Multifaceted biodiversity measurements reveal incongruent conservation priorities for rivers in the upper reach and lakes in the middle-lower reach of the largest river-floodplain ecosystem in China

Bioaccumulation and health risks of multiple trace metals in fish species from the heavily sediment-laden Yellow River

The health risk caused by metal pollution is a global concern due to potential metal bioaccumulation, toxicity, and carcinogenicity with multiple sources and pathways. Here, the factors influencing metal bioaccumulation in more than a thousand fish individuals were investigated along a 5464 km continuum of the heavily sediment-laden Yellow River and the health risks to humans were evaluated. The average concentrations of Cr, Zn, As, Cu, Cd, and Pb were below the permissible limits established by domestic and foreign organizations. The fish showed biomagnification of Se and Sn through trophic transfer and a growth dilution effect for V, Mn, Co, Ni, Cu, Zn, As, Cd, and Ba. The concentrations and distributions of most metals in fish were mainly influenced by the trophic levels (δ¹⁵N) of fish and the content of the metals in the aquatic environment. The consumption of fish from the Yellow River does not pose a noncarcinogenic risk to the health of adults and juveniles. Cr and As could cause carcinogenic risks, and Cd and Pb also have carcinogenic risks, but these were within an acceptable range. The carcinogenic risks of fish consumption were relatively low in regions with low levels of metal pollution, such as the source region, while the risks were high in regions with heavy pollution and carnivorous fish at high trophic levels. In response to this threat, people can minimize these risks by adjusting their diet and appropriately reducing their consumption of aquatic products from the Yellow River.

Assessment of heavy metal accumulation in freshwater fish of Dongting Lake, China: Effects of feeding habits, habitat preferences and body size

We measured the concentrations of Cr, Fe, Ni, Cu, Zn, Cd, Pb and Hg, and the stable isotope ratios (δ¹³C and δ¹⁵N) in 87 fish samples within 12 economic fish species collected from the Dongting Lake, the second largest freshwater lake in China. With few exceptions in concentration of Cr, most of fish species showed lower concentrations of the 8 metals than legislation thresholds. Piscivorous fishes had significantly higher values of δ¹⁵N (possessing higher trophic level) and metal concentrations than planktivorous and herbivorous fishes. Moreover, demersal fishes showed higher concentrations of Cu, Zn, Cd and Pb than pelagic and benthopelagic fishes. We found positive correlations between concentrations of Fe, Pb and Hg and δ¹⁵N ratio, confirming the biomagnification of the three metals through trophic transfer. In contrast, fishes showed clear growth dilution effect for Ni, Zn, Cu, Pb and Hg, indicated by the negative correlations between their concentrations and fish weight or length. Multiple regression analysis demonstrated that growth dilution and biomagnification effects simultaneously governed the metal concentrations in fish muscle, and the two effects' importance varied among different metals. The human health risk assessment indicated that all 8 metals gave target hazard quotient (THQ) values < 1.0, i.e., the estimated daily intake (EDI) of metals did not exceed the oral reference dose (RfD), indicating a safe consumption of these fish species for consumer. Our study provides comprehensive approaches to better understand the determining processes and potential risk of heavy metals in freshwater lake fishes.

Fish taxonomic, functional, and phylogenetic diversity and their vulnerabilities in the largest river in southeastern China

Freshwater biodiversity is currently under multiple threats. Conservation of freshwater fish biodiversity needs to be prioritized because natural conservation resources are always limited.Samples were collected at 24 sites in the Min River, the largest basin in southeastern China. Taxonomic, functional, and phylogenetic diversity were analyzed. Biodiversity vulnerability was measured by removing one species each time out of the community with replacement.Results suggested that hotspots for taxonomic and phylogenetic diversity were located at two impounded sites, while for functional diversity were those sites with no upstream dams. Little congruence was observed between taxonomic, functional, and phylogenetic diversity. Fragmentation of river network connectivity caused by dams was a significant factor affecting the biodiversity patterns. Beta turnover was the driving component for beta diversity, indicating that biodiversity dissimilarity along the river was mostly explained by environmental sorting. Fifteen out of 16 species that contributed the most to different facets of biodiversity were mostly endemic, either they had distinctive functional traits or they were the most prevalent species. Sites with the highest diversity vulnerability were characterized by these distinctive species. Functional diversity was more vulnerable to species loss comparing with the other two biodiversity facets.Prioritizing those biodiversity hotspots, sites with extreme functional vulnerability, and those distinctive endemic species which contributed the most to biodiversity vulnerability is suggested in the Min River. The study found evidence that congruence among different facets of biodiversity is hard to achieve, and functional diversity is the most vulnerable in a freshwater system fragmented by intensive dam constructions. This work will help to develop systematic conservation planning from the perspective of different biodiversity facets.

Effects of long-term floodplain disconnection on multiple facets of lake fish biodiversity: Decline of alpha diversity leads to a regional differentiation through time

Hydrological disconnection is increasingly threatening biodiversity in river floodplain ecosystems worldwide, but studies reporting long-term change of aquatic biodiversity in relation to floodplain disconnection are seldom, especially from multifaceted biodiversity perspectives. Here, we examined how loss of river-lake connectivity affected multifaceted (taxonomic, functional and phylogenetic) alpha and beta diversity of fish assemblages in 11 Yangtze River floodplain lakes over the past 70 years. We found that all three facets of alpha diversity significantly decreased through time, but the decrease rate was highest (31.4%) in taxonomic richness, second in functional (26.4%) and lowest in phylogenetic facet (4.7%). Nevertheless, taxonomic, functional and phylogenetic structures of fish fauna all exhibited differentiation. The taxonomic and phylogenetic differentiations were due to the joint increases in their turnover and nestedness-resultant component, whereas the functional differentiation was mainly driven by the increase in its turnover component. Such distinct results were because of the imbalanced extirpations of fish species (especially from species-poor orders and families) in disconnected lakes and connected lakes. With few exceptions of strong correlations between changes in taxonomic dissimilarities and phylogenetic dissimilarities, we generally found weak correlations between changes in different facets of both alpha and beta diversity. This discrepancy highlights that measuring different biodiversity facets offer distinct information about biodiversity dynamics and can enhance our ability to detect and evaluate the impacts of floodplain disconnection on biodiversity. We therefore recommend an integrative approach embracing taxonomic, functional and phylogenetic diversity is essential to effective biodiversity assessment and conservation in large river floodplains.