Suhua Meng

Due to the lack of research on the temporal variation in As in the lower Yellow River and the extreme rainfall during the 2021 rainy season, this study aimed to investigate the As distribution patterns and their evolution driven by water level changes. Principal component analysis (PCA) revealed that As mobilization was predominantly controlled by redox conditions and mineral dissolution/desorption processes. The distribution of high-As water exhibited significant spatial variability, mainly located in the alluvial fan plain (14.97 μg/L) and marine-alluvial plain (22.5 μg/L). The average As concentrations in the study area decreased by 3.78 μg/L(11.55 μg/L in May and 7.77 μg/L in September). High-As groundwater was highly sensitive to water level fluctuations, while low-As groundwater was less affected. In the alluvial fan plain, As decreased with a 0–2 m groundwater level rise but increased when the level exceeded 4 m. A sedimentary zone–As distribution–water level sensitivity response model was proposed, which provides important reference value for developing groundwater exploitation and utilization plans.

(1) Background: This study aims to provide a viable theoretical framework for wetland ecological restoration in the lower reaches of the Yellow River within the city of Kaifeng, China. (2) Methods: Using remote sensing and image interpretation to identify the long-term evolution characteristics of wetlands in the study area and analyzing the impact of runoff, riverway changes, and groundwater flow fields in the lower reaches of the Yellow River on wetland conditions along the Yellow River. (3) Results: With natural wetland as its major wetland type, the study area saw an increase in the total wetland area from 2000–2021. Among others, the total area of artificial wetlands increased by 43%, while that of flooding wetlands in natural wetlands decreased by 37%. Surface water discharge and water level saw a year-by-year drop. Moreover, the significant wandering and oscillations of riverways led to a direct impact on the area and stability of tidal flat wetlands. After 2010, affected by rainfall and exploitation, the groundwater level declined sharply. The degraded areas of artificial wetlands were mainly distributed at the northern embankment of the Yellow River, where the groundwater burial depth decreased significantly. In contrast, at the southern embankment, for the sake of the irrigation canal diverted from the Yellow River, new back river depressions had formed and helped build a more stable ecological environment. Yellow River water levels and discharge directly impacted the area of rivers and flooding wetlands. The decline in groundwater levels led to the degradation of ponds in artificial wetlands. (4) Conclusions: The reduction of groundwater exploitation and an adequate supply of diverted Yellow River water were conducive to the development of wetlands in the back river depressions on the outside of the Yellow River embankment.