| River ecosystem health assessment is helpful to understand the impact of human living environment on river ecosystem,and the evaluation results can also reflect the relationship between human and ecosystem.Xitiaoxi watershed is one of the main lake systems of Taibu Lake,located in the upper reaches of Taiho Lake Basin.In this study,30 sites in Xitiaoxi watershed were sampled twice in October 2021 and April 2022,respectively.All sites were divided into Xitiaoxi main stream,Xitiaoxi tributaries and reservoirs.The physicochemical indexes of water quality were monitored.Water quality index(WQI)and index of biological integrity of periphytic algae(P-IBI)were used to systematically evaluate the water quality in Xitiaoxi watershed.An index system of water quality assessment was established.The main environmental factors and land use types affecting the two indexes were analyzed,and the two methods were compared.The main research results are as follows:1.The analysis of water environmental factors showed that the three groups of water quality parameters with significant differences in October 2021 were chemical oxygen demand,magnesium ion,chloride ion,sulfate and electrical conductivity(P<0.05).The mean values of COD,Mg ion and conductivity were the highest in Xitiaoxi main stream and the lowest in Xitiaoxi tributary stream.The mean values of chloride ions and sulfate were the highest in Xitiaoxi stream and the lowest in reservoir.Three groups of water quality parameters with significant differences in April 2022 were chemical oxygen demand,magnesium ion,sulfate,water temperature,dissolved oxygen,calcium ion,chloride ion,and electrical conductivity(P<0.05).The mean values of COD,water temperature and dissolved oxygen were the highest in the reservoir,the mean values of COD and water temperature were the lowest in Xitiaoxi tributaries,and the mean values of dissolved oxygen were the lowest in Xitiaoxi main stream.The average values of magnesium ion,calcium ion,chloride ion,sulfate and electrical conductivity were the highest in Xitiaoxi main stream and the lowest in Xitiaoxi tributaries.Dissolved oxygen,temperature and p H in April 2022 were significantly higher than those in October 2021,while the other indexes had no significant change.2.Eleven physical and chemical parameters were selected to calculate the WQI.The average value of WQI in October 2021 was 60.52,and the overall water quality was medium.The average WQI in April 2022 was 80.28,and the overall water quality was good.The water quality in the tributaries of Xitiaoxi was the best in both seasons,while the water quality in the main stream of Xitiaoxi was the worst.The environmental factors with the highest correlation with WQI in both quarters were total phosphorus and chemical oxygen demand(P<0.01),both were negatively correlated with WQI;The land use types with the highest correlation with WQI were forest land and cultivated land(P<0.05),forest land had a significant positive correlation with WQI in both quarters,while cultivated land had a significant negative correlation with WQI in both quarters.3.A total of 134 species in 6 phyla,55 genera were collected in the two quarters.A total of 118 species in 6 phyla,48 genera were identified in the autumn of 2021,and 89 species in 6phyla,47 genera were identified in the spring of 2022.In the autumn of 2021,the average biological density and biomass of the algae were 6.63×10~4 ind/cm~2 and 0.26 mg/cm~2,respectively.In the spring of 2022,the average biological density and biomass of the algae were7.07×10~4 ind/cm~2 and 0.09 mg/cm~2,respectively.On the whole,there were significant differences in the community structure in time and space between the two quarters.Bacillariophytes and Cyanophytes dominated the dominant species in both seasons.4.In this study,30 candidate indexes were selected according to the data of peripheral algae at all sites,and a P-IBI system suitable for Xitiaoxi watershed was constructed after the indexes were screened.The average P-IBI values of Xitiaoxi watershed in October 2021 and April 2022 were 0.993 and 1.053,respectively,which were normal.The environmental factors significantly correlated with P-IBI in dry season were total nitrogen,total phosphorus and sulfate ion,but had no significant correlation with land use type.The environmental factors significantly correlated with P-IBI in wet season were total nitrogen,total phosphorus,chemical oxygen demand and electrical conductivity,which were positively correlated with the proportion of forest land.5.According to the evaluation results of P-IBI and WQI were compared and analyzed,there is a significant correlation between WQI and P-IBI in two quarters(P<0.01).According to the water quality evaluation results,it can be found that P-IBI is more distinguishable and different than WQI,indicating that P-IBI evaluation results are better.WQI was more responsive to water environment factors and land use type. |
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