Study On The Effect Of Variation Of Water And Sediment Regime On Wetland Vegetation In The Lower Yellow River

Wetland ecological environment is mainly determined by wetland hydrological state index.The change of runoff at the main hydrological stations of Huayuankou,Gaocun,Aishan and Lijin in the lower Yellow River is the most important factor affecting the wetland hydrology in the lower Yellow River.Under the influence of climate change and human activities,the runoff from the four hydrological stations decreased significantly.The change of runoff initially leads to the change of wetland hydrological state,and then leads to the change of wetland ecological environment.Therefore,scientific assessment of the impact of water and sediment variation on the wetland ecological environment is beneficial to the protection and restoration of wetlands,as well as to the selection and formulation of scientific and reasonable water resource control measures.The wetland in the lower Yellow River is selected as the study area,and the results are as follows:(1)Based on the data of annual runoff and sediment transport from four hydrological stations of Huayuankou,Gaocun,Aishan and Lijin in the lower Yellow River,the trend,mutation,periodicity and correlation of annual runoff and annual sediment transport in the lower Yellow River are analyzed by using mathematical statistics method.The results show that the annual runoff and sediment transport in each hydrological station are significantly reduced;the lower Yellow River The annual runoff changed in 1979,1980,1982 and 1985,and the runoff in the lower reaches of the Yellow river changed in 1994,1997 and 1999.The annual runoff mainly changed from 13 to 14 years,and the runoff mainly changed from 13 to 21 years.(2)Before and after the impact of human activities,the cumulative sediment transport decreased by 90.53 billion tons,56 billion tons,58.75 billion tons and 24.36 billion tons respectively in 2016.The water sediment correlation of Huayuankou and Gaocun hydrometric stations is moderate,while that of Aishan and Lijin hydrometric stations is high.In the lower Yellow River,runoff and sediment transport are mainly affected by human activities,while climate change has little impact on the annual runoff and sediment transport.(3)Based on the remote sensing image data of 1994,1999 and 2015,using envi software,this paper analyzes the wetland evolution in the lower Yellow River from three aspects: total wetland change,wetland composition and change,as well as the change of primary wetland.During the 21 years from 1994 to 2015,the total wetland area in the typical wetland areas of the lower Yellow River showed a downward and increasing trend,with a downward trend in general,the proportion of river wetland showing a downward trend,lakes and constructed wetlands showing a downward and then upward trend,and tidal wetlands showing an upward trend.(4)Using pixel dichotomy model and normalized vegetation index,and using envi software,the average vegetation coverage and the area of different levels of vegetation coverage in different periods of the lower Yellow River wetland were calculated and analyzed.In 1994,1999 and 2015,the average vegetation coverage of the lower Yellow River wetland was 0.425001,0.41258 and 0.642301.(5)The correlation coefficient method was used to construct the area correlation between water and sediment factors and wetland area,average vegetation coverage,different levels of vegetation coverage.The total wetland area and primary wetland area were highly and moderately correlated with runoff and sediment transport,respectively.The correlation between water and sediment and the average vegetation coverage is very low,and the overall correlation between water and sediment and the vegetation coverage is significant.The wetland habitat of the lower Yellow River was evaluated,and the relevant measures to protect the wetland of the lower Yellow River were put forward.