Heavy metal composition in stormwater and retention in ponds dependent on pond age, design and catchment type

Abstract

Heavy metals have toxic effects on flora and fauna in the aquatic environments and are of great concern in stormwater. Heavy metal runoff was studied in 37 stormwater ponds in Denmark with varying heavy metal load, catchment type and pond design. The studied metals were Cu, Cr, Cd, Pb, Ni and Zn. The concentrations varied considerably depending on the catchment type, with the highest concentrations coming from industrial areas and the lowest from uncultivated and rural areas. Ponds can effectively remove heavy metals in particulate forms through sedimentation processes, but the dissolved forms are more difficult to retain. The removal efficiency in the ponds varied considerably, with the highest retention of Pb, Ni and Zn due to higher particulate fraction. The retention increased with increased pond volume-to-reduced catchment area ratio. In addition, the pond age affected the efficiency; whereas ponds less than 1–2 years efficiently removed all metals, 30–40-year-old ponds only removed Pb, Ni and Zn, but steeply decreasing over the years. Physical parameters such as pond size, age and sedimentation patterns were found to play a more significant role in the removal compared with chemical parameters such as pH, oxygen and organic matter. Input of metals to the ponds was reflected in the sediment content, but not significantly for all heavy metals probably due to low or varying retention caused by mineralization and re-suspension. The heavy metal concentration in the outlets was reduced to non-toxic levels, except for Cu and Cr at a few study sites.

Keywords:

• urban runoff
• sedimentation
• water quality
• xenobiotics
• ponds

Acknowledgements

We are grateful to the supply company Arwos, which owns the studied stormwater ponds, for fruitful cooperation during this study by providing all kinds of background data and information. We thank laboratory technicians at University of Southern Denmark for their invaluable help with the chemical analysis. The study was supported by Centre for Lake Restoration (CLEAR, Denmark)– a Villum Kann Rasmussen Centre of Excellence project, an industrial/commercial PhD project (Melanie J. Sønderup) granted by the Danish Ministry of Science, Innovation and Higher Education FI case number 11-109519 and an Oticon Scholarship Award granted to Anna Grudinina.