Ecological Indicators (Dec 2021)
Influence of saline intrusion on the wetland ecosystem revealed by isotopic and hydrochemical indicators in the Yellow River Delta, China
Abstract
Yellow River Delta wetland is a nature reserve with important ecological function and service values. It is of great significance for regional ecological protection and species diversity maintenance to systematically evaluate the impact of saline intrusion on wetlands. Based on the sampling campaigns for precipitation, seawater, river water and wetland water in dry, transition and wet season, this study aims to assess the temporal and spatial characteristics of hydrochemistry and water quality in wetland areas and quantify the ecological risks brought by saline intrusion. Isotopic evidence shows that wetland water is affected by intense evaporation, and its source has significant seasonal variation. Piper diagram suggests that the hydrochemical characteristics of wetland water are controlled by the supply from Yellow River water and saline intrusion. Water quality assessment based on metrics of soluble sodium percentage (Na %), sodium adsorption ratio (SAR) and Kelley's radio (KR) indicates that the sodium and salinity hazards caused by saline intrusion lead to negative effects on plant growth for most wetland sites. The risk from high salinity is more serious than that from sodium hazard for the wetland ecosystem. From dry to wet season, water quality in wetlands shows a pronounced trend of deterioration. End member mixing analysis (EMMA) based on principal component analysis (PCA) is employed to quantify the spatio-temporal characteristics of saline intrusion. The results show that the proportion of seawater in wetlands increases at first and then decreases along the stream direction, reflecting the influence of hydrogeological and hydrodynamic variation on water interaction. The proportion of seawater in wetland water ranges between 0 % and 11.86 %, but it poses a severe threat to water quality and ecosystem safety in wetland area. This study will provide insights for environmental risk assessment and water resources management in coastal wetlands.
