Characteristics_of_preferential_flow_during_simulated_rainfall_events_in_an_arid_region_of_China1.docx
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1、1 3 Environ Earth Sci (2016) 75:566 DOI 10.1007/s12665-015-5101-4 O R I G IN AL ARTI CL E Characteristics of preferential flow during simulated rainfall events in an arid region of China Jialiang Yan1,2 Wenzhi Zhao1 Received: 8 April 2015 / Accepted: 14 December 2015 / Published online: 26 March 201
2、6 Springer-Verlag Berlin Heidelberg 2016 Abstract Little is known about preferential flow and its effects on vegetation under natural conditions in an arid oasis ecotone. In this study, we performed dye-tracer experiments using 5, 15, 35, and 55 mm water-sprinkling treatments at three sites: Grass (
3、G), Haloxylon (H), and Populus (P). At each site, we determined soil texture and saturated hydraulic conductivity of the soil (Ks) and water flow parameters; we also defined characteristics of soil fracturing and measured plant biomass at site P. The tracer experiments revealed that the three sites
4、displayed signifi- cant differences in the degree of preferential flow. Soil structure and surface characteristics were the primary controlling factors, however, they played a different role in different rainfall events. For small rainfall events, soil surface characteristics controlled the preferen
5、tial flow pattern; for large or extreme rainfall events, soil structure was the critical factor. The effects of different rainfall events were complex and strongly varied among sites. Our results further indicated that preferential flow could impact the growth of annual plants. We conclude that pref
6、erential flow in an arid oasis ecotone is a common phenomenon affected by complex factors, and it may be important in soil water distribution and plant growth. & Wenzhi Zhao 1 Linze Inland River Basin Research Station, Key Laboratory of Inland River Ecohydrology, Cold and Arid Regions, Environmenta
7、l and Engineering Research Institute, Chinese Academy of Sciences, Donggang West Road 320, Lanzhou 730000, Gansu, China 2 University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing 100049, China Keywords Preferential flow Dye-tracer experiment Arid and semiarid ecosystems Soil water dis
8、tribution Small rainfall event Introduction Preferential flow is a physical process describing how water and solutes move along certain pathways through soil while bypassing other volume fractions of the porous soil matrix (Gerke 2006; Allaire et al. 2009). It is widely accepted that preferential fl
9、ow is the rule rather than the exception in a variety of soils. Preferential flow can be classified into general types of: macropore flow, which refers to the water and nutrient movement through con- tinuous root channels, earthworm tunnels, or cracks within well-structured and mostly fine-textured
10、soils (Blake et al. 1973; Zehe and Fluhler 2001); fingering flow, which is a distribution-flow pattern reminiscent of fingers, that is due to water repellency in the topsoil (Ritsema et al. 1993; Dekker and Ritsema 2000); funnel flow, which is due to lateral redirection and funneling caused by textu
11、ral boundaries (Kung 1990a, b); unstable flow, which involves instabilities of the wetting front and is mostly observed in coarse-textured soils (Dekker and Ritsema 1996a; Heijs et al. 1996). Preferential flow may cause fast and deep downward movement of water and solutes, Zhang et al. (2014) found
12、that preferential flow could impact seasonal changes in ground-penetrating radar (GPR) signals. Hardie et al. (2013) suggested that high frequency soil moisture moni- toring was needed to determine the frequency, depth, and velocity of preferential flow. Therefore, without a full understanding of fl
13、ow patterns, movement of water and solutes may be over- or underestimated (Ghodrati and Jury 1 3 566 Page 2 of 12 Environ Earth Sci (2016) 75:566 1990; van der Heijden et al. 2013), with consequences for soilwater management. This is of particular concern in arid lands, where water is scarce (Voro s
14、marty et al. 2000) and water movement is critical for the maintenance of plant processes (Schlesinger et al. 1990). Numerous studies reported on preferential flow under different land use types, including farmland, grassland, and forest. We know from these studies that site-specific vari- ables such
15、 as vegetation, soil structure, topsoil matrix properties, and other soil physical properties can render a location susceptible to preferential flow (Bachmair et al. 2009; van Schaik 2009; Lichner et al. 2012; Ganz et al. 2013; Zhang et al. 2014). Most of these studies, however, focused on humid or
16、semi-humid regions. Insufficient information exists for semi-arid and arid environments, including the arid oasis ecotone, which is critical to the maintenance of stability of the oasis ecosystem. For example, variability in topsoil matrix properties and soil structure, which play an important role
17、in preferential flow generation (Zhou et al. 2008; Bachmair et al. 2009), was often not explicitly considered in the few studies in the arid oasis ecotone. Therefore, a greater understanding is needed about relevant preferential flow characteristics to fully understand water movement in arid and sem
18、i-arid systems; this will support management strategies in arid regions especially under global climate change scenarios with increasing frequency of extreme precipitation events (Alexander et al. 2006; IPCC 2007; Wang et al. 2013a, b). In this study, we conducted dye-tracing experiments that simula
19、ted a series of natural rainfall amounts. We used sprinkling treatments at sites with different vegetation patterns in an arid oasis ecotone. The goals of this study were to: (1) investigate the effects of different land cover and site characteristics on preferential flow with identifi- cation of un
20、derlying control factors, (2) explore the effects of different rainfall amounts on preferential flow, and (3) determine the effects of preferential flow on soil water and plant growth in arid lands. Materials and methods Study sites The study was conducted in the Pingchuan oasis ecotone, located in
21、the middle of the Heihe River basin, near Pingchuan Town, Linze County, Gansu Province, China (Fig. 1). The region has a typical temperate desert climate, characterized mainly by drought, with high temperatures and frequent strong winds. Average annual precipitation is 117 mm, with 65 % occurring be
22、tween July and Septem- ber. Mean annual air temperature is 7.6 C. Table 1 illus- trated the rainfall depth and temperature per day from April to September over the 20052013 period. Soils are sandy, sandy loam, and grayish brown desert soils with loose crumb structure and little organic matter (Su et
23、 al. 2010). Aboveground plant distribution is discontinuous, and veg- etation cover is low, ranging from 5 to 7 % (Zhao and Liu 2010). Main vegetation types include a poplar protection forest (Populus gansuensis, Populus alba, and others), shrub protection vegetation (Haloxylon ammodendron, Nitraria
24、 sphaerocarpa Maxim., and others), and annual desert plants (Bassia spp, Eragrostis pilosa, and others). We selected three experimental sites for the dye-tracer experiments (Fig. 1). The Grass (G) site was covered pri- marily with naturally occurring grasses (including Suaeda glauca, Artemisia scopa
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