Study And Simulation On Characteristics Of Nutrients Evolvement In The Process Of Eco-Rehabilitaion In The Zhifanggou Watershed On Loess Hilly Region

The land use types adjust and vegetation construction in severe soil erosion region based on vegetation eco-rehabilitation not only can ameliorate ecology and environment, but also can deeply influence nutrients cycling process in whole watershed scale. This research use Zhifanggou watershed as a model which located in Ansai soil and water conservation integration station of loess hilly region, long term monitor and experiment results as support, different vegetation types and land use types nutrients cycling and balance characteristics were systemic studied in plot scale and watershed scale. The nutrients evolvement characteristics during the process of vegetation eco-rehabilitation in watershed were quantitative analysis and simulated in order to discover the coupling relationship between watershed eco-rehabilitation and nutrients evolvement and rules of nutrients evolvement and their influence factor. The watershed comprehensive remedy effect will be evaluate and nutrients optimistic adjusting and controlling plan will be made from the point of nutrients cycling and balance characteristics. Scientific basis will be offered for watershed vegetation eco-rehabilitation and nutrients resource management. The main results were as follows:1. The nutrients recycling and balancing characteristics of different vegetation of arbor, shrub and herbage were different in Zhifanggou watershed of loess hilly region. The N profit amount of arbor vegetation was 333.1kg/km2.a,while shrub and herbage vegetation were 509.1kg/km2.a and 601.3kg/km2.a, respectively. The P2O5 profit amount of arbor vegetation was 332.9kg/km2.a, while shrub and herbage vegetation were 422.5kg/km2.a and 532.0kg/km2.a, respectively. The EPIC model simulated nutrients recycling and balancing characteristics of different vegetation of arbor, shrub and herbage were different. The simulated N profit amount of arbor vegetation was 305.3kg/km2.a,shrub vegetation deficit amount was 119.0kg/km2.a, herbage vegetation profit amount were and 506.2 kg/km2.a,. The simulated P2O5 surplus amount of arbor vegetation was 224.1kg/km2.a, while shrub vegetation and herbage vegetation were 54.5kg/km2.a and 323.4kg/km2.a, respectively. Because of different vegetation type deeply decreased runoff and soil erosion, cycling and balance characteristics of nutrients begin profit.2. The nutrients recycling and balancing characteristics of plain field, sloping field and terrace were different. The treatment of MNP, N1P1 and MNP of plain field, sloping field and terrace nutrients profit amount were as follows. The N profit amount of plain field was 0.615t/km2.a, P2O5 was 5.006t/km2.a. The N deficit amount of sloping field was 8.448t/km2.a, P2O5 was 9.348t/km2.a. The N surplus amount of terrace were 7.528t/km2.a, P2O5 were 9.971t/km2.a. The EPIC model simulated nutrients recycling and balancing characteristics of plain field, sloping field and terrace were as follows. The simulated N profit amount of plain field was 4.208t/km2.a, simulated P2O5 was 5.995t/km2.a. The N deficit amount of sloping field was 7.827t/km2.a, simulated P2O5 profit amount was 3.006t/km2.a. The N surplus amount of terrace were 5.936t/km2.a, P2O5 were 9.071t/km2.a. Plain field and terrace compare with sloping field, nutrients profit amount increase a lot because of channel of nutrients loss via soil erosion eliminated.3. Zhifanggou watershed in the process of vegetation eco-rehabilitation and comprehensive remedy during past 20 years, the area of arbor, shrub and herbage vegetation increased ceaselessly, so the nutrients profit amount increased ceaselessly also. The N profit amount of totally arbor, shrub and herbage vegetation increased from 1.73t per year on 1983 to 3.92t per year on 2003, P2O5 from 1.54t per year on 1983 to 3.51t per year on 2003. The area of sloping field decreased year after year, while the area of terrace increased year after year, so the nutrition profit amount on terrace increased year after year, the nutrients deficit amount on sloping field decreased year after year. N profit amount on terrace increased from 0.79t per year on 1983 to 6.19t per year on 2003, P2O5 from 1.06t per year on 1983 to 8.20t per year on 2003. N deficit amount on sloping field decreased from 29.95t per year on 1983 to 1.27t per year on 2003, P2O5 from 33.14t per year on 1983 to 1.40t per year on 2003. With the eco-rehabilitation and comprehensive remedy policy were implementing in Zhifanggou watershed, a healthy system of nutrients recycling and balancing is forming and developing in this typical watershed on loess hilly region.4. The difference between analysis results and simulation results were large in nutrients cycling and balance characteristics results of EPIC model simulated, especially soil loss results and nutrients loss results. This research showed that EPIC model can not simulate nutrients cycling and balance characteristics directly. So in order to successful running EPIC model in nutrients cycling and balance characteristics simulation on loess plateau, EPIC model source code, different parameter need revised, also field experiment need to carry out long term and continuity.