Temporal and spatial changes of water quality in intensively developed urban rivers and water environment improvement: a case study of the Longgang River in Shenzhen, China.

The water quality status, spatial and temporal change processes, and water environment improvement process of urban rivers are valuable lessons to be learned under the sustainable development strategy. This study aims to reveal the water environment improvement process of intensively developed urban rivers, elucidate the spatial and temporal distribution characteristics of major pollutants, and provide recommendations for their water environment management. Water quality data from eight monitoring sites (2007-2020) in the Longgang River basin in Shenzhen, China, and comprehensive pollution index method (CPI), modified comprehensive pollution index method (M-CPI), and Pearson correlation analysis method were used for comprehensive analysis. The study shows that TN, TP, NH3-N, and COD have the greatest influence on the water quality of Longgang River, with the average pollution contribution of 53.39%, 14.49%, 11.66%, and 4.92%, in order. In 2015-2020, the water quality of the main stream of the Longgang River in the wet season was worse than that in the dry season, while the water quality of the tributaries Dingshan River and the Huangsha River in the dry season was worse than the wet season. The spatial distribution characteristics based on M-CPI indicate that the water quality of the lower reaches of Longgang River, the tributaries Dingshan River and Huangsha River, is relatively poor. In addition, the water environment improvement process of Longgang River can be divided into 3 stages: engineering stage (2007-2013, rating changed from heavily polluted to basically qualified), bottleneck stage (2013-2017, rating fluctuated slightly above and below basically qualified), and ecological restoration stage (2017-2020, rating reached qualified in 2019).

Purification performance from bypass ecological treatment systems treating WWTPs effluents and improvement of water quality in receiving rivers: A case study in southern China.

Effluents from wastewater treatment plants (WWTPs) is the main source of pollution in rivers in developing countries. In this case study, three bypass ecological treatment systems along urban rivers achieved high removal efficiencies for chemical oxygen demand (COD; 55.7-64.0%), ammonium N (NH4+-N; 63.1-89.4%) and total phosphorous (TP; 27.6-76.7%). 16 S rRNA gene sequencing analysis confirmed that Proteobacteria was the main bacterial phylum (44.4%) in the ecological treatment system, and members were enriched significantly in the non-aeration area (59.3%). The relative abundance of Nitrospirae was highest in the inflow area (25.0%), but restrained in the non-aeration area (5.7%). 18 S rRNA gene annotation results indicated that phylum Rotifer was gradually inhibited with the direction of water flow and diffusion, while phylum Rhodophyta displayed the opposite trend. After implementation of bypass ecological treatment systems, receiving rivers were improved significantly from Grade Ⅴ to Ⅳ, and the biodiversity of zooplankton, zoobenthos and fish communities was greatly improved.

[Pollution Characterization and Comprehensive Water Quality Assessment of Rain-source River: A Case Study of the Longgang River in Shenzhen].

Rain-source urban rivers are an important part of the urban ecosystem. Due to the small water environment capacity and the rapid development of the regional economy and society, they are vulnerable to serious pollution. The goal of this study was to identify the main pollution characteristics of river water quality and to carry out a scientific comprehensive water quality assessment. Water samples from 12 sampling locations of the Longgang River in Shenzhen, a typical rain-source urban river, were collected from January to December in 2018. According to the Environmental Quality Standard for Surface Water (GB 3838-2002), 22 water quality indicators were analyzed, and the water quality of Longgang River was comprehensively evaluated using the single-factor assessment method, comprehensive pollution index method, and principal component analysis method. The results of the single-factor assessment method showed that water quality of all sampling sites of the Longgang River met the Class V of the Environmental Quality Standard for Surface Water (GB 3838-2002), and the Tiaojiao Shui and Longxi River met the Class Ⅳ and Class Ⅲ of the Environmental Quality Standard for Surface Water (GB 3838-2002), respectively. The results of the comprehensive pollution index method showed that the water quality of 12 sampling sites was clean or relatively clean. Both the results of the comprehensive pollution index and principal component comprehensive score showed that the water quality of Longxi River, Nanyue River, and Tianjiao Shui were the best among all sampling sites. There is still room for improvement in the Wutongshan River, Dakang River, Ailian River, Dingshan River, and Huangsha River, and significant consideration should be given to parameters such as nutrients (TN, TP, and NH4+-N), organic matter (COD and BOD5), fecal coliform, and anionic surfactants. The three methods were a combination of qualitative and quantitative evaluation. The results of each method were not identical. Thus, it is very necessary to explore the comprehensive water quality assessment using various methods for making scientific and reasonable water pollution control strategies.

Effects of air quality and vegetation on algal bloom early warning systems in large lakes in the middle-lower Yangtze River basin.

Studies of algal bloom early warning systems have rarely paid attention to the dynamics of excessive proliferation of phytoplankton (EPP), which occurs prior to algal blooms, or to the sensitivity of a lake to EPP based on multiple environmental factors. In this study, we investigated EPP dynamics in large lakes and identified major factors that influenced the lake's vulnerability to EPP, to improve algal bloom early warning systems. High temporal moderate resolution imaging spectroradiometer (MODIS) images and multi-source daily site monitoring data of large lakes in the middle-lower Yangtze River basin were analyzed. Then, the floating algal index (FAI) and resource use efficiency (RUE) by phytoplankton were used to investigate the EPP dynamics and lake's vulnerability to EPP, respectively. Moreover, generalized linear models were used to assess the relative importance of environmental factors on RUE. The results indicate that the lakes freely connected (FC) to the Yangtze River (Dongting Lake and Poyang Lake) had lower FAIs but higher RUEs than the non-connected lakes (NC; Chaohu Lake and Taihu Lake). The key factors affecting RUE-FC were standard deviation of water level within 30 days(WL30), particulate matter <10 µm(PM10), and relative humidity(Hum), which explained 15.91% of the variations in RUE. The key factors affecting RUE-NC were ozone(O3), basin normalized difference vegetation index standard deviation(BNDVISD), and dissolved oxygen(DO), which explained 35.28% of the variations in RUE. These results emphasize the importance of air quality in influencing or reflecting EPP risks in large lakes. In addition, basin vegetation and hydrological rhythms can influence NH4+ through non-point source loading. Algal bloom early warning systems can be improved by routine monitoring and forecasting of potential environmental factors such as air quality and basin vegetation.

[Allelopathic Effects and Allelochemicals of Myriophyllum elatinoides on Microcystis aeruginosa and Selenastrum capricornutum].

The allelopathic effects of Myriophyllum elatinoides on algal growth were investigated and potential allelochemicals secreted by Myriophyllum elatinoides were analyzed. Myriophyllum elatinoides were co-cultivated with different initial concentrations (105, 106, 107, 108, and 109 ind.·L-1) of Microcystis aeruginosa and Selenastrum capricornutum. The optical density of each group was measured daily. The results showed that 2.5 g·(200 mL)-1 of Myriophyllum elatinoides has significant inhibition effect on Microcystis aeruginosa growth with initial concentrations of 107 ind.·L-1 and 108 ind.·L-1. However, there was no significant inhibition on the growth of Selenastrum capricornutum. Through solvent extraction and GC-MS analysis, hexadecanoic acid was extracted and determined as an allelochemical in Myriophyllum elatinoides. Additionally, three potentially novel allelochemical compounds secreted by Myriophyllum elatinoides were determined as follows:3-ethyl-3-methylheptane, triethyl phosphate and dibutyl phthalate.