Monitoring of reducing conditions in soils and implications for biogeochemical processes

摘要: Reducing conditions in soils alter a variety of biogeochemical processes that affects the mobility nutrients and pollutants, emission greenhouse gases, formation redoximorphic features. Hence, precise characterization monitoring reducing is important for land use management risk assessment. Conventionally, platinum (Pt) electrodes are used to measure redox potential (EH) delineation soil status. In combination with data-logger system EH can be monitored at high temporal resolution but shortcoming cost-intensive technical equipment. Alternatively, Indicator Reduction Soils (IRIS) method delineate consists synthesized iron (FeIII) oxides coated onto white polyvinyl chloride (PVC) bars. The bars installed period 30 days visually assessed effects reduction by depletion FeIII oxide coating. Currently, differentiation into classes oxidizing (EH > 300 mV; oxygen (O2) present soil), weakly 100 manganese (MnIII,IV) reduc-tion), moderately –100 reduction) only achieved Pt electrodes. The objectives this thesis investigate spatial distribution different approaches. Automated electrode measurements on hourly basis (2011 2014) were compared weekly (1990 1993) query benefit monitoring. Additionally, IRIS was adopted coating MnIII,IV PVC (in following referred as ‘Mn Fe bars’) evaluated their differentiate field laboratory experiments. An characteristic functioning sorbent ele-ments solution. Therefore, coatings previously field-installed extracted analyzed element sorption behavior. Finally, long-term groundwater data (1997 2012) assess trends water table (WT) depth development along 17 km2 sized mesotrophic fen, which relevant onset impact All field-experiments conducted study sites North-West Germany. Daily readings sufficient equally derive class over time loss information occurred when or monthly performed. Since fluctuations up 540 mV measured within day, essential identify biogeo-chemical processes. Besides electrodes, it possible facili-tate durable enabling monitor Laboratory experiments defined EH-pH went dissolution under conditions. capillary fringe above surface identified hot spot minor remov-al. simultaneous application Mn enabled zones It found presence ferrous Fe2+ (reductant) solution mediated an abiotic reaction for-mation Subsequently, (oxidant) transformed manganous Mn2+ being removed from surface. precipitates remaining differed remarkably color quantify percentage area these patterns time. Thereby, temporally spatially diverse pathways forming studied. Selective chemical ex-traction verified preferential cati-onic elements (e.g. copper, lead, zinc) oxides, whereas posi-tively charged situ formed enriched having oxyanionic character arsenic, molybdenum, phosphorus, vanadium). Moreover, (‘field’-Fe oxides) revealed higher loadings (‘lab’-Fe oxides). accordance find-ing, field-Fe solely composed short-range ordered minerals exhibiting capacity. WT main driver above-mentioned pro-cesses controlled (i) dynamics, (ii) removal bars, (iii) relocation topsoil rise. regard, read-ings fen indicated lowering average 20 cm 39 out 46 wells. A meteorological forecast climatic balance until year 2100 decreasing depths will intensified. Obvious-ly, have status associated top soil. Overall, improves understanding does not capture ‘true’ dynam-ic nature determined continuous re-dox decadal scales evaluate climate change waterlogged soils.