Evaluating the relative importance of stormwater for nutrient and metal contamination to the urban, groundwater dependent Yellagonga Wetlands, through wetland budgeting
Wetlands provide numerous ecosystem services and can be utilised as pollutant sinks, however excessive contamination of wetlands can induce adverse effects to wetland ecology and lead to degradation of its values. Runoff from precipitation mobilizes contaminants from impervious surfaces which are, in some case, transported directly to wetlands through stormwater drainage. Urban stormwater can be a significant source of contaminants to wetlands, although its overall importance needs to be assessed for each wetland individually. Wetland budgeting is a management tool used to evaluate the relative importance of contaminant sources to wetlands, by comparing contaminant loads. Environmental management of the Yellagonga Wetlands, a chain of groundwater-dependent wetlands located in southwest Western Australia, has previously focused on limiting stormwater flow to the wetland park, to minimise contaminant inputs. While this management approach was based on the notion that relatively high contaminant concentrations measured in stormwater represented high loading, this assumption was not formally verified. The broad aim of this research was to evaluate the relative importance of stormwater supplied by all major sources (atmosphere as well as surface-, ground-, and stormwater) of the Yellagonga Wetlands (Lake Joondalup, Wallubuenup Swamp and Beenyup Swamp). This broad aim was achieved by comparing annual input loads of total and dissolved nutrients (N, P) and metals (Al, Cr, Co, Cu, Cd, Hg, U, and Zn)., The study also analysed stormwater for pharmaceuticals to assess whether stormwater transports other harmful substances to the wetlands. A mixture of existing data from a variety of sources was combined with original data to calculate input loads. Specifically, surface water (quantity), atmospheric fallout (quality), and stormwater drainage (quality and quantity) were determined by this study, while the remaining components were derived externally. Budgeting indicated that atmospheric fallout contributed the overall highest masses of contaminants to the wetlands, followed by groundwater and surface water while stormwater was overall least important. These results suggest that continued management focus on the reduction of contaminant loads from stormwater may not significantly impact water quality of the wetlands, however targeting of air quality and groundwater could be beneficial for their ecological health and functionality. Contrary to common belief, the results also indicate that the excess of filterable reactive phosphorus (FRP) entering the southern section of Lake Joondalup was derived from Wallubuenup Swamp, rather than Beenyup Swamp. This finding may advance the FRP source investigation and could help lowering the chances of eutrophication and algal blooms at Lake Joondalup.
Wetland budgeting, urban wetlands, wetland contamination, contaminant loading, stormwater, Environmental Sciences, Life Sciences
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Edith Cowan University, Research Online, Perth, Western Australia