This article showcases the static chamber-based method for measurement of greenhouse gas flux from soil systems. With relatively modest infrastructure investments, measurements may be obtained from multiple treatments/locations and over timeframes ranging from hours to years.
Measurement of greenhouse gas (GHG) fluxes between the soil and the atmosphere, in both managed and unmanaged ecosystems, is critical to understanding the biogeochemical drivers of climate change and to the development and evaluation of GHG mitigation strategies based on modulation of landscape management practices. The static chamber-based method described here is based on trapping gases emitted from the soil surface within a chamber and collecting samples from the chamber headspace at regular intervals for analysis by gas chromatography. Change in gas concentration over time is used to calculate flux. This method can be utilized to measure landscape-based flux of carbon dioxide, nitrous oxide, and methane, and to estimate differences between treatments or explore system dynamics over seasons or years. Infrastructure requirements are modest, but a comprehensive experimental design is essential. This method is easily deployed in the field, conforms to established guidelines, and produces data suitable to large-scale GHG emissions studies.
Understanding the contributions of both human activities and natural systems to radiative properties of the atmosphere is an area of critical importance as we strive to mitigate anthropogenic contributions to the greenhouse effect. In addition to carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) are also potent GHGs, accounting for an estimated 7% and 19% of global warming, respectively, with the majority of emissions coming from landscape sources1,2. These range from managed systems such as agricultural fields, rice paddies, and landfills, to natural systems such as forest floors, wetlands, and termite mounds. Accurate measurement, supporting well-informed modeling of such landscape-based emissions is critical in order to understand the drivers of climate change as well as to identify mitigation opportunities.
A variety of greenhouse gas measurement strategies exist, each with their own strengths and weaknesses2-5. Mass balance techniques rely on wind-based dispersion of gases and are suited to measurement of flux from small, well-defined sources such as landfills and animal paddocks. Micrometeorological approaches such as eddy covariance are based on real-time direct measurement of vertical gas flux, and can provide direct measurements over large areas. However, homogeneity in source topography is an implicit assumption (in that measurements yield a mean for the area under study), and costly infrastructure can limit deployment possibilities. Finally, chamber-based methods focus on change in gas concentration at the soil surface by sampling from a restricted above ground headspace. They allow measurements to be obtained from small areas and numerous treatments, but are subject to high coefficients of variation due to spatial variation in soil gas flux.
Here we discuss the most prevalent and easily implemented form of chamber-based measurement, utilizing the type of closed chambers without air flow-through commonly referred to as “static” or “non-steady-state non-flow-through” chambers. In this approach, gas emissions from the soil surface are trapped within a vented chamber, and rates of flux are determined by measuring the change in gas concentration over time within the chamber headspace. The static chamber technique has been widely deployed across both managed and natural landscapes and underpins the bulk of data reporting soil-based flux of greenhouse gases, particularly N2O6,7. It is ideally suited to the study of small experimental plots, diverse sites over variable terrain, or in other situations where multiple distinct locations must be studied without significant infrastructure investments. Typical experimental uses might include the exploration of alternative landscape management practices and their impact on soil-based CO2, N2O, and/or CH4 emissions, examination of landscape-based flux dynamics under artificially induced climate change scenarios such as warming and rainfall exclusion/supplementation, or the descriptive study of natural and agricultural ecosystems and subsystems.
As a critical tool in GHG measurement and flux estimation, the static chamber method has been thoroughly evaluated, and significant efforts have been made towards standardization of techniques and harmonization of data reporting4,6,8,9. Of particular note are the detailed reviews and guidelines produced by the U.S. Department of Agriculture – Agricultural Research Service’s Greenhouse gas Reduction through Agricultural Carbon Enhancement network (GRACEnet)8 and by the Global Research Alliance on Agricultural Greenhouse Gases (GRA)9. Such guidelines provide an invaluable resource and platform for coordination, as ultimately the interoperability of data from a myriad of studies is critical for scaling up local findings to global modeling, and for translating research results into viable mitigation strategies.
