Design an experiment that uses pond water and algae to demonstrate the importance of light energy to pond life?

In a large flat tub you could mark out and separate sections in such a way that water can flow freely but light will not (thick separations with pores facing upwards so water will flow but since the light scource will be overhead the light will be well contained) and light each section with a different light source such as HMI lights - Has a color temperature of 5600K (Same color as the sun) Tungsten lights 3200 K Xenon lights, LEDs etc and also a section where you allow daylight to fall on it.. (You must understand that no artificial light can substitute the sun as effectively) You could use black paper lining to contain the light in the different sections.. The fact that the water can flow freely between the sections removes the doubt that other factors such as anti biotic agents or an antagonistic species may act on a particular specimen, thereby preventing corruption of your data. However the pores must be low so that the algae doesn't flow. Now just fill in the pond water and observe the different sections for the varied levels of algal growth

simple take two large plastic tubs (opaque) fill one with pond water and add algal growth (use fast growing alga). fill the other with distilled water and disturb this one everyday (to avoid any chance of fungal or algal grwoth). after , say four weeks, carefully take samples of both water and test for purity acid content (ph test) and other tests. it will show that eutrophication results in spoilage of water