Spatial Ana Temporal Characteristics And Influencing Factors Of The Transparency Of Shahu Lake In Ningxia

Ningxia is located in northwest China,with little rainfall,large amounts of evaporation,arid climate and fragile ecological environment.The plain lake wetland in Ningxia is like a pearl inlaid in arid regions.It plays an important role in water ecology and water security,and its ecological status is very important.Shahu is the largest lake in Ningxia and faces severe water quality degradation and ecological degradation.Therefore,it is of great theoretical and practical significance to study the evolution of lake water quality and its influencing factors for lake conservation and sustainable utilization.Studies at home and abroad have shown that water transparency is of great ecological significance.On the one hand,the transparency of water itself is an important water quality monitoring index;on the other hand,it directly affects the distribution of underwater light field,and then affects the primary productivity of water bodies,and affects other water quality monitoring indicators.In addition,remote sensing technology has the advantages of rapidity,macroscopicity,low cost,and periodicity.By studying the relationship between reflection spectrum characteristics of water and the concentration of water quality monitoring indicators,a water quality index inversion algorithm is established to monitor water pollution on a large scale and dynamically.The characteristics of change provide technical support for lake ecological management.This study applied three periods,multi-site water quality monitoring,water body spectral measurement data,and simultaneous high-resolution remote sensing data(GF-1)to evaluate the current water quality and eutrophication status of Shahu Lake,and analyze the spatial and temporal distribution of transparency and its relationship with other water quality parameters.Based on sensitive bands,a new empirical model and semi-analytical model and GF-1 remote sensing image data were used to estimate the transparency of the Shahu Lake.The transparency of the Shahu Lake water body was obtained,and the main factors affecting the transparency of the Shahu Lake were analyzed.The main research contents and results are as follows:(1)Based on the three measured water quality data of Shahu Lake,the assessment of the water quality of Shahu Lake was carried out using the Nemerowan pollution index.The results showed that the Shahu Lake comprehensive pollution index was greater than 1.2,and the water body was in a light pollution state.In terms of time distribution,the comprehensive pollution indices in June,August,and October were 1.52,2.20,and 2.09,respectively,showing the characteristics of first increasing and then decreasing.In terms of spatial distribution,the Lake District water quality assessment Nemerowan pollution index is higher in Bird Island,dock area,and aquaculture area.As a result of eutrophication assessment,the TLI values of monitoring sites in Shahu Lake of Ningxia were all greater than 50 during the monitoring period,and the water quality of Shahu Lake was in a mild eutrophication state.In terms of time,Shahu Lake was the most affluent in August,followed by October and June.(2)The key factors affecting the transparency of the Shahu Lake are pH value,dissolved oxygen,chlorophyll-a concentration,and suspended solids.The Pearson correlation coefficient shows a significant negative correlation.Furthermore,through correlation analysis,suspended solids and chlorophyll were the main driving factors affecting the transparency of the water body,and their correlation coefficients R2 were 0.4053 and 0.3978,respectively.By analyzing the spatial distributions of transparency,suspended solids,chlorophyll and integrated eutrophic status indices,it was found that the spatial and temporal distributions of suspended solids and transparency are consistent,the water body suspended solids directly affects the transparency of the water body,and the chlorophyll and integrated eutrophic state index and transparency are spatial and temporal.The degree of coincidence of the distribution is not high,and the influencing factors are more complicated.(3)Using the band ratio method to build an empirical model and introducing a semi-analytical model and verify its accuracy/.comparing the determination coefficients,root mean square errors,and relative errors of the two methods.The results show that empirical models are comparative The accuracy of the semi-analytical model is high.The best model for the final selection of the transparency of the Shahu water body is:SD = 0.3336 ×(1/B4)+ 27.94.(4)The spatial-temporal analysis based on the estimated value of the Shahu Lake water transparency model is basically consistent with the measured numerical characteristics.Namely:In terms of time distribution,the transparency of Shahu Lake in summer is the lowest,followed by autumn and spring,and in spatial distribution,transparency is higher in Lake Core,Inlet,etc,and numerical values are lower in The Third Drainage Inlet,Bird Island,and Old Dock.There is an error between the estimated model value and the measured value,mainly because the sample points and the number of repetitions are insufficient,which affects the accuracy of the empirical model.(5)The factors affecting the transparency of the Shahu Lake are:water quality indicators,tourism activities,exogenous ecological water supply,reeds and their distribution.