Implications for Global Change

Thus, warming in high latitudes may lead to an increased release of currently sequestered carbon through

(i) Enhancement of temperature-controlled DOC production processes

(ii) Raised precipitation, thereby increasing DOC mobilization from its large pool in the upper organic layer

(iii) Introduction of a new source of DOC from older and deeper layers, caused by permafrost degradation.

tu Q

20 40 60 80 DOC concentration, mg C l-1

Fig. 16.4 DOC concentrations in a soil profile (forest floor leachate; 2-, 5- and 20- cm depths of mineral soil) during June-September

20 40 60 80 DOC concentration, mg C l-1

Fig. 16.4 DOC concentrations in a soil profile (forest floor leachate; 2-, 5- and 20- cm depths of mineral soil) during June-September

High permafrost

O layer

Active layer

Permafrost wm

Lateral flow

Sorption

Bed rock

Deep or discontinuous permafrost

Sorption Sorption Sorption

Fig. 16.5 Schematic illustration of flux of dissolved organic matter depending on the depth of the active layer (adapted from Kawahigashi et al. 2004)

The fate of DOC in soils is largely determined by the hydraulic residence of soil DOC and mineralization. As a result, although the production and release of DOC from the forest floor is greater in warmer soils, the deeper active layer increases the contact with mineral soils and thus the likelihood of DOC adsorption, allowing for C stabilization in soil and/or microbial mineralization to CO2. The likely behavior of DOC in subsoils as affected by the permafrost degradation is illustrated in Fig. 16.5. However, on a regional basis there is large uncertainty as to how effectively diverse soil types (highly varying in pH, content of clay, C etc.) distributed throughout the subarctic area may retain DOC. In particular, the basins of Ob' and Lena rivers, mantled with fluvial-glacial sandy soils, have likely comparatively less capacity to adsorb DOC than the basins of eastern tributaries of Yenisey river-draining clayey soils developed on basalts.

Was this article helpful?

0 0

Post a comment