Dairy manure total solid levels impact CH<inf>4</inf> flux and abundance of methanogenic archaeal communities
Citation
Habetwold, J., Gordon, R.J., Wood, J.D., Wagner-Riddle, C., VanderZaag, A.C., Dunfield, K.E. (2017). Dairy manure total solid levels impact CH4 flux and abundance of methanogenic archaeal communities. Journal of Environmental Quality, [online] 46(1), 232-236. http://dx.doi.org/10.2134/jeq2016.11.0451
Plain language summary
Dairy farms are a large source of greenhouse gas emissions, especially methane (CH4) gas. Liquid dairy manure storages are CH4 hotspots because of the large amount of volatile solids (VS) that are converted into CH4 by microbiological processes. Our previous research indicated that a reduction of total solids (TS) of liquid manure before storage can reduce CH4 emissions, however the mechanisms were not fully investigated. In this study, the abundance of microorganisms producing methane, methanogens, were measured in tanks with different CH4 emissions. Using slurry storage facilities equipped for continuous emission monitoring, dairy slurries were stored having a range of TS contents (from 9.5% to 0.3%). Samples were taken from the upper and bottom layers of the slurry storage after day 30 and day 120. Methanogen microorganism communities were studied by targeting the gene that is responsible for the last step of the production of methane. The amount of methanogens increased by ~8% and 23% at the top and bottom sections respectively while cumulative CH4 emissions decreased by ~70% as slurry TS decreased from 9.5% to 0.3%. Moreover, the mean abundances of methanogens were higher at day 120 compared to day 30 (up to 19% higher), which is consistent with an increase in cumulative CH4 emissions. The results suggest that the availability of carbon and not the methanogen abundance may be limiting CH4 emissions at reduced TS levels of dairy slurries. It is important to continue studying the microbiological environment and the effect of carbon availability in dairy slurries to better understand the effects they have on greenhouse gas emissions.
Abstract
Stored liquid dairy manures are methane (CH4) emission hotspots because of the large amount of slurry volatile solids (VS) converted into CH4 by methanogens under anaerobic conditions. Our research has indicated that a reduction of total solids (TS) of slurries before storage can reduce CH4 emissions. In the current study, methanogen abundance was characterized in tanks with different CH4 emissions. Using mesoscale slurry storage facilities equipped for continuous gaseous emission monitoring, we stored dairy slurries having TS from 9.5 to 0.3% for up to 6 mo. Samples were taken after Day 30 and Day 120 of the storage (20 May-16 Nov. 2010) from the upper and bottom layers of the slurries. Methanogenic communities were studied by targeting the gene encoding the a subunit methyl-coenzyme M reductase (mcrA), which catalyzes the final step of methanogenesis. Interestingly, mean abundances of methanogens increased by ~8 and 23% at the top and bottom sections, respectively, as slurry TS decreased from 9.5 to 0.3%. Cumulative CH4 emissions, however, decreased by ~70% as slurry TS decreased from 9.5 to 0.3%. Nevertheless, compared with Day 30 of storage, mean abundances of methanogens were relatively higher at Day 120 (up to 19%), consistent with an increase in the cumulative CH4 emissions. Polymerase chain reaction denaturing gel electrophoresis analysis indicated a low methanogen diversity, with most bands sequenced closely related to the genus Methanocorpusculum (>95% amino acid sequence similarity), the hydrogenotrophic methanogens. Results suggest that available carbon substrate and not methanogen abundance may be limiting cumulative CH4 emissions at reduced TS levels of dairy slurries.