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[Display omitted] • Organic matter from VFCW's sludge deposits is less soluble after aging. • Truly dissolved organics (<3kDa) are leached under acidic conditions. • Larger colloids (>3 kDa) are leached under alkaline conditions. • Truly dissolved organics leached around neutrality are very aromatic. • Leached colloids are all poorly aromatic regardless of pH and molecular size. The very rapid development of vertical flow constructed wetlands (VFCW) in Europe and throughout the world has induced a growing concern on the conditions of management of their surface sludge deposits (SD). The leaching of organic components from SD was explored in this study with respect to their potential impact on biochemical oxygen demand (BOD) and their role as complexing agents in the release of trace contaminants. The aromaticity and molecular size of leached organic compounds was investigated over a large range of pHs. Experimental results showed that the pH of the leaching aqueous solution influenced the concentration and characteristics of leached OC. Around the natural pH of SD aqueous suspensions (6 to 8), truly dissolved organics (<3 kDa) exhibited high aromatic content. Under alkaline conditions (pH > 8), large organic colloids (>30 kDa) were found predominant, exhibiting a low aromaticity growing with pH. Under acidic conditions (pH < 6), hydrophilic truly dissolved organics were leached. Comparison of concentration, aromaticity and molecular size of OC leached from 14-year and 7-year SD suggested that ageing of SD reduced their sensitivity to pH conditions and may improve their agronomic properties. [ABSTRACT FROM AUTHOR]

Saisonal dynamics of concentration and optical properties (aromaticity and molecular weight) of dissolved organic carbon in a restored perculation mire (Burgwald, Hesse)Lukas Ditzel (1), Eberhard Leicht (2), Martin Reiss (1), Peter Chifflard (1)1 Philipps-Universität Marburg, Faculty of Geography, Germany2 HessenForst, Burgwald, GermanyAlthough peatlands are significant carbon storages, the understanding of the export of dissolved organic carbon of percolation mires is still insufficient. Especially in the low mountains areas in middle Europe percolation mires were widely spread before they were cultured. Currently the questions arises, whether it is necessary to restore such percolation mires since in one hand it is not an easy feat and in the other hand the functioning of their organic matter turnover is not well studied. Thus, in this study we will investigate and identify the seasonal dynamics of concentration and optical characteristics of dissolved organic carbon in a restored percolation mire in the low mountain ranges (Burgwald, Hesse, Germany) to assess the functioning in exporting dissolved organic carbon, especially during spring and early summer, when the influence of an increasing dehydration is recognizable. The study took place in the restored percolation mire Franzosenwiesen, located in the Burgwald Forrest near Wetter (Hesse, Germany). This moor is the last percolation mire to be found in the German low mountain range. During the period of February to July 2018 water samples were taken weekly at different locations within the percolation mire and at the outlet to analyze concentration and optical characteristics of dissolved organic carbon. Additionally, water level was recorded automatically at the inlet and at the outlet of the percolation mire. Concentration and optical characteristics (aromaticity and molecular weight) of dissolved organic carbon were analyzed by a TOC-Analyzer (Shimadzu, TOC-L), a fluorescence spectrometer (RF-6000, Shimadzu) and a UV–VIS spectrophotometer (Genesys 10S, ThermoFisher), respectively. Factor analysis and The results indicate that the dynamics of dissolved organic carbon in the restored percolation mire Franzosenwiesen are contrary to the dynamics predicted in the literature. The quality of dissolved organic carbon in the percolation mire during the summer period is growing instead of declining. The results of this study underlines the important role of percolation mires as carbon storage and demonstrated the importance to restore similar destroyed percolation mires, which still exist in the low montain range in middle Europe. [ABSTRACT FROM AUTHOR]