| As an important component of aquatic ecosystems,microorganisms in sediment influence the energy flow and material cycling of aquatic ecosystems.Microorganisms in sediment are important indicators of ecological change in rivers and are affected by the combined effects of riparian soils,runoff and sediment environments.This study investigates the structure of microbial community composition and distribution characteristics in the sediment of the aeolian sand region and loess region of the Wuding River basin and the spatial and temporal characteristics of their enzymatic activities.The relationships between enzyme activity,bacterial and fungal composition and their abundance in sediment and environmental factors of riparian soil,runoff and sediment were explored by combining redundancy analysis and taxonomic variation analysis.A microbial indicator method suitable for environmental monitoring of sedimentary sediment in different geomorphic areas of the Wuding River basin was established to provide a theoretical reference for water ecological protection in the middle reaches of the Yellow River.The main results are as follows:(1)There are significant differences(p<0.05)in total nitrogen and total phosphorus contents of soil in the riparian of the aeolian sand region and loess region,but not significant differences(p>0.05)in soil heavy metal contents.The total phosphorus concentration and ammonia nitrogen concentration in runoff and the total nitrogen content,carbon to nitrogen ratio and nitrogen to phosphorus ratio in sediment in the Wuding River basin were significantly different in April and August(p<0.05),and the total nitrogen concentration in runoff and the percentage of clay and silt in sediment were significantly different in the aeolian sand region and loess region(p<0.05),while the remaining physicochemical factors were not significantly different in time and space(p>0.05).The particle gradation of sediment in the aeolian sand region is dominated by silt grains,while the particle gradation of sediment in the loess region is dominated by clay grains,with a large proportion of silt grains.In April,the sediment is mainly consuming phosphate,and the sediment in August is mainly consumed nitrogen.The first pollutant of runoff is total nitrogen,followed by total phosphorus.The potential risks of heavy metals in the riparian zone and sedimentat are mild ecological risks.(2)There is no significant difference in carbon cycle-related enzyme activity and phosphorus cycle-related enzyme activity between aeolian sand region and loess region(p>0.05),but there are significant differences in LAP enzyme(Leucine aminopeptidase)and nitrogen metabolism enzyme activity in nitrogen cycle-related enzyme activity(p<0.01 and p<0.05).Except for the enzyme nitrogen-phosphorus ratio(1.43)in the loess area in April,the values of the enzyme stoichiometric ratio in the sediment are less than 1.The enzyme vector angles of all samples are less than 45°,showing nitrogen limitation.In April,the significant influencing factors of enzyme activity and its stoichiometric ratio in sediment of the aeolian sand region were total phosphorus in runoff and arsenic in sediment;the main influencing factors in the loess region in April were runoff temperature and organic carbon in sediment.In August,the significant influencing factors in sediment of the aeolian sand region are the conductivity of runoff and the ratio of nitrogen to phosphorus in sediment;the main influencing factors in the loess area were total nitrogen in sediment and pH of runoff.95.30%of the changes in enzyme activity and its stoichiometric ratio in sediment in the aeolian sand region are explained by three groups of environmental factors(runoff,sediment and riparian soil environmental factors),while 75.84%of the changes in enzyme activity and its stoichiometric ratio in sediment in the loess region are explained by three groups of environmental factors.The activities of LAP and nitrogen metabolism enzymes can be used as indicators of enzyme activity in sediment in loess region.(3)The bacterial Alpha diversity index in the sediment of the aeolian sand region is higher than that in the loess region,but the fungal Alpha diversity in the sediment of the aeolian sand region is lower than that in the loess region,and the difference are not significant(p>0.05).The two dominant phyla of bacterial communities in sediments are Proteobacteria(34.13%-92.23%)and Bacteroidetes(0.80%-51.25%).The differential phyla present in April in the aeolian sand region and loess region are Actinobacteria,Acidobacteria,Patescibacteria and Verrucomicrobia,and the differential phyla present in August in the eolian sand region and loess region are Actinobacteria,Bacteroidetes,Acidobacteria,Gemmatimonadetes,Verrucomicrobia,Nitrospirae and Proteobacteria.The two dominant phyla of fungi in sediments are Ascomycota(6.04%-79.05%)and Basidiomycota(1.40%-29.91%).The phyla that differed between the sandy zone and the loess zone in April were Ascomycota,Basidiomycota,Mortierellomycota and Zoopagomycota;the phyla that differed between the eolian sand region and loess region in August are Blastocladiomycota,Mortierellomycota,Basidiomycota and Ascomycota.(4)There are differences in the significant influencing factors of species changes at the bacterial phylum level and the fungal phylum level.In April,the significant influencing factors of bacterial phylum level species in the sediment of the aeolian sand region were organic carbon in the sediment and cadmium in runoff,and the main influencing factors of fungal phylum level species were dissolved oxygen and ammonia nitrogen in runoff.In April,the significant influencing factors of bacterial phylum level species in loess region were runoff temperature and arsenic,and the main influencing factors of fungal phylum level species were runoff conductivity and ammonia nitrogen.In August,the significant influencing factors of bacterial phylum level species in the aeolian sand region were carbon-phosphorus ratio and nitrogen-phosphorus ratio in sediment,and the main influencing factors of fungal phylum level species were total nitrogen in runoff and total nitrogen in riparian soil.In August,the significant influencing factors of bacterial phylum level species in loess region were total nitrogen in riparian soil and dissolved oxygen in runoff,and the main influencing factors of fungal phylum level species were ammonia nitrogen and clay proportion in sediment.71.88%and 47.56%of the variation patterns of bacterial communities in sediments in the eolian sand region and loess region could be explained by three groups of environmental factors.The total explanation of the differences in fungal communities by the three groups of environmental factors in sediment of the eolian sand region(69.60%)is greater than that of the loess region(5.71%). |
