The Study On Ecological And Hydrological Processes Of Typical Plantation In The Loess Plateau

The relationship between vegetation and water is the core issue of the ecological hydrology. The mechanism of interaction between hydrological processes and ecological processes lays the theoretic foundation for ecological restoration depending on vegetation construction in arid and semi-arid regions. Therefore, understanding of the mechanism is urgently needed to guide the governmental ongoing efforts in reforestation and afforestation in Loess Plateau. Vegetation restoration has recently been paid more attention due to its role in preventing soil and water loss. Anjia gou catchment in Longzhong Loess Plateau will be selected as a study area in the project. The study will focus on the soil hydrological processes under different vegetation types.First we collected nearly 30 years of rainfall data in the study area, and analyzed the rainfall distribution pattern. Then we build several field survey plots to observe and analyze the mechanism of the hydrological processes under Pinus tabuliformis, Caragana korshinskii and Hippophae rhamnoides plantations. In this research paper, the soil water infiltration, the vegetation canopy interception, the plant transpiratio, the soil evaporation and the soil water balance have been analysed and discussed. Our objectives are to understanding the soil water variation by supplying water and depleting water in soil layer, to derive the carrying capacity of soil water for plant growing in the study area. We hope that the research results can provide some insights into feasibility of a large-scale planning for ecological restoration and agricultural activities in the entire Chinese Loess Plateau. The main contents were as follow:1. Rainfall data were collected to systematic study rainfall patterns and pulse characteristics from 1981 to 2010 in Loess Plateau of Anjiagou catchment. The majority of rainfall events were characteristic by ≤5 mm, and the large rainfall events(≥10 mm) were infrequent but the interannual variability was wide comparatively. Inter-rainfall period of < 10 d accounted for the most proportion and the variability were relative small. In past 30 years, it was found that the annual precipitation in Anjiagou catchment showed a decreasing trend, the days with light rain( ≤5 mm d- 1) have been reduced slightly, the days above moderate rain( ≥10 mm d- 1) have been increased slightly, the frequency of short dry periods( ≤10 days) showed no significant trend, the frequency of long dry periods( ≥10 days) is found to increase remarkably, and rainy days display decreasing trend.2. The spatial variability of soil physical and chemical properties at Anjiagou valley were studied. Results indicated that: ① There are some differences in soil properties of different slope. Shady soil organic matter、 total porosity、capillary porosity and noncapillary porosity are greater than sunny; Shady soil bulk density is greater than sunny; different slope positions of soil properties showed different variation. ② The biggest soil bulk density was at gully bottom. Overall, soil bulk density was exhibited a high-low- high variation from top to ditch. From top to ditch, Organic matter showed a growing trend; total porosity, capillary porosity and non-capillary porosity is showing a low- high- low variation. ③ Method of single-ring was employed to study soil water infiltration characteristics and its influencing factors under typical vegetations in Loss hilly region. Water infiltration characteristics were the same as Pinus tabuliformis > Hippophae rhamnoides > Caragana korshinskii. Both the initial infiltration rates and stable infiltration rates under typical vegetations decreased with soil depths in 0-100 cm soil profile, the vegetations increased the IIRs and SIRs in surface soil mostly, the influence over IIRs and SIRs by vegetations decreased with soil depths.3. Soil infiltration process under typical vegetations was better fitted by Philip infiltration models than by Horton infiltration model and Kostiakov model.4. The canopy interception of Caragana korshinskii, Hippophae rhamnoides and Pinus tabuliformis accounts for 28%, 18.3% and 22.4% of rainfall, respectively, Caragana korshinskii, Hippophae rhamnoides and Pinus tabuliformis through accounted for 59.7%, 73.3% and 72.5% of rainfall, rainfall and trunk stem flow respectively accounted for 12.3%, 8.4% and 1.1% of rainfall. Based on the observed data, the revised Gash analytical model was employed to simulate the canopy interception for further research of Pinus tabulaeformis, Caragana korshinskii, and Hippophae rhamnoides plantation ecological hydrological process. The simulated results are underestimated. We find that the revised Gash analytical model is highly sensitive to canopy storage capacity(S), forest coverage(c) and the climate parameters of rainfall intensity(R) and evaporation(E), but it was found to be insensitive to the stem parameters(pt) and(St).5. The spatial heterogeneity of throughfall and related factors, as well as the minimum number and locations of collectors needed to measure throughfall accurately, were analyzed by statistical techniques. The results indicated that the throughfall was concentrated at the canopy edge, indicating that the edge of the canopy of P. tabulaeformis had a convergence effect on throughfall. The analysis of semivariance of throughfall demonstrated that canopy structure was a key factor influencing spatial variation of throughfall in low rainfall events, but measurement errors and other nonspatial variables were the primary factors affecting the variation of throughfall in high rainfall events.6. The sap flow of Caragana korshinskii, Hippophae rhamnoides and Pinus tabuliformis was observed by the compensation heat pulse method, which provides individual tree scale transpiration rates. The sapwood area is used as a biophysical variable for scaling-up canopy transpiration from the individual scale to the stand scale. The transpiration of Caragana korshinskii, Hippophae rhamnoides and Pinus tabuliformis was 305.09 mm, 243.17 mm and 203.4mm, respectively in the 2013 growing season. And it was 251.24 mm, 220.02 mm and 189.35 mm, respectively in the 2014 growing season. The transpiration of Pinus tabuliformis was greater than the shrubs. Stand transpiration was mainly influenced by environmental factors such as photosynthetically active radiation, vapor pressure deficit and soil water content. When soil water content was sufficient, photosynthetically active radiation and vapor pressure deficit were the dominant factors, but soil water content was the primary factor under low soil moisture levels.