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Aquatic humic substances (AHSs) from the eutrophic Lake Kasumigaura, Japan, significantly inhibited the growth of Microcystis aeruginosa at a concentration level similar to that found in the lake. AHSs were isolated and quantified using XAD-8 resin. The effects of these isolated AHSs on the growth of M. aeruginosa cultures were evaluated in a chemically defined medium. The production of siderophores, iron-specific complexing agents, of M. aeruginosa under iron limitation was also examined. Fulvic acid (the lower molecular size fraction of the AHSs) accounted for more than 85% of AHSs in Lake Kasumigaura. Under iron limitation, M. aeruginosa produced hydroxamate-type siderophores; however, they were not effective in enabling substantial recovery of growth. Microcystis aeruginosa growth was significantly inhibited when fulvic acid was 2 mg dry weight·L-1, similar to the concentration in the lake, even when siderophores were produced. Growth inhibition was probably due to a deficiency of iron caused by iron complexation with the fulvic acid. It was suggested that AHSs play an important role in formation and disappearance of M. aeruginosa blooms in eutrophic lakes.

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Remote sensing (RS) has been considered as the most promising tool for evapotranspiration (ET) estimations from local, regional to global scales. Many studies have been conducted to estimated ET using RS data, however, most of them are based partially on ground observations. In this study, we developed a new dual-source Simple Remote Sensing EvapoTranspiration model (Sim-ReSET) based only on RS data. One merit of this model is that the calculation of aerodynamic resistance can be avoided by means of a reference dry bare soil and an assumption that wind speed at the upper boundary of atmospheric surface layer is homogenous, but the aerodynamic characters are still considered by means of canopy height. The other merit is that all inputs (net radiation, soil heat flux, canopy height, variables related to land surface temperature) can be potentially obtained from remote sensing data, which allows obtaining regular RS-driven ET product.