Stormwater wetlands for the enhancement of environmental ecosystem services: case studies for two retrofit wetlands in Brisbane, Australia

Constructed stormwater wetlands are examples of 'blue-green' ecological engineering in the urban environment providing a range of ecosystem services. A study was undertaken in Brisbane, Australia to examine the enhancement of environmental ecosystem services in 2 retrofit wetlands. Originally concrete drainage channels in existing residential catchments, a series of wetlands and ponds were created i.e. green infrastructure in a brownfield setting. Boardwalks, pathways and interpretive signage were incorporated into the design. Golden Pond wetland was only 0.2% of the catchment whereas Bridgewater Creek - Bowie's Flat wetland was 0.4% of the catchment. The larger 0.8 ha Bridgewater Creek wetland had an overflow bypass channel. Water quality (suspended solids and nutrients) and the diversity of aquatic macro invertebrates were monitored for 2-4 years after construction. During storm events suspended solids increased at Golden Pond due to resuspension from the high velocities in this small linear flow system. Resuspension was minimised at Bridgewater Creek due to the by-pass channel. During dry weather suspended solids in both wetlands increased due to resuspension from the activity of waterbirds. Both wetlands were effective in reducing nutrient concentrations especially NOx-N and PO4-P, attributed to biological uptake; but during dry periods NH4-N increased within the system. The concept of irreducible background concentrations in wetland systems is discussed. Open water and aquatic vegetation provided habitats for macroinvertebrates. Species richness increased by more than 50% in both stormwater wetlands, compared to the concrete drains. Wetland sizing and design are essential parameters for water quality improvement and biodiversity. (C) 2016 Elsevier Ltd. All rights reserved.