Abstract
It’s vital to explore critical indicators when identifying potential pollution sources of urban rivers. However, the variations of urban river water qualities following temporal and spatial disturbances were highly local-dependent, further complicating the understanding of pollution emission laws. In order to understand the successional trajectory of water qualities of urban rivers and the underlying mechanisms controlling these dynamics at local scale, we collected daily monitoring data for 17 physical and chemical parameters from seven on-line monitoring stations in Nanfeihe River, Anhui, China, during the year 2018. The water quality at tributaries were similar, while that at main river was much different. A seasonal ‘’turning-back” pattern was observed in the water quality, which changed significantly from spring to summer but finally changed back in winter. This result was possibly regulated by seasonally-changed dissolved oxygen and water temperature. Linear mixed models showed that the site 2, with the highest loads of pollution, contributed the highest (β = 0.316, P < 0.001) to the main river City Water Quality Index (CWQI) index, but site 5, the geographically nearest site to main river monitoring station, did not show significant effect. In contrast, site 5 but not site 2 contributed the highest (β = 0.379, P < 0.001) to the main river water quality. Therefore, CWQI index was a better index than water quality to identify potential pollution sources with heavy loads of pollutants, despite temporal and spatial disturbances at local scales. These results highlight the role of aeration in water quality controlling of urban rivers, and emphasized the necessity to select proper index to accurately trace the latent pollution sources.
Highlights
It’s vital to explore critical indicators when identifying potential pollution sources of urban rivers
River quality was monitored for 297–319 days at the continuous on-line monitoring stations at both tributaries and main river
This result paralleled the temporal variation pattern of dissolved oxygen (DO) and water temperature at all the on-line monitoring stations, where the concentrations of DO were low in summer ( DOsummer = 2.94–5.37 mg/L) but high in winter (DOwinter = 6.10–8.79 mg/L) (Fig. 2a), and the water temperature was high in summer (Tsummer = 29.08–30.25 °C) but low in winter ( Twinter = 8.74–11.34 °C) (Fig. 2b)
Summary
It’s vital to explore critical indicators when identifying potential pollution sources of urban rivers. The variations of urban river water qualities following temporal and spatial disturbances were highly local-dependent, further complicating the understanding of pollution emission laws. CWQI index was a better index than water quality to identify potential pollution sources with heavy loads of pollutants, despite temporal and spatial disturbances at local scales. Human activities severely affected river water quality and hydrological cycles[3] This can result in negative effects on the aquatic ecosystems, including accelerated degradation of river ecosystems and damaged ecological values of freshwater[4]. The number of water quality parameters that can be accurately monitored in situ has increased, including for instances, dissolved organic matter, dissolved organic carbon, nitrate and chlorophyll-a7,10 Other technological advances, such as colorimetry on river banks for determinants, permit sampling and rapid chemical analysis at trace c oncentrations[11]. Significant and positive spatial correlations among water quality physical and chemical parameters were observed across 48 monitoring stations for the aquatic ecosystem in the first-grade freshwater ecoregions of Ji’nan, C hina[4]
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