Composition and Genesis of Organic Matter in Soils and Bottom Sediments of the Residential Zone of Khabarovsk

Data are presented on the distribution and composition of organic abiotic (TOC, HC, and CHC/TOC, %) and biotic (phytopigments and microbial communities) components of soils and bottom sediments (BS) that formed during long-term anthropogenic transformation of the landscape. Average concentrations of TOC in the soils and bottom sediments did not significantly differ and varied at the level of 4.9%. HC content was 20–560 mg/kg in the soils and 3–20 mg/kg in BS. The BS contain 1.4–6.0 μg/g chlorophyll (chl.) a, up to 2.8 μg/g chl. b, and up to 3.9 μg/g chl. c. The soil contains no more than 4.4 μg/g chl. a, 2.8 μg/g chl. b, and 3.9 μg/g chl. c. Carotenoids dominated among the phytopigments, and their concentrations varied from 6.8 to 12.2 μg/g in the sediments and from 4.1 to 9.5 μg/g in the soils. The fraction of primary-production carbon in TOC was 0.01 to 1.36% in the river sediments and 0.18 to 0.76% in the soils, which is one to two orders of magnitude higher than the fraction of HC. Diatoms were found out to actively participate in the production of organic matter (OM) in the river sediments. Using molecular markers, a more significant role of the primary production of microalgae than higher vegetation was identified in the formation of organic matter in the soils and BS. A leading role in the formation of OM in soils and sediments belongs to the microbial-destructive component (∑C20–C25 = 33.9–48.2%), which is consistent with the relatively high (up to 63.6%) fraction of hydrocarbon-oxidizing bacteria in the microbial communities. It has been shown that during secondary soil formation on ash dumps, a significant role in the formation of organic matter is played by microalgae: the proportion of the corresponding markers (∑C15, C17, and C19) reached 42.6% of the total n-alkanes.