Cascade dams altered taxonomic and functional composition of bacterioplankton community at the regional scale.

Dams are increasingly disrupting natural river systems, yet studies investigating their impact on microbial communities at regional scale are limited. Given the indispensable role of bacterioplankton in aquatic ecosystems, 16S rRNA gene sequencing was performed to explore how these communities respond to dam-influenced environmental changes at the regional scale in the Shaying River Basin. Our findings revealed that cascade dams create distinct environments, shaping bacterioplankton communities near the dams differently from those in natural rivers. In the upstream of the cascade dams, water quality was superior, while bacterioplankton community structure was simple with weak community interactions. In the midstream, nutrient and heavy metal content were increased, making bacterioplankton structures more susceptible to environmental changes. In the downstream of the cascade dams, water quality had a significant impact on the community and the bacterioplankton structures were highly complex. Additionally, environmental variables significantly influenced bacterioplankton functional groups. However, the response to these factors, as well as the interplay between functional and taxonomic diversity, varied markedly depending on the specific region of the cascade dams. We here delved into the effects of cascade dams on the taxonomic diversity and functional groups of bacterioplankton to provide a theoretical basis for segmentally regulating these dams.

Intensive human land uses cause the biotic homogenization of algae and change their assembly process in a major watershed of China.

Human land uses are a crucial driver of biodiversity loss in freshwater ecosystems, and most studies have focused on how cities or croplands influence alpha diversity while neglecting the changes in community composition (beta diversity), especially in algae. Here, we examined the taxonomic and functional composition of algae communities and their underlying drivers along the human land-use intensity gradient in the Huai River basin, the third largest basin in China. Our results indicated that the increased intensity of human land use caused biotic homogenization (decreasing compositional dissimilarity between sites) of algae communities in terms of both taxonomic and functional traits. Functional beta diversity was more sensitive to human land uses than taxonomic beta diversity. Furthermore, we found that the increased intensity of human land use altered algae assemblage processes. As opposed to the low- or moderate-intensity human land uses, in high-intensity groups, species sorting rather than dispersal limitations dominated algae community assembly. NO2-N, HCO3, and Fe were the major factors explaining the variance in the taxonomic and functional beta diversities of algae. Human land use reshaped the taxonomic and functional structures of algae, raising concerns about the ecological processes altered by human activity.

Damming has changed the migration process of microplastics and increased the pollution risk in the reservoirs in the Shaying River Basin.

The impact of damming on river ecosystems has received increasing attention, but a comprehensive understanding of the occurrence, drivers and exposure risks of microplastic (MP) pollution in multigate dam-type rivers is lacking. We investigated the characteristics and abundance of MPs in water, sediment and biological tissues from samples collected in the vicinity of ten dams in the Shaying River basin and analyzed the effect of environmental and food web structural changes on MP accumulation in freshwater animals under the influence of dams. Dam construction affects the transportation, suspension, and deposition of MPs at different dam locations (upstream, reservoir, and downstream) by altering hydrodynamihas changed the migration process of MPs. The dams intercepted a large amount of MPs from upstream sediments in the reservoir but had no significant capturing effect on MPs in water. The structure of the food web in the reservoir was simplified and the animals in the reservoir had the highest risk of MP contamination. A high MP abundance (or high microplastic diversity integrated index (MDII) values) in the environment or simplification of the food web may have led to higher MP accumulation in animals. More effort is needed to monitor MP pollution in reservoirs and control it sources.

Can snakes use yolk reserves to maximize body size at hatching?

We experimentally miniaturized freshly laid eggs of the Chinese cobra Naja atra (Elapidae) by removing ∼10% and ∼20% of original yolk. We tested if yolk-reduced eggs would produce 1) normal-sized hatchlings with invariant yolk-free body mass (and thus invariant linear size) but dramatically reduced or even completely depleted residual yolk, 2) smaller hatchlings with normal-sized residual yolk but reduced yolk-free body mass, or 3) smaller hatchlings of which both yolk-free body mass and residual yolk are proportionally reduced. Yolk quantity affected hatchling linear size (both snout-vent length and tail length) and body mass. However, changes in yolk quantity did not affect incubation length or any hatchling trait examined after accounting for egg mass at laying (for control and sham-manipulated eggs) or after yolk removal (for manipulated eggs). Specifically, yolk-reduced eggs produced hatchlings of which all major components (carcass, residual yolk, and fat bodies) were scaled down proportionally. We show that snakes cannot use yolk reserves to maximize their body size at hatching. Furthermore, our data also suggest that the partitioning of yolk in embryonic snakes is species-specific.