The Response of Shallow Groundwater Levels to Soil Freeze–Thaw Process on the Qinghai‐Tibet Plateau

Abstract

The Qinghai‐Tibet plateau has the world's largest area of seasonally frozen ground. Here, shallow groundwater displays behavior that is distinct from that elsewhere in the world. In the present study, we explore the seasonal and interannual variation of the shallow groundwater levels from 2012 to 2016, and attempt to quantitatively evaluate the relative influences of individual driving factors on the shallow groundwater levels based on boosted regression trees. The results show that: (1) on a seasonal scale, the groundwater levels were characterized by a double peak and double valley relationship, while on an interannual scale the groundwater levels showed a slightly downwards trend from 2012 to 2016; and (2) during the frozen period, the seasonal variation of groundwater levels was determined by mean air temperature through its effect on the soil thaw–freeze process, accounting for 53.15% of total variation. Meanwhile, ET0 and rainfall exerted little impact on the seasonal variation of groundwater levels, which might be attributed to the aquitard of frozen soil that impedes the exchange between surface water and groundwater. Moreover, there was a lag between groundwater levels and soil freezing–thawing. During the non‐frozen period, the mean air temperature was again the most important factor impacting the variation of groundwater levels, through its effect on ET0, and accounted for 40.75% of total variation, while rainfall had little effect on groundwater levels when rainfall intensity was less than 12 mm/day. These results will benefit predictions of future trends in groundwater levels within the context of global warming.

Much stronger tundra methane emissions during autumn freeze than spring thaw

“…By contrast, spring soil thaw can directly expose CH 4 to more oxygen, and melting of the oxygen-rich ice also provides an indirect route for oxygen delivery (Arndt et al, 2020). (Dai et al, 2019). It is worth noting that climate warming may increase the duration of the active layer freezing period and lead to a longer and more productive autumn freeze, which will greatly enhance soil CH 4 production and storage during this period (Arndt et al, 2019;Euskirchen et al, 2016;Natali et al, 2015;Raz-Yaseef et al, 2017).…”

Nitrogen controls the net primary production of an alpine Kobresia meadow in the northern Qinghai‐Tibet Plateau

“…For instance, the plants in our alpine ecosystem were limited by the low temperature and short growing season (Dai, Ke, et al, ). Moreover, the soil moisture was relative abundance relatively abundant during the growing season due to the replenishment from precipitation and thawing of seasonally frozen soil (Dai et al, ). Meanwhile, the soil in our study site was belonged to loamy soil with abundance abundant SOM in the top soil, lead to yielding a strong water‐holding capacity (Zhang et al, ).…”

Light Grazing Significantly Reduces Soil Water Storage in Alpine Grasslands on the Qinghai-Tibet Plateau

“…In this study, there was a significant negative correlation between the depth to groundwater and soil water storage (i.e., a shallow ground water level is associated with greater water storage). The deepest groundwater level under the alpine grassland was observed in the peak growing season [18], coincident with the minimum in soil water storage. Air temperature was the second most important environmental factor affecting grassland water storage: an increase in temperature significantly reduced the amount of soil water storage.…”

“…The first peak in soil water storage observed in mid-May could be due to the presence of water from the thawing of seasonally frozen soil [18]. The lowest value of soil water storage occurred in July or August, during the peak growing season, which is when both the transpiration capacity of the vegetation and precipitation reached a maximum.…”