Effects of peat drainage on labile organic carbon and water repellency in NE Poland


Abstract: Hot and cold water-extractable organic carbon (HWC and CWC, respectively) fractions, as good indicators of organic matter quality, as well as water repellency (WDPT test) and state of secondary humification were analyzed in topsoil samples of peatland drained for agricultural purposes 160 years ago. The examined sites (drained and used as grassland) at the peatland had been affected by the moorsh-forming process. During this process, intense mineralization and secondary humification of organic matter took place. The state of transformation of organic soils varied from weak to complete degradation. The HWC contents ranged between 2.623 and 3.572 g kg^{-1} in field-moist samples and 3.999 and 6.074 g kg^{-1} in air-dried soil samples. The CWC contents were generally lower than HWC and ranged between 0.411 and 0.535 g kg^{-1} in field-moist samples and 0.696 and 0.939 g kg^{-1} in air-dried soil samples. The examined soils were extremely water repellent when dried. The measures of transformation of peat after drainage and WDPT were not significantly correlated, but a tendency for higher values of water repellency at the site regarded as degraded was noted. Deep drainage caused an increase of HWC fraction, which in light of the moorsh-forming process should be regarded as negative. The topsoil of the peatland became dry and resistant to rewetting. However, when the ground water level is maintained at not deeper than 0.50 m, the changes in peat matter do not lead to degradation. HWC is a good measure to show differences occurring within the ecosystem. Given its correlation with state of transformation (W1 index) and water repellency (WDPT test), HWC is a good measurement of peat quality. HWC and WDPT measurements may be helpful in determining degradation of peat soil after drainage.

Keywords: Dissolved organic carbon, fens, grasslands, moorsh-forming process, hydrophobicity

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