Anthropogenic effects on the chemical characteristics of freshwater streams near Sydney, Australia, during low flows

Streams near Sydney were sampled for 18 water quality parameters at 90 sites in 86 different waterways during low flow conditions. They were generally low in salinity, soft, of poor buffering capacity and dominated by sodium and chloride, consistent with their location in a coastal basin with a high sandstone content. Calcium, magnesium and (bi‐)carbonate dominance, or at least co‐dominance, occurred in a number of cases where other rocks, such as igneous and metamorphic formations, were present. Multivariate analyses indicated three groups, separated primarily by levels of dissolved nutrients, trace metals, turbidity and colour. Chemical groupings were associated strongly with the type and level of catchment development. Streams in areas relatively unaffected by human influence had notable uniformity in chemistry; any observed variability was derived mostly from the major ions, reflecting geological influences. In comparison, streams in catchments affected by human developmental activities were highly varied. Since very high concentrations of nutrients and metals were not frequent in samples, the findings were consistent with occasional or localized elevation of contaminant levels. Climatic trends ensured the sampling period was dominated by low stream flow conditions, that is, conditions not favourable for an assessment of the influence that flow and discharge have on surface water chemistry.