Sarah Marnell, Spring Hill College

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Abstract:

Emergent aquatic plants that can readily take up nitrates and phosphates are often used in stormwater ponds to reduce the amount of nutrients that enter ground and surface waters. Two ten-day studies were conducted to determine TN and TP uptake rates for four freshwater plants: variegated water celery (Oenanthe javanica), canna lily (Canna glauca), bogbean (Menyanthes trifolia) and alligator-gat or water canna (Thalia dealbata). Plants were kept in solution with a target concentration of 3.0 mgTN and 0.5 mgTP. Relative growth rate and TN and TP uptake rates were measured and recorded. Average relative growth rates (% increase per day) for the first replication were as follows: C. glauca (3.18 %), O. javanica (2.72 %), T. dealbata (1.45 %) and M. trifolia (1.17 %). TN and TP uptake rates were calculated from initial and final nutrient composition and plant weights. Uptake rates for the first replication were C. glauca (179 mgN/g day^-1, 18.6 mgP/g day^-1), O. javanica (112 mgN/g day^-1, 35 mgP/g day^-1), T. dealbata (36 mgN/g day^-1, 1 mgP/g day^-1) and M. trifolia (25 mgN/g day^-1, 5 mgP/g day^-1). Using the same techniques, average relative growth rates for the second replication were as follows: M. trifolia (1.22 %), C. glauca (0.56 %), O. javanica (0.08 %) and T. dealbata (0.04 %). There were no significant differences among these relative growth rates. Two uptake rates were determined for each nutrient in the second replication. These uptake rates were: C. glauca (194 mgN/g day^-1 and 209 mgN/g day^-1, -17 mgP/g day^-1 and -20 mgP/g day^-1), O. javanica (26 mgN/g day^-1 and 14 mgN/g day^-1, -7 mgP/g day^-1 and  -12 mgP/g day^-1), T. dealbata (53 mgN/g day^-1 and 39 mg/g day^-1, 103 mgP/g day^-1 and -112 mgP/g day^-1), and M. trifolia (20 mgN/g day^-1 and 17 mgN/g day^-1, 1 mg/g day^-1 and 1 mg/g day^-1). C. glauca's TN uptake rates were significantly higher than all other TN uptake rates. There were no statistical differences among TP uptake rates.