A 0.23-ha pilot wetland was constructed to examine its effectiveness for the control of nonpoint source pollution (NPS) from a 7.42-ha agricultural watershed in Korea. This research emphasised the removal patterns of particulate and dissolved forms of pollutants on both dry (base flow) and wet days (storm flow). The hydraulic loading rates were high on rainy days, with an average value of 0.78 m/day, but around 0.08 m/day on dry days. Particulate forms of pollutants, such as TSS, COD and TP, were removed to a greater extent on wet days due to sedimentation. On wet days, the incoming concentrations of NH4-N and soluble reactive phosphorus (SRP) were higher than during dry days, and can be partly retained via filtration and adsorption as they go through the wetland. The retention of TP and TSS on dry days could be affected by short antecedent dry days (ADDs), which will cause frequent hydraulic fluctuations in the wetland. Nitrogen removal is not influenced by this condition, with an average retention of around 20% on dry days, higher than the 6% removal on wet days.

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