“…One heavy rainfall event creates a hydraulic gradient that causes or increases retained water to move downward to recharge the deep soil and mix with the existing soil water. Previous studies have indicated that heavy rainfall events not only recharge deep SWC through the piston and preferential flow, but also have a higher positive effect on water availability, which effectively relieved DSLs and is helpful for the sustainable development of forests and the conservation of water and soil under drier conditions (Ji et al, 2021; Wang et al, 2020; Yaseef et al, 2009). As illustrated in Figure 2, the vertical green bands in the SWC profile were saturated at the shallow layers.…”
Planting Robinia pseudoacacia in water-limited regions can promote soil and water conservation and ecological service functions. However, it can cause the formation of below ground dried soil layers (DSLs), causing land degradation and tree mortality.To ascertain the spatial-temporal dynamics and recovery processes of DSLs, we monitored the deep soil water content (SWC) to a depth of 500 cm at 27 sites on a typical R. pseudoacacia forest from 2017 to 2020 and calculated the evaluation indices of DSLs based on plant-available SWC (PASWC) and stable field capacity (SFC).Compared with PASWC-identified DSLs, the degree of SFC-identified DSLs was more severe, although the spatial-temporal characteristics were similar. Severe soil desiccation was identified as 79% of the 500 cm profile dried out below 101 cm. The mean thickness of DSL and mean SWC within a DSL were 396 cm and 9.0%, respectively, and the quantitative index reached Grade III (severe) DSLs. All DSL indices demonstrated weak or moderate variability in space and strong variability in time.
“…One heavy rainfall event creates a hydraulic gradient that causes or increases retained water to move downward to recharge the deep soil and mix with the existing soil water. Previous studies have indicated that heavy rainfall events not only recharge deep SWC through the piston and preferential flow, but also have a higher positive effect on water availability, which effectively relieved DSLs and is helpful for the sustainable development of forests and the conservation of water and soil under drier conditions (Ji et al, 2021; Wang et al, 2020; Yaseef et al, 2009). As illustrated in Figure 2, the vertical green bands in the SWC profile were saturated at the shallow layers.…”
Planting Robinia pseudoacacia in water-limited regions can promote soil and water conservation and ecological service functions. However, it can cause the formation of below ground dried soil layers (DSLs), causing land degradation and tree mortality.To ascertain the spatial-temporal dynamics and recovery processes of DSLs, we monitored the deep soil water content (SWC) to a depth of 500 cm at 27 sites on a typical R. pseudoacacia forest from 2017 to 2020 and calculated the evaluation indices of DSLs based on plant-available SWC (PASWC) and stable field capacity (SFC).Compared with PASWC-identified DSLs, the degree of SFC-identified DSLs was more severe, although the spatial-temporal characteristics were similar. Severe soil desiccation was identified as 79% of the 500 cm profile dried out below 101 cm. The mean thickness of DSL and mean SWC within a DSL were 396 cm and 9.0%, respectively, and the quantitative index reached Grade III (severe) DSLs. All DSL indices demonstrated weak or moderate variability in space and strong variability in time.
