The Evolution Of Runoff&Sediment And Its Impact On Wetland Vegetation In The Lower Yellow River Region

In recent years, the runoff and sediment in the lower reaches of the Yellow River reduce significantly because of climate change and effect of human activity, leading to the wetland area to degrade seriously and wetland ecosystem health to be threatened. It is great significant for protect and restore wetland to study the impact of climate change and human activity on wetland ecosystem in the lower Yellow River. The paper takes the runoff and sediment process and variation as the main clue, and studies the coupling relationship between hydrological, sediment factors and vegetation from macroscopic view.(1)The runoff and sediment in the lower Yellow river Huayuankou during1960-2010are analyzed with linear regression, accumulated deviation and Mann-Kendall examination method, it has been shown that the runoff and sediment decrease in Huayuankou, and the abrupt changes of annual runoff and sediment discharge occur in1990and1998, respectively. The distribution of runoff and sediment within the year is considerable, runoff and sediment discharge smaller in January and February, and larger in summer and autumn, especially from July to October, runoff accounting for47%of the total annual amount, and sediment discharge for82.6%.(2)Based on daily meteorological data of seventy-one weather stations in the Yellow River basin during1960-2010, the area average precipitation, temperature and potential evaporation of the Yellow River basin are explored with Thiessen Polygons. It has been shown that the area average precipitation exhibits a slight decrease, area average temperature takes on an obvious ascending tendency, especially after the1990s, the potential evaporation exhibits a decreasing trend. The relationship between runoff, sediment and climate factors is analyzed with correlation coefficient method, it has been shown that the temperature considerably influences the runoff and sediment discharge, next, precipitation, then there is no significant correlation between the potential evaporation and runoff-sediment. The runoff and sediment discharge increase with the rainfall, and decline with the temperatures. In order to quantitatively forecast the tendencies of runoff and sediment under the influence of climate change in the future, the quantitative model for climate and runoff-sediment is established with the genetic programming.(3)The thirty-three indicators of hydrological alteration are chosen with IHA, RVA is adopted to assess the effect of the water-sediment regulation of Xiaolangdi on the hydrological alteration of the lower reaches of the Yellow River. It has been shown that the occurrence of annual maximum discharges, number of year flow reversal, the monthly discharge in September and base flow index are subject to a great change, being followed by the occurrence of annual minimum discharge, the frequency of low flow, the monthly discharge in July and August, and the annual minimum30-day means. The duration of high flow, the monthly discharge in February, June, November, December, the annual minimum7-day means, and the annual maximum30-day means, these indicators change moderately. The rest of indicators change slightly. After the running of Xiaolangdi, the monthly sediment discharge at Huayuankou decreases significantly. The percentage, for which sediment discharge in flood season accounts of the total annual amount, decreases from83%to68%, whereas the sediment discharge percentage in June significantly increases from2.2%to10.9%, the percentage in non-flood season increasing from17%to32%.(4)After2000, the frequency of overbank flow at Huayuankou decreases sharply owing to the influences of climate change and the water-sediment regulation at Xiaolangdi, leading to a negative effect on the growth of the wetland vegetation. The paper selects vegetation coverage and biomass as wetland vegetation ecosystem typical factors, and establishes the coupling model for runoff-sediment and ecology in the lower Yellow River with the genetic programming, which is used to quantitatively forecast the change tendency of vegetation in the future, and to provide scientific foundation for protecting and restoring the wetland vegetation ecosystem.