Teresa Serra, Aina Barcelona and Jordi Colomer, together with other members of the Department of Physics, the Department of Chemistry and the Laboratory of Chemical and Environmental Engineering (LEQUIA) of the University of Girona, publish the paper entitled Optimal light conditions for Daphnia filtration in the Science of the Total Environment journal (STOTEN).

STOTEN is an international multi-disciplinary journal for publication of original research on the total environment, which includes the atmosphere, hydrosphere, biosphere, lithosphere, and anthroposphere.

In this publication, the authors explain that Daphnia populations are present in lakes and ponds. They are known to experience diurnal vertical migrations according to their feeding needs. During the day they migrate downwards to avoid predation in light-receiving layers and at night they migrate upwards, searching for food in the shallow productive layers. The light photoperiod and light intensity vary depending on the latitude and, therefore, the precise location of lakes and ponds will be an additional and crucial parameter in determining the development of Daphnia. The authors focus on a population of Daphnia magna (a genus of the Cladocera order). The effect of both light intensity and photoperiod on Daphnia filtration was studied in laboratory experiments. An increase in the light intensity resulted in two D. magna responses depending on the exposure time of individuals to light. Short time exposures to a decrease in the light intensity of less than one day produced an increase in the D. magna filtration. However, exposures of longer than one day resulted in a decrease in the D. magna filtration along with a decrease in the light intensity. Photoperiod exposures of 8, 12 and 16 h produced greater D. magna filtrations than photoperiods of 0, 4 and 24 h. In this study, regulation of the light intensity and the period of exposure were used in laboratory experiments to establish D. magna development thresholds by latitudinal variation in the photoperiod.

This study was conducted within the framework of the Wastewater Treatment and Reuse line of the Environmental Physics research group, and was supported by the University of Girona funding MPCUdG2016 and by the INNOQUA project from the European Union's Horizon 2020 research and innovation program (Grant agreement 689817). Data on short wave radiation has been obtained from the website of the meteorological station at the University of Girona: nuclierdata.udg.edu.