Author(s)

K. Soosaar, M. Maddison & Ü. Mander

Abstract

The aim of this study was to estimate water purification capacity and greenhouse gas fluxes in a semi-natural reedbed receiving effluent from a wastewater treatment plant (WTP) in Lihula, which is located on the southern border of Matsalu National Park, Estonia. The values of BOD7 and COD in the treated water were low (<8 and <70 mgL-1 respectively), whereas the COD level increased within the reedbed. The average concentrations of ammonia N and total N significantly decreased from the WTP outflow to the reedbed outflow (from 6.8 and 9 to 0.2 and 1.2 mg L-1 respectively). Nitrate and nitrite N levels were low but decreased along the flow. The average concentration of both PO4-P and total P in water decreased rapidly toward the reedbed outflow (from 2.8 and 3.2 to 0.04 and 0.09 mg L-1 respectively). Redox potential and dissolved O2 saturation showed the lowest values in the reedbed inflow. The C, N, and P concentration in soil decreased from the reedbed inflow towards the outflow. The average N2 and N2O fluxes from the reedbed were relatively low, varying from 4.0 to 16.1 mg N2 m-2 h-1 and from -5.0 to 3.7 μg N2O m-2 h-1 respectively. The spatial-temporal variation of methane emission was great (10.5-16397 μg CH4 m-2 h-1), showing higher values in the inflow. The average CO2 emission from the reedbed varied from 14.3 to 334 mg CO2-C m-2 h-1, being somewhat higher in the inflow area. Accumulation of C, N and P in soil, increasing COD values and falling redox potential/dissolved O2 values in water, and higher CH4 and CO2 emission rates in the inflow site of the reedbed demonstrate the long-term impact of sewage loading. Keywords: carbon dioxide, dinitrogen, methane, nitrous oxide, reedbed, seminatural wetland, wastewater, water quality.

Keywords

carbon dioxide, dinitrogen, methane, nitrous oxide, reedbed, seminatural wetland, wastewater, water quality