Distribution, influencing factors and ecological risk assessment of arsenic in sediments during the water and sediment discharge regulation in the Yellow River Estuary

The water and sediment discharge regulation (WSDR) has been implemented since 2002 to address the water and sediment imbalance in the Yellow River. The arsenic content in the sediments of the Yellow River Estuary in the early, middle, and late stages of the WSDR from 2021 to 2023 was ascertained by inductively coupled plasma mass spectrometry, the distribution changes in As content in the sediments after the implementation of WSDR were studied, and the main factors affecting its distribution were discussed preliminarily. Results show that the average content of As in the sediments in the Yellow River Estuary in 2021, 2022, and 2023 was (13.3±4.3), (11.1±1.8), and (15.3±6.6) mk/kg, respectively. The distribution of sedimentary As in 2021 exhibits a generally gradual decrease off the estuary. In 2022, the low-value area of sedimentary As is predominantly situated in the southern part of the estuary, while the high-value area was concentrated in the northeastern part. Before and after the WSDR in 2023, a high concentration of sedimentary As was observed in the northern and eastern waters of the estuary, with a gradual decrease in distribution during the WSDR. The single-factor index method and land accumulation index method were used to evaluate the pollution status of sedimentary As in the Yellow River estuary. Results show that sedimentary As in most of the observation stations were nil, but during the WSDR it was more serious and concentrated near the estuary. In addition, the effects of WSDR, sediment types, and physical and chemical properties of bottom water on the distribution of sedimentary As in the Yellow River Estuary were discussed. Results indicate that under high runoff conditions, the higher the sand content in the water input from terrestrial sources, the more favorable for the enrichment of sediment As, and the WSDR can affect the sediment particle size effect and thus affect the distribution of sediment As. The increase of bottom water temperature and pH is beneficial to the enrichment of As in sediments, while the effect of dissolved oxygen is just the opposite.