Spatial variability of the vertical saturated hydraulic conductivity of sediments around typical thermokarst lakes

The formation and development of thermokarst lakes is a key factor causing permafrost degradation, in which the vertical hydraulic conductivity (Kv) of lakebed sediments plays an important role as it affects the water and heat transfer between thermokarst lakes and permafrost. However, the spatial variability of Kv of lakebed sediments in the Qinghai-Tibet Plateau (QTP) remains unclear. Hence, in this study, the Kv values of sediments in two thermokarst lakebeds were measured in situ using the standpipe method, and the grain size of the sediments was analyzed. The statistical results showed that BLH-A and B (lakes A and B in Beiluhe) had moderate and strong spatial variabilities, respectively. Lilliefors test results showed a log-normal distribution of the Kv measurements of the sediment samples. From the results of the geostatistical method, it was concluded that the Gaussian model best fitted the variograms of the Kv values. The d50 (grain size for which 50 % of grains are finer) had the strongest correlation with Kv, and the relationship between Kv and the grain size of d50 was a quadratic function. The estimated Kv value (0.03 m/d) was close to the measurements (0.005-0.58 m/d), and the specific discharge of BLH-B ranged from - 0.0038 to 0.00056 m/d. BLH-A and BLH-B would gradually expand under the influence of future climate due to the special geology (low Kv). This basic research on thermokarst lake regions can help understand the properties of thermokarst lakebed sediments and provide parameters for the numerical simulations of the hydrological cycle in thermokarst lake regions.