Research On Water Ecological Functional Zoning In The Ningxia Section Of The Yellow River Basin

Ningxia Hui Autonomous Region is one of the most ecologically fragile provinces in China,with a sensitive and complex ecological environment,water scarcity and serious soil erosion.The Yellow River flows through the northern part of Ningxia from west to east,covering most of the region,and plays a crucial role in supporting the ecological environment and socio-economic development of Ningxia.This study is conducted based on the actual needs of water environmental management in Ningxia.Guided by the concept of "zoning,classification,grading and staging",the study focuses on the Ningxia section of the Yellow River Basin to investigate the characteristics of the water ecosystem in the basin.It examines and analyzes the spatial and temporal distribution and spatial differences of major water environmental factors and aquatic biological communities.The study identifies the main influencing factors of the water ecological pattern in the Ningxia section of the Yellow River Basin and conducts research on the index system and zoning scheme for the first,second and third levels.The research findings can provide scientific basis and technical support for the construction of a comprehensive and systematic water ecological management technology system in Ningxia,thereby achieving effective protection and sustainable development of the watershed’s water ecosystem.The main content and results of this study are as follows:(1)Samples of water and surface sediment were collected,surveyed,and analyzed in the Ningxia section of the Yellow River Basin.Principal component analysis was used to identify the main environmental factors in the two media.The primary physicochemical parameters of the water in the Ningxia section of the Yellow River Basin include conductivity,total dissolved solids,salinity,ammonia nitrogen,available phosphorus,chlorophyll-a,total phosphorus,pH,and dissolved oxygen.The surface sediment’s main physicochemical parameters include organic matter,ammonia nitrogen,available phosphorus,lead,arsenic,total phosphorus,and conductivity.Spatial heterogeneity analysis shows that,except for pH and dissolved oxygen,the other water environmental factors exhibit high spatial variability.The Distance Decay Relationship(DDR)demonstrates a clear decline in the similarity of water environmental conditions as distance increases within the study area.The similarity of surface sediment environments does not exhibit a clear distance decay phenomenon.The degree of difference in water environment is higher than that in surface sediments.Significant differences in the main physicochemical parameters of water environments exist between natural rivers and artificial water systems in the study area,as shown by the comprehensive analysis of their spatial and temporal distributions and differences.(2)A total of 140 species(genera)of phytoplankton from 8 phyla,101 species(genera)of zooplankton from 4 categories,43 species(genera)of macrobenthos from 3 phyla,73 phyla of bacterioplankton,and 88 phyla of sediment bacteria were identified in the Ningxia section of the Yellow River Basin.The distribution of aquatic biomes varied in different patterns.Phytoplankton density and biomass showed great spatial differences,while diversity indices showed smaller differences.Zooplankton density and biomass also varied greatly,with a moderate degree of variability in the diversity index.Macrobenthos density and biomass showed highly variable distribution,with a moderate degree of variability in the diversity index.There was moderate variability in the number of bacterioplankton ASVs and Chao1 index,with some spatial differences.The spatial variation of sediment bacterial communities was not significant.Significant differences exist in the Shannon-Wiener diversity index and Margalef richness index of phytoplankton and zooplankton,the Shannon-Wiener diversity index and Margalef richness index of benthic fauna,and the Simpson index,Chaol index,and Pielou evenness index of planktonic bacteria between natural rivers and artificial water systems.Additionally,the Simpson index and Pielou evenness index of sediment bacteria also show significant differences between these two types of water systems.The comprehensive analysis of differences in the water environment and aquatic biological communities indicates that the artificial water system meets the basic requirements for water ecosystem patterns in zoning concepts.Therefore,it can be included in the study system for water ecological function zoning.(3)Based on the zoning objectives,the candidate indicator types for the first-level zoning of water ecological functions in the Ningxia section of the Yellow River Basin include climate,landform,and hydrological factors.On this basis,the second-level zoning indicator types include vegetation and soil factors.After screening,the first-level zoning indicators are absolute elevation and relative humidity,while the second-level zoning indicators are absolute elevation,relative humidity,runoff depth,and NDVI.Using both top-down and bottom-up zoning techniques,the Ningxia section of the Yellow River Basin is divided into three first-level water ecological function zones and six second-level water ecological function zones.(4)The candidate indicators for the third-level zoning of water ecological functions in the Ningxia section of the Yellow River Basin include factors such as land use type,terrain and landform,river characteristics,and socio-economic factors.The third-level zoning indicators,after screening,are urban area ratio,average slope,river network density,and water volume.The entropy weight method was used to assign weights to the selected indicators,resulting in the establishment of a new comprehensive indicator.The Ningxia section of the Yellow River Basin was divided into 16 third-level water ecological function zones using the ’bottom-up’ zoning technique,and the main functions of each zone were analyzed.The primary function of each third-level zone in the study area is to support agricultural production.The above findings provide a scientific basis and technical support for water ecological environment management in Ningxia.They contribute to the effective protection and sustainable development of the water ecosystem in the Yellow River Basin.