Effects of hydroperiods on plant growth and water quality in constructed wetlands

Abstract

Three experiments were conducted to determine the effects of hydroperiod on plant growth and water quality in wetiands constructed for treatment of agricultural wastewater. Paspalum distichum (knot grass), Typha latifolia (cattails), and Eichhomia crassipes (water hyacinth) specimens were subjected to variable hydroperiod loading regimes and monitored for survival rate and biomass productivity. Test scale knot grass treatment wetlands were subjected to variable hydroperiod regimes and monitored for biomass productivity and water quality improvements. Effective treatment cell length and fate of nitrogen were determined through examination of influent versus effluent total nitrogen, biomass production, plant nitrogen assimilation, and soil nitrogen accumulation as a function of distance down the cells. The fate of total nitrogen (TN) in the system was examined in an evaluation of the mass balance of total nitrogen throughout the systems. Variable hydroperiods examined ranged from 1 day wet and 1 day dry to 28 days wet and 14 days dry. Continuously flooded control systems were also examined. Total nitrogen loading rates in the systems ranged from 30 to 45 mg/1. In experiments conducted to monitor water quality and fate of nitrogen, hydraulic loading rates were maintained to achieve 2 day hydraulic retention times in the treatment cells. The test scale wetiand system was comprised of 21, 3.15 m long x 0.31 m wide x .31 m deep cells, which could be independently loaded and drained.