Research articleCharacteristics of denitrifying bacteria in different habitats of the Yongding River wetland, China
Introduction
Constructed wetlands are widely used to control water pollution (Pelissari et al., 2016; Chen et al., 2015; Jan Vymazal, 2011). Microorganisms are essential in constructed wetlands (Ibekwe et al., 2007), as they play an important role in the biogeochemical cycle (Saeed and Sun, 2012). Different microbial communities generate different biochemical reactions, and remove salt nutrients from water bodies (Truu et al., 2009; Ligi et al., 2014).
Typically, constructed wetland systems remove nitrogen from water bodies through a combination of physical (deposition and volatilization), chemical (matrix adsorption), and biological (plant absorption and microbial action) pathways (Lu et al., 2006). Among these, nitrification, denitrification, and anaerobic ammonia oxidation by microorganisms are the main mechanisms of nitrogen removal in constructed wetlands (Mulder et al., 1995; Pynaert et al., 2003; Faulwetter et al., 2009; Zhang and He, 2012; Ansola et al., 2014), accounting for 60–90% of the total nitrogen removed. These microorganisms with nitrogen conversion functions are the main implementers of nitrogen removal in constructed wetlands (Huang et al., 2007) and their population structure and activity directly affect the purification capability of the system.
Over the last 20 years, the development and application of molecular biological techniques such as fluorescence quantitative PCR (q-PCR), in situ fluorescence hybridization (FISH), and high-throughput DNA sequencing technology (Schmittgen, 2001; Margulies et al., 2005; Faulwetter et al., 2013; Bian et al., 2014) has helped identify the functional microbial abundance, community structure, and spatial and temporal distribution of constructed wetlands. However, there is still a lack of research on the structure of constructed wetlands and microorganisms in cold areas in terms of sewage purification. There is no systematic analysis of such habitats, and information on the ecological distribution of denitrogen bacteria is not systematic. Previous analyses have been performed on the diversity of denitrogen bacteria in various habitats, but their sampling was not thorough enough (Chen et al., 2017; Zhao et al., 2018; Hong et al., 2019). Two items must be addressed to help guide whether the wetland structure layout is beneficial to water purification; specifically: 1) whether differences exist in the microbial structure of different habitats in the same wetland; and 2) identification of the main environmental factors leading to this difference.
Constructed wetlands are dynamic and changeable systems, which necessitate studying nitrogen removal and microbial diversity in different structures at multiple scales. The present study first sampled and analyzed three types of habitats (fish ponds, surface flow wetlands–cattails and reeds, and ditches) in the Yongding River wetland in China. Subsequently, microbiological diversity sequencing techniques were used to study the structural characteristics of microbiological communities in different constructed wetlands of Yongding River. Differences to microbial species distributions across habitats were then analyzed. This information was applied to establish the relationship between microbial structure and wetland structure, and to determine environmental impact.
Section snippets
Study site
This study used the Yongding River Constructed Wetland located in Huailai County, Zhangjiakou City, China (40°21′05"~40°22′25″ N and 115°17′05"~115°31′10″ E). The research area is about 5 km2. The wetland is located on the edges of the Yongding River, and is a floodplain wetland. After artificial treatment and many years of natural forces, it is now mainly composed of constructed wetlands, such as ditches, surface flow wetlands (reed and cattail wetlands), and fish ponds.
Ditches
Ditches in the wetland
Physical and chemical indicators
The physical and chemical index data for the 16 samples measured in the experiment are shown in Table 1. The results showed that the nitrogen concentration was higher in the habitat samples of ditch wetlands (HL07, HL09, and HL10). Surface flow wetland (HL05) had the lowest NH4+ concentration, whereas ditch wetlands (HL09) had the highest concentration. For NO3−, the HL05 sample had the lowest concentration and HL10 had the highest concentration. The HL05 sample also had the lowest NO2−
Discussion
Previous studies on the community structure of denitrogen bacteria in different habitats were primarily based on single habitats. Consequently, there is no systematic analysis of multiple habitats or the ecological distribution of denitrifying bacteria. In addition, analyses of denitrogen bacteria diversity in samples are not sufficiently in-depth. In the current study, samples were used from different habitats in the same wetland (fish pond, surface flow wetland, ditch). The diversity of
Conclusion
The main conclusions of this study are:
- (1)
The highest number of OTUs and diversity were found in the fish pond wetland, while the lowest were found in the ditch wetland.
- (2)
Proteobacteria had the highest relative abundance at the phylum level (54.57%). At the genus level, a dominant group of bacteria was apparent; however, denitrogen bacteria accounted for 36.78% of total relative abundance, which was relatively high.
- (3)
PCoA analysis showed that the surface flow and fish pond wetlands had similar
CRediT authorship contribution statement
Xinyong Chen: Data curation, Writing - original draft. Jianjian Lu: Conceptualization, Methodology, Supervision. Jing Zhu: Investigation, Software, Validation. Cunqi Liu: Writing - review & editing.
Declaration of Competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
Funding: This work was supported by the Major Science and Technology Program for Water Pollution Control and Treatment [grant number 2015ZX07203-005-06].
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