ESTIMATION OF ORGANIC CARBON STOCKS IN THE SOIL COVER OF ISLAND ECOSYSTEMS OF THE KUIBYSHEVSK WATER RESERVOIR
Authors: Kulagina V. I. , Ryazanov S. S. , Shagidullin R. R. , Alexandrova A. B. 
Published: April 2022

Assessment of organic carbon stocks in soils and other components of ecosystems are becoming increasingly important as a necessary reference point for a reliable determination of the amount of greenhouse gas removals at country scale. The gradual tightening of carbon balance requirements dictates the urgency of the problem under consideration.
The aim of the work was to assess the stocks of organic carbon in the soils of the islands of the Kazan region of the variable backwater of the Kuibyshev reservoir in the
0–20 cm layer, and also to determine which type of soils makes the greatest contribution to the sequestration of carbon.
The reserves of organic carbon in the soils of the islands of the Kuibyshev water reservoir were determined in the area from the Zelenodolsk – Nizhnie Vyazovye bridge (55°49’27.1 «N; 48°31’05.6″E) to the islands in front of the Teteyevo village (55°24’11.8 «N; 49°07’59.6» E). Surveys of the islands’ soil cover and selection of the soil samples were carried out in 2018-2019. The calculation of the organic carbon content was carried out for the 0–20 cm layer. The calculations took into account the total carbon content in the organogenic, organic-mineral and mineral horizons. It was found that the highest carbon content in the upper soil layer was observed in the profile of marsh-podzolic soils – 51.7 t / ha. The lowest organic carbon content was noted in sod-alluvial soils (12.0 t / ha) and artificial sandy deposits (3.8 t / ha).
Carbon stocks in soil profiles and proportion of carbon in organogenic horizons increased with increasing of hydromorphic properties in the following row: 1) sod-podzolic soil < marsh-podzolic soil; 2) light gray forest soil < gray forest gley soil; 3) sod-alluvial soil < alluvial meadow-marsh soil < marsh-alluvial soil.
The total reserves of organic carbon in the islands’ soils were calculated taking into account the areas occupied by individual soil contours. The total stock of organic carbon in the 0–20 cm layer of the studied area of the water reservoir was 49,190.9 tons. About 83 % of the total stock of organic carbon stored in the form of humus of accumulative mineral horizons and only 17 % in the organogenic and organic-mineral horizons. It was shown that alluvial meadow-marsh (23,125.9 t) and sod-podzolic soils (8,957.5 t), occupying the largest areas on the territory of the islands, make the largest contribution to the organic carbon reserves. An interesting point is that on the islands of floodplain origin, a greater contribution to the total humus reserves was made by soils with pronounced hydromorphic properties – alluvial meadow-marsh soils and alluvial meadow soils. On the islands of terrace origin, the bulk of carbon was concentrated in automorphic soils. A possible reason is the features of the islands’ relief of different origins.
Reasonable data on the rate of organic carbon accumulation were obtained only for alluvial marsh soils, the organogenic horizon of which was formed after the creation of the reservoir – 390 kg / ha annually.
Flooded soils are the most promising reservoirs for organic carbon deposition from greenhouse gases.
Thanks to the research carried out using accurate GPS referencing of soil profiles, the islands’ soils are becoming a very valuable object for monitoring the rate of organic carbon accumulation, the volume of absorption of greenhouse gases and the increase in total organic carbon stocks.