Natural wetlands efficiency assessment in removing sugarcane fields' drainage contaminants: a case study in Khuzestan, Southwest Province of Iran.

The present study investigated the efficiency of a real-scale natural wetland (Naseri Wetland) in the qualitative treatment of agricultural drainage of Khuzestan sugarcane for 1 year (2019-2020). This study divides the wetland length into three equal parts in W1, W2, and W3 stations. The efficiency of the wetland in removing contaminants such as Cr, Cd, BOD, TDS, TN, and TP is evaluated by field sampling, laboratory analysis, and t-test. Results indicate that the highest mean difference in Cr, Cd, BOD, TDS, TN, and TP are observed between W0 and W3. At W3, the farthest station from the entry point, the highest removal efficiency is obtained for each factor. Removal percentage of Cd, Cr, and TP in all seasons is equal to 100% up to station 3 (W3), and BOD5 and TN are 75% and 65%, respectively. Also, the results show a gradual rise in TDS along the wetland's length due to high evaporation and transpiration in the area. Naseri Wetland reduces the Cr, Cd, BOD, TN, and TP compared to the initial level. This decrease is more significant at W2 and W3, and it is worth mentioning that W3 has the most considerable reduction. With increasing distance from the entry point, the effect of timing of 1.10, 1.26, 1.30, and 1.60 on removing heavy metals and nutrients is high. The highest efficiency is observed for each retention time at W3.