It may contain nutrients that encourage algae growth that may eventually also reduce available oxygen. Research sponsored by the Louisiana Rice Research Board and conducted by personnel of the Louisiana State University AgCenter is investigating several aspects of the problem. The dissolved oxygen in the flood, and drainage and outlet structure influence on dissolved oxygen of water leaving the field, were studied in 1999. Dissolved oxygen below 2 ppm is considered to limit aquatic life. The dissolved oxygen of drainage water was increased significantly, usually at least 2 ppm, by the drop outlet that is frequently used in southwest Louisiana to carry the water from the field to a drainage ditch.
Air is mixed into the water and absorbed as it free-falls from the outlet.
Drop outlets often used in southwest Louisiana add oxygen to the draining water. In eight fields, the flood is analyzed monthly during the season for pesticides and nutrients. The water drained before harvest is also analyzed. As the time for drainage approaches, the depth of flood is monitored, daily water use is considered and water use is forecast to the drainage date with the idea of minimizing drainage volume. In arid rice-growing areas, rainfall will be of little concern.