From permafrost soil to thermokarst lake sediment: A view from C:N:P stoichiometry

Abstract

Thermokarst lakes are formed as a result of thawing ice-rich permafrost, transforming vast permafrost soil into lake sediment and changing the biogeochemistry of carbon (C), nitrogen (N), and phosphorus (P). Degraded permafrost soil and thermokarst lake sediment are two distinct fates of pristine permafrost in the thermokarst processes. However, we do not clearly understand the differences and relationships between degraded permafrost soil and thermokarst lake sediment from a stoichiometric perspective. In this study, 44 thermokarst lakes across the Qinghai-Tibet Plateau were investigated to collect lake sediment and surrounding degraded permafrost soil. In general, C, N, and P concentrations as well as C:N, C:P, and N:P ratios in soil and sediment decreased with increasing latitude, while increased with increasing mean annual precipitation. The degraded permafrost soil had much higher C, N, and P concentrations and C:N:P stoichiometric ratios than the lake sediment, particularly for C. Moreover, the concentrations of C, N, and P, as well as the ratios of C:P and N:P in sediment showed significant positive relationships with their corresponding components in soil but with different slopes. Standard major axis regression showed allometric scaling relationships between C, N, and P. The C:N:P ratio was 269:18:1 in degraded permafrost soil and 178:15:1 in lake sediment. The results suggest that the process from pristine permafrost to lake sediment releases more C, N, and P than the process from pristine permafrost to degraded permafrost soil, and that C changes more profoundly than N and P. Moreover, thermokarst processes substantially change the elemental balance and decouple the C:N:P relationship between degraded permafrost soil and lake sediment, suggesting that the further transformation from degraded permafrost soil to lake sediment will lose more C, which can be intensified by increasing precipitation. The results enriched our understanding of the variations in C, N, and P biogeochemistry during thermokarst processes.

Differentiation of cognate bacterial communities in thermokarst landscapes: implications for ecological consequences of permafrost degradation

“…This suggests that permafrost soil and lake sediments are likely to have high levels of similarity in bacterial diversity and community composition. Additionally, our prior research has shown that there are close correlations between the abiotic features of the two environments (Ren et al, 2022b). However, despite these similarities and connections, we found substantial differences in the bacterial communities of permafrost soil and lake sediments.…”

Active thermokarst regions contain rich sources of ice nucleating particles

“…This analysis reveals unexpected differences between similar sample types, such as the active layer and permafrost samples and indicates TKL sediments harbor INP populations unique from the other collected samples. TKL sediments are comprised of former permafrost, but undergo loss of organic carbon, nitrogen, and phosphorous during the transition (Ren et al, 2022), (Wilson et al, 2015) and were found to overpredict corresponding North Atlantic INP aerosol concentrations (McCluskey et al, 2018). Based on heating to 95 °C (Fig.…”