Response of the microbial community to salt stress and its stratified effect in constructed wetlands

Authors: WANG, XINYI - Chinese Academy Of Agricultural Sciences; ZHU, HUI - Chinese Academy Of Agricultural Sciences; YAN, BAIXING - Chinese Academy Of Agricultural Sciences; SHUTES, BRIAN - Middlesex University London; Banuelos, Gary; CHENG, RUI - Chinese Academy Of Agricultural Sciences

Submitted to: Environmental Science and Pollution Research
Publication Type: Other
Publication Acceptance Date: 12/1/2020
Publication Date: 1/6/2021
Citation: Wang, X., Zhu, H., Yan, B., Shutes, B., Banuelos, G.S., Cheng, R. 2021. Response of the microbial community to salt stress and its stratified effect in constructed wetlands. Environmental Science and Pollution Research. 28:18089-18101. https://doi.org/10.1007/s11356-020-11937-z.
DOI: https://doi.org/10.1007/s11356-020-11937-z

Interpretive Summary: The salinization of rivers and/or lakes has been causing a complicated problem of water pollution, including salinization and eutrophication, which directly affects the growth and reproduction of aquatic organisms, and even destroys the structure and function of aquatic ecosystems. Nitrogen is one of the most common pollutants existing in saline wastewaters and is one of the main factors causing eutrophication. Constructed wetlands (CWs) is an ecological and efficient purification technology used for treating saline wastewater. In this study, CW mesocosms were established with varied salinity and nitrogen levels. We studied the denitrification capacity, nitrogen removal efficiency and identification of different bacteria in the CWs for 30 days. Results showed that nitrogen removal and bacteria communities associated with denitrification decreased with increased salinity. Moreover, the microbial community varied with different salinity levels and among sampling depths in the CW microcosms. There was an obvious stratification effect on the spatial distribution of microorganisms in CWs. In summary, a variety of aerobic nitrifying bacteria were detected in upper gravel samples of CW microcosms, and multiple denitrifying bacteria were detected in bottom gravel samples. Consequently, CWs ability to effectively remove nitrogen pollutants from saline wastewater may vary due to salinity’s effect on microorganisms present on the surface of substrate and roots of plants in CWs. This observation indicates that CW's used to remove nitrogens from saline wastewaters must be designed in a way that preserves the existence of selective microbial communities for their denitrification capacity.

Technical Abstract: Nitrogen is one of the most common pollutants existing in saline wastewaters and is one of the main factors causing eutrophication. Constructed wetlands (CWs), as an ecological and efficient purification technology, provide new options for saline wastewater treatment. The nitrogen removal capacity of CWs can vary widely under saline conditions caused by the inhibition of the growth and activity of microorganisms in saline CWs. The specific objectives of this 30 day practical microcosm study were :(1) investigate the denitrification capacity of CWs under various salinity levels (EC of ~0.51, 15 and 30 mS/cm with NaCl, respectively); (2) reveal the response of the abundance and structure of microbial communities to salinity in CWs; and (3) explore the effect of depth change on the abundance of microbial communities in CWs based on high-throughput sequencing (HTS) technology. This study showed that the removal percentages of ammonia nitrogen (NH4+-N), nitrate nitrogen (NO3--N) and total nitrogen (TN) significantly (p < 0.05) decreased in CW microcosms with increasing salinity. High-throughput sequencing technology revealed that the structure and abundance of the microbial community varied with different salinity levels and sampling depths in CW microcosms. Compared with non-saline water, the abundances of some bacteria with a denitrification function (e.g., Arthrobacter) significantly (p < 0.05) decreased in CW microcosms under saline conditions (i.e., EC of 15 and 30 mS/cm). Furthermore, the structure and abundance of microbial communities changed with the sampling depth of CW microcosms. Aerobic bacteria (e.g., Sphingomonas) exhibited more abundance in soil and upper gravel samples in CW microcosms than those in bottom gravel samples, while the abundance of some denitrifying bacteria (e.g., Thauera and Azoarcus) was significantly (p < 0.05) higher in bottom gravel samples compared with soil and upper gravel samples, respectively. This study provides both microbiological evidence for explaining the impact of excessive salinity on nitrogen removal in CWs and scientific reference for developing enhanced strategies to improve the nitrogen removal capacity of CWs under saline conditions.