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Sci Total Environ. 2018 Mar 15;618:15-25. doi: 10.1016/j.scitotenv.2017.11.039. Epub 2017 Nov 7.

Nitrate attenuation in low-permeability sediments based on isotopic and microbial analyses.

Author information

1
Key Laboratory of Watershed Geographic Sciences, Nanjing Institute of Geography & Limnology, Chinese Academy of Sciences, 73 East Beijing Road, 210008 Nanjing, PR China; Institute of Water Sciences, College of Engineering, Peking University, No. 5 Yiheyuan Road, 100871 Beijing, PR China.
2
Key Laboratory of Watershed Geographic Sciences, Nanjing Institute of Geography & Limnology, Chinese Academy of Sciences, 73 East Beijing Road, 210008 Nanjing, PR China. Electronic address: lgxu@niglas.ac.cn.
3
Center for Hydrogeology and Environmental Geology, China Geological Survey, No. 1305 Qiyi Road, North District, Baoding, Hebei Province, PR China.
4
College of Urban and Environmental Science, Peking University, 100871 Beijing, PR China.
5
College of Resources & Environmental Science, China Agricultural University, 100193 Beijing, PR China.
6
School of Environmental Science and Engineering, South University of Science and Technology, 518025 Shenzhen, PR China.

Abstract

This study investigated nitrate attenuation in low-permeability sediments (LPS) in a multi-layer aquifer by integrating hydrochemical, isotopic and microbiological molecular techniques in a field site. In the meantime, the overlying high-permeability sediment (HPS) was also examined on the nitrate attenuation for the sake of comparison. Additionally, laboratory flow-through experiments were conducted to assess the overall nitrate reduction rate in the two types of sediment. The δ15N-NO3- and δ34S-SO42- values were more enriched by approximately 37‰ and 15‰ in the LPS than the overlying HPS associated with substantial reductions of the NO3- and SO42- concentration, indicating the occurrence of strong bio-reductions in nitrate and sulfate. The microbial community diversity analyses showed a higher diversity of the denitrifiers encoding nirS- (Shannon Index SI=6.3) and nrf-type gene (SI=2.7), and the sulfate reduction bacteria (SRB) encoding the dsr gene (SI=6.4) in the LPS than in the HPS. The bacterial community structure was influenced by the groundwater hydrochemistry and the redox conditions. Due to the presence of anoxic groundwater with low levels of nutrients, the LPS featured higher abundances of nitrate reducers belonging to Alphaproteobacteria and SRB belonging to the strictly anaerobic class Clostridia relative to the HPS. Notably, chemolithotrophs were abundant in the LPS and likely coupled the reduction of nitrate with the oxidation of iron. Furthermore, the LPS was demonstrated to attenuate nitrate at a rate two times of the HPS in flow-through experiments, and denitrification accounted for approximately 93% of the nitrate reduction. The high nitrate reduction rate of the LPS was likely attributable to its high functional genes diversity. This study confirmed the occurrence of strong nitrate attenuation in the LPS. The LPS was found to play a significant role in protecting aquifers from anthropogenic contamination.

KEYWORDS:

Isotopic analyses; Low-permeability sediments; Microbial diversity; Nitrate attenuation; Sulfate reduction

PMID:
29126024
DOI:
10.1016/j.scitotenv.2017.11.039
[Indexed for MEDLINE]

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