Water and sediment regulation aimed at aquatic ecosystems and preserving reservoir capacity to minimize the negative consequences of dams can fundamentally change the distribution of heavy metals (HMs) in the reservoir and downstream reaches. However, the effects of water and sediment regulation on variation in HMs are still poorly understood. In this study, the variations in concentration, contamination, human health risk, potential sources, and influencing factors of the metalloid As and HMs (Cr, Hg, Ni, Pb, and Zn) in surface water in the reservoir and the downstream reach of the Xiaolangdi Dam (XLD) following the operation of the water-sediment regulation scheme (WSRS) were determined. These results indicate that HM concentrations in the two post-WSRS seasons were much lower than the water quality standards, but were significantly increased over time due to the trapping effects of the XLD (p < 0.05, except for Zn). However, As concentration in the reservoir was significantly lower than that observed in downstream reaches, likely due to anthropogenic input from agricultural activities. Meanwhile, HM concentrations varied with distance to the dam, which displayed a distinct accumulation closer to the dam in the post-WSRS II season. The contamination of HMs, the carcinogenic risk of exposure to As, and the noncarcinogenic risks associated with exposure to Hg, Ni, Pb, and Zn via the direct ingestion pathway of drinking water were all within acceptable levels following the WSRS, but increased over time. The carcinogenic risk of Cr in the post-WSRS II season was at an unacceptably high level, particularly at sites near the dam. Hydrological characteristics (water level and flow rate) were the dominant factors in determining the distribution of HMs. These results can provide new insight for a better understanding of the variations in HMs following the water and sediment regulation practices, and guide future management in regulating the trapping effects of dams.
Species turnover is fundamental for understanding the mechanisms that
influence large-scale species richness patterns. However, the
large-scale spatial variation and the causes in soil animal species
turnover remain elusive. In addition, the determinants of species
turnover depend on the dispersal ability of guilds. In this study, we
explored the large-scale patterns of meso-micro soil fauna turnover
pattern and the driving factors based on fourteen sampling sites in East
Asia. The patterns of soil fauna species turnover increased
significantly with increasing latitude differences in East Asia. The
environment explained 54.09, 50.62, and 57.34% of the total variance,
and spatial factors explained 13.84, 15.91, and 21.04% of the total
variance in species composition of overall, phytophage, and predacity
faunas, respectively. Meanwhile, the effects of climate factors in
environmental processes were stronger than that of soil factors in these
three groups. Our results support the hypothesis that the effect of
environment processes on soil animal species turnover is more important
than the effect of the neutral. Climatic factors explained more
variation for turnover of phytophage faunas, but soil and environment
factors explained equally for predacity. Our results provide evidence
supporting both environmental filtering and dispersal limitation
hypotheses on the reginal and population scales. At last, this study has
important theoretical significance and applied value in maintaining and
promoting soil biodiversity and ecosystem services on the large scale.
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