This article sorts out China’s blue carbon trading-related policies, trading cases and their distribution, industry standards and methodologies, analyzes the characteristics of the current blue carbon market, and explores the challenges faced and future solutions. Currently, China’s blue carbon market is characterized by regional specialization, diversified types, and scientific accounting, but it also faces issues such as market irregularities, unclear trading entities, and inadequate maintenance of blue carbon’s resilience. We suggest promoting the healthy development of the blue carbon market by establishing a comprehensive blue carbon trading system, diversifying trading entities and methods of value realization, and enhancing risk assessment research on coastal carbon sink ecosystems, so as to provide support for China’s achievement of carbon neutrality goals.

Based on the monitoring data of 18 river sections, this study investigated the spatiotemporal distribution, sources and ecological risks of 8 heavy metal ions in the upper reaches of Wujiang River, and analyzed the influence of dissolved organic matter (DOM) on the migration and distribution of heavy metals. The results showed that the overall content of heavy metals in the upper reaches of Wujiang River was low with significant seasonal variations, and the average concentrations of Cr, Fe, Co, Ni, Cu, As, Cd and Sb were 0.71, 19.20, 0.17, 1.09, 0.73, 0.65, 0.06 and 1.22 μg/L, respectively, which were all lower than the level of Class III of the Environmental Quality Standard for Surface Water. Principal component analysis revealed a homology among Cr, Fe, Co, Ni, Cd and Sb, primarily sourced from natural origins. Cu was additionally affected by industrial activities including electroplating, printing and dyeing, while as was partially originated from the application of pesticides and fertilizers. Heavy metals showed positive correlations with DOM and its fluorescent components C1–C4, indicating that DOM could promote the migration and enrichment of heavy metals in water. Cr, Fe, Co, Ni and Sb showed significant positive correlation with DOM characteristic parameters SUVA₂₅₄ and BIX, further confirming that DOM with higher aromaticity and biological reactivity showed higher metal affinities. The evaluation results of single factor and Nemerow comprehensive pollution index suggested that the pollution level of heavy metals in the upper reaches of the Wujiang River retained relatively low, rendering it an ideal source of drinking water. However, the potential ecological risks of heavy metals under the influence of DOM need more concern. 

Based on the hydrogen and oxygen isotope data of water bodies, this study identifies the streamflow components of the mainstream channels using the MixSIAR mixed model for 22 sample sub-basins in the Tarim Basin. The relationships between streamflow components and basin characteristics for endorheic rivers were analyzed by further combining climate and underlying surface conditions of sub-basins. It appears that the sub-basins in the southern Tarim Basin primarily rely on precipitation for their streamflow, accounting for 39%−55%, 23%−30%, 22%−32% for precipitation, and glacial meltwater sources, respectively. The sub-basins located in the oasis area of the northern Tarim River are predominantly influenced by groundwater recharge, with a component proportion of 14%−32%, 44%−76%, 0%−39% for streamflow sources. Furthermore, the sub-basins primarily supplied by meltwater are predominantly found in the southwest region of the Tarim Basin, with a proportion of 29%−33%, 14%−31%, 40%−53%. Among various basin factors examined, actual evaporation, soil water content, vegetation index, and area proportion of desert area and glacier area emerged as key influencing factors on streamflow composition for the sub-basins of the Tarim Basin. It was also found that basin underlying surface conditions substantially impact variations in streamflow components. This result provides a scientific foundation for effective water resources management and ecological preservation within inland river basins amidst changing climatic conditions. 

Through the extraction and analysis of Landsat 5, 7 and 8 long time series remote sensing image data, the practical single channel algorithm was used to invert the monthly long series water temperature data set of the Yangtze River Estuary from 1997 to 2016. Meanwhile, based on the global runoff data, the annual monthly mean heat flux at the Yangtze River Estuary during the same period was calculated. The temporal and spatial variations and response characteristics to climate change and human thermal emission were analyzed. On this basis, combined with the global ocean surface temperature data and the Copernicus global ocean color and biogeochemical data set, the influence of the heat flux change from the Yangtze River to the sea on the offshore water temperature and the offshore ecological environment was explored. The results show that the total heat flux in the Yangtze River Estuary is 77.5 EJ per year, and the seasonal variation of heat flux is obvious. The heat flux mainly used for heat transport to the coastal area is significantly higher than that in other typical river systems, and the average annual heat input to the coastal area is estimated to be 6.1 EJ, and the warming effect is obvious. Compared with the coastal zone, the influence of the Yangtze River Estuary on the temperature of the coastal waters is greater and the influence on the spatial range is further. The spatial influence on offshore water temperature can be divided into two gradients, namely, the riverine strong influence zone with decreasing temperature (0–40 km) and the ocean strong influence zone with increasing temperature (more than 40 km). From 1997 to 2016, the temperature of the coastal waters of the Yangtze River Estuary as a whole increased first and then decreased. Further analysis shows that the heat flux change in the Yangtze River Estuary has a profound effect on the offshore water temperature (R²=0.7495), and is closely related to the offshore primary productivity (R²=0.9651), indicating that the heat input from the Yangtze River to the offshore water is an important factor regulating the offshore thermal environment and ecological environment. 

Based on monitoring data of monthly average COD, TN, and TP concentrations at Chenglingji hydrological station in Dongting Lake from 1990 to 2015, the intra-annual variation, inter-annual variation patterns of nutrients in the water column of Dongting Lake were systematically studied by trend analysis, and further revealed their stoichiometric ratio characteristics and discussed the effects of nutrient concentrations and structure on algal growth. The findings showed that the intra-annual variation patterns of average COD, TN, and TP were similar, indicating that the nutrient content in dry season was higher than that in wet season. However, as for multi-year trend, the annual average COD, TN, and TP in Dongting Lake showed a significant increase since 1990, while C:N and C:P ratios decreased and N:P ratio increased over time. The average C:N:P ratio in the water column of Chenglingji station in Dongting Lake was 13:18:1, and redundancy analysis showed that nutrient concentrations and stoichiometry ratios in the water would affect algae growth, with C:N, C:P and COD playing a dominant role. During the study period, the overall nitrogen and phosphorus content of the water column in Chenglingji station was generally high and has already met the algae growth demand. In order to avoid adverse ecological consequences such as harmful algal bloom events, external nitrogen and phosphorus inputs should be controlled to maintain the stoichiometric ratio balance in the water column of Dongting Lake.