Accumulation of dry matter, nitrogen and phosphorus by cultivated water Hyacinths

Abstract

Nutrient absorption by controlled populations of Eichhornia crassipes (Mart) Solms (water hyacinth), or other species of aquatic plants, might reduce concentrations of nitrogen and phosphorus in eutrophic lakes or in effluents prior to their .release into natural waters (5, 14, 15, 18). Steward (15), assuming dried water hyacinths contained 4% nitrogen and 0.4% phosphorus, suggested that 1 ha of plants in subtropical regions might remove up to 6,000 kg nitrogen and 600 kg phosphorus per year. Boyd (5), using more conservative values for growth and nutrient content, estimated potential annual uptake of nitrogen and phosphorus by water hyacinths in warm climates as 1,980 and 322 kg/ha, respectively. Rogers and Davis (14), after measuring nutrient uptake by E. crassipes in growth chamber experiments, concluded that absorption by 1 ha of water hyacinths would exceed 2,500 kg of nitrogen and 700 kg of phosphorus per year if maximum growth could be sustained. Many aquatic plants, including water hyacinth, have a high protein content (3, 4) and plants removed to reduce nutrient enrichment of natural waters could probably be used as animal feed. In this study, water hyacinths were cultivated in nutrient-enriched water of earthen ponds to determine rates of growth and absorption of nitrogen and phosphorus under conditions similar to those in eutrophic lakes or effluent holding ponds. The effects of water hyacinths on nutrient concentrations in waters and on phytoplank-