Plants - Slow Moving Waters
Plant life is abundant in this habitat and includes rooted vascular plants such as pond weeds and grasses, firmly attached aquatic mosses and multicellular filamentous algae. Minute floating plants such as duck weeds may cover most of the surface of the slow moving streams especially in the slowest backwaters. Motile algae, such as diatoms and flagaellates may abound in the open water.
As plants are more in this habitat the productivity is comparatively higher hi than that of the rapid waters and so the community here is relatively less dependent on nutrients from outside.
While in the fast-water streams the main controlling factor is the current, in the slow-water streams the main limiting factor is the concentration of dissolved oxygen. In this ecosystem a large quantity of oxygen can be withdrawn by the high level of animal activity coupled with active detritus food chain. In addition, the low level of turbulence means that less oxygen is incorporated into the water at the surface. Thus, the concentration of dissolved oxygen in a slow moving stream can be substantially less than saturation and so the community must be much more tolerant of low oxygen conditions as a result. For example the salmon and trout occurring in fast water need high oxygen levels while the most common fishes of slow water are often low oxygen concentration tolerant species such as carp and catfish.