What do plants and algae in Lake Balaton feed on?

When we say “plant nutrients,” we usually mean the elements mostly needed for the growth of plants. These are carbon, nitrogen and phosphorus (C:N:P), which, as the basic building blocks of living organisms, are available in generally well defined ratios and in various forms. Carbon is extracted from the air in the form of carbon-dioxide by plants, so there’s no shortage of it. (They make sugar and oxygen out of it using the sun’s energy.) Nitrogen and phosphorus are usually obtained from the soil by most plants. These elements are usually supplemented by fertilizers and manure in agricultural areas for a growth in production or maintenance, but are also spread in smaller gardens for greener and richer grass (N-P-K in Hungarian, meaning nitrogen, phosphorus and potassium).

These nutrients are found in several different chemical forms in nature. Living organisms can absorb them in various amounts: nitrogen, for example, is available for some bacteria from the air, but most algae can only consume nitrogen compounds dissolved in water. However, some algae species can utilize nitrogen from the air as well. These are usually called blue-green algae, which belong to a more ancient group. Within a water system, the availability of phosphorus typically limits the reproduction of green algae. Whenever nitrogen and other nutrients are readily available in the water, many different algae species can grow, but when the lack of nitrogen creates an advantage for blue-green algae: while the growth of other algae groups is restricted by the accessible amount of nitrogen, blue-green algae can reproduce substantially faster.