River systems have critical roles in the natural water environment and the transportation of nutrients. Anthropogenic activities, including wastewater discharge and river damming, raise adverse impacts on ecosystem and continuum of rivers. An increasing amount of attention has been paid to riverine bacterioplankton as they make vital contributions to biogeochemical nutrient cycle. A comprehensive study was conducted on the bacterioplankton community along the Yarlung Tsangpo River, which is the longest plateau river in China and is suffering from various anthropogenic impacts. The results indicated that nutrient variations corresponded to anthropogenic activities, and silica, nitrogen and phosphorus were retained by the dam. River damming influenced the biomass and diversity of the bacterioplankton, but significant alterations in the community structure were not observed between upstream and downstream of the dam. Moreover, the spatial distribution of the bacterioplankton community changed gradually along the river, and the dominant bacterioplankton in the upstream, midstream and downstream portions of the river were Firmicutes, Bacteroidetes and Proteobacteria, respectively. Soluble reactive phosphorus, elevation, ammonium nitrogen, velocity and turbidity were the main environmental factors that shape the bacterioplankton community. Our study offers the first insights into the variation of a bacterioplankton community of a large river in plateau region.

In recent decades, damming has become one of the most important anthropogenic activities for river regulation, and reservoirs have become hotspots for biogeochemical cycling. The construction of dams changes riverine hydrological conditions and alters the physical, chemical, and biological characteristics of rivers, eventually leading to significant variations in nutrient cycling. This review mainly explores the effects of river damming on nutrient transport and transformation, including i) nutrient (N, P, Si, and C) retention in reservoirs, ii) greenhouse gas (GHG) emissions, and iii) interactions between the nutrient stoichiometry ratio and the health of the reservoir ecosystem. The important drivers of nutrient transport and transformation, such as river connectivity, hydraulic residence time, hydropower development mode, microbial community variation, and anthropogenic pollution, have also been discussed. In addition, strategies to recover from the negative effects of damming on aquatic ecosystems are summarized and analyzed. To provide theoretical and scientific support for the ecological and environmental preservation of river-reservoir systems, future studies should focus on nutrient accumulation and GHG emissions in cascade reservoirs.

The inhibition of cyanobacteria growth by allelochemicals, which controls harmful algal blooms has been examined in many studies. The objective of this work was to compare the efficiencies of different allelochemicals and determine a mixing proportion corresponding to the highest algae inhibiting activity and smallest adverse effect. The obtained results demonstrated that artemisinin, nonanoic acid, malonic acid, and ethyl acetate inhibited algal growth more efficiently than D-menthol and lactic acid. Synergies were observed in five groups of allelochemical combinations with inhibition ratios exceeding 80%, and the concentrations of extracellular microcystin-LR in the groups with high algal inhibition ratios were lower than that in the control group on the 7th day. No changes in extracellular polymeric substances compositions were detected after treatment. The permanganate indices of the treated groups were higher than that of the control group; however, this disparity gradually decreased with time. In addition, a sharp decrease in the concentration of dissolved inorganic phosphorus was observed for all treated groups. From the obtained data, the optimal proportion of mixed allelochemicals corresponding to 3.94 mg L⁻¹ of artemisinin, 6.27 mg L⁻¹ of nonanoic acid, 8.2 mg L⁻¹ of malonic acid, and 6.38 mg L⁻¹ of ethyl acetate was suggested.

Blooms of harmful cyanobacteria have been observed in various water bodies across the world and some of them can produce intracellular toxins, such as microcystins (MCs), which negatively impact aquatic organisms and human health. Iron participates significantly in cyanobacterial photosynthesis and is proposed to be linked to MC production. Here, the cyanobacteria Microcystis aeruginosa was cultivated under different iron regimes to investigate the relationship between photosynthetic capacity and MC production. The results showed that iron addition increased cell density, cellular protein concentration and the Chl-a (chlorophyll-a) content. Similarly, it can also up–regulate photosynthetic capacity and promote MC–leucine–arginine (MC–LR) production, but not in a dose–dependent manner. Moreover, a significant positive correlation between photosynthetic capacity and MC production was observed, and electron transport parameters were the most important parameters contributing to the variation of intracellular MC–LR concentration revealed by Generalized Additive Model analysis. As the electron transport chain was affected by iron variation, adenosine triphosphate production was inhibited, leading to the alteration of MC synthetase gene expression. Therefore, it is demonstrated that MC production greatly relies on redox status and energy metabolism of photosynthesis in M. aeruginosa. In consequence, more attention should be paid to the involvement of photosynthesis in the regulation of MC production by iron variation in the future.