Land use impact on the levels of fluorescent dissolved organic matter, phytoplankton and zooplankton in urban lakes

Urban lakes are vulnerable ecosystems, sensitive to environmental challenges, such as pollution, land use transformation and climate change. Closed and open lakes play relatively different roles in the accumulation, transport and transformation of pollutants and organic matter. Land use can influence the concentration of dissolved organic matter and the abundance of phytoplankton. Little is known about the relationship between fluorescent dissolved organic matter (FDOM), phytoplankton and zooplankton in open and closed lakes, relative to the impact of land use. This study aims to determine the connection between various types of land use and FDOM characteristics, as well as phytoplankton and zooplankton abundances in urban lakes. For the closed lakes samples, results showed positive associations between Bacillariophyceae and Testacea, and the protein-like fraction, while for open lakes, positive associations were found between these groups and the microbial humic-like fraction. Also, copepods and rotifers were associated with the humic-like fraction, in closed lakes, but in open lakes copepods correlated with the biological index, and rotifers with the humification index and fluorescence T/C ratio. Results suggested that discontinuous urban fabric, dump sites and abandoned lands decreased the abundance of protein-like fraction and phytoplankton. However, lakes with the highest quantity of protein-like FDOM also had the highest coverage of continuous urban fabric around the lake. Green urban areas decreased the quantity of humic-like FDOM. No impact by land use type was observed on zooplankton groups, suggesting that zooplankton may be less vulnerable to land use. Our findings will contribute to an improved urban water management and to an effective control of FDOM and phytoplankton abundances in urban lakes.