Quantifying nutrient removal processes within a constructed wetland designed to treat urban stormwater runoff

• Published in: Ecological engineering Vol. 2; no. 4; pp. 347 - 366
• Main Authors: Johengen, Thomas H., LaRock, Paul A.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.12.1993
• Subjects: Freshwater
• ISSN: 0925-8574; 1872-6992
• DOI: 10.1016/0925-8574(93)90003-X

Mesocosm enrichment experiments were used to quantify nutrient removal rates for various ecological components within a constructed wetland designed to treat urban stormwater runoff. Mesocosms isolated emergent macrophytes (Pontedaria sp.), floating macrophytes (Lemna sp.), sediments, and plankton. Experiments were performed by enriching concentrations of nitrate (NO3−), ammonium (NH4+), and phosphate (PO43−) to levels between 0.5 and 1.5 mg 1−1, and then following changes in the concentrations over time. Plant mesocosms produced the highest removal efficiencies avaraging 67, 87 and 62% per day for NO3−, NH4+, and PO43− respectively. However, removal efficiencies for sediment mesocosms averaged 52, 59, and 49% per day respectively indicating that much of the removal processes may have occurred at the substrate surface. In all mesocosm treatments, PO43− was removed at a much greater rate than needed to meet biological demands, and nutrients were removed at nearly the 2:1 N:P mass ratio in which they were added. Removal rates in mesocosm experiments were compared to rates calculated by mass balance for a storm which generated 12 days of flow through the marsh. Mesocosm results agreed closely with mass balance calculations for NO3− and PO43− but did not agree with NH4+ calculations. NH4+ concentrations in the stormflow were too low and removal rates for NH4+ may have been affected by internal production within the marsh.