Spatial variability of soil moisture at typical alpine meadow and steppe sites in the Qinghai-Tibetan Plateau permafrost region

Abstract

Permafrost degradation has the potential to significantly change soil moisture. The objective of this study was to assess the variability of soil moisture in a permafrost region using geostatistical techniques. The experiment was conducted in August 2008 in alpine steppe and meadow located in the Qinghai-Tibetan Plateau permafrost region. Four soil depths (0-10, 10-20, 20-30 and 30-40 cm) were analyzed using frequency domain reflectometry, and sampling made of 80 points in a 10 m 9 10 m grid were sampled. Soil moisture was analyzed using classical statistics to appropriately describe central tendency and dispersion, and then using geostatistics to describe spatial variability. Classical statistical method indicated that soil moisture in the permafrost region had a normal distribution pattern. Mean surface soil moisture in alpine meadow was higher than that in alpine steppe. The semivariograms showed that soil moisture variability in alpine cold steppe was larger than that in alpine meadow, which decreased with depths. Nugget values in alpine steppe were low (0.1-4.5), in contrast to alpine cold meadow. Soil moisture in alpine steppe had highly structured spatial variability with more than 93.4% spatial heterogeneity, and the range decreased with depth. Soil moisture content in alpine cold meadow had a moderate spatial dependence with a range of 51.3-169.2 m, increasing with depth.

Mesoscale spatial variability of soil‐water content in an alpine meadow on the northern Tibetan Plateau

“…Figures b and d also illustrate this phenomenon. The range was fluctuant during the 22 measuring occasions (Figure c), however, was significantly larger at 30 cm than at 10 and 20 cm (Table ), because SWC was lower at 30 cm than 10 and 20 cm and was more homogeneous in drier soil, consistent with the studies by Yang et al () in a similar alpine meadow on the Tibetan Plateau and by Western et al () in the Tarrawarra River catchment in Australia. C was initially stable and then increased rapidly with increasing SWC and was lowest at 5‐17% SWC (Figure ), indicating that variation caused by systemic factors, such as soil properties, vegetation, terrain, and climate, increased with SWC.…”

“…Low SWCs would produce large sampling and measurement errors. C + C 0 had an apparent temporal variation at depths of 10, 20, and 30 cm, but the mean was significantly higher at 10 cm than 20 and 30 cm (Table ) and was inconsistent with the studies by Yang et al () and Li et al (), who found no apparent variation and an increasing trend with depth, respectively. Close inspection of their data indicated that the trend of the sill was consistent with that of SWC.…”

“…Many studies have verified the special effect of the mattic epipedon on soil properties on the Tibetan Plateau (Yang et al, 2016;Zeng et al, 2013). Yang et al (2011), however, reported that SWC in the mattic epipedon layer did not differ significantly with SWC in the subsurface layers in a similar alpine-meadow ecosystem on the Tibetan Plateau. This discrepancy was mainly caused by two reasons: (a) the soil was nearly saturated at various depths and (b) the meadow was degraded.…”

“…These types of studies, however, are rare for the high‐altitude Tibetan Plateau. Yang et al () studied the spatial variability of SWC on a mesoscale at typical alpine‐meadow and steppe sites in the hinterland of the Qinghai–Tibetan Plateau using geostatistical techniques. Li et al () studied the spatial variability of SWC on a mesoscale using a geostatistical approach in a desertified aeolian riparian ecotone on the Tibetan Plateau.…”

Improvement of Soil Moisture Retrieval from Hyperspectral VNIR-SWIR Data Using Clay Content Information: From Laboratory to Field Experiments

“…[21], are based on site-scale or local survey and do not allow for the characterization of the high spatial and temporal variability at large scale of the SMC [22,23]. Remote sensing techniques can overcome these limitations as they provide better temporal and spatial coverages [24].…”