Geochemical impact of urban development on fragile freshwater wetlands

Urbanization is associated with increased cover of impervious surfaces, which poses significant challenges to freshwater ecosystems globally. Implications of catchment urbanization include altered natural hydrology, erosion, weed invasions and modified water chemistry. Blue Mountains Upland Swamps are sensitive freshwater ecosystems located in the Blue Mountains region in south-eastern Australia. They have high conservation value as they are located within a World Heritage Area, are a listed 'endangered ecological community' in Australia and contain endemic and endangered flora and fauna. Water chemistry was assessed in four naturally vegetated and four urban swamps. Urban swamps had higher impervious cover and modified water chemistry, with elevated pH, electrical conductivity and major ions compared to non-urban swamps. Water in urban swamps had elevated calcium, potassium and bicarbonate compared to non-urban catchments, by 19.8, 5.2 and 10.3 times respectively. Although further research is needed, we hypothesize that common concrete materials, particularly drainage infrastructure, strongly influenced differences between urban and nonurban catchments. This adds to growing international research highlighting the potential role of concrete in modifying urban water chemistry due to gradual dissolution and mobilization of ions. In an increasingly urban world, consideration of the ecological consequences of urbanization is required to guide future management approaches.