What are boundary zones?

The creation of microenvironments.

Flowing water interacts with benthic communities to create microhabitats which are important for the development of the river’s developing ecosystem. The extent of these microenvironments depends on the spatial development of the benthic biomass and the conditions of water flow in each part of the river.

The accumulation of biomass on the bottom of the stream leads to major changes in the hydraulic characteristics of the benthic environment. Zones of low-velocity or stationary water develop within and around bacterial biofilms, algal biofilms and periphyton communities, forming a variety of supplementary boundary zones in addition to the main benthic boundary layer. These boundary zones range from the thin high-velocity biofilm sublayer that occurs on surfaces directly exposed to the current, to large regions of quiescent, low-velocity biofilm contained within the internal spaces of benthic communities.

The zones of quiescent water form important regions within which unattached organisms such as algae, protozoa and small invertebrates can exist. Quiescent boundary zones prevent downstream displacement of biota by the strong advected forces of flowing water, thus counteracting one of the fundamental problems of life in fast-flowing river ecosystems. Such microenvironments are a general feature of attached benthic communities and are important in maintaining biodiversity and nutrient cycling. The local regeneration of inorganic nutrients by this process is a major factor in maintaining nutrient supply to primary producers and sustaining high rates of primary productivity in benthic systems.



TWC is an artificial boundary zone that also establishes small eddy zones on the underneath of the TWC block. This allows TWC to establish a full microenvironment been the top thin laminar sublayer to the underneath low-velocity biofilms on the block; this completes the processes of nutrient cycling through the flow of the artificial river. In summer this process allows these microenvironments to then naturally spread from the TWC block, establishing themselves into the soil of the artificial river, therefore establishing a natural biological system that can maintain itself.



The importance of establishing natural boundary zones within man-made river systems and the re-establishment of boundary zones in polluted river systems is to re-establish nutrient cycling through microenvironments to progress the health of the waterway for the benefit of wildlife, people and farmland within the proximity of these river systems.

Man-made river systems struggle to conduct nutrient cycling due to no boundaries zones being in place for natural nutrient cycling through the fast flow of the river system. Boundary zones in artificial rivers take years to naturally establish or may never establish due to the build-up of pollutants, meaning nutrients cannot be processed. This building up of pollutants is the cause of large Cyanobacteria blooms which also stop or restrict the development of these critically needed boundary zones.

TWC in Rivers

importance of establishing natural