Water Management: Self Cleaning

Index Education

Introduction

Water Quality: Management, Sanitation and Investigation

Limnological Fundamentals

Limnochemistry, Aquatic Biology: Self cleaning

The quality of water in lakes and reservoirs is not only determined by the properties of water flowing into them but also by processes of material decomposition and energy conversion in the lake itself. These natural self-cleaning processes can be supported and encouraged by intervening into the ecosystem.

The basic principles for self-cleaning of waters are as follows:

Limitation of growth factors for harmful organisms (algae) by removing these factors via other organisms (competition for food and light).
Conversion of dissolved pollutants and nutrients into particles, sediment or in a separable and detachable form (Plant, bacterial, and protozoic biomass),
Conversion of small biomass particles difficult to separate (algae cells, pathogens) by animal biofiltration in larger living organisms within the food chain
Conversion of dissolved organic substances to mineralized substances.

Graphic generally example

Graphic example of bacteria metabolism

The structure of the food web has a decisive influence on water quality. Quality is especially determined by availability of plant nutrients (nitrogen and phosphorus compounds), since these control the growth of harmful phytoplanktons (usually single celled algae and cyanobacteria). Phytoplanktons can considerable reduce the quality of untreated water (smell, taste, toxic algae) and can greatly impede the treatment of water in reservoirs. Phytoplankton is the primary producer of basic nutrients for zooplankters, which is eaten by other consumers (fish, predators on zooplanktons). The food cycle through the levels of organism is closed by bacteria which mineralise the biomass into nutrients (Figure, Graphic example).