Abrupt seasonal fluxes of methane from northern lakes and ponds

Lead Research Organisation: University of Bristol
Department Name: Earth Sciences

Abstract

Methane is a powerful long-lived greenhouse gas that is second only to carbon dioxide in its radiative forcing potential. Understanding the Earth's methane cycle at regional scales is a necessary step for evaluating the effectiveness of methane emission reduction schemes, detecting changes in biological sources and sinks of methane that are influenced by climate, and predicting and perhaps mitigating future methane emissions. The growth rate of atmospheric methane has slowed since the 1990s but it continues to show considerable year-to-year variability that cannot be adequately explained. Some of the variability is caused by the influence of weather on systems in which methane is produced biologically. When an anomalous increase in atmospheric methane is detected in the northern hemisphere that links to warm weather conditions, typically wetlands and peatlands are thought to be the cause. However, small lakes and ponds commonly are overlooked as potential major sources of methane emissions. Lakes historically have been regarded as minor emitters of methane because diffusive fluxes during summer months are negligible. This notion has persisted until recently even though measurements beginning in the 1990s have consistently shown that significant amounts of methane are emitted from northern lakes during spring and autumn. In the winter time the ice cover isolates lake water from the atmosphere and the water column become poor in oxygen and stratified. Methane production increases in bottom sediment and the gas spreads through the water column with some methane-rich bubbles rising upwards and becoming trapped in the ice cover as it thickens downward in late winter. In spring when the ice melts the gas is released. Through changes in temperature and the influence of wind the lake water column mixes and deeper accumulations of methane are lost to the atmosphere. In summer the water column stratifies again and methane accumulates once more in the bottom sediments. When the water column become thermally unstable in the autumn and eventually overturns the deep methane is once again released although a greater proportion of it appears to be consumed by bacteria in the autumn. Lakes differ in the chemistry of their water as well as the geometry of their basins. Thus it is difficult to be certain that all lakes will behave in this way but for many it seems likely. The proposed study will measure the build-up of methane in lakes during spring and autumn across a range of ecological zones in North America. The focus will be on spring build-up and emissions because that gas is the least likely to be influenced by methane-consuming bacteria. However, detailed measurements of methane emissions will also be made in the autumn at a subset of lakes. The measurements will then be scaled to a regional level using remote sensing data providing a 'bottom-up' estimate of spring and autumn methane fluxes. Those results will be compared to a 'top-down' estimate determined using a Met Office dispersion model that back-calculates the path of air masses for which the concentration of atmospheric methane has been measured at global monitoring stations in order to determine how much methane had to be added to the air during its passage through a region. Comparing estimates by these two approaches will provide independent assessments of the potential impact of seasonal methane fluxes from northern lakes. In addition measurements of the light and heavy versions of carbon and hydrogen atoms in methane (C, H) and water (H) will be measured to evaluate their potential use as tracer for uniquely identifying methane released by lakes at different latitudes. If successful the proposed study has the potential to yield a step-change in our perception of the methane cycle by demonstrating conclusively that a second major weather-sensitive source of biological methane contributes to year-to-year shifts in the growth rate of atmospheric methane.

Planned Impact

Researchers interested in modelling lake ice and carbon dynamics will benefit from the significant data set linking ice characteristics to hydrochemistry, lake morphometrics and trace gas cycling. The project will add significantly to the current database of such measurements available for lakes globally. For example, methane dynamics have been studied in fewer than 100 lakes to date and this study aims to investigate ~250 across several ecological regions in North America (but clearly not in the same level of details as many of the existing studies). Improved lake ice models and remote sensing of lakes will benefit communities and individuals that rely upon lacustrine environments for water, transportation or income. Individuals in remote areas will benefit from employment on this project as field guides or fieldwork assistants. Data from the study will be lodged in NERC data archives and Government of Canada data bases. The wider methane and carbon cycling research communities will benefit from access to these data which will also be dissemination through peer-reviewed literature, conference presentations, MethaneNet, and possibly the NERC Arctic Thematic Programme. Stable isotope data will enable methane cycle modellers to better interpret shifts in the isotope composition of atmospheric methane recorded in modern monitoring networks and collected from air trapped in glacial ice. The project postdoctoral fellow and technician will gain a range of skills that are transferable to the study of other systems that produce and emit greenhouse gases. They will also have an opportunity to network widely with researchers in North America because of the significant number of supporting organisations involved in the proposed work. This study has the potential to yield a step-change in our understanding of the global methane cycle and causes of interannual variability in the growth rate of atmospheric methane. Anyone interested in climate or global change, greenhouse gas accounting or mitigation of emissions should benefit from the findings of this research.

