Effects of surface characteristics on infiltration patterns in an arid shrub desert

Abstract

Abstract:Precipitation is often the sole source of water replenishment in arid and semi-arid areas and, thus, plays a pertinent role in sustaining desert ecosystems. Revegetation over 40 years using mainly Artemisia ordosica and Caragana korshinskii at Shapotou Desert Experimental Research Station near Lanzhou, China, has established a dwarf-shrub and microbiotic soil crust cover on the stabilized sand dunes. The redistribution of infiltrated moisture through percolation, root extraction, and evapotranspiration pathways was investigated. Three sets of time-domain reflectometry (TDR) probes were inserted horizontally at 5, 10, 15, 20, 30 and 40 cm depths below the ground surface in a soil pit. The three sets of TDR probes were installed in dwarf-shrub sites of A. ordosica and C. korshinskii community with and without a microbiotic soil crust cover, and an additional set was placed in a bare sand dune area that had neither vegetation nor a microbiotic soil crust present. Volumetric soil moisture content was recorded at hourly intervals and used in the assessment of infiltration for the different surface covers. Infiltration varied greatly, from 7Ð5 cm to more than 45 cm, depending upon rainfall quantity and soil surface conditions. In the shrub community area without microbiotic soil crust cover, infiltration increased due to preferential flow associated with root tunnels. The microbiotic soil crust cover had a significant negative influence on the infiltration for small rainfall events (¾10 mm), restricting the infiltration depth to less than 20 cm and increasing soil moisture content just beneath the soil profile of 10 cm, whereas it was not as strong or clear for larger rainfall events (¾60 mm). For small rainfall events, the wetting front depth for the three kinds of surface cover was as follows: shrub community without microbiotic soil crust > bare area > shrub community with microbiotic soil crust. In contrast, for large rainfall events, infiltration was similar in shrub communities with and without microbiotic soil crust cover, but significantly higher than measured in the bare area. Soil water extraction by roots associated with evapotranspiration restricted the wetting front penetration after 1 to 3 h of rainfall.

Review of the ecohydrological processes and feedback mechanisms controlling sand-binding vegetation systems in sandy desert regions of China

“…The saturated hydraulic conductivity rate and the unsaturated hydraulic conductivity rate near saturation (soil water potential >−0.01 MPa) of the surface soils covered by BSCs were a magnitude lower than the values for moving sand and moss crusts, which, in turn, were greater than algae crust values. However in dry conditions, the unsaturated hydraulic conductivity (soil water potential <−0.01 MPa) rose as the number of sand-fixed years increased [28,29]. The special hydrological and physical characteristics of BSC improved and promoted the soil microhabitats in desert areas and increased water holding capacity.…”

“…They showed that runoff was greater on leeward slopes and these were covered mainly by algal crusts, whereas drier windward slopes were covered with moss crusts. The results of experiments and simulations undertaken by Li et al [25,33] and Wang et al [29] suggested that the influence of BSCs on rainfall infiltration depended primarily on the intensity of the rainfall, regional rainfall levels, the physical and chemical properties of the soil matrix under the crust and cryptogam composition. This comprehensive assessment resolved an international debate that had been ongoing between scientists.…”

“…Compared to A. ordosica, C. korshinskii had a deeper root distribution and could use deep soil water through the dry periods when precipitation did not supply the deep soil. A. ordosica had a greater proportion of its root distribution in the shallow soil, layers and was therefore limited to using precipitation [13,29,102]. The seasonal dynamics of fine roots were significantly influenced by SWC.…”

“…When SWC is lower than this threshold, the plants are water stressed and need a large root system so that they can obtain sufficient water to maintain normal physiological activities. This study revealed the response of the desert plant roots to water variation and the ecological countermeasures taken by them [29,102]. The ecological mechanism adapted by many desert plants seemed to be to produce large root systems [6].…”

Desert shrub stemflow and its significance in soil moisture replenishment

“…The low water content of desert soils limits the number of shrubs and its stabilization. The effects of both rainfall and soil surface characteristics on soil water replenishment in re-vegetated desert ecosystems have been studied by Wang et al (2007Wang et al ( , 2008. However, the effect of stemflow on infiltration patterns associated with the soil moisture replenishment is almost totally unexplored.…”