Effects of large river dam regulation on bacterioplankton community structure

Abstract

Large rivers are commonly regulated by damming, yet the effects of such disruption on prokaryotic communities have seldom been studied. We describe the effects of the three large reservoirs of the Ebro River (NE Iberian Peninsula) on bacterioplankton assemblages by comparing several sites located before and after the impoundments on three occasions. We monitored the abundances of several bacterial phylotypes identified by rRNA gene probing, and those of two functional groups (picocyanobacteria and aerobic anoxygenic phototrophic bacteria-AAPs). Much greater numbers of particles colonized by bacteria were found in upstream waters than downstream sites. Picocyanobacteria were found in negligible numbers at most sites, whereas AAPs constituted up to 14% of total prokaryotes, but there was no clear effect of reservoirs on the spatial dynamics of these two groups. Instead, damming caused a pronounced decline in Betaproteobacteria, Gammaproteobacteria and Bacteroidetes from upstream to downstream sites, whereas Alphaproteobacteria and Actinobacteria significantly increased after the reservoirs. Redundancy analysis revealed that conductivity, temperature and dissolved inorganic nitrogen were the environmental predictors that best explained the observed variability in bacterial community composition. Our data show that impoundments exerted significant impacts on bacterial riverine assemblages and call attention to the unforeseen ecological consequences of river regulation.

Impacts of the Three Gorges Dam on microbial structure and potential function

“…These results support our hypothesis that the bacterial community composition was significantly impacted by damming and the associated environmental changes. This was further confirmed by the Mantel test (Table 1), and also in agreement with a recently reported study showing that bacterioplankton community structure was affected by a large dam in the Ebro River9.…”

“…In addition, since plankton are at the bottom of the food chain, biological impacts of damming will present first effects on the plankton community as shifts in composition or abundance9. Water flow velocity, which is one of the most important factors affecting plankton in river systems3, can be significantly decreased by damming regulation.…”

“…This may be attributed to: (i) a greater abundance of protozoa and rotifer, and more zooplankton taxa in the riverine sites (Table S2) exerting a strong top-down effect on the bacterioplankton3134; and/or (ii) the lake-like conditions in the backwater sites, characterized by low flow velocity, low turbidity and greater nitrogenous nutrients (Table S1), may support a greater variety of bacterioplankton lineages79. Similar to the bacterial community composition observed in other rivers935, Betaproteobacteria was present at a much higher proportion in upstream waters than in downstream waters, whereas Actinobacteria was at a much higher percentage in backwater sites (Table S4). These results support our hypothesis that the bacterial community composition was significantly impacted by damming and the associated environmental changes.…”

“…Construction of river dams can significantly alter river hydrology and aquatic ecology upstream and downstream of the dam6, creating environments that have been significantly altered physically, chemically and biologically. These changes can, in turn, greatly affect the aquatic microorganisms living in the reservoir systems, especially environmentally sensitive organisms, such as bacterioplankton789. However, most of the investigations on the effects of dams to planktonic organisms has focused on community composition and has primarily relied on morphological methods for examining community changes.…”

Distribution of Aerobic Anoxygenic Phototrophs in Freshwater Plateau Lakes

“…Even though large rivers are commonly segregated by damming, it was not clear whether reservoirs explained the spatial dynamics of AAP bacteria as documented by Ruiz-Gonzalez et al (2013) [27]. In addition, salinity and pH were also potential factors regulating AAP bacterial diversity and community composition [12].…”