Self purification of rivers is a natural process. What is the limit of pollution load of rivers to get self purified?
I think it is not purification but the contamination is absorbed and adsorbed by fine sediments or some fractions of hydrocarbon etc volatalize and other get photodegraded. Large fractions is lost due to biological uptake, but it is all there in the system in one form or the other. So what is self purification?
The process of purification is conducted by filtration, through which contaminants are get cleared. river flow i.e. water current plays vital role in this process, as it helps to conduct the process of adsorption and addition of valued Oxygen continuously.
@Saif Uddin, biological systems are also part of River. So the term used is River purification. How long distance is needed for river to get self-purified???? @Sanindhar Gaikwad, Yes i do agree that water current is main factor, But if the river is flowing in plains???? then water current will be very low.
This is a hugely complicated question, related to so many factors, that there is no easy answer. For a start, it depends on the pollutant. Putrescable waste such as sewage or farm waste will be removed from the system in very different ways to persistent polluants such as pesticides or heavy metals. If we are talking about material which is able to decompose realtively rapidly. then flow is very important, but this is, in itself, related to typology. If the river is on hard geology and responds rapidly to rainfall events, the pollutant can be physically flushed. If the bulk of the flow is from groundwater, then you must depend more on bacterial action to self-purify. For that, you need a complex substrate, so rich plant-growth facilitates the process. The latter is, in turn, influenced by typology.
If, however, the pollutant is a pesistent one, then bio-accumulating systems, including plants and filtering invertebrates, will sequester the pollutant. Soil-type will also be a factor if the pollutant can sediment-bind and be taken out of the food chain, then gradually reduce as the sediment is flushed-out. Again, this depends on flow, river typology, previling weather conditions for the region and incoming sediment-load.
In practice, the most polluted sorts of rivers have a cocktail of anthropogenic organic matter and biocides and the latter will almost certainly influence the decomposition of the former. You could write a book on this!
Many factors may take in consider, I think the most one is morphology of the river.
River flow rate/pattern plays an important role often underestimated
Very interesting topic and good answers. Rivers have been flowing for thousands or years; mostly in a sustainable manner. However, anthopogenic interventions can cause major problems to the fauna and flora though alternations of the quality of water. These alao dramatically affect not only all living creatures in the river, but also all water bodies supplied by this polluted river.
For example, when the levels of either phosphates or nitrogen, or both increase as runoff of fertilizer, reserviour water get hyper eutrophication. This is the commonest cause for dangerous algae blooms; some of th which produces toxins that can harm animals and humans. Basically we the human created most of these pollution and as a result we all suffer from unintended consequences.
Sunil Wimalawansa ([email protected])
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