Hydrological conditions and peat constitution effect on DOC leaching from permafrost-affected soils: model experiment (Western Siberia, Russia)

In the northern ecosystems’ soils, the carbon stock is preserved in peat soils which includes frozen peat. It is vulnerable to any climate changes. The permafrost degradation can affect both the quantity and the composition of dissolved organic carbon of permafrost-affected soils, especially peat soils.

The main aim of our study was to determine the relationship among peat type, water regime and the quantity and composition of water borne carbon export. The research site was located in the discontinuous permafrost zone (N65º18’, E72º52’). Monoliths of various peat soils were collected in summer 2019 for a laboratory experiment.

The experiments were carried out with 6 types of monoliths (oligotrophic fibric peat; oligotrophic hemic peat with lichen debris; eutrophic hemic peat with reindeer moss debris; eutrophic sapric peat; eutrophic sapric peat with a burnt horizon; oligotrophic fibric peat, underlied with sand). We try to understand how organic matter is leached from peat soils with different constitution and different degree of decomposition. In the model experiment, we simulated 3 types of hydrological conditions. Soil monoliths were watered, and the contents of DOC and POC were determined in the collected soil waters.

1. Simulation of the moderate rainfall (70 mm) by adding distilled water during the week. DOC in this case ranged from 44,2±3.0 mg/l in oligotrophic peat to 80,6±28,7 mg/l in eutrophic peat.
2. The simultaneous flow of large quantities of water, simulating prolonged rainfall or spring snowmelt. In this case DOC content leaching from fibric oligotrophic peat didn`t change much while DOC leaching from sapric eutrophic peat decreased in comparison with moderate rainfall.
3. During modeling short stagnant regimen (spring conditions) we observed increase DOC, especially in sapric eutrophic peat (up to 291,0±11,3 mg/l). The mineral horizon under the peat layer reduced the rate of leaching of organic substances from the soil.

Our results indicate the significant role of both the peat constitution and hydrological regime of soils on the rate and amount of organic matter entering the hydrological basin from peat permafrost-affected soils. The data can be used to simulate the dynamics of permafrost ecosystems with changing climatic parameters or with the activation of anthropogenic load.

This research was supported by the Russian Foundation for Basic Research (Grant 18-04-00952)