GRACEnet, GRA, and other reviews also highlight the fact that specific techniques in static chamber-based greenhouse gas flux measurement are extremely diverse, with significant methodological variations possible at nearly every step of the way, including chamber design, temporal and spatial deployment, sampling volumes, sample analysis, and flux calculations. The method described here presents one possible variant, while showcasing best practices and highlighting critical considerations for the generation of high quality, broadly transferrable data. It is intended to provide an accessible overview of this standardized procedure, and a platform from which to explore further nuances and variations described in the literature.
Den statiske kammer tilgang beskrevet her er en effektiv metode til måling af drivhusgasser fluxen fra jord-systemer. Den relative enkelhed af dens komponenter gør det særligt velegnet til betingelser eller systemer, hvor flere infrastruktur-intensive metoder er umuligt. For at generere data af høj kvalitet, men den statiske kammer fremgangsmåde skal udføres med nøje opmærksomhed på eksperimentelle design 6. En bemærkelsesværdig overvejelse, som skal tages i betragtning, er den rumlige variabilitet af gas-flux jord, hvilket kan resultere i store variation blandt replikere kammer-baserede målinger. Ved udformningen af eksperimenter, er det derfor vigtigt at medtage nok gentagelser til at levere tilstrækkelig strøm til statistisk analyse. Kan eksistere kompromiser mellem antallet af behandlinger, som kan studeres samtidig opretholde tilstrækkelig replikation, og mindst fire gentagelser pr behandling er en generel retningslinje 14.
NDHOLDET "> Hvis der skal bruges målt fluxe at estimere daglige emissioner skal daglige variationer i lufttemperatur, jordtemperatur og drivhusgasser blive taget i betragtning. Hvis forsknings mål kræver målinger, der skal opnås i midten af formiddagen, når temperaturerne afspejler daglige gennemsnit, den begrænsede vindue for prøvetagning kan påvirke antallet af kamre, der let kan overvåges. En yderligere vederlag, der skal evalueres, er den effekt, optagelse eller udelukkelse af planterødder og overjordiske biomasse vil få på gas flux. Chamber placering i forhold til plante væv vil have indflydelse på fortolkningen af flux data, især i tilfælde af CO 2, hvor ikke bare mikrobiel respiration, men også rod og skyde respiration og fotosyntese skal være en passende balance. For yderligere diskussion af disse faktorer, se Parkin og Venterea 8..Som tidligere nævnt, mange variationer på denne metode findes, herunder kammer design og prøvetagningvolumen. En sådan variation er i de beskæftigede til at overføre prøver mellem sprøjten og indsamling hætteglas metode. Den her beskrevne teknik først skyller hætteglasset samling med prøve inden påfyldning hætteglasset til positivt tryk 5.. En mere almindeligt anvendt teknik er overførsel af prøver fra sprøjter til hætteglas, der har været præ-evakueret ved hjælp af en vakuumpumpe, og anvendelsen af ikke-evakuerede hætteglas uden skylning er også blevet rapporteret 8,17. En anden væsentlig punkt, hvor en række forskellige tilgange findes i dataanalyse og udvælgelsen af flux-modellen mest hensigtsmæssigt at systemet under studiet. Ud over den lineære regression her beskrevne fremgangsmåde kan ikke-lineære modeller også anvendes, især når længere opstartsfase anvendes. Disse modeller omfatter algoritme udviklet af Hutchinson og Mosier 18 og afledninger heraf 19,20, den kvadratiske procedure beskrevet af Wagner et al. 21, og den ikke-steady-tilstand diffusive flux estimator beskrevet af Livingston et al 22. For en grundig diskussion af ikke-lineære flux-modeller under Parkin et al. 12 og Venterea et al 23.
