Geocryological state of croplands in the Lena–Amga interfluve in a warming climate

Abstract

This article examines the climate warming effects on thermokarst development on cropland surfaces in the Lena–Amga interfluve. An increasing number of cropland fields have to be abandoned due to enhanced thermokarst. The main purpose of this study is to assess the condition of the abandoned lands. Historically, land for agriculture in the Lena–Amga interfluve was cleared by clear-cutting larch forests in inter-alas terrain underlain by ice-rich permafrost. Monitoring observations by the Melnikov Permafrost Institute have been conducted mainly in the Dyrgyabai field which is representative of the Tyungyulyu terrace of the Lena River. Increasing air temperatures have resulted in deeper soil thawing and degradation of the Ice-Complex permafrost. During the monitoring period, the permafrost table has lowered from 1.8 m to 2.7 m. In wet areas, thawing has reached the depths of 3.5–4.5 m. The abandoned cropland surface is now dotted by numerous thermokarst features, including byllars and incipient to mature thaw lakes. An assessment of abandoned cropland condition is provided for five administrative districts in the region by three categories: 1) land disturbed by thermokarst; 2) land unaffected by thermokarst; 3) undisturbed land overgrown with shrubs and trees. Presently, 33 % of the abandoned croplands in the region is distorted by residual polygonal landforms and incipient thermokarst lakes, 57 % is undisturbed, and 10 % is overgrown with trees and shrubs. Further warming in the region will increase the percentage of disturbed land.