Methane and nitrous oxide cycling microbial communities in soils above septic leach fields: Abundances with depth and correlations with net surface emissions

Cristina P Fernández-Baca; Allison M Truhlar; Amir-Eldin H Omar; Brian G Rahm; M Todd Walter; Ruth E Richardson

doi:10.1016/j.scitotenv.2018.05.303

Methane and nitrous oxide cycling microbial communities in soils above septic leach fields: Abundances with depth and correlations with net surface emissions

Sci Total Environ. 2018 Nov 1:640-641:429-441. doi: 10.1016/j.scitotenv.2018.05.303. Epub 2018 Jun 1.

Authors

Cristina P Fernández-Baca¹, Allison M Truhlar², Amir-Eldin H Omar³, Brian G Rahm², M Todd Walter⁴, Ruth E Richardson⁵

Affiliations

¹ Department of Civil and Environmental Engineering, 220 Hollister Hall, Cornell University, Ithaca, NY, United States. Electronic address: cpf45@cornell.edu.
² New York State Water Resources Institute, 230 Riley-Robb Hall, Cornell University, Ithaca, NY, United States.
³ Department of Molecular Biology and Genetics, 107 Biotechnology Building, Cornell University, Ithaca, NY, United States.
⁴ Department of Biological and Environmental Engineering, 232 Riley-Robb Hall, Cornell University, Ithaca, NY, United States.
⁵ Department of Civil and Environmental Engineering, 220 Hollister Hall, Cornell University, Ithaca, NY, United States.

PMID: 29860012
DOI: 10.1016/j.scitotenv.2018.05.303

Abstract

Onsite septic systems use soil microbial communities to treat wastewater, in the process creating potent greenhouse gases (GHGs): methane (CH₄) and nitrous oxide (N₂O). Subsurface soil dispersal systems of septic tank overflow, known as leach fields, are an important part of wastewater treatment and have the potential to contribute significantly to GHG cycling. This study aimed to characterize soil microbial communities associated with leach field systems and quantify the abundance and distribution of microbial populations involved in CH₄ and N₂O cycling. Functional genes were used to target populations producing and consuming GHGs, specifically methyl coenzyme M reductase (mcrA) and particulate methane monooxygenase (pmoA) for CH₄ and nitric oxide reductase (cnorB) and nitrous oxide reductase (nosZ) for N₂O. All biomarker genes were found in all soil samples regardless of treatment (leach field, sand filter, or control) or depth (surface or subsurface). In general, biomarker genes were more abundant in surface soils than subsurface soils suggesting the majority of GHG cycling is occurring in near-surface soils. Ratios of production to consumption gene abundances showed a positive relationship with CH₄ emissions (mcrA:pmoA, p < 0.001) but not with N₂O emission (cnorB:nosZ, p > 0.05). Of the three measured soil parameters (volumetric water content (VWC), temperature, and conductivity), only VWC was significantly correlated to a biomarker gene, mcrA (p = 0.0398) but not pmoA or either of the N₂O cycling genes (p > 0.05 for cnorB and nosZ). 16S rRNA amplicon library sequencing results revealed soil VWC, CH₄ flux and N₂O flux together explained 64% of the microbial community diversity between samples. Sequencing of mcrA and pmoA amplicon libraries revealed treatment had little effect on diversity of CH₄ cycling organisms. Overall, these results suggest GHG cycling occurs in all soils regardless of whether or not they are associated with a leach field system.

Keywords: Denitrifier; Methane; Methanogen; Methanotroph; Nitrous oxide; Septic leach field.