Optimizing manure use and reducing chemical fertilizers are crucial for achieving the Sustainable Development Goals. However, optimal manure redistribution for cropland yield, nitrogen emissions, and greenhouse gas benefit remains unclear at large spatial scales. Here, we employed genetic algorithms and meta-analysis to obtain an optimal substitution rate for major crops in China. This could reduce synthetic nitrogen use and reactive nitrogen pollution by 13.3 and 2.0 Tg, cut ammonia and nitrous oxide emissions by 15.6% and 16.2%, and lower nitrogen runoff and leaching by 32.9%. The yield of eight major upland crops could be increased by 2.0-19.5%. The strategy involves relocating about 255 million pig equivalents, with 32.3% moved across provinces, mainly from central to northern and northeastern China. An estimated US$6.1 billion investment in livestock relocation could yield US$25.9 billion in benefits.

Sewage leakage, including uncollected, collected but exfiltrated, and collected but discharged with stormwater in combined sewer overflows, becomes a key challenge to clean water around the world. This study proposed a mass balance model to quantify sewage leakage and analyzed its influencing factors. Approximately 56% (53%–59%) of domestic total nitrogen loads in the Yangtze River basin of China leak out without treatment, two-thirds are exfiltrated or overflowed, significantly impacting receiving water quality. Cities with higher precipitation have greater leakage, indicating overflows are important. Pipe density has limited impact, showing higher importance of pipe quality over quantity. The per capita leakage rate first increases with city size and then decreases, showing the economies of scale. Yet uneven distribution of population and economy within megacities leads to greater leakage. Hence, separated sewage systems of rainwater and wastewater, regular maintenance and adapting centralized and decentralized systems are recommended, tailored to city-specific leakage characteristics.