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 baserte tilnærmingen som er beskrevet her er en effektiv metode for måling av GHG fluks fra jordsystemer. Den relative enkelhet av komponentene gjør det spesielt godt egnet til forholdene eller systemer der flere infrastrukturkrevende metoder er umulig. For å generere data av høy kvalitet, men den statiske kammeret metode må utføres med strenge hensyn til eksperimentell design 6.. En viktig faktor som må tas i betraktning er den romlige variasjonen av jord karbonflux, noe som kan resultere i høy variabilitet blant replikere kammerbaserte målinger. I utformingen eksperimenter, er det derfor viktig å inkludere nok replikater for å gi tilstrekkelig kraft for statistisk analyse. Avveininger kan eksistere mellom antall behandlinger som kan studeres samtidig opprettholde tilstrekkelig replikering, og et minimum av fire gjentak per behandling er en generell retningslinje 14.
ontent "> Hvis målt flukser vil bli brukt til å estimere daglige utslipp, må dagaktive variasjoner i lufttemperatur, jordtemperatur, og gasser tas i betraktning. Hvis forskningsmål krever målinger som skal innhentes i midten av morgenen når temperaturen reflektere daglig gjennomsnitt, begrenset vindu for prøvetaking kan påvirke antall kamre som er praktisk mulig å bli overvåket. Et tilleggsvederlag som skal evalueres er virkningen at inkludering eller ekskludering av planterøtter og over bakken biomasse vil ha på karbonflux. Chamber plassering i forhold til plante vevvilje påvirke tolkningen av strømningsdata, særlig i tilfelle av CO 2 hvor ikke bare mikrobiell respirasjon, men også rot og skyte respirasjon og fotosyntese må være riktig balansert. For ytterligere diskusjon av disse faktorene, se Parkin og Venterea 8..Som nevnt tidligere, er mange varianter av denne metode finnes, inkludert kammer konstruksjon og prøvetakingvolum. En slik variant er i det anvendt for å overføre prøvene mellom sprøyten og samling ampulle metode. Teknikken er beskrevet her først spyler samlingen hetteglass med prøven før du fyller ampullen til overtrykk fem. En mer vanlig brukt teknikk er overføring av prøvene fra sprøyter små medisinflasker som har blitt pre-evakuert ved hjelp av en vakuumpumpe, og bruken av ikke-evakuerte ampuller uten spyling er også rapportert 8,17. Et annet viktig punkt hvor en rekke metoder finnes i data-analyse, og valget av flussmiddel modellen er mest passende for systemet som studeres. I tillegg til den lineære regresjon metoden som er beskrevet her, kan det ikke-lineære modeller også anvendes, spesielt når lengre installasjonstiden blir brukt. Disse modellene omfatter algoritmen utviklet av Hutchinson and Mosier 18 og avledninger derav, 19,20, den kvadratiske fremgangsmåten beskrevet av Wagner et al. 21, og den ikke-likevektstate diffusive flux estimator beskrevet av Livingston et al 22. For en grundig drøfting av ikke-lineære flux modeller, se Parkin et al. 12 og Venterea et al 23.
Metoder som ligner den statiske kammeret metode omfatter bruk av gjennomstrømnings målesystemer med Fourier overførings infrarød (FTIR)-spektrometri som et alternativ til å sprøyte prøvetaking og gasskromatografi, samt automatisering av kammerlukking og sampling på forskjellige måter. Automatiserte systemer gjør hyppigere målinger med redusert personell, men også kreve ytterligere investeringer i infrastruktur. Grace et al. 24 gir en omfattende oversikt over alternativer og avveininger i automatisert kammer-baserte N 2 O måling.
Karakterisering av klimagassen fluks fra begge klarte og naturlige systemer er viktig å informere prosessbaserte modeller, forstå konsekvensene av management praksis og informere reduserende strategier, og for å støtte globale regnskap og klimamodellering. Dermed mens enkelte studier er informativ på lokal skala, er mye ekstra verdi utledes gjennom å bidra til, og trekke fra, en global mengde kunnskap om gassutveksling mellom landskapet og atmosfæren. Det er nøkkelen, derfor, at data samles inn og rapporteres på en måte som sikrer lang levetid og interoperabilitet med den bredere kunnskapsgrunnlag. Dette inkluderer følgende beste praksis for å sikre datakvalitet, samt innsamling av supplerende tiltak og omfattende rapportering av metadata for å tillate utvidelse av funn utover diskrete undersøkelser. Gode retningslinjer for rapportering av data er tilgjengelige fra GRACEnet prosjektet 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 |