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Fate of Nitrogen and Phosphorus in a Waste-water Retention Reservoir Containing Aquatic Macrophytes¹

ABSTRACT

Potential use of retention/detention reservoirs stocked with vascular aquatic macrophytes was evaluated, using a microcosm reservoir for reducing the N and P levels of agricultural drainage effluents (waste water). The treatments evaluated were reservoirs stocked with (i) pennywort (Hydrocotyle umbellata L.), (ii) water hyacinth (Eichhornia crassipes [Mart] Solms), (iii) cattails (Typha latifolia L.) and elodea (Egeria densa P), and (iv) control (no macrophytes). Labeled ¹⁵N was used to differentiate preferential uptake of ¹⁵NH₄⁺ and ¹⁵NO₃^–, and to follow the fate of added ¹⁵NH₄⁺ and ¹⁵NO₃^–.

Results showed that 34 to 40% of the added inorganic ¹⁵N (¹⁵NH₄⁺ + ¹⁵NO₃^–) was removed through plant uptake, while 45 to 52% of the added ¹⁵N was unaccounted for, presumably lost through NH₃ volatilization and nitrification-denitrification processes. In the control reservoir, algal biomass removed 4.4% of added ¹⁵N, while 41% of the added ¹⁵N was not accounted. Pennywort and cattail-elodea systems were found to be most effective, with about 50% inorganic N removal in a 4-day detention period. All aquatic macrophytes preferred ¹⁵NH₄⁺ over ¹⁵NO₃^–, but the difference in uptake was not significant, except for pennywort and cattails, which removed 84 and 92% of the added ¹⁵NH₄⁺ as compared to 16 and 8% of the added ¹⁵NO₃^–, respectively. About 25 to 29 d were required by the systems with macrophytes to remove 50% of the wastewater P. Plant removal of P was in the range of 3 to 65% of added P, while 7 to 87% of the added P was lost through precipitation and adsorption reactions.

Key Words: water hyacinth • pennywort • cattails • elodea • aquatic system

¹ Florida Agricultural Experiment Stations Journal Series no. 3766.

² Associate Professor, University of Florida, Inst. of Food & Agricultural Sciences, Agricultural Research & Education Center, P.O. Box 909, Sanford, FL 32771.

Received for publication March 6, 1982.