Potential Use of Irrigation Drains as Wetlands

Abstract

There are over 6000 km of irrigation drains in the Murray-Darling Basin, Australia. The maintenance of aquatic plants may be critical to the utility of the watercourses in scavenging nutrients, yet the plants are often removed by extensive herbicide spraying and large-scale mechanical excavation and desilting. Results for four out of five experiments showed that water clarity improved when vegetation was left unmanaged. High concentrations of inflowing nitrate from subsurface tile drainage was quickly dissipated. There was an unexpectedly poor correlation between turbidity and phosphorus concentration overall; but in four experiments concentrations of total phosphorus declined during transport through vegetated stretches of channel. There was an important interaction between plant cover and sediment bioperturbation, since in bare stretches of channel the roiling of carp increased the concentrations of suspended sediments and nutrients. Irrigation drainage water quality may be improved by management of aquatic plants to trap suspended paniculate load and reduce the effects of carp.