Soil moisture and matric potential-an open field comparison of sensor systems

Soil water content and matric potential are central hydrological state variables. A large variety of automated probes and sensor systems for state monitoring exist and are frequently applied. Most applications solely rely on the calibration by the manufacturers. Until now, there has been no commonly agreed-upon calibration procedure. Moreover, several opinions about the capabilities and reliabilities of specific sensing methods or sensor systems exist and compete. A consortium of several institutions conducted a comparison study of currently available sensor systems for soil water content and matric potential under field conditions. All probes were installed at 0.2mb.s. (metres below surface), following best-practice procedures. We present the set-up and the recorded data of 58 probes of 15 different systems measuring soil moisture and 50 further probes of 14 different systems for matric potential. We briefly discuss the limited coherence of the measurements in a cross-correlation analysis. The measuring campaign was conducted during the growing period of 2016. The monitoring data, results from pedophysical analyses of the soil and laboratory reference measurements for calibration are published in Jackisch et al. (2018, https://doi.org/10.1594/PANGAEA.892319)

Arsenic release and speciation in a degraded fen as affected by soil redox potential at varied moisture regime

Soil surveys have demonstrated arsenic (As) contents of up to 1600 mg kg(-1) in surface horizons of degraded fens in the Bavarian Molasse basin, Germany. Ground water from the Tertiary aquifer seems to be the primary source of As. Yet, the cause of its accumulation in the topsoil is unclear. Focussing the influence of redox processes on As redistribution, we conducted soil column experiments with the A (716 mg As kg(-1)), Ag (293 mg As kg(-1)) and 2Ag (37 mg As kg(-1)) horizons of a Mollic Gleysol (pH 7.2). The fixed beds were equipped with redox electrodes and suction cups and subjected to a saturation-drainage-saturation cycle. Water table fluctuations were simulated by defined pressure heads applied to the lower column boundaries via a digitally controlled vacuum system. After water saturation, the redox potential (E(H)) dropped to minimum values of around 0 mV in the A/Ag and-400 mV in the 2Ag horizon. Soil drainage resulted in a quick return to oxidising conditions. Both in the A and Ag horizons total aqueous As concentrations were low (up to 20 mu g l(-1)) and not related to E(H). In contrast, aqueous As concentrations of the 2Ag horizon were between 5 and 140 mu g l(-1) and increased as the E(H) decreased. However, the As species distribution showed no clear trend with E(H) since both As(III) and As(V) were detected under reducing conditions. High release of As in the 2Ag horizon is consistent with low contents in Fe (hydr)oxides. In the A and Ag horizons, pedogenetic enrichment of sesquioxides contributes to a comparably lower sensitivity of E(H) to water saturation and favours As retention. Thereby, As released under saturated conditions in the 2Ag horizon may be stabilised in the topsoil following capillary rise. Thus, surface horizons may act both as historic and as recent sinks for geogenic As at the site. (C) 2010 Elsevier B.V. All rights reserved