Urban closed lakes: Nutrient sources, assimilative capacity and pollutant reduction under different precipitation frequencies

• Published in: The Science of the total environment 2020-01, Vol.700, p.134531-134531, Article 134531
• Main Authors: Yang, Heng, Zhao, Yong, Wang, Jian-Hua, Xiao, Wei-Hua, Jarsjö, Jerker, Huang, Ya, Liu, Yang, Wu, Jia-Peng, Wang, He-jia
• Format: Article
• Language: English
• Subjects: Assimilative capacity; Pollutant reduction; Precipitation frequency; Trophic status; Urban closed lakes
• ISSN: 0048-9697; 1879-1026; 1879-1026
• DOI: 10.1016/j.scitotenv.2019.134531

[Display omitted] •Describe the pollution status and problems of urban closed lakes.•Calculate the pollutant loads and assimilative capacity under different frequencies for urban closed lakes.•Calculated the amount of required pollutant reduction and analysed influenced factors for algal blooms in urban closed lakes. Many natural and man-made urban lakes have been developed under urbanization. A unique feature of these lakes is the lack of an outlet; thus, they are defined as urban closed lakes (UCLs). UCLs are facing unexpected eutrophication under climate change and human activities. Our study assessed the trophic state, assimilative capacity (AC) and pollutant reduction of UCLs under different precipitation frequencies in Wuhan, China based on Carlson’s Trophic State Index, assimilative capacity modelling, field investigations and observed data. The UCLs in Wuhan are nearly eutrophic in summer. Three primary nutrient sources are atmospheric deposition, pollutants carried in rainfall and nutrients released by sediments. TN and TP in the UCL water column are primarily contributed by surface runoff. The ACs of TN and TP in 2015 for Lingjiao Lake, Yue Lake, and Houxianghe Lake were 3472.07 kg, 13,800.99 kg, and 2805.58 kg, respectively, and 641.66 kg, 8386.79 kg, and 800.14 kg, respectively. The ACs of TN and TP were much higher at a 25% precipitation frequency (wet year) compared with a 50% frequency, and the lowest AC was observed at a 75% precipitation frequency (dry year). A comparison of the pollution load and AC showed that TN and TP reduction was highest in the dry and wet years, respectively. We found that specific meteorological conditions in the early stage led to the algal bloom. These results can facilitate governmental decision making in the future.