作者机构：
[Liu, Muxing; Wang, Qiuyue; Zhang, Hailin; Yi, Jun] Cent China Normal Univ, Coll Urban & Environm Sci, Wuhan 430079, Peoples R China.;[Liu, Muxing; Guo, Li; Lin, Henry; Fan, Bihang] Penn State Univ, Dept Ecosyst Sci & Management, University Pk, PA 16802 USA.;[Zhu, Qing] Chinese Acad Sci, Nanjing Inst Geog & Limnol, State Key Lab Lake Sci & Environm, Nanjing 210008, Peoples R China.
通讯机构：
[Guo, Li] P;Penn State Univ, Dept Ecosyst Sci & Management, University Pk, PA 16802 USA.
关键词：
interception;infiltration;lateral flow;soil water storage;forest;pasture
摘要：
Rainfall provides essential water resource for vegetation growth and acts as driving force for hydrologic process, bedrock weathering and nutrient cycle in the steep hilly catchment. But the effects of rainfall features, vegetation types, topography, and also their interactions on soil water movement and soil moisture dynamics are inadequately quantified. During the coupled wet and dry periods of the year 2018 to 2019, time-series soil moisture was monitored with 5-min interval resolution in a hilly catchment of the Three Gorges Reservoir Area in China. Three hillslopes covered with evergreen forest (EG), secondary deciduous forest mixed with shrubs (SDFS) and deforested pasture (DP) were selected, and two monitoring sites with five detected depths were established at upslope and downslope position, respectively. Several parameters expressing soil moisture response to rainfall event were evaluated, including wetting depth, cumulative rainfall amount and lag time before initial response, maximum increase of soil water storage, and transform ratio of rainwater to soil water. The results indicated that rainfall amount is the dominant rainfall variable controlling soil moisture response to rainfall event. No soil moisture response occurred when rainfall amounts was <8 mm, and all the deepest monitoring sensors detected soil moisture increase when total rainfall amounts was >30 mm. In the wet period, the cumulative rainfall amount to trigger surface soil moisture response in EG-up site was significantly higher than in other five sites. However, no significant difference in cumulative rainfall amount to trigger soil moisture response was observed among all study sites in dry period. Vegetation canopy interception reduced the transform ratio of rainwater to soil water, with a higher reduction in vegetation growth period than in other period. Also, interception of vegetation canopy resulted in a larger accumulated rainfall amount and a longer lag time for initiating soil moisture response to rainfall. Generally, average cumulative rainfall amount for initiating soil moisture response during dry period of all sites (3.5-5.6 mm) were less than during wet period (5.7-19.7 mm). Forests captured more infiltration water compared with deforested pasture, showing the larger increments of both soil water storage for the whole soil profile and volumetric soil water content at 10 cm depth on two forest slopes. Topography dominated soil subsurface flow, proven by the evidences that less rainfall amount and less time was needed to trigger soil moisture response and also larger accumulated soil water storage increment in downslope site than in corresponding upslope site during heavy rainfall events.
作者机构：
[Liu, Muxing; Tian, Pei; Wu, Tieniu; Zhang, HL; Liu, MX; Zhang, Hailin; Yi, Jun; Jiang, Yan] Cent China Normal Univ, Hubei Prov Key Lab Geog Proc Anal & Simulat, Wuhan 430079, Peoples R China.;[Qiu, Weiwen; Hu, Wei] New Zealand Inst Plant & Food Res Ltd, Private Bag 4704, Christchurch 8140, New Zealand.;[Zhang, Dongyou] Wuhan First Hosp, Dept Imaging, Wuhan 430079, Peoples R China.
通讯机构：
[Zhang, HL; Liu, MX] C;Cent China Normal Univ, Hubei Prov Key Lab Geog Proc Anal & Simulat, Wuhan 430079, Peoples R China.
关键词：
Puddling;Plow pan;Soil physical properties;Computed tomography;Infiltration rate;Dye tracer experiment;Paddy field
摘要：
Soil properties, especially physical properties and macropore characteristics, are controlling factors for vertical water flow in paddy fields. However, the effects of paddy rice cultivation history on vertical water flows and related soil properties have been rarely studied. The objectives were to identify the differences in soil physical properties and macropore parameters and to reveal the effects of these soil properties on vertical water flow patterns in paddy fields under different cultivation times. In this study, soil physical properties in a very young paddy field (2 y, VYPF), a young paddy field (18 y, YPF), and an old paddy field (> 100 y, OPF) were analyzed. Meanwhile, macropore parameters (resolution of 0.6 mm) and vertical water flow patterns in these fields were identified by computed tomography and dye tracing experiment, respectively. As cultivation history lengthened in paddy rice, the average content of soil clay and organic carbon in the 80 cm depth soil profile increased, as did the thickness and bulk density of the plow pan. Also, macroporosity, macropore area density, macropore number density, node density, macropore angle, and hydraulic radius significantly decreased as length of cultivation age increased. As a result, differences in these soil propeties affected vertical water flow in three studied paddy fields. Steady-state infiltration rates decreased significantly in accordance with the reduced saturated hydraulic conductivity of soil cores from the plow pan; median values were 9.76 cm d(-1), 2.93 cm d(-1), and 0.13 cm d(-1) for VYPF, YPF, and OPF, respectively. A greater abundance and distribution of a dye tracer and a higher stained area ratio under the plow pan in younger paddy fields indicated that more obvious preferential water flows occurred in VYPF and YPF than in OPF. This implied that the conversion of farmland from upland field to paddy field resulted in greater use of irrigation water and also posed a risk of groundwater pollution through increased percolation. Therefore, a longer puddling time before planting paddy rice should be conducted in paddy fields (i.e. YPF and VYPF) with a short cultivation history, which can reduce water percolation by enhancing bulk density, reducing macropores, and lowering the saturated water conductivity of the plow pan.
摘要：
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Preferential flow can develop in soil macropores, and macropores are sensitive to human disturbances. This study investigated soil macropore features and the main factors controlling preferential flow at four sites with different levels of human disturbance in a mountainous area in Central China. The level of human disturbance decreased with increasing elevation, with the lowest elevation areas covered with coniferous trees (LF) &gt; middle mountain areas covered with tea gardens (TG) &gt; middle mountain areas covered with deciduous trees and mixed shrubs (MF) &gt; subalpine areas covered with evergreen coniferous trees (HF). At each site, the soil macropore structure at 0–20 cm soil depth was analysed using computed tomography scans (0.6 mm resolution) and Image J software. Preferential flow was determined by analysing the breakthrough curve (BTC) of nitrate. The macroporosity, surface area density, mean macropore size, macropore number density, length density and node density were all ranked in the order of HF ≥ MF ≥ TG = LF. Less disturbed sites had stronger evidence of preferential flow as shown by faster breakthrough, longer tails and greater asymmetry of the BTCs. There were significant (P &lt; 0.05) positive influences of soil macropore properties on pore water velocity and the solute dispersion coefficient. The dispersivity parameter was mainly affected by the macropore equivalent hydraulic radius. This study showed that human disturbance in the mountain forest areas significantly decreased soil macropores by changing soil physical properties (e.g. bulk density, texture and soil organic matter content) and root distribution, thus increasing the risk of surface runoff and nutrient losses.
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