Vertical profiles of sediment methanogenic potential and communities in two plateau freshwater lakes

Yuyin Yang,Bingxin Li,Wei Wang,Shuguang Xie,Ningning Li,Yong Liu

doi:10.5194/bg-14-341-2017

Abstract

Abstract. Microbial methanogenesis in sediment plays a crucial role in CH4 emission from freshwater lake ecosystems. However, knowledge of the layer-depth-related changes of methanogen community structure and activities in freshwater lake sediment is still limited. The present study was conducted to characterize the methanogenesis potential in different sediment-layer depths and the vertical distribution of microbial communities in two freshwater lakes of different trophic status on the Yunnan Plateau (China). Incubation experiments and inhibitor studies were carried out to determine the methanogenesis potential and pathways. 16S rRNA and mcrA genes were used to investigate the abundance and structure of methanogen and archaeal communities, respectively. Hydrogenotrophic methanogenesis was mainly responsible for methane production in sediments of both freshwater lakes. The layer-depth-related changes of methanogenesis potential and the abundance and community structure of methanogens were observed in both Dianchi Lake and Erhai Lake. Archaeal 16S rRNA and mcrA genes displayed a similar abundance change pattern in both lakes, and the relative abundance of methanogens decreased with increasing sediment-layer depth. Archaeal communities differed considerably in Dianchi Lake and Erhai Lake, but methanogen communities showed a slight difference between these two lakes. However, methanogen communities illustrated a remarkable layer-depth-related change. Order Methanomicrobiales was the dominant methanogen group in all sediments, while Methanobacteriales showed a high proportion only in upper layer sediments. The trophic status of the lake might have a notable influence on the depth-related change pattern of methanogenesis activity, while the methanogen community structure was mainly influenced by sediment depth.

Highlights

Methane (CH4) is an effective greenhouse gas in atmosphere, and lacustrine ecosystems may be responsible for 6–16 % of natural methane emission (Bastviken et al, 2004)
Total methane production (TMP) varied remarkably with both lake and sediment depth except for the uppermost sediments layers, which were remarkably similar between Dianchi Lake and Erhai Lake (Fig. 1)
In Dianchi Lake, the total methane production (TMP) generally increased with increasing depth, varying from 68.9 to 315.3 nmol gDW−1 in a 5–20 cm layer (DW stands for dry weight, which was determined gravimetrically), while in Erhai Lake, the MPP decreased from 59.6 to 11.2 nmol gDW−1

Summary

Introduction

Methane (CH4) is an effective greenhouse gas in atmosphere, and lacustrine ecosystems may be responsible for 6–16 % of natural methane emission (Bastviken et al, 2004). In anoxic sediment of a freshwater lake, a large amount of methane can be produced through microbial methanogenesis (Bastviken et al, 2008; Gruca-Rokosz and Tomaszek, 2015). Biogenic methane is produced by the activity of methanogens, a strictly anaerobic microbial group belonging to the archaeal phylum Euryarchaeota. Organic matter is fermented to acetate, CO2, and H2, which are further converted to CH4 by methanogens. There are two major methanogenic pathways, namely hydrogenotrophic pathways (using H2/CO2) and acetoclastic pathways (using acetate, i.e., the methyl group) (Conrad et al, 2010). The relative contribution of these two pathways varies in different lakes (Conrad, 1999). To determine the contribution of both methanogenic pathways, approaches including isotope labeling, δ13C analysis, and inhibitor study have been applied (Conrad, 2005).

Methods

Results

Discussion

Conclusion