Growth of Four Aquatic Plants and Their Removal of Total Nitrogen and Total Phosphorus in Eutrophication Water Under Different Plant Density:A Laboratory Experiment

Aquatic plants,used to purify the waste water during fish farming period, play an important role in constructed wetlands of water circulating aquaculture pond systems. A simulated experiment was conducted from September to November for seven weeks to compare the growth of four aquatic plants, Myriophyllum spicatum, Potamogeton crispus, Lemna minor L., and Ceratophyllum demersum L., and their removal of total nitrogen and total phosphorus in eutrophication water under different plant density. Biomass of M. spicatum and L. minor L. had a significant positive correlationship with planting time and density, and showed good removals of total nitrogen and total phosphorus from water. Potamogeton crispus and C. demersum L. showed similar trends during the six weeks, but began to die and ceased removals of nitrogen and phosphorus at the 7thweek due to sharp decline in air temperature. Multifactor analysis showed that growth time contributed most to biomass and nitrogen and phosphorus removals, compared with plant density and type. These findings indicate that M. spicatum has high purifying capacity and low temperature-tolerance and is the best aquatic plant in aquaculture constructed wetlands. Maintaining appropriate plant density is also critical for purification of eutrophication water.