An integrated dataset of ground hydrothermal regimes and soil nutrients monitored during 2016-2022 in Northeast China

Under a climate warming, wildfires have been occurring frequently in the boreal permafrost regions. Wildfires can lead to rapid degradation of permafrost, triggering significant changes in soil nutrients. Since 2016, we have systematically established a network for studying soil nutrients (0-3.6 m in depth) and hydrothermal state of the active layer and permafrost (0-20 m in depth) in some previously burned areas in the northern Da Xing’anling (Hinggan) Mountains in Northeast China. The datasets included soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), total potassium (TK), soil moisture content (SMC), ground temperatures and active layer thickness (ALT). The data were collected from eight sites in four burned areas with two categories of fire severity (severely burned and unburned) from 2016 to 2022. The research showed that wildfires cause rapid degradation of permafrost and evident changes in soil nutrients. At depths of 0-4 m, ground temperatures were 0.5-9.9^oC higher at the burned sites than those at the unburned sites. At depths of 12-20 m, the differences were 0-2.1^oC between at the burned and unburned sites, and less than those at depths of 0-4 m. ALTs were 0.13-2.75 m deeper at the burned sites than those at the unburned sites. SMC values were lower at the burned sites than those at the unburned sites. Wildfires affected the ground freeze-thaw processes in permafrost regions, delaying the ground freezing or advancing the ground thaw by about a month. A large amount of SOC and TN were stored in the active layer and near-surface permafrost layer, especially in the soil organic layer. At depths of 0-1.5 m at the unburned sites, average contents of SOC and TN were 1.5-3.9 and 1.6-3.5 times those at the severely burned sites, respectively, and 2.5-2.9 and 1.5-2.0 times those of at the slightly burned sites, respectively. The contents of TP and TK also changed significantly in different burned years. With increasing fire severity, changes in the ground hydrothermal regimes and soil nutrient contents became more obvious. Moreover, 30 years after fire, there were still remarkable difference in ground hydrothermal regimes and soil nutrient contents between the burned and unburned sites. Wildfires lead to rapid ground warming and great loss of SOC, and the effects may last for at least 30 years.