[Mechanism of Urban Black Odorous Water Based on Continuous Monitoring: A Case Study of the Erkeng Stream in Nanning].

Black odorous water seriously endangers urban ecological functions. The "Water Pollution Prevention Action Plan" promulgated by the State Council has attached great importance to this issue and set a timetable for achieving the goal of pollution remediation of the urban black odorous water problem. However, in the process of managing the city's black odorous water, we found that the apparent governance effect is not sustainable. Many of the urban waters that have been treated to become clear have returned to a black odorous state. This problem has constrained the completion of the black odorous water control plan, and urgently needs to be resolved. To explain the reason for this phenomenon, we chose the Erkeng Stream in Nanning as the research object, which is a water body that returns to a black odorous state after treatment. We used a multi-parameter water quality tester and chemical analysis method to carry out daily continuous monitoring for 24 h and monthly dynamic monitoring of the water body. The results showed that the rainfall process was significantly correlated with the ammonia nitrogen concentration in the water (<0.01), and the temperature was positively correlated with the trend of ammonia nitrogen concentration in the water (=0.23, <0.05), which in turn was negatively correlated with the change trend of water transparency (=-0.33, <0.01). The above results show that the return of the black odorous state may be related to the microbial degradation of endogenous pollutants and the input of external pollutants. The reason may be:① The microorganisms are driven by light and temperature to promote the development of water in the direction of the black odorous state; ② Contaminants carried by rainfall promote the formation of black odor in water bodies. In short, in the context that internal pollution cannot be completely eradicated and external pollutants are difficult to control effectively, to prevent the treated urban water body from returning to a black odorous state, attention should be paid to endogenous pollutants such as river sediment and its control technology. Moreover, ecological control measures should be comprehensively adopted to reduce the input of external source indicators.