Yuhu Chang

A series of coastal development initiatives have been recently implemented in the East Harbor area of Tieshan Harbor, Guangxi Province, China. However, the ecological impacts of these reclamation activities on toxic metal pollution levels in shallow mangrove sediments within the intertidal zones adjacent to Langen Village, Tieshan Bay (Beibu Gulf), remain poorly understood. This study investigated the distribution patterns, ecological risks, and potential sources of seven toxic metals (Pb, Cu, Zn, As, Cr, Cd, and Hg) in surface sediments collected from 26 sampling locations across dead mangrove zones, severely degraded mangrove areas, and currently intact mangrove ecosystems near Langen Village during April 2022. We employed multiple assessment metrics including the pollution load index (PLI), geoaccumulation index ( I _geo ), sediment quality guidelines, individual potential ecological risk factors, and potential ecological risk index (RI) to evaluate contamination status and associated ecological hazards. Results indicate moderate contamination and medium ecological risk according to I _geo , PLI and RI in intertidal sediments, with significantly higher toxic metal concentrations in dead and severely degraded mangroves than in temporarily undamaged areas. Total unit toxic index analysis revealed generally low biological toxicity from surface sediment metals, with Hg, Cd, and As identified as dominant ecological hazard factors. These findings provide a critical scientific basis for enhancing mangrove conservation strategies and developing targeted management protocols.

This study analyzed the multivariate drought risks for the Wei River basin by characterizing the interdependence between the standardized precipitation index (SPI) and the standardized precipitation evapotranspiration index (SPEI). Both parametric and nonparametric copulas were adopted to quantify the dependence between the SPI and SPEI. The results indicated that the Gaussian copula demonstrated the best fit in most cases, while the nonparametric copula method showed superiority over the parametric models at only one out of eighteen meteorological stations. The joint return periods (T^OR, T^AND, and T^Kendall) were computed through copula modeling, providing valuable insights into the co-occurrence of extreme drought events. For the SPI and SPEI with a 50-year return period, the T^OR values range from 25.5 to 37.9 years, the T^AND values fluctuate between 73.4 and 1233 years, and the T^Kendall values range from 60.61 to 574.71 years, indicating a high correlation between the SPI and SPEI in the study area. The spatial analysis revealed varying patterns across the basin with some regions more prone to experiencing simultaneous drought conditions characterized by both the SPI and SPEI. Furthermore, our results indicated that the SPEI exhibited more severity in drought characterization than the SPI due to its consideration of temperature effects. The disparities in the spatial features of the SPI and SPEI underscore the importance of incorporating multiple meteorological factors for a comprehensive drought risk analysis. This research contributes to a better understanding of the drought patterns and their joint risks in the Wei River basin, offering valuable information for drought preparedness and water resource management.