How dam construction affects the activity of alkaline phosphatases in reservoir sediments: A study of two highly regulated rivers.

Dam construction causes phosphorus (P) accumulation in reservoir sediments and significantly affects the generation of available P. However, the effect of dam construction on the activity of sediment alkaline phosphatase (ALP), which is encoded by the bacterial phoD gene and participates in P mineralization, in river sediments remains unclear. Here, we investigated the ALP activities in 78 sediment samples collected from the cascade reservoir regions located in the Lancang River and the Jinsha River, two highly regulated rivers in southwestern China. The abundance and community composition of phoD-harboring bacteria were determined based on the phoD gene using quantitative real-time PCR and MiSeq sequencing, respectively. Comparison of control and affected sites indicated that dam construction significantly increased sediment ALP activity in both rivers. The abundances of phoD-harboring bacteria increased and their community compositions varied in response to dam construction; the relative abundances of the dominant genera Methylobacterium and Bradyrhizobium were particularly higher in affected site than control site. Co-occurrence network analyses revealed much higher network connectivity and relative abundances of keystone species in affected sites. Some microbial factors including phoD-harboring bacterial abundances, network clustering coefficients, and relative abundance of keystone species were positively correlated with ALP activity. The relative abundance of keystone species was identified as the most important microbial factor contributing to variation in ALP activity based on structural equation modeling analysis. These findings enhance our understanding of how dam construction affects the functions of phoD-harboring bacteria and their role in the P biogeochemical cycle in highly regulated rivers.

Shift in bacterioplankton diversity and structure: Influence of anthropogenic disturbances along the Yarlung Tsangpo River on the Tibetan Plateau, China.

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.