Downstream Evolution of Particulate Organic Matter Composition From Permafrost Thaw Slumps

Permafrost soils, which store almost half of the global belowground organic carbon (OC), are susceptible to thaw upon climate warming. On the Peel Plateau of northwestern Canada, the number and size of retrogressive thaw slumps (RTS) has increased in recent decades due to rising temperatures and higher precipitation. These RTS features caused by the rapid thaw of ice-rich permafrost release organic matter dominantly as particulate organic carbon (POC) to the stream network. In this study, we sampled POC and streambank sediments along a fluvial transect (∼12 km) downstream from two RTS features and assessed the composition and degradation status of the mobilized permafrost OC. We found that RTS features add old, Pleistocene-aged permafrost POC to the stream system that is traceable kilometers downstream. The POC released consists mainly of recalcitrant compounds that persists within stream networks, whereas labile compounds originate from the active layer and appear to largely degrade within the scar zone of the RTS feature. Thermokarst on the Peel Plateau is likely to intensify in the future, but our data suggest that most of the permafrost OC released is not readily degradable within the stream system and thus may have little potential for atmospheric evasion. Possibilities for the recalcitrant OC to degrade over decadal to millennial time scales while being transported via larger river networks, and within the marine environment, do however, still exist. These findings add to our understanding of the vulnerable Arctic landscapes and how they may interact with the global climate.

SLOPE STABILITY ASSESSMENT USING MODIFIED D-SLOPE METHOD OF WESTERN PART OF SANDAKAN, SABAH

Slope stability assessment using modified D-Slope method is been conducted on five (5) rock slopes from Sandakan, Sabah. D-slope method comprises of G-Rating determination and Potential Instability. G-Rating includes 17 parameters of field observation and laboratory analysis to assess the slope condition. Kinematic analysis is used for Potential Instability analysis to determine the type of failures for each slope. This later is to determine the level of slope’s risk: No Risk, Low Risk, Moderate Risk or High Risk. Based on the results of G-Rating, only slope C1 and C2 have value more than 0.4 while other slopes have less than 0.4 which indicates stable slopes. Based on kinematic analysis, slope C1 and C3 experienced wedge failures, slope C4 with toppling failure, slope C5 with wedge/planar failures and no failure shown for slope C2. D-slope analysis indicates that slope C1 is considered as Low Risk with mitigation suggestions of stream system inspection and vegetation on exposed area of the slopes, while other slopes (C2, C3, C4 and C5) have no suggestion for mitigation as been assessed as No Risk.