Transparency water column: here, a relative measure indicates the water transparency (transparency/depth), in which it is assumed that positive photosynthesis of water plants is not possible if transparency (Secchi) is roughly half the water depth, corresponding with a 3% light reduction to the soil.

Soil light penetration is essential to Charales because of their low growth.

Water depth: this relation is based on the deduction of the reference depth limit for aquatic plants to determine the “growable zone” (ref 2). The described maximum depth (in the figure indicated at 3m) is water type specific.