What is algae and what causes it?

The term "algae” refers to a wide variety of photosynthetic organisms. Algae range in size from microscopic phytoplankton to giant marine kelp that may grow to 60 meters long.  During periods of excessive growth, or algal blooms, of one, two or more species which may cause certain problems for other organisms and degrade water quality. Large amounts of decaying algae consume oxygen in the water, causing fish kills if oxygen levels drop too low. A scum of algae floating on the surface can shade out beneficial plants that provide habitat for fish and wildlife.
Like all plants, algae require nutrients to grow and reproduce. Algae are free-floating, so they must get their nutrients from the water. They do not have the ability to obtain nutrients from the pond bottom. The higher the nutrient level in the pond, the more algae you will have.

Also, the older a pond gets the more nutrients it will have accumulated and the more susceptible it will be to algae problems.  The runoff from fertilized lawns and gardens, fields, pastures, feedlots, septic tanks and leach fields will accelerate algae growth in the pond.

The amount and type of nutrient loading in your pond can determine the type of algae that will grow.  At slightly higher nutrient levels, the algae community is often dominated by filamentous algae. This is particularly true during summer. But with very high nutrient levels, the algae blooms are typically composed of plank tonic algae rather than filamentous algae.

In nature, algal blooms are usually short-lived, on the order of a month or two, typically because of the combined effects of nutrient depletion and "grazing" by planktivores.

Algal blooms are often successional, i.e. a green algae bloom can be followed by blue - green algae, called a cyanobacteria bloom. Or for example, when the N: P ratio exceeds 29, there is a shift in dominance from the blue-green cyanobacteria to green algae and diatoms (Smith 1983).

Algal production is correlated to the levels and ratios of nitrogen (N) and phosphorous (P) in the water. Generally, a phosphate concentration of 0.01 mg. /l will support plankton, while concentrations of 0.03 to 0.1 mg /l phosphate or higher will likely trigger blooms (USEPA, 1986; Dunne and Leopold, 1978). (More information about..... Algae and nutrient reduction)

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