Distribution of carbon and nitrogen forms in Histosols of headwater areas - a case study from the valley of the Kamienna Creek (northern Poland)

The aim of the study was to recognize the vertical variability in the content of different forms of carbon and nitrogen in Histosols of a forest spring niche located in the upper course of the Kamienna Creek (the Słupia River catchment). Soil samples were taken from three profiles and analyzed with standard methods used in the soil science. Analyses included the degree of peat mass decomposition, content of soil organic matter, pH, content of total organic carbon (TOC), total nitrogen (TN) and forms of carbon and nitrogen after sequential extraction in 0.25 mol KCl dm-3, 0.25 mol H2SO4 dm-3 and 2.5 mol H2SO4 dm-3. The following fractions were isolated: nonhydrolyzable carbon (NHC) and nitrogen (NHN), weakly hydrolyzable carbon (WHC) and nitrogen (WHN), easy hydrolyzable carbon (EHC) and nitrogen (EHN), dissolved organic nitrogen (DON), and its ammonium (NH4-N) and nitrate (NO3-N) form. The Histosols were t up to 0.9 m hick. The degree of peat mass decomposition was 3-9. The content of organic matter ranged from 317.3 to 829.0 g kg-1, and TOC from 162.2 to 459.5 g kg-1. The soils were acid at pHH2O equal 5.6-6.5. The NHC form predominated in TOC. The content of the form was 117.3-399.7 g kg-1, and contribution in TOC 72.3-89.2%. Soils contained 17.1-41.7 g kg-1 of WHC (4.5-10.6% in TOC), and 27.3-62.2 g kg-1 EHC (6.4-17.2% in TOC). The soils were rich in total nitrogen (TN), whose content was 11.1-33.6 g kg-1. The content of NHN was 5.50-18.89 g kg-1 (37.18-69.84% in TN), WHN 4.28-14.17 g kg-1 (21.23-43.72 in TN), EHN 1.16-8.02 g kg-1 (8.06-24.32% in TN), and DON ranged from 0.029-0.394 g kg-1 (0.10-1.20% in TN). The concentration of NH4-N was 0.043-0.337 g kg-1, and NO3-N 0.003-0.012 g kg-1. Similar regularities in the vertical distribution of the investigated forms of carbon and nitrogen were observed in every soil profile. In general, an increase in the nonhydrolyzable forms of carbon and nitrogen and a decrease in EHC, EHN, DON and NH4-N were observed with depth. The maximum concentration of EHC, EHN, DON and NH4-N found in bog horizons is probably an effect of the highest intensity of biochemical processes in the topsoil and the influx of fresh litterfall. A constant underground flow of water and leaching are the factors which caused a low contribution of labile forms of C and N in lower parts of the soil profiles.