Comparison of Rhodamine-WT and bromide as a tracer for elucidating internal wetland flow dynamics

Artificially constructed wetlands offer a low-cost treatment alternative to remove a number of pollutants found in effluent water from industry, mining, agriculture, and urban areas. The determination of treatment efficiency cannot be determined without understanding the flow dynamics of individual parcels of water through the wetland. A method for tracking parcels of water is proposed, using Rhodamine-WT as a tracer. A series of tracer tests were conducted on a 1.2 ha treatment wetland. Bromide and Rhodamine-WT were simultaneously dosed into the inlet and monitored at 60 sampling locations for 5 weeks. Rhodamine-WT concentrations were found to be coincident with bromide. For all three events the relationship between Rhodamine-WT concentration and bromide concentration was linear at each sampling point with a slope of 0.82. The peak concentration of Rhodamine-WT and bromide was also found to coincide throughout the wetland. Rhodamine-WT can be used to determine the movement of individual parcels of water through a treatment wetland and used to determine treatment efficiencies at individual locations within a wetland.