Characteristics of soil moisture in permafrost observed in East Siberian taiga with stable isotopes of water

Abstract

Abstract:Soil moisture and its isotopic composition were observed at Spasskaya Pad experimental forest near Yakutsk, Russia, during summer in 1998Russia, during summer in , 1999Russia, during summer in , and 2000. The amount of soil water (plus ice) was estimated from volumetric soil water content obtained with time domain reflectometry. Soil moisture and its υ 18 O showed large interannual variation depending on the amount of summer rainfall. The soil water υ 18 O decreased with soil moisture during a dry summer (1998), indicating that ice meltwater from a deeper soil layer was transported upward. On the other hand, during a wet summer (1999), the υ 18 O of soil water increased due to percolation of summer rain with high υ 18 O values. Infiltration after spring snowmelt can be traced down to 15 cm by the increase in the amount of soil water and decrease in the υ 18 O because of the low υ 18 O of deposited snow. About half of the snow water equivalent (about 50 mm) recharged the surface soil. The pulse of the snow meltwater was, however, less important than the amount of summer rainfall for intra-annual variation of soil moisture.Excess water at the time just before soil freezing, which is controlled by the amount of summer rainfall, was stored as ice during winter. This water storage stabilizes the rate of evapotranspiration. Soil water stored in the upper part of the active layer (surface to about 120 cm) can be a water source for transpiration in the following summer. On the other hand, once water was stored in the lower part of the active layer (deeper than about 120 cm), it would not be used by plants in the following summer, because the lower part of the active layer thaws in late summer after the plant growing season is over.

Net ecosystem exchange of carbon dioxide and water of far eastern Siberian Larch (<I>Larix cajanderii</I>) on permafrost

“…We will explore this issue in a later section in this paper. In support of this, Sugimoto et al (2003) note that soil moisture content in 2000 was much higher than the previous years, causing high evaporation and transpiration rates, or perhaps more precisely, the presence of enough soil moisture caused evaporation and NEE to be non-restricted.…”

“…The largest rainfall deficit approaches 60 mm, towards the end of the growing season. It is worth noting that at this time, the thawing depth approaches 120-140 cm (Sugimoto et al, 2003). For the loamy sandy soil around the site, Sugimoto et al (2003) estimate the total soil water content at roughly 400 mm, with some 10% of that supplied by spring snow melting in 2000.…”

“…It is worth noting that at this time, the thawing depth approaches 120-140 cm (Sugimoto et al, 2003). For the loamy sandy soil around the site, Sugimoto et al (2003) estimate the total soil water content at roughly 400 mm, with some 10% of that supplied by spring snow melting in 2000. However, the variation in soil moisture content below 60 cm, roughly half of the thawing depth is small.…”

“…The work of Sugimoto et al (2003) at the same site suggests that soil moisture deficits may not be that restrictive in 2000 as melting of lower permafrost water provides a continuous source of water to the trees (see also above, Sect. 3.2).…”

“…However, the variation in soil moisture content below 60 cm, roughly half of the thawing depth is small. Once the clay soil is saturated after melting, the top 30-40 cm soil would contain roughly 100 mm of water (Sugimoto, et al, 2003). Towards the end of July this water would be depleted by a maximum of 60 mm Bowen ratios (the ratio of sensible heat and latent heat) are generally well above 1 (Fig.…”