Abstract
Soil seepage is an important component used for quantifying hydrological processes that remains unclear in high-altitude alpine meadows. Shallow soil seepage was continuously measured using an auto-logged micro-lysimeter (diameter = 30 cm, depth = 30 cm) from July 2018 to June 2019 in a piedmont summer pasture of alpine meadow on the Northeastern Qinghai–Tibetan Plateau. The results showed that all the shallow soil seepage events occurred during the non-frozen period from April to September and that the cumulative amount was 106.8 mm, representing about 1/5 of the annual precipitation. The maximum and minimum monthly soil seepage were 30.7 mm in September and 1.0 mm in April, respectively. The boosted regression trees (BRT) model’s area under the curve averaged 0.92 and revealed that the daily half-hour rainfall frequency, volumetric soil water content, and air temperature played significant roles in the daily soil seepage probability, with the cumulative relative contribution of 68%. The stepwise linear regression analysis showed that the rainfall amount accounted for 59% of the variation in the daily amount of soil seepage. The monthly soil seepage was found to be significantly correlated with the monthly rainfall frequency (r = 0.86, p = 0.005). Our results highlighted that rainfall, including its amount and frequency, was the key determinant of the probability and amount of shallow soil seepage in the piedmont summer pasture of alpine meadows. These findings will be helpful for improving predictions of the water budgets of piedmont alpine meadows.
Highlights
The performance of the boosted regression trees (BRT) model was good (Figure The forward method (S1)) and clearly revealed that rainfall frequency played a substantial role in the probability of occurrence of daily shallow soil seepage events (Figure 3, Table S1), which agreed well with the similar results of field experiments [10,11]
All shallow soil seepage events occurred during the non-frozen period from April to September in a piedmont summer pasture of alpine meadow
The daily half-hour rainfall frequency and soil water content were able to determine the probability of daily soil seepage
Summary
Soil seepage is a key element of terrestrial water budgets and plays an essential role in aquifer charges and river flows [1,2]. This is especially true for high-altitude alpine regions, which are generally referred to as “water towers” for the lowlands [3,4]. Quantifying the soil seepage and its underlying environmental controls would further improve our knowledge of the ecohydrological processes in alpine regions and enhance our ability to estimate water resources in them [12,13]
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