Spatial And Temporal Variations Of Net Primary Productivity In The Modern Yellow River Delta

The Modern Yellow River Delta is located at the mouth of the Yellow River,and the sediment carried by the Yellow River is accumulated for a long time.Under the interaction of sea,land and river,a typical estuarine delta wetland is formed,with rich vegetation resources,which plays an important role in maintaining the stability of the regional ecological environment and regulating the local climate.The soil salinization of the Modern Yellow River Delta is high,and the spatial difference is large,the fresh water resources are insufficient and the spatial and temporal distribution is uneven.The vegetation growth and development of the Modern Yellow River Delta has obvious temporal and spatial variation characteristics.The net first productivity of vegetation(NPP)means that the total amount of organic matter produced by photosynthesis in the unit area of the unit time is deducted from the remaining part of the autotrophic respiration,which can clearly reflect the growth of vegetation,analyze its temporal and spatial changes and influence factors on the net first productivity of the vegetation in the Modern Yellow River Delta.The ecological environment of good region has important guiding significance.Under the support of the National Natural Science Foundation Project and the Shandong province science and technology project,this research takes the modern the Modern Yellow River Delta as the research object.With the combination of ENVI and Arc GIS,high resolution remote sensing images are used to extract the vegetation types in the study area,and the related data such as temperature,rainfall and solar radiation are used to use The CASA model estimated the vegetation parameters,estimated the temporal and spatial variation of net primary productivity in the study area,and analyzed the influencing factors.In addition to estimating the NPP of natural vegetation,in order to monitor the growth of grain crops,this study estimated the vegetation NPP at different growth stages of winter wheat,and analyzed the changes of the vegetation,and provided a case for remote sensing monitoring of crops.The preliminary results are as follows:(1)According to the regional characteristics of the Modern Yellow River Delta,the main vegetation is classified,mainly divided into nine plants,including Robinia Pseudoacacia,Tamarix,Tamarix Chinensis,Reed Tamarix,Reed Tamarix,Reed Willow,Reed,Rice Grass and Rice,and Crops.The total precision of the vegetation classification is 92.465%,the kappa coefficient is0.883,and the accuracy of vegetation classification is high,which accords with the requirement of computation.(2)The distribution of NPP in the Modern Yellow River Delta is higher than that in coastal area.In the past 1998-2016 years,the total NPP in the study area was 3.058 x1010 g C,with an average of 71.550 g C/m2.The inland area is higher and more 120-160 g C/m2,mainly because of the different water resources and soil salt content in the inland and coastal areas,which lead to different vegetation habitats,leading to the difference between the coastal and inland of the vegetation NPP in the study area,and the high NPP value of the freshwater rivers along the Modern Yellow River Delta and the reservoir near the reservoir,which generally reach160-180 g C/m2 and far away from the fresh water.Domain NPP is generally low,most of which is40-80 g C/m2.(3)The total amount of NPP total in the Modern Yellow River Delta was declining of the1998-2016 year period,mainly in 2.057x1010-3.899x1010 g C,of which the total amount of vegetation NPP in 1996 was the largest,3.899x1010 g C,and the smallest in 2004,2.057 x1010 g C.In the past 1998-2016 years,the NPP value of vegetation in the Modern Yellow River Delta did not change significantly,but the total NPP content of vegetation decreased obviously.The change of NPP mean value of vegetation is relatively small,but the total NPP change is obvious.This indicates that the area of vegetation growth in the Modern Yellow River Delta has been gradually reduced and replaced by other ground objects.The vegetation NPP in the spring study area is mostly 100 g C/m2 except the Yellow River and the Yellow River old road and the reservoir near the reservoir.Only a few areas of vegetation NPP are in 100-150 g C/m2.In summer,the solar radiation is strong,the temperature is high,the vegetation growth state reaches the peak,showing a higher effective photosynthesis,and the most area of summer vegetation NPP is the highest in 100 g C/m2.The autumn deciduous plants began to wither and harvest the crops,which resulted in the rapid reduction of vegetation productivity and the average vegetation NPP of 41.764 g C/m2,low temperature in winter,less solar radiation,less precipitation,less suitable vegetation growth and a minimum of 14.691 g C/m2 for vegetation NPP.(4)The NPP difference of different vegetation in the Modern Yellow River Delta is significant.The mean NPP is the largest black locust,175.690 g C/m2;Tamarix Chinensis Suaeda-Imperata minimum mean NPP 61.581 g C/m2.Robinia Pseudoacacia is artificial vegetation,growing in high soil fertility and abundant fresh water resources,its growth conditions are suitable,vegetation photosynthesis is strong,organic matter accumulation is rapid,and vegetation NPP is the highest.Tamarix Chinensis and Suaeda Salsa have better salt tolerance and grow in coastal areas where salinity and alkalinity are relatively high.Because of poor growth conditions,NPP is relatively low.In this study,the NPP spatial differentiation pattern of Winter Wheat in the area of sowing overwintering,turning out,jointing and booting and heading filling period was evaluated.On the time scale,the maximum NPP of winter wheat was 64.413 g C/m2,followed by the heading filling period,the mean value was 53.503 g C/m2,the rest were the jointing heading period and the sowing more Winter.(5)Through field investigation,the factors affecting NPP in the Modern Yellow River Delta are mainly water,soil salinity and human activities.The water conditions of vegetation growth and development in the Modern Yellow River Delta mainly include precipitation and river recharge,and the correlation coefficient between precipitation and vegetation NPP is 0.367(P<0.01).In this study,it is believed that the Modern Yellow River Delta is prone to drought season(spring and winter)to monitor the growth of vegetation in advance and monitor vegetation by remote sensing technology,and to recharge the vegetation in time to improve the vegetation NPP.The correlation between the vegetation NPP value and the salt content of the soil surface was calculated.The change of vegetation NPP in the study area was negatively correlated with the salinity condition,and the correlation coefficient was-0.389(P<0.02).The influence of human activities on the growth and development of vegetation is more and more obvious.Changing the growth conditions of vegetation will play a certain role in the change of vegetation NPP.