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1. chinaXiv:202005.00093 [pdf]

Flow regime changes in three catchments with different landforms following ecological restoration in the Chinese Loess Plateau

LUO Zhidong; LIU Erjia; QI Shi; ZHAO Nan; SUN Yun
Subjects: Biology >> Botany >> Applied botany

The Chinese Loess Plateau is known as one of the most severe soil erosion regions in the world. Two ecological restoration projects, i.e., the integrated soil conservation project since the 1970s and the ''Grain for Green'' project since 1999, have been progressively implemented to control the soil erosion in this area. Ecological restoration has greatly changed flow regime over the past five decades. However, the mechanism of how flow regime responds to ecological restoration among landforms remains poorly understood. In this study, we investigated the temporal dynamics of flow regime in three catchments, i.e., Wuqi, Honghe and Huangling hydrological stations, respectively representing the loess hilly-gully, loess table-gully and rocky mountain (covered by secondary forest) areas in the Chinese Loess Plateau, using daily hydrological data during the 1960s–2010s. The nonparametric Mann-Kendall test, Pettitt's test and daily flow series were used to investigate the changes of flow regime. Significantly negative trends of annual streamflow were detected at the Wuqi and Honghe stations, except for the Huangling station. The annual baseflow at the Wuqi station showed a significantly positive trend whereas a significantly negative trend was observed at the Honghe station, and there was no significant trend at the Huangling station. It was interesting that baseflow index significantly increased during the whole period in all catchments. However, the trends and change points of daily flow series derived by different percentages of exceedance and extreme series in different consecutive days varied among individuals. Based on the change points analysis of annual streamflow, we divided data series into three periods, i.e., the baseline period (from 1959 and 1963 to 1979, PI), the integrated soil conservation period (1980–1999, PII) and the ''Grain for Green'' period (2000–2011, PIII). We found that streamflow decreased due to the reduction of high streamflow (exceeding 5% of time within a year) and median streamflow (50%) in PII and PIII at the Wuqi and Honghe stations. However, low flow (95%) increased in PII and PIII at the Wuqi station while decreased at the Honghe station. Streamflow change at the Huangling station was more stable, thus potentially resulting in much less soil erosion in the forestry area than in the other areas. The great improvement in ecological environment on the Chinese Loess Plateau revealed the advantages of ecological restoration in reducing flood amount and compensating streamflow at a regional scale.

submitted time 2020-05-31 From cooperative journals:《Journal of Arid Land》 Hits1455Downloads288 Comment 0

2. chinaXiv:202004.00047 [pdf]

Flow regime changes in three catchments with different landforms following ecological restoration in the Chinese Loess Plateau

LUO Zhidong; LIU Erjia; QI Shi; ZHAO Nan; SUN Yun
Subjects: Environmental Sciences, Resource Sciences >> Basic Disciplines of Environmental Science and Technology

The Chinese Loess Plateau is known as one of the most severe soil erosion regions in the world. Two ecological restoration projects, i.e., the integrated soil conservation project since the 1970s and the ''Grain for Green'' project since 1999, have been progressively implemented to control the soil erosion in this area. Ecological restoration has greatly changed flow regime over the past five decades. However, the mechanism of how flow regime responds to ecological restoration among landforms remains poorly understood. In this study, we investigated the temporal dynamics of flow regime in three catchments, i.e., Wuqi, Honghe and Huangling hydrological stations, respectively representing the loess hilly-gully, loess table-gully and rocky mountain (covered by secondary forest) areas in the Chinese Loess Plateau, using daily hydrological data during the 1960s–2010s. The nonparametric Mann-Kendall test, Pettitt's test and daily flow series were used to investigate the changes of flow regime. Significantly negative trends of annual streamflow were detected at the Wuqi and Honghe stations, except for the Huangling station. The annual baseflow at the Wuqi station showed a significantly positive trend whereas a significantly negative trend was observed at the Honghe station, and there was no significant trend at the Huangling station. It was interesting that baseflow index significantly increased during the whole period in all catchments. However, the trends and change points of daily flow series derived by different percentages of exceedance and extreme series in different consecutive days varied among individuals. Based on the change points analysis of annual streamflow, we divided data series into three periods, i.e., the baseline period (from 1959 and 1963 to 1979, PI), the integrated soil conservation period (1980–1999, PII) and the ''Grain for Green'' period (2000–2011, PIII). We found that streamflow decreased due to the reduction of high streamflow (exceeding 5% of time within a year) and median streamflow (50%) in PII and PIII at the Wuqi and Honghe stations. However, low flow (95%) increased in PII and PIII at the Wuqi station while decreased at the Honghe station. Streamflow change at the Huangling station was more stable, thus potentially resulting in much less soil erosion in the forestry area than in the other areas. The great improvement in ecological environment on the Chinese Loess Plateau revealed the advantages of ecological restoration in reducing flood amount and compensating streamflow at a regional scale.

submitted time 2020-04-23 From cooperative journals:《Journal of Arid Land》 Hits293Downloads147 Comment 0

3. chinaXiv:201712.00399 [pdf]

Spatio-temporal variations of soil water content and salinity around individual Tamarix ramosissima in a semi-arid saline region of the upper Yellow River, Northwest China

YANG Benman; WANG Ruoshui; XIAO Huijie; CAO Qiqi; LIU Tao
Subjects: Agriculture, Forestry,Livestock & Aquatic Products Science >> Soil Science

Ecological restoration by Tamarix plants on semi-arid saline lands affects the accumulation, distribution patterns and related mechanisms of soil water content and salinity. In this study, spatio-temporal variations of soil water content and salinity around natural individual Tamarix ramosissima Ledeb. were investigated in a semi-arid saline region of the upper Yellow River, Northwest China. Specifically, soil water content, electrical conductivity (ECe), sodium adsorption ratio (SARe), and salt ions (including Na+, K+, Ca2+, Mg2+ and SO42–) were measured at different soil depths and at different distances from the trunk of T. ramosissima in May, July, and September 2016. The soil water content at the 20–80 cm depth was significantly lower in July and September than in May, indicating that T. ramosissima plants absorb a large amount of water through the roots during the growing period, leading to the decreasing of soil water content in the deep soil layer. At the 0–20 cm depth, there was a salt island effect around individual T. ramosissima, and the ECe differed significantly inside and outside the canopy of T. ramosissima in May and July. Salt bioaccumulation and stemflow were two major contributing factors to this difference. The SARe at the 0–20 cm depth was significantly different inside and outside the canopy of T. ramosissima in the three sampling months. The values of SARe at the 60–80 cm depth in May and July were significantly higher than those at the 0–60 cm depth and higher than that at the corresponding depth in September. The distribution of Na+ in the soil was similar to that of the SARe, while the concentrations of K+, Ca2+, and Mg2+ showed significant differences among the sampling months and soil depths. Both season and soil depth had highly significant effects on soil water content, ECe and SARe, whereas distance from the trunk of T. ramosissima only significantly affected ECe. Based on these results, we recommend co-planting of shallow-rooted salt-tolerant species near the Tamarix plants and avoiding planting herbaceous plants inside the canopy of T. ramosissima for afforestation in this semi-arid saline region. The results of this study may provide a reference for appropriate restoration in the semi-arid saline regions of the upper Yellow River.

submitted time 2017-12-08 From cooperative journals:《Journal of Arid Land》 Hits8127Downloads913 Comment 0

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