Response time lag of benthic integrity to water quality in the urban section of Yitong River
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Abstract:
With the development of social economy, the river ecosystem function is gradually degraded, and the health status of river is increasingly declining. These problems restricted the sustainable development of cities. Therefore, it is of great significance to evaluate the health of urban rivers and studied the response time lag of river ecosystem to water quality change. The response between aquatic ecosystem and environmental factors had nonlinear characteristics and time lag. Macroinvertebrates were used as important indicators for river health assessment because of their obvious response to water environment changes. However, the time scale of most current studies was usually one month or different hydrological seasons within a year. Few studies analyzed the changing trend of benthic integrity on an interannual scale and evaluated its time lag effect on river water quality change.Taking the urban section of Yitong River as an example, macroinvertebrates communities were investigated in 2015 and from 2019 to 2021, and the monitoring data of water quality under the state control section were collected. The benthic index of biotic integrity was used to evaluate the ecological health of the urban section of the Yitong River. Pearson correlation analysis was used to screen the collinearity of water quality factors, and Redundancy analysis was used to analyze the relationship between benthic integrity and water quality, to determine the key water quality factors affecting the benthic index of biotic integrity. The response time lag between benthic integrity and water quality was determined by Pearson correlation analysis. The results showed the following:(1) Aquatic insects and mollusks were the main groups of macroinvertebrates communities in the urban section of the Yitong River. During the study period, the proportion of Oligochaeta decreased from 33.3% to 9.5%, and the proportion of Gastropoda and Valmobranchia increased from 25% to 35.7%. There was no significant difference in the number of benthic species between different months ( P >0.05) and had significant difference between years ( P<0.05);(2)Four biological metrics were selected for the benthic index of biotic integrity, including the total number of taxa, relative abundance of the most dominate taxa, the relative abundance of Diptera and Marglef richness index. Compared with 2015, the benthic index of biotic integrity value increased slightly in 2019, but it was still "fair". In 2020 and 2021, the benthic index of biotic integrity upgraded to "sub-healthy". Two of the three reference sites were "healthy" and one was "sub-healthy". Three sampling sites were "sub-healthy", six were "fair", and only one was "poor"; (3)Total phosphorus was seriously polluted in the urban section of Yitong River, the mean value ranging from 0.06 mg/L to 0.57 mg/L. The first two axes of Redundancy analysis explained 77.96% of the variation in the benthic index of biotic integrity index system. Total phosphorus could explain 57.9% of the benthic index of biotic integrity core index, and the response time of benthic integrity to total phosphorus was about 9 months ( r=?0.88). The conclusions are: (1) The community structure of macroinvertebrates changed in the urban section of Yitong River, the number of species decreased first and then increased, and the main taxa changed from tolerant groups to intolerant groups. (2) The water ecological health status fluctuated and rose annually in the urban section of Yitong River. The health status of the upper reaches was better than that of the lower reaches. (3) Total phosphorus was the key water quality factor affecting the benthic index of biotic integrity in the urban section of Yitong River. The benthic integrity had a time lag in the response of total phosphorus. This study could provide a scientific basis for urban river health assessment and management.
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