Impact of concrete on urban stream chemistry and ecosystems

Abstract

Urbanisation has major effects on nearby streams, particularly on sensitive waterways such as those in the Sydney and Blue Mountains regions. Urban streams exhibit a distinct pattern of degradation, including elevated pH, elevated electrical conductivity, and elevated concentrations of ions and heavy metals, such as calcium, potassium, bicarbonate, chromium, copper, and lead. Recent research indicates that the weathering of urban concrete infrastructure impacts nearby stream chemistry in a manner consistent with this distinct urban geochemical stream signature. However, data explaining the source of these contaminants is limited and there is little research regarding how these chemical differences will affect stream ecosystems. This study investigated the continued effects of urbanisation on sensitive, endangered, high conservation ecosystems known as Blue Mountains Upland Swamps. The naturally acidic and dilute water chemistry of these ecosystems means that they are ideal for examining the urban geochemical signature seen in streams across the world. Water, sediment and plant tissue chemistry was examined for four naturally vegetated and four urban Blue Mountains Upland Swamps, to assess the extent of the impact of urban development on these fragile ecosystems. Additionally, through conducting water recirculation experiments, this study aimed to provide further experimental verification of the link between concrete and changed stream chemistry. Finally, this study examined the effect of urban water on the growth and tissue content of a prevalent weed species, with the aim of assessing the broader ecosystem effects that geochemical modification of urban streams may have. Findings of this study indicate that the water chemistry of urban BMUS is significantly degraded. Results also demonstrate the potential for concrete materials to significantly modify water chemistry and leach numerous metal contaminants. Furthermore, findings indicate that concrete-exposed water in some way gives a growth advantage to invasive species. Overall, results of this study indicate that the weathering of urban concrete infrastructure likely plays a key role in the degradation of urban streams, affecting water and sediment chemistry. It is therefore recommended that concrete materials be used with caution in settings that may be exposed to water and that alternative materials be sought, particularly in catchments of fragile or high conservation waterways. Additionally, future water sensitive urban design principles should take the chemical modification of urban streams and the potential contribution of concrete into account.

Date of Award	2019
Original language	English