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The fate of aquatic macrophyte production : the decomposition, mineralization and nutrient recycling of a submerged aquatic vascular plant Myriophyllum spp Kistritz, Ron Udo

Abstract

Decomposition, mineralization and phosphorus (P) and nitrogen CN). regeneration of a submerged aquatic macrophyte, water-milfoil (Myriophyllum spp.), were investigated both in laboratory and field experiments. Existing chemical methods of plant analysis were modified to provide a procedure which simultaneously measured N and P in one small sample of live or dead plant material. A laboratory experiment was designed to investigate the effect of nutrient rich reservoir water and nutrient poor pond water on the process of aerobic decomposition and nutrient regeneration in water-milfoil. Measurements were also made of dry weight, and nutrient content of dying macrophyte material and three size catagories of macrophyte detritus. In the laboratory, higher amounts of N in reservoir water significantly increased decomposition and N and P regeneration of macrophyte material. Dying macrophytes and detritus showed 25-40 percent increases in total protein due to colonizing decomposer microorganisms. An "in situ" field study was designed to investigate the regeneration and mineralization of N and P compounds of aquatic macrophytes (Myriophyllum spicatum L.) decomposing under periodically anaerobic condition in nutrient rich reservoir water. Measurements were related to levels of N and P compounds liberated by sediment and decaying algae (almost entirely Anabaena spirula) and to N and P represented by total suspended bacteria. It was estimated that suspended bacteria contained up to 31 and 21 percent of the water's total organic P and N, respectively. Both laboratory and field results showed that P was regenerated rapidly and almost entirely as orthophosphate. Nitrogen was released predominately as ammonia, appreciable amounts of which were also liberated by sediment and phytoplankton.

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