ИСТИНА

Summarized the results of long-term observations (2014-2018) of soil emissions and net CO2 fluxes (2017-2018) in natural and human-modified (HM) ecosystems of Arctic tundra in archipelago of Svalbard (78о04N, 14о13E). Factors associated with local land use, during the period of their active impact may redouble the emissions of carbon dioxide from soil (0.111±0.021 > 0.064±0.011 gС m-2h 1). During warm period the net C-balance at the sites with active land use was estimated as a source to the atmosphere. Self-recovering after human influence plots (2) demonstrate intermediate values of soil emissions of СО2 between unaffected tundra (1) and plots with active land use (3). With that they demonstrate the greatest net C-sink within the observed range of Photosynthetically Active Radiation as compared to (1) and (3). At the height of the vegetation period unaffected tundra demonstrate a neutral net C-balance. The greatest contribution to soil emissions variance make spatial factors (56-66% of variance), whereas temporal controls are responsible for 3.8-5.5% only. Inter-annual fluctuations of key controls, among which the most important are the soil moisture and temperature of the upper layer, both affect HM and natural ecosystems. Hence the spatial differences between them remained constant from year to year. We conclude that HM arctic ecosystems during periods of active land use with high probability become an additional net carbon sources to the atmosphere. But if the human pressure is halted, under recovery they convert into a sinks of C, which compensate for the first effect. The rate and degree of the compensation depends on particular type of human footprint. This often leads to overcompensation and positive atmospheric effects, but native plant communities are not restored, which is associated with permafrost degradation. The study was supported by RFBR grant18-05-60279-Arctica, and state assignments AAAA–A18–118052400130–7 and 0148-2017-0005 of Russia.