|Description of Static Non-steady State Flux Chambers Used in Field Studies|
Note: All product names and suppliers mentioned below have been used in our research, but are mentioned only for convenience and imply no endorsement on the part of the USDA.
Our chamber anchors and tops are fabricated using 20-gauge rectangular stainless steel 4-inch restaurant "steam pans" equipped with a flange around the edges available from restaurant equipment suppliers (e.g., Hockenbergs) Anchors are made by cutting out the bottom section of the pan resulting in a frame measuring approximately 0.50 m X 0.29 m X 0.086 m deep. The anchor is inserted into the soil so that the flange is nearly flush with the soil surface (photo). A piece of plywood and a mallot can be used for uniform insertion of the base (photo). Chamber tops are made from an identical steam pan, without the bottom removed. Weather-stripping material (EPDM) to serve as a gasket is attached to the flange on the underside of the chamber top using all purpose cement (e.g. Barge). The outer surfaces of the top are covered with reflective insulation (e.g. Reflectix brand) using aluminum tape. A vent tube (3.5 mm ID X 0.15 m long) is installed horizontally through one side of the chamber top. A brass fitting (Part no. B-200-1-OR, Swagelok) is attached in the center of the top and lined with rubber septum material to serve as a sampling port. The sampling port is connected (glued) on the inside of the chamber top to a manifold (Part no. STCM-13-20/4, Small Parts, may no longer be available) which in turn is connected to 4 sections of FEP tubing (0.8-mm ID X 0.2 m long) (photo) using aluminum tape. A metal handle can be attached (rivetted) to the chamber top to facilitate handling. During sampling, the chamber top is sealed to the anchor using standard 2- to 3-inch binder clips on each edge. Gas samples are collected by inserting a syringe needle through the septum (photo). For additional practical and theoretical issues regarding flux-chamber design and construction, including proper anchor and vent tube design, see the ARS GRACEnet Chamber Protocol, Venterea, 2010; Venterea et al. 2009, Venterea and Baker 2008, and references cited by these articles.