Wheat straw (WS) has long been subjected to rough treatment by traditional incineration, which not only results in the waste of biomass resources but also poses a risk of atmospheric pollution and is not conducive to the sustainable utilization of natural resources. With great humification potential, WS can be utilized as a valuable composting material. The study optimized the C/N ratio by mixing WS and chicken manure (CM) as composting raw materials, and found that this method could significantly improve the compost quality. In comparison to the conventional poplar woodchip (PW) conditioning, the incorporation of WS resulted in an elevated composting temperature, an extended high-temperature period, a more expeditious lignocellulose degradation, a notable enhancement in the organic matter content, a suppression of hydrogen sulfide production under low C/N ratio, and a promotion of elemental sulfur conversion, collectively contributing to an enhanced overall quality and environmental friendliness of the compost. Correlation analysis of microbial communities and environmental factors demonstrated that the mixed compost facilitated the growth of actinomycetes and sulfur-transforming bacteria. Additionally, structural equation model indicated that parameters such as temperature and pH value played a key role in the composting process.

Nitrate (NO₃⁻) contamination in water is an environmental problem of widespread concern. In this study, we combined the stable isotopes of NO₃⁻ (δ¹⁵N and δ¹⁸O) and water (δ²H and δ¹⁸O) with a Bayesian mixing model (SIAR) to identify the sources and transformation of NO₃⁻ in groundwater and rivers in the Ye River basin of North China. The results showed that the mean NO₃⁻ concentrations in groundwater were 133.5 and 111.7 mg/L in the dry and flood seasons, respectively, which exceeded the required Chinese drinking water standards for groundwater (88.6 mg/L) (GB14848-2017). This suggests that groundwater quality has been severely impacted by human activity. Land use significantly affected the concentration of NO₃⁻ in the Ye River basin (p < 0.05). However, the NO₃⁻ concentrations in groundwater and river water had no obvious temporal variation (p > 0.05). The principal mode of nitrogen transformation for both groundwater and river water was nitrification, whereas denitrification did not significantly affect the isotopic compositions of NO₃⁻. The sources of NO₃⁻ mainly originated from sewage and manure, soil nitrogen, and NH₄⁺ in fertilizer for groundwater and from sewage and manure for the river water. According to the SIAR model, the primary sources of nitrate found in groundwater and river were sewage and manure in the Ye River basin. The proportional contributions of sewage and manure to nitrate contamination of groundwater and river were 58% and 48% in the dry season and 49% and 54% in the flood season, respectively. Based on these results, we suggest that the local government should enhance the sewage treatment infrastructure, construct an effective waste storage system to collect manure, and pursue a scientific fertilization strategy (such as soil formula fertilization) to increase the utilization rate of nitrogen fertilizer and prevent nitrate levels from increasing further.