Abstract
Removing dissolved nutrients from river water flowing into lakes and marshes is an effective method of preventing eutrophication of them. We have proposed the continuous cultivation of filamentous algae outdoors in artificial waterways to remove phosphorus and nitrogen from the water.
The ability of filamentous algae to absorb dissolved nutrients depends on the radiation (illuminance on the water surface in the daytime, diurnal periodicity), the concentration of nutrient in raw water, the temperature, and the stream regime (flow velocity, shape of the substratum which the filamentous algae are attached to, water depth). This study investigated the effects of the diurnal periodicity on the ability of filamentous algae to absorb phosphorus and nitrogen.
The results of field experiments in the artificial waterway have clearly confirmed that the ability of filamentous algae to absorb phosphorus and nitrogen is influenced by the diurnal periodicity of the radiation. The results indicated that in the case of river, lake, or marsh water in which the major constituents of inorganic nitrogen in the water are NO3-N, more dissolved orthophosphate is absorbed at night than during the day, and more inorganic nitrogen is absorbed during the day than at night.
