Water quality response to hydropeaking regulation of the Three Gorges Dam and Gezhouba Dam, China

Hydropeaking as the most prominent feature of flow alterations resulting from hydropower plants has received attention worldwide. Ramifications of hydropower on the downstream river systems mainly focus on hydrological regimes or long-term water quality changes. Exceptional knowledge is expected on the sub-daily changes of water qualities in the downstream river reach that is affected by the hydropeaking. In this study, we investigate the dynamics of hydropeaking and thermopeaking at the outlet of the Three Gorges Dam TGD using a high temporal resolution dataset, and inspect its association with water chemistry indices. Hourly measurements are analysed for the downstream station Yunchi , and compared with the upstream station Nanjinguan. The results show that along with water temperature, water quality indices such as dissolved oxygen, total Phosphorus, total nitrogen, PH, and electricity conductivity all show evident ‘peaking’ phenomenon in a short time. These divergent variations, however, are not valid for non-hydropeaking affected indicators including turbidity, permanganate index, and ammonia nitrogen. These hydropeaking-induced perturbations are mitigated by the flood control operation from July to September. This study demonstrates that water quality indices are sensitive to hydropeaking and thermopeaking with respect to the magnitude of change and the seasonal component during a year. The results provide additional evidence for the environmental impacts of hydropower regulation on the receiving river reach, and bridge the gap between hydropeaking studies and thermopeaking, and study water qualities variations that were seldom connected from the same temporal perspective in river research.

Filtering Effect of Rhinogobio cylindricus Gut Microbiota Relieved Influence of the Three Gorges Dam on the Gut Microbiota Composition

Fish gut microbiota were potentially influenced by habitat changes. However, the fish gut has been shown to have a filtering effect on habitat microorganisms. Here, we hypothesized that the filtering of fish gut microbiota could counteract the effect of dam construction on the gut microbiota composition. To test this hypothesis, we collected water and Rhinogobio cylindricus individuals from four sampling sites located upstream of the Three Gorges Dam (TGD) and analyzed the microbiota composition in the water samples (n = 48) and R. cylindricus gut samples (n = 89) by high-throughput sequencing of the 16S rRNA gene. A total of 6,772,720 (49,435.91 ± 3762.80) high-quality sequences were obtained from 137 samples. The microbiota in the water environment was significantly more diverse than that in the gut of R. cylindricus. The β-diversity of microbiota in the water was significantly lower than that in the gut of R. cylindricus. The water microbiota composition varied greatly according to the distribution of the sampling sites upstream of the TGD, but the gut microbiota of R. cylindricus did not show the same pattern. Rather, the gut microbiota of R. cylindricus were not significantly affected by the TGD. This consistency in the internal tract of R. cylindricus is presumedly a result of a filtering effect on the water microorganisms. Our study furthers our understanding of the stabilization mechanism of the gut microbiota composition of fish and the impact of dams on river ecosystems.

The Lifestyle-Dependent Microbial Interactions Vary Between Upstream and Downstream of the Three Gorges Dam

Dams represent the most significant anthropogenic disturbance to global rivers. Previous studies have shown that free-living and particle-attached microbes exhibited differentially in river and reservoir ecosystems. However, little is known about the dam’s effect on their co-occurrence patterns. Here, a random matrix theory (RMT)-based network approach was used to construct microbial ecological networks for free-living and particle-attached communities in the immediate vicinity of the Three Gorges Dam (TGD), based on a high-throughput sequencing of 16S rRNA gene. Microbial distribution pattern showed that differences caused by lifestyle (free-living vs. particle-attached) were greater than those caused by geographic position (upstream vs. downstream of the TGD). Network analysis revealed higher connectivity and a lower number of modules in the overall downstream networks. Furthermore, considering the lifestyle, the network structures and properties for free-living and particle-attached microbes were different between upstream and downstream of the dam. Specifically, free-living communities located upstream of the dam exhibited a more complex co-occurrence pattern than the particle-attached communities, whereas the opposite was true for those located downstream of the dam. This variation indicated a strong impact of the dam on microbial interactions for microbes with similar lifestyle in the vicinity of the dam. We identified 112 persistent operational taxonomic unit (OTU)-level species that stably coexisted regardless of lifestyle and geographic positions. These persistent species occupied 21.33–25.57% of the total nodes in each network, and together with their first neighbors, they contributed more than 50% of the nodes and edges belonging to each network. Furthermore, we found that taxonomic affiliations for central nodes (with high degree) varied in these persistent species sub-networks. Collectively, our findings expand the current understanding of the dam’s effect on species interaction variation patterns for free-living and particle-attached communities in the vicinity of the dam, which are more complex than traditional alpha and beta microbial diversity.

Response of vegetation to submergence along Jingjiang Reach of the Yangtze River

This work explores the changes in vegetation coverage and submergence time of floodplains along the middle and lower reaches of the Yangtze River (i.e., the Jingjiang River) and the relations between them. As the Three Gorges Dam has been operating for more than 10 years, the original vegetative environment has been greatly altered in this region. The two main aspects of these changes were discovered by analyzing year-end image data from remote sensing satellites using a dimidiate pixel model, based on the normalized difference vegetation index, and by calculating water level and topographic data over a distance of 360 km from 2003–2015. Given that the channels had adjusted laterally, thus exhibiting deeper and broader geometries due to the Three Gorges Dam, 11 floodplains were classified into three groups with distinctive features. The evidence shows that, the floodplains with high elevation have formed steady vegetation areas and could hardly be affected by runoff and usually occupied by humans. The low elevation group has not met the minimal threshold of submerging time for vegetation growth, and no plants were observed so far. Based on the facts summed up from the floodplains with variable elevation, days needed to spot vegetation ranges from 70 to 120 days which happened typically near 2006 and between 2008 and 2010, respectively, and a negative correlation was detected between submergence time and vegetation coverage within a certain range. Thus, floods optimized by the Three Gorges Dam have directly influenced plant growth in the floodplains and may also affect our ability to manage certain types of large floods. Our conclusions may provide a basis for establishing flood criteria to manage the floodplain vegetation and evaluating possible increases in resistance caused by high-flow flooding when these floodplains are submerged.