Sort of at the level of kingdom (bacteria, fungi, Protoctista (protozoa), microbiologists don’t use kingdom phylogenetic tree of living things, based on RNA data and proposed by Carl Woese, Separation of all organisms into 3 domains: bacteria (prok), archaea [(prok) eg thermophiles, halophiles] eukaryotes(algae, fungi).
Most algae are euk except blue-green algae which are prok (1/2 bacterial) Actinomycetes – found in soil, Actinomycin-D is one of the older chemotherapy drugs which has been used in therapy for many years 

Phytoplankton are a diverse group, incorporating algae eukaryotes and both eubacterial and archaebacterial prokaryotes.

Euphotic zone in a lake is approximately the same as the epilimnion – can extend below it though.

Algae and aquatic plants prefer ammonium to nitrate. This is because the nitrogen is in a reduced state which the algae can directly utilize for the production of amino acids (the building blocks of proteins). Nitrate must first be reduced to nitrite and then ammonium in order for the algae and plants to utilize nitrogen in this state. This takes energy and, as a result, the plants and algae cannot grow with equal efficiencies given the same amount of nitrate nitrogen as they would on ammonium nitrogen.