Metal distribution, environmental risk assessment, and microbial community shifts along the Old Course of Yellow River (Shangqiu Section)

The Old Course of Yellow River (OCYR), serving as a vital reminder of ancient civilizations and ecosystems, contributes significantly to agricultural irrigation, tourism growth, and acts as a natural barrier against floods and erosion. Unfortunately, it’s rare to find research about the OCYR and there are no reports about the metal distribution characteristics, environmental risk assessment, and microbial communities along the OCYR. In this report, 18 water samples, 18 sediment samples, and 162 soil samples were collected from 6 sampling sites (A-Fanzhuang Village, B-Xinwen Village, C-Linqi Reservoir, D-Forest Park, E-Tianmu Lake, F-Liuyang Village) along the OCYR (Shangqiu section). Average water metal concentrations (Co: 3.028 ± 1.367, Cu: 16.88 ± 15.28, Ni: 15.73 ± 14.67, Mn: 79.58 ± 74.95, Ba: 174.7 ± 108.9, and Ti: 16.71 ± 9.812 μg·L−1) were below the WHO limits, but Co (notably in E and F) and Ni (particularly in D) need closer attention. Soil and sediment metal averages (Co: 7.891 ± 2.053, Cu: 4.446 ± 1.853, Ni: 17.90 ± 13.38, Mn: 224.6 ± 57.63, Ba: 246.7 ± 57.68, and Ti: 948.5 ± 152.3 mg·kg−1) remained below the Chinese background levels, yet continuous monitoring is crucial to prevent future accumulation, especially at sites A and F. Vertical distribution analysis revealed that metal distribution varies across sites (A-F) in enrichment depths and statistical significance. Speciation distribution analysis revealed most metals were in the residual fraction, posing minimal risk to the environment, while RAC analysis showed medium-high risk for Ba and Mn in some regions. Microbial community analysis revealed the dominance of Proteobacteria and Actinobacteriota, with Pseudorhodobacter and unclassified genera belonging to the order Vicinamibacterales being the most abundant genera. The microorganisms associated with metals were Sphingomonas, Pseudorhodobacter, and Thiobacillus, which were likely to be the potential carriers of metals.