Humic substances are polydisperse mixtures of structurally complex matters with different molecular weights. The complexity of molecular composition of humic substances is reflected through their physical and chemical properties and results in diverse interactions both with inorganic components and living organisms. The correlation of the molecular composition of humic and fulvic acids and their molecular weight distribution were analyzed by means of CP/MAS 13C NMR spectroscopy and size exclusion chromatography. Humic acids are a dynamic system containing macromolecular, oligomeric and low-molecular components. Fulvic acids are a monodisperse mixture of relatively low-molecular (up to 2 kDa) organic compounds. A significant correlation between the content of high and medium weight molecular fractions with labile fragments and low molecular weight fractions with hydrophobous fragments of humic acids has been revealed.
Diatom communities sampled in the vicinity of the Polish Antarctic Arctowski Station (King George Island, South Shetland Islands) have been investigated. Soil and sediment samples were collected from Petrified Forest Creek and Ornithologist Creek valleys. A total of 98 diatom taxa belonging to 30 different genera were recorded in the counts. Nine taxa have a marine origin but all together constitute only 0.14% of all counted valves. Three species: Staurosira pottiezii, Psammothidium germainioides and Sellaphora jamesrossensis dominated the flora. Some differences in the diatom assemblages were observed between soil samples from two stream valleys and between soil and sediments from the same catchment area. The highest species diversity was recorded in samples from the dried-up bed of the Ornithologist Creek, where both freshwater and terrestrial species were found. The soil samples from both investigated valleys showed a comparable number of species, but a different species composition. Based on the PCA analysis a clear separation of the assemblages from both creeks could be observed.
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