Stratification and its consequences in two constructed urban stormwater wetlands

Sherif S. Ahmed, Wenming Zhang, Mark R. Loewen, David Z. Zhu, Tadros R. Ghobrial, Khizar Mahmood, Bert van Duin

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

Stratification in constructed urban stormwater wetlands is one of the fundamental physical processes that affect hydrodynamics, transport and fate of stormwater pollutants. Adverse effects of stratification include decreasing pollutant retention capacity, causing the water at lower depths to become anoxic, degrading water quality and increasing stress on the downstream aquatic communities. The current study reports on a comprehensive field monitoring program of stratification and hydrodynamics in two ice-free seasons (May – October) in two constructed urban stormwater wetlands in Calgary, Canada, with different inlet, outlet, morphometric and vegetation designs. Despite their small sizes of 0.5 and 1.2 ha and shallow water depths of 0.8 m, stratification was strong and persistent in the wetlands. The response of stratification and mixing to atmospheric forcings (e.g., air temperature, atmospheric instability, rainfall depth, wind speed) and the impact of design characteristics (inlet/outlet design, water depth, surface area and aquatic vegetation) were examined and discussed. Thermal stratification, defined as a vertical temperature gradient >1 °C/m, was found to be significantly higher (up to ten times) near the inlets and last longer (up to twice) than in the main cells and the outlet basins due to the relatively cold summer inflows. The wetland with twice the permanent water volume and surface area and half the length-to-width ratio had denser submerged aquatic vegetation, higher (by up to 2 °C) water temperature and more severe (up to eight times) thermal stratification. Strong densimetric stratification and low wind stress on the water surface caused hypoxic conditions near the bed, potentially adversely affecting water quality and downstream aquatic communities.

Original languageEnglish
Article number162179
JournalScience of the Total Environment
Volume872
DOIs
StatePublished - 10 May 2023
Externally publishedYes

Keywords

  • Aquatic vegetation
  • Hydrodynamics
  • Physical processes
  • Stormwater
  • Stratification
  • Water quality
  • Wetlands

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