Fish in Chip I am by no means a specialest on Plankton. I have however have done research & been some what educated a little on the subject in the past. Plankton blooms have been a interest to me because of my love for ocean fishing and understanding why fishing around them is so good.

The Green looking plankton you see is from Chlorophyll in the Phtyoplankton. Zooplankton that alot of our freshwater fish feed on may be present and not visable since they are an animal plankton.

1> Yes for Phytoplankton (aka Plant plankton) phosphorus, and nitrogen also play a key role in growing plants (FA INCLUDED). However high N & P have been known to produce a bloom that is less productive (because Aphanizomenon is often present) and tends to make phytoplankton less grazeable for the more desireable Zooplankton (AKA animal plankton like BG eat).

2> Some FA present can be an alternate food source for the Zooplankton (animal plankton and BG food) while it also takes vital N & P from Phytoplankton.

3> Phytoplankton (food for zooplankton) needs longer sunny days, Nutrients & a substainable water temperature for growth. Most places I would say have there best production during late spring with water temps between 70 to 75 degrees. After this alot of the nutrients tend to be used up for the larger phytoplankton blooms. The zooplanton also generally have some other form of algea to feed off of other than the Phytoplankton.

4> Longer blooms provide visable food for the much sought after Zooplankton. Extending more production of grazable phytoplankton helps increase the biomass of the zooplankton. However physical enviroment can also influence the length of time a larger Phytoplankton bloom can exist. Often you will have a late Spring early summer bloom. As the nutrients are used up the phytoplankton bloom dies down or the zooplankton reaches the typing point of more consuming than what is being produced. Warmer water temps often then supress the reproduction of Phytoplankton in my area until near fall when the water temps again cool enough to allow another bloom (with enough sunlight, nutrients and more viable water temperature all come together at the same time).

Just a side note I often fertilize and use some pond dye at the same time to prevent nutrients being used for lower growing algea to provide more for top growing phytoplankton.

When building a pond I also take notes from the ocean that if your pond is designed where upwelling (slight underwater currents that will bring nutrients from depths to the surface) can take place your phytoplankton bloom will also last longer. This can be done by elavation changes when building instead of a flat bottom. Often spring thunderstorms will provide the wind power for currents. I got this idea from fishing a placxe called the Midnight lump off of the coast of Louisiana. It is underwater dome that causes an upwelling of rich oceans currents that makes for plankton rich waters in the winter. This in turn draws bait fish that bring in the yellow fin tuna.

Hope this kind of helps answer some of the questions you are asking.