Enhancing the engineering design of diversion routes to safeguard water quality: New insights from a carbon cycling perspective

Conserving the quality of transferred water ensures the success and sustainability of interbasin water diversion works, which are increasingly crucial for global water security. Despite intensive scientific and engineering efforts, carbon dynamics in these artificial rivers have been overlooked. The accumulation of organic mud in some water transfer canals, for example, in the Middle Route of the South-to-North Water Diversion (SNWT) in China, poses multifaceted risks, including jeopardized water quality, disrupted water supply, and surging mud removal expenses. In contrast, natural channels for water delivery, such as the parallel East Route of the SNWT, do not experience mud accumulation challenges. Our study reveals that the open concrete canal of the Middle Route, devoid of connections to local water bodies, compromises hydrological connectivity, contrasting with the East Route, which enhances it. This, in turn, undermines microbial stochastic assembly processes, impedes the introduction of habitat-generalist microbial species, and facilitates detrital carbon accumulation within the ecosystem, presumably due to constraints on bacterial community functions. These findings can improve future engineering designs of water transfer schemes, including water diversion approaches and channel construction, for preserving transferred water quality.