Nitrogen removal in hyacinth ponds, due primarily to nitrification/denitrification and plant uptake, can be very effective. The plant uptake will not represent permanent removal, however, unless the plants are routinely harvested. A complete harvest is not typically possible, as another function of the hyacinth plant is to shade the water surface so restricted light penetration will limit algal growth. Because harvest might remove only 20 to 30% of the plants in the basin at any one time, the full nitrogen-removal potential of the plants is never realized.
Nitrification and denitrification are possible in shallow hyacinth ponds even if mechanical aeration is used, due to the presence of aerobic and anaerobic microsites within the dense root zone of the floating plant and the presence of the carbon sources needed for denitrification. Nitrogen removals observed in hyacinth ponds range from less than 10 to over 50 kg/ha/d (9 to 45 lb/ac/d), depending on the season and frequency of harvest. Some of these were carefully managed pilot-scale or research facilities.
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