Impact of concrete on riparian ecosystems

Throughout the world, concrete is used extensively in urban development. Due to its convenience and durability, most paths, carparks, dams, and even drainage systems are constructed from concrete. However, recent studies indicate that concrete significantly affects water chemistry and that concrete infrastructure may have a major effect on the chemistry of nearby streams. This is particularly relevant for sensitive waterways such as those in the Blue Mountains region in Sydney, Australia. This study aimed to investigate the chemical changes associated with concrete exposure by conducting water recirculation experiments. Water collected from a pristine Blue Mountains Upland Swamp (BMUS) was mildly acidic (average pH of 4.65) with a low electrical conductivity (EC of 57.99μS/cm) before concrete exposure. After the water was continuously recirculated through a concrete pipe for 120 minutes, pH and EC increased significantly, to 7.87 and 137.72μS/cm respectively. Significant increases in concentrations of ions such as bicarbonate, calcium and sulphate were also observed. Results verify previous findings that concrete significantly and rapidly affects water chemistry and support the hypothesis that concrete plays a significant role in the chemical differences seen between urban and non-urban waterways. Results also indicate that concrete is a source of metals such as copper, chromium, strontium, titanium, and lithium. Furthermore, this study aimed to investigate whether these metals have the potential to affect ecosystems more broadly. Salix babylonica, a common invasive plant species in the Sydney region, was grown in pristine BMUS water and concrete-recirculated BMUS water. Plants grown in concrete-recirculated water had significantly greater new growth and the tissue of these plants was significantly higher in concentrations of barium, copper, lead, manganese, and strontium. As metals in the water appear to be moving into plant tissue, results suggest that these metals are bioavailable and thus have the potential to move into higher trophic levels and the ecosystem more generally. Further investigation is required to determine how far these metals may permeate the food chain.