In situ removal of dissolved phosphorus in irrigation drainage water by planted floats: preliminary results from growth chamber experiment

Abstract

Dissolved phosphorus is a major cause of freshwater eutrophication. This study investigated the use of floats planted with procumbent macrophytes for the in situ treatment of nutrient rich irrigation drainage waters. The floats are designed: (1) to implement horizontally spreading water plants to the surface of irrigation drains, fields, or treatment ponds in order to eliminate dissolved P; and (2) to allow harvest of the standing crop and therefore removal of the accumulated P. The float provides a platform to stimulate the growth and spreading of the planted water plants. Growth chambers were used to study the growth of four plant species over 70 days in four simulated solutions comprising high and low levels of nutrients and salinity. Three species: parrot weather (Myriophyllum aquaticum), water couch (Paspalum paspalodes), and waterbuttons (Ranunculus repens) have performed P removal rates in the range of 0.043-0.086 g P m(-2) per day measured as P bioaccumulation in plant tissues. Results indicated that the float technology could utilize creeping-stem water plants in order to remove soluble reactive P from the water column. A pilot study for in situ treatment of agricultural drainage water by the float technology is currently being conducted in an irrigation drain feeding a floodplain wetland at the Lower River Murray in South Australia.