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The long‐term measurement of soil redox potential (EH) by permanently installed Pt electrodes may be restricted by electrode breakdown (electrode rupture and resin leakage) and contamination, especially under wet and strongly reducing soil conditions. The EH of a slightly alkaline (pH 7.1 to 7.3) Calcaric Gleysol developed from marine sediment in the dyked marsh of Schleswig‐Holstein, Northern Germany, was monitored weekly during a 4‐year period using permanently installed Pt electrodes. Measurements were performed in fivefold at 10, 30, 60, 100, and 150 cm. Furthermore, water table level was recorded. Sulfide occurred in 150 cm as a heritage of the previous marine environment. Mean water table level was 84 cm below the soil surface but was characterized by both short‐term and seasonally strong fluctuations. Levels of water table ranged from 33 to >200 cm below soil surface. In consistence with water table level, the EH continually decreased with soil depth. Mean redox conditions were oxidizing at 10 (550 mV) and 30 cm (430 mV), weakly reducing at 60 cm (230 mV), and moderately reducing at 100 (120 mV) and 150 cm depth (–80 mV). Soil hydrology differed markedly during the study as expressed by periods of water saturation for each depth. This was reflected by Pt electrodes response, since period of water saturation and EH were significantly negatively correlated as calculated for each year and depth (rs = –0.971; n = 20; P < 0.01). The 60‐cm depth was most frequently influenced by water table fluctuations, showed the largest EH range (920 mV) and the most distinct seasonal pattern in EH. Good function of the electrodes in this depth can be concluded even after long time of installation in soil. Although established in a sulfide‐bearing environment, three of five electrodes at 150 cm showed a substantial increase (+500 mV) in EH during summer of the third and fourth years of investigation, which had low water tables. It is not clear whether the non‐response of two electrodes was due to electrode contamination or spatial variation in EH. When operating in reducing systems, this problem can be circumvented by installing a large number of electrodes or by a regular replacement of electrodes. Using properly constructed and permanently installed Pt electrodes, soil EH can be monitored for extended periods under wet and reducing soil conditions.

Blast-furnace sludge is generated during the production of pig iron and is disposed of in the environment in large surface landfills. We investigated blast-furnace sludge samples of an abandoned landfill in order to determine its chemical and mineralogical nature and to evaluate some environmental hazards that may arise from this industrial waste. The mineralogical inventory, which was quantified by Rietveld refinement of XRD analyses using the fundamental-parameter approach, revealed that blast-furnace sludge is dominated by X-ray amorphous substances (with a mean of 590 g kg(-1)) including coke and (hydr)oxides of Fe, Si, Al, Zn, and Pb. Calcite (CaCO3) (136 g kg(-1)), dolomite (Ca,Mg[CO3]2) (14 g kg(-1)), quartz (SiO2) (55 g kg(-1)), kaolinite (Al2[OH]4Si2O5) (40 g kg(-1)), graphite (C) (27 g kg(-1)), and chemically not specified layered double hydroxides (28 g kg(-1)) were identified in almost all samples. Iron is present as magnetite (Fe3O4) (34 g kg(-1)), hematite (Fe2O3) (38 g kg(-1)), wuestite (FeO) (20 g kg(-1)) and alpha-iron (Fe0) (6 g kg(-1)). Chemically, blast-furnace sludge is dominated by C (190 g kg(-1)) and Fe (158 g kg(-1)) reflecting the process of pig-iron production. On the basis of total contents, environmentally problematic metals (including As) are Zn (32.6 g kg(-1)), Pb (10.3 g kg(-1)), Cd (81 mg kg(-1)), and As (129 mg kg(-1)). As the forested landfill is used by residents for leisure activities, the exposure assessment by pathway oral uptake of blast-furnace sludge particles by humans has to be critically evaluated, particularly as significant proportions of metals are acid-soluble. However, under the prevailing slightly alkaline pH values of the sludge (pH 7.6-9.2), the solubility of the metals is very low as indicated by low pore water concentrations. Currently, groundwater monitoring should be focused mainly on F- since the F- concentrations in the pore water of blast-furnace sludge are at high level (2.65-24.1 mg of F- L(-1)).

SummaryDissolved organic matter (DOM) is involved in many important biogeochemical processes in soil. As its collection is laborious, very often water-soluble organic matter (WSOM) obtained by extracting organic or mineral soil horizons with a dilute salt solution has been used as a substitute of DOM. We extracted WSOM (measured as water-soluble organic C, WSOC) from seven mineral horizons of three forest soils from North-Rhine Westphalia, Germany, with demineralized H 2 O, 0.01 M CaCl 2 , and 0.5 M K 2 SO 4 . We investigated the quantitative and qualitative effects of the extractants on WSOM and compared it with DOM collected with ceramic suction cups from the same horizons. The amounts of WSOC extracted differed significantly between both the extractants and the horizons. With two exceptions, K 2 SO 4 extracted the largest amounts of WSOC (up to 126 mg C kg -1 ) followed by H 2 O followed by CaCl 2 . The H 2 O extracts revealed by far the highest molar UV absorptivities at 254 nm (up to 5834 L mol -1 cm -1 ) compared to the salt solutions which is attributed to solubilization of highly aromatic compounds. The amounts of WSOC extracted did not depend on the amounts of Fe and Al oxides as well as on soil organic C and pH. Water-soluble organic matter extracted by K 2 SO 4 bore the largest similarity to DOM due to relatively analogue molar absorptivities. Therefore, we recommend to use this extractant when trying to obtain a substitute for DOM, but as WSOM extraction is a rate-limited process, the suitability of extraction procedures to obtain a surrogate of DOM remains ambiguous.