length, were 12.30 km in Scotland, 6.68 km in Wales and 5.29 km in England, reflecting different anthropogenic pressures. Our study indicates that 97% of the river network in Great Britain is fragmented and none of the rivers are free of artificial barriers.人工障碍物是河流生态系统面临的主要威胁之一，可引发栖息地破碎化与连通性丧失。然而，除高水头大坝（high head dams）外，绝大多数人工障碍物的丰度与分布情况鲜有公开记录。本研究对大不列颠境内人工障碍物的分布与类型进行了全域评估，并首次量化估算了区域内的河流破碎化程度。为此，研究团队从现有数据库中汇编障碍物相关数据，并通过英格兰、苏格兰及威尔士的野外实地调查对数据进行校核，以此推导得到大不列颠全境障碍物密度的校正系数。野外调查显示，现有障碍物数据库低估了68%的实际障碍物密度，尤其是高度低于1米的低水头构筑物（low-head structures），这类设施常未被现有记录收录。经野外校正后的障碍物密度估算值分别为：苏格兰0.48个/千米，威尔士0.63个/千米，英格兰0.75个/千米。以平均无障碍物长度为衡量指标的河流破碎化对应估算值分别为：苏格兰12.30千米，威尔士6.68千米，英格兰5.29千米，这一差异反映了三地不同的人为活动压力。本研究表明，大不列颠境内97%的河网已发生破碎化，无一条河流完全不受人工障碍物的影响。