Publications

10 25 50
 
Description In this project, we have developed new methods for estimating greenhouse gas emissions using atmospheric observations. Specifically: a) new methods for uncertainty quantification; b) new techniques for using satellite data. These methods have been applied to the estimation of methane emissions from India. Our findings indicate that India's emissions reports to the United Nations Framework convention on Climate Change (UNFCCC) are accurate, and that there was little trend in emissions between 2010 and 2015.
Exploitation Route Our work is of great interest to many groups around the world, who are interested in using atmospheric observations to evaluation national greenhouse gas emissions inventories. In addition to the methods described in our publications, our work is being shared through a freely available software library.
Sectors Environment

URL http://www.bristol.ac.uk/news/2017/october/methane-emissions-india.html
 
Description Our findings on Indian methane emissions have been disseminated to the Indian greenhouse gas inventory team. They have used our results to evaluate their National Inventory Report to the United Nations Framework Convention on Climate Change (UNFCCC). A summary of our findings will be included in the Ministry of Environment and Forests annual report.
First Year Of Impact 2017
Sector Environment
Impact Types Policy & public services

 
Description SPARC Report on the Mystery of Carbon Tetrachloride
Geographic Reach Multiple continents/international 
Policy Influence Type Participation in a advisory committee
URL https://doi.org/10.3929/ethz-a-010690647
 
Description Impact Accelerator Award
Amount £11,500 (GBP)
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 01/2014 
End 12/2014
 
Description Met Office Newton Fund - Brazilian methane emissions
Amount £179,000 (GBP)
Organisation Meteorological Office UK 
Sector Public
Country United Kingdom
Start 04/2018 
End 03/2020
 
Description NERC standard grant
Amount £800,000 (GBP)
Funding ID NE/R000921/1 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 01/2018 
End 12/2021
 
Description University of Bristol - internal equipment
Amount £9,500 (GBP)
Funding ID n/a 
Organisation University of Bristol 
Sector Academic/University
Country United Kingdom
Start 07/2013 
 
Title Air history maps 
Description High resolution air histories over Canada have been modelled based upon meteorological data for the years 2012 and 2013. 
Type Of Material Database/Collection of data 
Provided To Others? No  
Impact The air histories will be used in inversion modelling of methane emissions from northern lakes. 
 
Description Environment Canada 
Organisation Government of Canada
Department Environment Canada
Country Canada 
Sector Public 
PI Contribution My team is conducting inversion modelling of atmospheric methane data provided by Environment Canada.
Collaborator Contribution We have been given access to hourly atmospheric methane concentration measurements from all of Environment Canada's national atmospheric monitoring network. This data set includes recent measurements from three new stations in the Canada Arctic. My estimate of the in-kind value of the data set is high ($1M) because it is a unique dataset and the annual costs associated with the monitoring effort and equipment maintenance and purchase are considerable.
Impact None to date. The work is ongoing.
Start Year 2012
 
Description MET Office 
Organisation Meteorological Office UK
Country United Kingdom 
Sector Public 
PI Contribution The MET Office are a subcontracted partner. Our contribution is financial but also data sharing.
Collaborator Contribution Initially the MET Office was conducting inversion modelling, however, their role now is primarily providing advice. The modelling is being done at the University of Bristol because the MET Office have enabled access to the NAME modelling via the JASMIN portal.
Impact None to date. The project is ongoing.
Start Year 2012
 
Description NASA JPL 
Organisation National Aeronautics and Space Administration (NASA)
Department Jet Propulsion Laboratory
Country United States 
Sector Public 
PI Contribution Statistical investigation of model parameterisations in OCO-2 retrieval code.
Collaborator Contribution Provision of data and model output.
Impact No outcomes yet
Start Year 2016
 
Description University of Wollongong 
Organisation University of Wollongong
Country Australia 
Sector Academic/University 
PI Contribution Model runs, data provision and processing, expertise in atmospheric modelling and statistics.
Collaborator Contribution Expertise in statistics
Impact Several publications, with further work in the pipeline.
Start Year 2013
 
Title Automated chamber control software 
Description A prototype software-controlled automated system for trace gas sampling has been constructed. 
Type Of Technology New/Improved Technique/Technology 
Year Produced 2014 
Impact The work is ongoing via an NERC Accelerator Impact Award. A proposal is being submitted for an NERC Innovation grant to deploy and refine the system for 12 months with an industry partner. 
 
Description WMO Integrated Greenhouse Gas Information System (IG3IS) workshop on Moroccan, South African and Brazilian emissions 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Policymakers/politicians
Results and Impact Workshop with three countries to develop strategies for setting up greenhouse gas monitoring capabilities in each.
Year(s) Of Engagement Activity 2016,2017