Spatiotemporal changes of eutrophication and heavy metal pollution in the inflow river system of Baiyangdian after the establishment of Xiongan New Area

Metal contamination, their ecological risk, and relationship with other variables in surface sediments of urban rivers in a big city in Asia: case study of Hanoi, Vietnam

Urban rivers are significantly impacted by anthropogenic pressure. This study presents the updated assessment of the concentrations of 11 metals and other variables (pH, total organic carbon (TOC) and nutrients (total nitrogen, total phosphorus, and total silica)) in the sediments of four urban rivers in inner Hanoi city, Vietnam, during the period 2020-2022. The mean concentrations of Fe, Zn, As, and Cr were higher than the permissible values of the Vietnam National technical regulation on the surface sediment quality. Moreover, Zn and Cr were at the severe effect level of the US EPA guidelines for sediment quality. The calculation of pollution indices (Igeo and EF) demonstrated that Mn, Ni, and Fe were from natural sources whereas other metals were from both anthropogenic and natural sources. The ecological risk index revealed that metals in Hanoi riverine sediments were classified at considerable ecological risk. High values of metals, TOC, and nutrients in the sediments of these urban rivers mostly originate from the accumulation of untreated urban wastewater that is enhanced by low river discharge. Our results may provide scientific base for better management decisions to ensure environmental protection and sustainable development of Hanoi city.

Pollution in river tributaries restricts the water quality of ecological water replenishment in the Baiyangdian watershed, China

Natural rivers often have complex water network structures, and the continuous water inflow from tributaries may have crucial impacts on the water quality of ecological water replenishment in the mainstream. This study selected two main inflow rivers of the largest lake in Hebei Province (Baiyangdian), the Fu River and Baigou River, to explore the influence of tributaries on the quality changes of ecological replenishment water in the mainstreams. In December 2020 and 2021, water samples were collected along the two river routes, and eutrophic parameters and heavy metals were determined. The results showed that the tributaries of the Fu River were all severely polluted. With the inflows of the tributaries, the comprehensive pollution index of eutrophication greatly increased along the replenished water route of the Fu River, and the replenished water in the lower reaches of the Fu River mainstream was mostly considered moderate to heavy pollution. Whereas, because the Baigou River's tributaries were only moderately polluted, the water quality in the Baigou River's replenished water was mostly better than moderate pollution. Due to the slight pollution of heavy metals in the tributaries, the replenished water in both the Fu and Baigou Rivers did not show any impact from heavy metal pollution. Correlation and principal component analysis indicated that the main sources of serious eutrophic pollution in the tributaries of the Fu and Baigou Rivers were related to domestic sewage, industrial wastewater, plant decay, and sediment release. This non-point source pollution then caused the decline in the quality of the replenished water in the mainstreams. This study exposed a long-standing but neglected problem in ecological water replenishment and provided a scientific foundation for conducting better water management to improve the inland water environment.