To study the fluxes of the radiative active trace gases CH4, CO2, and N2O, a gas sampling and analytical device was developed. It is a useful tool for accurate gas sampling in the field and enables the subsequent fully automated analysis of the gas samples in the laboratory. The computer‐controlled analytical system consists of a gas chromatograph equipped with a flame ionization detector (FID), an electron capture detector (ECD), and a pressure‐controlled autosampler for 64 sample containers. The system automates sample injection, the analysis of CH4, CO2, and N2O in each sample and the subsequent evacuation of the sample containers. It is equipped with a second alternative sample inlet for manual syringe injection. This inlet is suitable for analyzing small volumes of gas samples (3 mL). The gas sampling system for use in the field consists of evacuated sample bottles (100 mL) with Teflon cocks combined with a small battery‐driven field sampler with a pressure sensor. This device enables an on‐site control of the vacuum integrity of the sample bottles during sampling and purging of the dead volumes between the sampler induction pipe and the sample container.
Fur die Untersuchung von Nadel-, Blatt-, Holz-, Rinden-, Wurzel-, Boden-und Gesteinsproben zur Klarung der Spurenstoffkreislaufe in Waldokosystemen wurde ein AufschluRsystem benotigt, das folgende Anforderungen erfiillt: a) einfache Handhabung b) geringe Kontaminationen c) Verwendbarkeit fiir unterschiedliche Probenmaterialien und Sauremischungen (HNO3, HNOdHF, HzSOdHF, HN03/H2SOdHF und unter ganz bestimmten Voraussetzungen HN03/HC104/HF und HClOdHF) d) geringe Kosten. Aufbauend auf einer uber zehnjahrigen Erfahrung mit einem DruckaufschluBsystem aus Aluminium (Wahler, 1964) wurde ein AufschluRsystem entwickelt, das von einer gut ausgeriisteten Werkstatt leicht nachgebaut werden kann. Das AufschluRsystem (s. Abb. 1) besteht aus einer Edelstahlhalterung (x 12 Cr Ni 18 8) und 6 aluminiumummantelten TeflongefaRen, die einzeln zwischen die Platten gestellt und arretiert werden. Die Edelstahlhalterung ist aus 3 verschraubten Teilen aufgebaut: einer runden Grundplatte rnit zentralem Gewinde, der Mittelsaule, die in die Grundplatte eingeschraubt wird, und der Deckplatte, die ebenfalls rnit der Saule verschraubt ist. In die Deckplatte sind kreisformig um das Zentralgewinde 6 Gewinde f i r M-10-Schrauben geschnitten. Mit diesen Schrauben werden Deckel und Becher der AufschluRgefaRe zusammengedriickt und gleichzeitig die 6 um den Mittelsteg angeordneten Becher arretiert. Die AufschluRbecher rnit einem Fassungsvermogen von ca. 30 ml und die Deckel sind aus gezogenem Teflon gedreht. Der Deckel hat eine PaRkante, die ein Verrutschen nach SchlieRen des Bechers verhindert. Der Becher ist rnit einem Aluminiumrohr ummantelt, wobei diese Ummantelung vom Rand des Teflonbechers uberlappt wird (Abb. 1). Wegen der Ausdehnung des Teflons beim Erwarmen ist zwischen Aluminiumummantelung und Teflonbecher in der Hohe und im Durchmesser ein Spiel von ca. 0.5 mm notig. Das Teflonmaterial muR vor der Verarbeitung uber eine langere Zeitspanne (ca. 10 Stunden) auf 200" C erhitzt werden, um spatere Verformungen zu vermeiden. Nach der 0044-3263/86/0306-0350 $ M.SO/O 0 VCH Verlagsgesellschaft mbH, D-6940 Wcinhcim, 1986
BackgroundThe repeated freeze-thaw events during cold season, freezing of soils in autumn and thawing in spring are typical for the tundra, boreal, and temperate soils. The thawing of soils during winter-summer transitions induces the release of decomposable organic carbon and acceleration of soil respiration. The winter-spring fluxes of CO2 from permanently and seasonally frozen soils are essential part of annual carbon budget varying from 5 to 50%. The mechanisms of the freeze-thaw activation are not absolutely clear and need clarifying. We investigated the effect of repeated freezing-thawing events on CO2 emission from intact arable and forest soils (Luvisols, loamy silt; Central Germany) at different moisture (65% and 100% of WHC).ResultsDue to the measurement of the CO2 flux in two hours intervals, the dynamics of CO2 emission during freezing-thawing events was described in a detailed way. At +10°C (initial level) in soils investigated, carbon dioxide emission varied between 7.4 to 43.8 mg C m-2h-1 depending on land use and moisture. CO2 flux from the totally frozen soil never reached zero and amounted to 5 to 20% of the initial level, indicating that microbial community was still active at -5°C. Significant burst of CO2 emission (1.2–1.7-fold increase depending on moisture and land use) was observed during thawing. There was close linear correlation between CO2 emission and soil temperature (R2 = 0.86–0.97, P < 0.001).ConclusionOur investigations showed that soil moisture and land use governed the initial rate of soil respiration, duration of freezing and thawing of soil, pattern of CO2 dynamics and extra CO2 fluxes. As a rule, the emissions of CO2 induced by freezing-thawing were more significant in dry soils and during the first freezing-thawing cycle (FTC). The acceleration of CO2 emission was caused by different processes: the liberation of nutrients upon the soil freezing, biological activity occurring in unfrozen water films, and respiration of cold-adapted microflora.
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