Generation, sink, and emission of greenhouse gases by urban soils of reclaimed filtration fields

PURPOSE: Intensive urbanization leads to the use of ecologically unfavorable areas for construction. Expensive remediation may not produce the desired results. Risks of boundary ecosystems include pollution, reducing biodiversity, and human health deterioration remains. This applies to the reclaimed sewage filtration fields. The main factor of their environmental hazard before remediation is the sludge rich in organic matter whose decomposition under reducing conditions leads to methane and carbon dioxide accumulation in soils and emission to the atmosphere. MATERIALS AND METHODS: Large areas of non-operational filtration fields were reclaimed and focused on the creation of residential areas in Moscow, outside the Garden Ring road and the Ring Highway. Conservative properties of technogenic surface-like soil formations (TSF) in parallel with their function were studied. Static soil properties were determined by the standard methods. Activity of bacterial methane formation and oxidation (biological indicators of function) were established using the kinetic methods by soil incubating in sealed vials and escaping or absorption of methane, respectively. Methane and carbon dioxide concentrations in soils and their emission to the atmosphere (gas characteristics of function) were determined by hole shooting method and closed chambers, respectively, with quantitative analysis at the gas chromatograph. RESULTS AND DISCUSSION: The ground with sewage silt fragments (GS), Gleyic Technosol (GT), Urbic Technosol (Arenic, Transportic) (UT (AT)), and sandy Urbic Technosol (Humic, Transportic) (UT (HT)) are consistently formed during the reclamation of filtration fields. At the final stage in the greening of built area, Urbic Folic Technosols (UFT) are formed. In summer, CH₄ generation decreases 10 times from GS and peat-compost horizons of new UFT to UT (HT), UT (AT), and UFT. Bacterial CH₄ oxidation also decreases in the same row, after reducing CH₄ content from 1,100-2,600 to 3–4 ppm. There is not enough oxidation intensity in GS and GT where high CH₄ emission is observed; in other soils, it is absent. CO₂ formation and emission, for an exception of UT (HT), decreases in the same row of soils. CONCLUSIONS: Greenhouse gases generation, sink and emission, environmental functions of young subaerial soils 0–10 years old, are estimated. Seasonal monitoring revealed the risks of atmosphere pollution by CH₄ during the cold period and by CO₂—all year. Formed soils don’t emit CH₄ in summer. Reclamation reduces atmospheric CH₄ concentration from 60 to 2–4 ppm. The CO₂ content is decreasing in the first years from 0.20 to 0.13–0.18 %, through 10 years—up to 0.08 %.