Human-caused effect on the content of organic substances in the water of rice fields

A good ability of rice fields for self-purification has been observed. By the end of the period of irrigation, the concentration of oxygen dissolved in water was not less than 5 mg O 2 /L, the biochemical consumption of oxygen for 5 days was no more than 6 mg O 2 /L, and, before discharge the water from the checks, the consumption did not exceed the maximum allowable concentration.