Abstract
Accurate estimation of groundwater evapotranspiration (ETG) is the key for regional water budget balance and ecosystem restoration research in hyper-arid regions. Methods that use diurnal groundwater level (GWL) fluctuations have been applied to various ecosystems, especially in arid or semi-arid environments. In this study, groundwater monitoring devices were deployed in ten lake basins at the hinterland of the Badain Jaran Desert, and the White method was used to estimate the ETG of these sites under three main vegetation covers. The results showed that regular diurnal fluctuations in GWL occurred only at sites with vegetation coverage and that vegetation types and their growth status were the direct causes of this phenomenon. On a seasonal scale, the amplitudes of diurnal GWL fluctuations are related to vegetation phenology, and air temperature is an important factor controlling phenological amplitude differences. The estimation results using the White method revealed that the ETG rates varied among the observation sites with different vegetation types, and the months with the highest ETG rates were also different among the sites. Overall, ETG was 600∼900 mm at observation sites with Phragmites australis during a growing season (roughly early May to late October), 600∼650 mm in areas with Achnatherum splendens, and 500∼650 mm in areas with Nitraria tangutorum and Achnatherum splendens. Depth to water table and potential evapotranspiration jointly control the ETG rates, while the influence of these two factors varied, depending on the specific vegetation conditions of each site. This study elucidated the relationship between diurnal GWL fluctuations and vegetation in desert groundwater-recharged lake basins and expanded the application of the White method, providing a new basis for the calculation and simulation of regional water balance.
Highlights
In arid and semi-arid regions where precipitation is scarce, most vegetation depends on groundwater for survival
From the observed water table records, regular diurnal groundwater level (GWL) fluctuations were detected at eight groundwater observation sites, except wells G1 and G2, which were almost entirely comprised of bare sand (Table 1). e observation sites where the fluctuations were detected were covered with various types of vegetation. is phenomenon emerged from May to October, which was consistent with the growing season of the desert lakeside vegetation at the observation sites (see Figure 2(d) for wells G6 and G8). e findings mentioned above indicated that the diurnal GWL fluctuations were related to the vegetation covering lakeside areas
Afterwards, the ETG was estimated via the White method, and the main controlling factors of ETG were explored. e observed series indicated that diurnal GWL fluctuations were consistent with the vegetation growing season, which was driven by groundwater consumption by phreatophytes. e amplitudes of diurnal GWL fluctuations showed marked differences among the sites, which was attributed to vegetation type and vitality
Summary
In arid and semi-arid regions where precipitation is scarce, most vegetation depends on groundwater for survival. The depth to water table (DTWT) determined the spatial distribution of riverside vegetation [4], and evapotranspiration was highly correlated with the spatial distribution of vegetation [5] in arid and semi-arid regions. Ese characteristics highlight the practicality of the White method for ETG estimation, and it has been continually developed and revised since its proposal [12,13,14,15] These methods have been applied to various ecosystems, such as wetland environments [16, 17] and riverside oases in arid and semi-arid regions [11, 18, 19]. In the hyper-arid hinterland of the Badain Jaran Desert, vegetation growing in groundwater-recharged lake basins depends on groundwater for survival. us, the White method could be used to estimate ETG in this hyper-arid desert lake ecosystem
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