Spatio-temporal patterns and drivers of CH4 and CO2 fluxes from rivers and lakes in highly urbanized areas.

Gaseous carbon exchange at the water-air interface of rivers and lakes is an essential process for regional and global carbon cycle assessments. Many studies have shown that rivers surrounding urban landscapes can be hotspots for greenhouse gas (GHG) emissions. Here we investigated the variability of diffusive GHG (methane [CH4] and carbon dioxide [CO2]) emissions from rivers in different landscapes (i.e., urban, agricultural and mixed) and from lakes in Suzhou, a highly urbanized region in eastern China. GHG emissions in the Suzhou metropolitan water network followed a typical seasonal pattern, with the highest fluxes in summer, and were primarily influenced by temperature and dissolved oxygen concentration. Surprisingly, lakes were emission hotspots, with mean CH4 and CO2 fluxes of 2.80 and 128.89 mg m-2 h-1, respectively, translating to a total CO2-equivalent flux of 0.21 g CO2-eq m-2 d-1. The global warming potential of urban and mixed rivers (0.19 g CO2-eq m-2 d-1) was comparable to that for lakes, but about twice the value for agricultural rivers (0.10 g CO2-eq m-2 d-1). Factors related to the high GHG emissions in lakes included hypoxic water conditions and an adequate nutrient supply. Riverine CH4 emissions were primarily associated with the concentrations of total dissolved solids (TDS), ammonia­nitrogen and chlorophyll a. CO2 emissions in rivers were mainly closely related to TDS, with suitable conditions allowing rapid organic matter decomposition. Compared with other types of rivers, urban rivers had more available organic matter and therefore higher CO2 emissions. Overall, this study emphasizes the need for a deeper understanding of the impact of GHG emissions from different water types on global warming in rapidly urbanizing regions. Flexible management measures are urgently needed to mitigate CO2 and CH4 emissions more effectively in the context of the shrinking gap between urban and rural areas with growing socio-economic development.

Effect of pretreatment approach on the ELISA-based detection of cyanotoxins in water: Analysis and application.

Common cyanotoxins, such as microcystins and nodularins, are produced by frequently occurring harmful cyanobacterial algal blooms in freshwater systems. The required routine monitoring of microcystins and nodularins in drinking water and ambient water demands cost-efficient and reliable enzyme-linked immunosorbent assay kits. We validated the performance of a self-produced broad-spectrum enzyme-linked immunosorbent assay kit and investigated two different methods of mitigating the matrix effects to elucidate the effect of the respective pretreatment approaches recommended by China and the United States on the quantitative detection of cyanotoxins in surface water. We found that the enzyme-linked immunosorbent assay kit achieved a detection limit of 0.15 µg/L with a linear detection range from 0.27 µg/L to 1.87 µg/L for microcystin-LR (the most studied and widely distributed cyanotoxin). The matrix effects could be mitigated both by dilution of water samples with an optimal dilution ratio and dilution of antibody with the buffer containing phosphate buffer solution (10×), bovine serum albumin (1 %) and ethylene diamine tetraacetic acid (0.5 %). In terms of the surface water samples being tested, the concentrations of microcystins and nodularins measured based on pretreatment approach recommended by the United States were 1- 5 times that measured based on pretreatment approach recommended by China, indicating that the pretreatment approach of China overlooks cyanotoxins. In addition, all the measured total microcystins and nodularins of the surface water samples were below the health advisory limit (1.6 µg/L) for microcystins in drinking water proposed by the United States Environmental Protection Agency for school-age children and adults. Our research could provide significant information for outbreak warnings and risk management of harmful cyanobacterial algal blooms.

Sediment information on natural and anthropogenic-induced change of connected water systems in Chagan Lake, North China.

This study discusses changes in connected water systems in Chagan Lake induced by the interference of natural and human activities, based on the analysis of sediment characteristics. In this study, the following sediment characteristics were investigated in the lake area, the natural supply area, and the lake drainage area: mineral composition; particle size distribution; magnetic susceptibility; nutrient content; content of isotopes δ13Corg and δ15N; and content of heavy metals and of metallic oxides. The results showed that silicate minerals quartz, orthoclase, and anorthose were abundant in the whole lake water system. Quartz accumulated more easily in the lake area, while carbonate masses in the lake mainly came from the Huolinhe River. Moving from the lake area to the water diversion and drainage areas, fine particles clearly decreased, while coarse particles significantly increased due to the increase in hydraulic erosion. The main sources of nutrients and of organic matter are: the residual of the drainage from the Qianguo irrigated areas; the surrounding villages and the tourist area; and the decomposition of aquatic organisms. A large number of anthropogenic heavy metals, such as Hg, Cu, and As, were accumulated in the artificial water diversion area and in the farmland drainage area. This study indicates that recovering the original connected water system during the wet season, while at the same time enhancing water supply during the dry season could improve the ecological quality of Chagan Lake.