Jinzhi Wang

Water nitrogen and phosphorus may exhibit pronounced diel changes as affected by diel temperature and DO fluctuations due to algal productivity (photosynthesis and respiration) in eutrophic lakes. Here, we used a laboratory experiment to evaluate the diel dynamics of water ammonium (NH4 +), nitrate (NO3 -), and soluble reactive phosphorus (SRP) in different periods of algal bloom in the highly polluted region of Taihu Lake, China. Results showed that diel changes of water NH4 +, NO3 -, and SRP depended on the different periods of algal bloom. Diel variations of NH4 +, NO3 -, and SRP showed increased trends during algal decomposition, and decreased trends at the beginning of algal growth, suggesting that their diel variations were mainly controlled by algae self through nutrients released by decomposing algae or algal assimilation. However, water NH4 +, NO3 -, and SRP decreased from predawn maxima to afternoon minima and subsequently increased when Chl-a was high, which might be governed by the combined effects of algal assimilation and geochemical processes (e.g., nitrification, denitrification, and Fe-bound P cycles). Overall, the diel biogeochemical cycles of inorganic nitrogen and SRP have important implications for the accuracy of pollution assessment and provide important support for the control and management of eutrophic lakes.

Different characteristics of wastewater have different effects on the diversity and abundance of bacteria and archaea in rivers. There are many creeks around Taihu Lake, and they receive a large volume of industrial wastewater and domestic sewage, which is discharged into these creeks, and finally into Taihu Lake. The present study determined Illumina reads (16S rRNA gene amplicons) to analyze the effects of industrial wastewater and domestic sewage on the bacterial and archaeal communities at the different sampling sites along two creeks. The bacterial and archaeal diversity of the creek receiving sewage was higher than that of the creek receiving industrial waste. Proteobacteria dominated the microbial communities of all samples in both creeks. Betaproteobacteria dominated in the sewage creek, and its abundance declined along the creek. Certain pollutant-resistant classes were more abundant at the site near to the pollution source of the industry creek (e.g., Epsilonproteobacteria and Flavobacteria). Halobacteria belonging to the phylum Euryarchaeota was the dominant archaea at all sites in both creeks, while Methanobacteria was more abundant in the industry creek. The bacterial community was more affected by the distance between the sampling site and the pollutant source than the archaeal community, indicating that bacterial diversity and abundance could be a good index to distinguish domestic and industrial pollution, especially when the main pollution sources are difficult to identify.