“…Further, with vegetation restoration, the areas of deep‐rooted plants have largely increased and led to a severe depletion in soil water and groundwater (Wang et al ., 2010; Huang et al ., 2013). However, with vadose zones of tens of meters, the deep soil water and groundwater can only be recharged by EPE with great intensities (Liu et al ., 2010; Li et al ., 2017c; Shao et al ., 2018; Xiang et al ., 2020; Ji et al ., 2021; Shi et al ., 2021). From this perspective, EPE is helpful in recharge of subsurface water and sustain vegetation construction in this region.…”
The intensive and frequent extreme precipitation events (EPE) greatly contribute to the severe soil loss in China's Loess Plateau, and it is thus essential to understand how and why EPE varies with space and time. Particularly, the combined influence of multiple factors on EPE has rarely been explored. This study analysed the spatiotemporal variability of EPE for 1961-2017 after defining six indices for intensity, frequency, and duration of EPE (R5d, SDII, R90t, R90n, CDD, CWD). We employed 12 atmospheric circulation factors to determine their combined effects on EPE on different time scales over time by the multiple wavelet coherence. The EPE indices spatially varied with obvious southeast-northwest gradients. Averaged across the whole plateau, SDII, R90t, and R90n increased insignificantly, while R5d, CDD, and CWD decreased insignificantly. In addition, the change trend had spatial variations with most wet EPE indices increasing in the north and the southernmost areas and decreasing in the middle-south areas. SDII, R90t, and R90n at 68%, 66%, and 53% of stations tended to increase, respectively, and R5d, CDD, and CWD decreased at 66%, 70%, and 77% of stations, respectively. The temperature had a greater correlation with the duration of EPE in summer and on the intensity and frequency of EPE in winter. El Niño-Southern Oscillation (ENSO), Pacific North American teleconnection pattern (PNA), ENSO-Arctic Oscillation (AO), and ENSO-AO-PNA were found to be the main factors influencing EPE individually or simultaneously. This study provides technical support for the identification of combined effects of multiple factors, and the results are helpful for regional environmental management. Specific to the Loess Plateau, the identified individual or multiple factors can be used to project future changes in EPE, and the more frequent and intensive EPE in some regions may increase the difficulty in future soil loss control.
“…However, nitrates accumulated through vertical infiltration into deep soils have often been ignored (Jia et al, 2018; Sebilo et al, 2013; Wu et al, 2020a). Figure 4 shows the relationship between the NO 3 − content and the δ 15 N-NO 3 − value in deep soils from the cropland ecosystem of the North China Plain, loess soil, and red soil (Ji, 2021; Wu et al, 2020a; Zhang et al, 2013). The values of soil δ 15 N-NO 3 − at 10 m in those studies are near 0‰ (Figure 4), indicating that nitrogen enrichment in this soil layer is probably mainly from N fertilizer.…”
Section: Vertical Variations In Soil Nitrogen Dynamics In Different C...mentioning
confidence: 99%
“…Thus, nitrate accumulated in deep soils should be considered an issue for policymakers to reduce environmental risks and protect water quality.Figure 4.Change of NO 3 − content, and δ 15 N-NO 3 − along with soil depth in different cropland regions. The NO 3 − content ranged from 8.7 to 632 mg kg −1 , and the datasets mainly included North China plain (Zhang et al, 2013), Loess soil (Ji, 2021), and Red soil (Wu et al, 2020a, 2020b). …”
Section: Vertical Variations In Soil Nitrogen Dynamics In Different C...mentioning
confidence: 99%
“…Change of NO 3 − content, and δ 15 N-NO 3 − along with soil depth in different cropland regions. The NO 3 − content ranged from 8.7 to 632 mg kg −1 , and the datasets mainly included North China plain (Zhang et al, 2013), Loess soil (Ji, 2021), and Red soil (Wu et al, 2020a, 2020b). …”
Section: Vertical Variations In Soil Nitrogen Dynamics In Different C...mentioning
Nitrogen dynamics at ecosystem levels profoundly impact the Earth’s surface system due to their environmental and ecological significance. Exploring the sources and transformation of nitrogen in various Critical Zones is vital to understanding biogeochemical cycles and sustainable development. This study summarized nitrogen characteristics in soil profiles and nitrogen dynamics in diverse terrestrial ecosystems based on data from typical Critical Zones of China. The results indicated that nitrogen accumulates in the deep soils of cropland ecosystems due to intensive fertilizer applications, which potentially harms soil functions and water quality. Therefore, it is necessary and meaningful to take adequate measures to alleviate nitrogen accumulation in deep soils. Additionally, surplus nitrogen transported into groundwater and riverine systems from soil has emerged as an important issue for environmental management. There are serious nitrogen pollution issues in many river water and groundwater areas, which could be addressed by reducing the fast leaching and considerable nitrogen accumulation in the vadose zone. Systematic and long-term observational studies are needed to achieve the ultimate goal of ecological conservation and high-quality development. Therefore, future research should consider monitoring and evaluating ecosystems based on the long-term Critical Zone Observatories networks to advance appropriate environmental management strategies that adapt to nature’s rules and strengthen the ecosystem service function for sustainable development.
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