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Alluvial soils of the Vistula River delta are one of the most fertile soils in Poland. Part of the area is a depression, whose agricultural utilization relies upon the efficient reclamation systems on polders. High ground water levels enhance redox processes, restriction of which is one of more important functions of the draining systems. This paper presents short characteristics of the redox status of alluvial soils in the delta and describes processes and consequences of oxygen deficits in soils. The importance of indices of oxygen deficit for the formation of water conditions, which would favour agricultural utilization of the delta soils, is underlined.
 The redox status of the cell is described by the ratio of reduced to non-reduced compounds. Redox reactions which determine the redox state are an essential feature of all living beings on Earth. However, the first life forms evolved under strongly anoxic conditions of the young Earth, and the redox status probably was based on iron and sulphur compounds. Nowadays, redox reactions in cells have developed in strict connection to molecular oxygen and its derivatives i.e. reactive oxygen species (ROS). Oxygen has started to accumulate on the Earth due to oxygenic photosynthesis. All aspects of aerobic life involve ROS, reactive nitrogen species (RNS), antioxidants and redox regulation. Many different redox-active compounds are involved in the complex of redox processes, including pyridine nucleotides, thioredoxins, glutaredoxins and other thiol/disulphide-containing proteins. Redox regulation is integrated with the redox-reactions in photosynthesis and respiration to achieve an overall energy balance and to maintain a reduced state necessary for the biosynthetic pathways that are reductive in nature. It underlies the physiological and developmental flexibility in plant response to environmental signals.
Chromium contamination in the area of the Radomka river basin in Poland has lead to significant environmental problems. Therefore, chromium redox transformations were investigated in the aquatic environment under conditions as close to natural as possible ± at intermediate pH and in the presence of original bottom sediment and dissolved oxygen. Reduction of Cr(VI) in the Radomka river water occurs at a low rate (t1/2 = 19 h). The rate of Cr(VI) reduction increased in the river water spiked by HA (t1/2 = 0.5 h), and Fe(II) (t1/2 = 2 min). The kinetics of Cr(VI) reduction by Fe(II) was dependent on the evolution of the forms of Cr(VI) and the competing Fe(II) oxidation reaction by dissolved oxygen. The reduction of Cr(VI) by humic acids appeared to be a significantly slower process than Fe(II) oxidation by O2. Chromium(III) present in the tanning liquor used and the aged solution of chromium sulphate was less prone to oxidation by MnO2 than Cr(III) introduced with chromium nitrate and sulphate solutions (7% and 10% conversion over 1 h in comparison with 55% and 32%, respectively). Chromium deposits in bottom sediment turned out to be resistant to oxidation by MnO2.
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