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.
ここで説明した静的室ベースのアプローチは、土壌システムからのGHGフラックスを測定するための効率的な方法である。その構成要素の相対的なシンプルさがより多くのインフラを集中的にメソッドが実行不可能である、条件やシステムへのそれは特に適しています。高品質なデータを生成するために、しかし、静的なチャンバのアプローチは、実験計画6に厳密に注意して行わなければならない。考慮されなければならない一つの注目すべき考慮事項は、反復室ベースの測定の間で高い変動性をもたらすことができる、土壌ガスフラックスの空間的な変動である。実験の設計において、従って、それは統計分析のために十分な電力を提供するのに十分な反復を含むことが重要である。トレードオフは、十分な複製を維持し、処理当たり4回の反復の最小値は一般的なガイドライン14の間に研究することができる治療の数の間に存在し得る。
測定されたフラックスは日々の排出量を推定するために使用する場合は、 "ontent>、気温、土壌温度、およびガス排出量の日内変動を考慮しなければなりません。研究目標は、温度が日次平均を反映する際に午前中で得られる測定値が必要な場合は、サンプリングのための制限されたウィンドウには、都合良く監視することができ室の数に影響することがあります。評価されるべき追加的な対価は、植物の根のと地上バイオマス上記包含または除外はガスフラックスに与える影響である。商工会議所の配置の相対植物組織になります適切にバランスでなければならない、フラックスデータの解釈に影響を与え、特にCO2 の場合には、微生物の呼吸だけでなく、根だけでなく呼吸や光合成を撃つ。これらの要因の追加的な議論については、パーキンおよびVenterea 8を参照してください。前述したように、この方法には多くのバリエーションがチャンバ設計及びサンプリングを含む、存在するボリューム。一つのこのような変化は、注射器と収集バイアルとの間でサンプルを転送するために用いられる方法である。ここに記載された技術は、まず正圧5バイアルを充填する前にサンプルを収集バイアルをフラッシュします。より一般的に使用される技術は、真空ポンプを用いて予備真空排気されてきたバイアルにシリンジからの試料の移転であり、フラッシングない非排気バイアルの使用はまた、8,17報告されている。アプローチの範囲が存在する別の重要な点は、データ分析および研究中のシステムに最も適したフラックスモデルの選択である。ここで説明する線形回帰法に加えて、非線形モデルも長い、展開時間が使用される場合は特に、使用することができる。これらのモデルは、21。そのハッチンソン19,20及びMosierから18及び導出により開発されたアルゴリズム、Wagner らにより記載され次の手順を含む、非定常リビングストンら 22によって記載された状態の拡散フラックス推定。非線形のフラックスモデルの全体的な説明については、パーキンら 12とVenterea ら 23を参照してください。
静的チャンバアプローチに類似の方法はフーリエ変換赤外線(FTIR)サンプリングし、ガスクロマトグラフィーシリンジする代替として分析、ならびに様々な手段を介してチャンバの閉鎖及びサンプリングの自動化フロースルー測定システムの使用を含む。自動化されたシステムを削減担当者とより頻繁な測定を可能にするだけでなく、追加のインフラストラクチャへの投資を必要とする。グレースら 24は、自動化されたチャンバーベースのN 2 Oの測定ではオプションとトレードオフの広範な概要を提供します。
両方の管理·ナチュラル系からの温室効果ガスフラックスの特徴付けはした運営の影響を理解し、プロセスベースのモデルに知らせることが重要です実践と緩和戦略を通知し、グローバルな会計と気候変動のモデル化をサポートするために、NT。個々の研究は、ローカルスケールで有益であるがこのように、多くの付加価値はに貢献し、景観と大気とのガス交換で知識のグローバルな身体からの描画によって導出される。したがって、そのデータが収集され、より広範な知識ベースと寿命との相互運用性が確保さ方法で報告することが、鍵となります。これは、個別の研究を超えた調査結果の拡張を可能にするために、データの品質だけでなく、補助的な対策やメタデータの包括的なレポートの収集を確実にするためのベストプラクティスを、次が含まれています。データ報告のための優れたガイドラインはGRACEnetプロジェクトとGRA 25から入手できます。
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 |