Analyzing factors driving of eutrophication of river-type urban landscape lakes.

The eutrophication of river-type urban landscape (RTUL) lakes is different from that of natural lakes. In this study, Xiaofu Lake, a typical RTUL lake with high anthropogenic interference, was used as the study area. Monitoring data from 2018 to 2020 were used to analyze the temporal and spatial distribution characteristics of chlorophyll a (Chl-a) concentrations with meteorological, hydrodynamic, and nutrient factors. Correlation and regression analyses were used to identify the relationship between the factors influencing eutrophication and the Chl-a. The MIKE21 model is used to simulate changes in water quality indicators. The study determined the relationship between river water quality and environmental factors and explored the causes of eutrophication in the water bodies of Xiaofu Lake. The results showed that from 2018 to 2020, the water quality showed seasonal variation and differences in spatial distribution. Except for total nitrogen, which remained at a high level (average 8.23 mg/L), other water qualities remained between classes II and IV. The proportions of mild, moderate, and severe eutrophication in the study area were 25%, 69%, and 6%, respectively. Indicators that were highly correlated with water eutrophication were turbidity, water temperature, total phosphorus, and permanganate index. The contribution of water temperature, ammonia nitrogen, and permanganate index to eutrophication was 30.5%, 22.6%, and 20.9%, respectively. The high proportion of sewage in the source of recharge water is one of the reasons for the deterioration of water quality. In addition, the change in water eutrophication was closely related to the gate operation in the region. PRACTITIONER POINTS: There are differences between river-type urban landscape (RTUL) lakes and natural lakes, and the conditions that cause eutrophication are different. RTUL are subject to strong human interference and rely on water transfer and gate scheduling to maintain water quantity. The high proportion of sewage treatment plant tailwater in upstream water is the main reason for the long-term pollution of RTUL. The indicators highly correlated with water eutrophication are turbidity, water temperature, total phosphorus, and permanganate index.

Multi-phase transformation model of water quality in the sluice-controlled river reaches of Shayinghe River in China.

To better understand the complex transformation mechanisms of pollutants in different phases in sluice-controlled river reaches (SCRRs), a multi-phase transformation model of water quality is proposed. This model mainly describes the interactions of the water body, suspended matter, deposited sediments, and organisms. Mathematical expressions were first derived to describe the mass transportation processes in different phases of the river system. The multi-phase transformation model in SCRRs was then established with defined physical mechanisms. Monitored data from the operation of Huaidian sluice were used to identify and validate the parameters of the transformation model and to simulate the spatial and temporal changes of pollutants in different phases. Four findings were made from the results. Firstly, the concentration values of pollutants in each phase in the upper and lower river reaches of the sluice are affected by flow, mode of sluice operation, and algal growth and enrichment. Secondly, the reaction processes in the upper and lower river reaches of the sluice indicate different dominant mechanisms according to the change in sluice operation. Thirdly, sluice operation leads to stronger exchanges between the water body and external materials because of the increased water disturbance. Fourthly, in the early period of the experiment, changes in the alga concentrations were mainly affected by water movement. In the later period, changes in the alga concentrations were mainly affected by the obstruction of the sluice in the upstream section, while these were affected by flow velocity, flow volume, and changes in nutrient concentration in the downstream section.

Identification of key factors affecting the water pollutant concentration in the sluice-controlled river reaches of the Shaying River in China via statistical analysis methods.

The construction of sluices creates a strong disturbance in water environmental factors within a river. The change in water pollutant concentrations of sluice-controlled river reaches (SCRRs) is more complex than that of natural river segments. To determine the key factors affecting water pollutant concentration changes in SCRRs, river reaches near the Huaidian Sluice in the Shaying River of China were selected as a case study, and water quality monitoring experiments based on different regulating modes were implemented in 2009 and 2010. To identify the key factors affecting the change rates for the chemical oxygen demand of permanganate (CODMn) and ammonia nitrogen (NH3-N) concentrations in the SCRRs of the Huaidian Sluice, partial correlation analysis, principal component analysis and principal factor analysis were used. The results indicate four factors, i.e., the inflow quantity from upper reaches, opening size of sluice gates, water pollutant concentration from upper reaches, and turbidity before the sluice, which are the common key factors for the CODMn and NH3-N concentration change rates. Moreover, the dissolved oxygen before a sluice is a key factor for the permanganate concentration from CODMn change rate, and the water depth before a sluice is a key factor for the NH3-N concentration change rate. Multiple linear regressions between the water pollutant concentration change rate and key factors were established via multiple linear regression analyses, and the quantitative relationship between the CODMn and NH3-N concentration change rates and key affecting factors was analyzed. Finally, the mechanism of action for the key factors affecting the water pollutant concentration changes was analyzed. The results reveal that the inflow quantity from upper reaches, opening size of sluice gates, permanganate concentration from CODMn from upper reaches and dissolved oxygen before the sluice have a negative influence and the turbidity before the sluice has a positive influence on the permanganate concentration from CODMn change rates and that the opening size of sluice gates, NH3-N concentration from upper reaches, and water depth before the sluice have a negative influence and the inflow quantity from upper reaches and turbidity before the sluice have a positive influence on the NH3-N concentration change rates, which provides a scientific grounding for pollution control and sluice operations in SCRRs.