Andreas Hubert

Exchange of reduced volatile sulfur compounds between leaf litter and the atmosphere

Abstract Leaf litter collected from the uppermost litter horizon and the fermentation horizon from a 60-yr-old beech forest was investigated for its exchange of volatile reduced sulfur compounds with the atmosphere. A close linear correlation between the water content and the microbiological respiration was found. This biological activity was closely related to the exchange of dimethyl sulfide (DMS) and carbonyl sulfide (COS). We found a DMS emission exponentially correlated with the respiration rates of samples from both horizons. In contrast, COS was deposited to the leaf litter samples, and the uptake was not found to correlate linearly or exponentially with either the water content or the respiration rates. Deposition of COS was high when respiration was low. At higher respiration rates, as observed with increasing high water content, no COS uptake was detected. Under these conditions, we assume high levels of CO 2 , inferred from the high respiration rates observed, to cause a competitive inhibition of carbonic anhydrase, the well-known key enzyme for the consumption of COS. Though the enclosure technique results in gas exchange rates which provide an upper limit to the actual rates that might occur in situ within a forest, the measured exchange rates indicate that the contribution of the leaf litter to the atmospheric burden is not significant in the case of DMS but might be of relevance as a sink for COS.

Accelerated Solvent Extraction - More Efficient Extraction of POPs and PAHs from Real Contaminated Plant and Soil Samples

102 INTRODUCTION 103 1. EXTRACTION TECHNIQUES IN ENVIRONMENTAL ANALYSIS 104 1.1 Requirements on modern procedures 104 1.2 Modern extraction procedures 105 1.3 Design and function of the ASE 200 extraction unit 107 1.3.1 Basic design 107 1.3.2 The extraction process 107 1.3.3 Selection of the solvent 113 2. DEVELOPMENT OF A WORK STRATEGY 116 2.1 Extraction problems from different environmental compartments... 116 2.2 Aims of methodological improvements 117 2.3 Working hypothesis and the resulting work programme 117 3. EXPERIMENTAL PART 119 3.1 Sampling: plant material 119 3.2 Sampling: soil material 120