Ecohydrology and stormwater nutrient attenuation of constructed wetland in Western Australia

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T. Adyel, A. Conti, J. Coletti, C. Ocampo, M. Hipsey, C. Oldham

Wednesday 1 july 2015

9:30 - 9:45h at Asia (level 0)

Themes: (T) Hydro-environment, (ST) Ecohydraulics and ecohydrology

Parallel session: 8G. Environment - Impact

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The present study investigated ecohydrology and urban stormwater nutrient attenuation of Anvil Way Compensation Basin (AWCB) of Western Australia. This constructed wetland enjoys stormwater runoff through main inlet and an ungauged drain plus groundwater input, and discharges at main outlet. The hydrological assessment establishes a basic water balance for the wetland from June 2012 to December 2013. Volumetric contribution from ungauged areas (drain and groundwater) is large (40-80%) for small and frequent rainfall events, particularly between the spring and summer season, and 13-27 % for mid-size to large rainfall events. Concentration of NH3, NOX, TKN, DON, TN, FRP and TP at outlet is compared with targets guideline of freshwater ecosystem. TN complies with the targets on most of the sampling occasions, while AWCB fails to reduce TP concentration below the target. Several limitations i.e., the presence of ungauged inputs and lack of flow data, are encountered to quantify the nutrient attenuation. Therefore an alternative approach i.e., standardized delta concentration (SDC) is proposed to calculate and describe nutrient attenuation. SDC depends on nutrient species, season, wetland restoration and input (main inlet or ungauged drains). Positive SDC arises most of the time when the influence of ungauged drain flows considered as being equal to the main inlet. The relative SDC of inorganic dissolved fractions of N (NOx and NH3) is higher than total (TN) and organic (DON) fractions. SDC of inorganic N and TP is more effective in summer and winter, respectively. Nutrient attenuation also increases after reconstruction of AWCB. Sediments and macrophytes of AWCB accumulate or uptake significant mass of nutrient. Overall findings to be used to understand nutrient attenuation processes and optimization of wetland function.