Document Type : Research Paper
Authors
1
Department of Irrigation and Reclamation Engineering, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran.
2
Department of Irrigation and Reclamation Engineering, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran
3
Senior Researcher, National Rice Research Institute, Rasht, Guilan, Iran
4
Department of Water Engineering, Faculty of Agricultural Science, University of Guilan, Rasht, Iran.
Abstract
Agricultural drainage water, containing inorganic minerals (nitrogen, phosphorus, and metals) and organic pollutants (pesticides and agricultural toxins), is considered a major threat to aquatic ecosystems, leading to eutrophication and damage to downstream water resources. Undredged vegetated ditches can potentially serve as effective beds for removing nutrients and suspended solids from agricultural drainage water. This study investigates the efficiency of non-dredged drainage channels in removing nutrients from drainage water in the paddy fields of Gilan province. For this purpose, two treatments of natural drainage channels, without vegetation (V1) and with vegetation (V2), with lengths of 200 and 105 m respectively, containing specific plant species (Reed, Typha, Sparganium) were examined under high (C1) and low (C2) pollutant concentrations in July and August. The study measured the initial nitrogen and phosphorous content in water, sediment, and plants to compute the mass balance for the V1C1, V1C2, V2C1, and V2C2 treatments. Analysis of variance revealed significant removal of nitrogen and phosphorus, with the highest removal percentages observed in the V2C2 treatment. Phytoextraction was the primary nitrogen and phosphorous removal process in V2C2 at the rate of 37.06% and 61.69%, respectively, while seepage losses dominated in V2C1 treatment at 27.42% and 20.04% per 100 meters, respectively. Sediment absorption was notable, particularly for nitrogen in V2C2 and phosphorus in V1C1 treatments. Thus, our findings suggest that natural un-dredged drainage ditches possess promising capabilities in eliminating typical pollutants discharged from agricultural areas, thereby substantially improving the quality of drainage water that flows into downstream water sources.
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