Metoder svarende til den statiske kammer tilgang omfatter anvendelse af flow-through målesystemer med Fourier transfer infrarød (FTIR) spektrometri som suppleant til sprøjte prøvetagning og gaskromatografi, samt automatisering af lukning og prøveudtagning kammer gennem forskellige midler. Automatiserede systemer gør det muligt hyppigere målinger med reduceret personale, men også kræve yderligere investeringer i infrastruktur. Grace et al. 24 giver en omfattende oversigt over muligheder og kompromiser i automatiserede kammer-baserede N 2 O måling.
Karakterisering af drivhusgas flux fra både forvaltes og naturlige systemer er vigtigt at informere proces-baserede modeller, forstå virkningerne af management praksis og informere afbødningsstrategier og støtte globale regnskabs-og klimaændringer modellering. Så mens de enkelte studier er informative på lokalt plan, er meget ekstra værdi udledt ved at bidrage til, og trække fra, en global samling af viden om udveksling af gas mellem landskabet og atmosfæren. Det er nøglen, derfor indsamles, at data og rapporteres på en måde, der sikrer lang levetid og interoperabilitet med den bredere videngrundlag. Dette omfatter følgende bedste praksis for at sikre kvaliteten af data, samt indsamling af supplerende foranstaltninger og omfattende rapportering af metadata for at muliggøre en udvidelse af fund over diskrete undersøgelser. Fremragende retningslinjer for indberetning af data er tilgængelige fra GRACEnet projektet og GRA 25.
The authors have nothing to disclose.
This material is based upon work supported by the National Science Foundation under Grant Number 1215858, by the US Department of Agriculture under Grant Number 2013-68002-20525, and by the US Department of Energy Great Lakes Bioenergy Research Center – DOE BER Office of Science (DE-FC02-07ER64494) and DOE OBP Office of Energy Efficiency and Renewable Energy (DE-AC05-76RL01830). In-field video and images were recorded at the Wisconsin Integrated Cropping System Trial project of the University of Wisconsin–Madison. The authors are grateful to Ryan Curtin for skillful videography and editing.
5.9 ml soda glass flat bottom 55 x 15.5 mm | Labco Limited | 719W | Collection vials |
16.5 mm screw caps with pierceable rubber septum | Labco Limited | VC309 | Caps for vials |
90-well plastic vial rack, 17.1 mm well I.D. | Wheaton | 868810 | Rack for organizing vials |
Regular bevel needles 23G x 1" | BD | 305193 | Needles for sample collection |
Stopcocks with luer connections, 1-way, male slip | Cole-Parmer | EW-30600-01 | Stopcocks for syringes |
30 ml syringe, slip tip | BD | 309651 | Syringes for sample collection |
Stopwatch or timer | Various | N/A | For timing field sampling |
Stainless steel or galvanized utility pans with rim, or fabricated stainless steel or PVC chambers and lids, dimensions as appropriate to experimental system | Various | N/A | Chamber anchor and lid – bottom cut out of anchor, holes for septum and vent tubing bored in lid |
Gray butyl stoppers 20 mm | Wheaton | W224100-173 | Chamber septa for syringe sampling – insert into hole bored in lid top |
Tygon tubing 4.0 mm I.D. x 5.6 mm O.D. | Sigma-Aldrich | Z685623 | Chamber vent tubing – insert in hole bored in lid side, flush with exterior, approximately 25 cm coiled in lid interior (a 1ml syringe tip may be used as an attachement mechanism) |
Adhesive foam rubber tape or HDPE O-ring | Various | N/A | Chamber sealing mechanism – fastened to underside of lid rim |
Reflective insulation, 0.3125" thickness | Lowe's | 409818 | Insulating and reflective coating – affix to exterior of chamber lid |
Large metal binder clips, 2" size with 1" capacity, or manufactured draw latch as appropriate | Staples / McMaster | 831610 (Staples) / 1863A21 (McMaster) | Lid attachment mechanism – for clamping lid to anchor during sampling |
Gas chromatography equipment fitted with electron capture detector for nitrous oxide, infrared gas analyzer or thermal conductivity detector for carbon dioxide, flame ionization detector for methane | Various | N/A | For sample analysis |