Metals, nutrients and total suspended solids discharged during different flow conditions in highly urbanised catchments.

Stormwater discharged from highly urbanised catchments on the southern shore of Sydney estuary, Australia, has been identified as the primary source of contaminants responsible for ecological degradation and reduction in recreational value of the waterway. Effective management of this pollution requires knowledge of contaminant loads associated with various stormwater flow conditions in three highly urbanised catchments in Sydney estuary catchment. The majority (>90%) of metal (Cu, Pb and Zn) and total suspended solid annual loads were contributed during high-flow conditions (>50 mm rainfall day(t1)), whereas ≤55% of TN and ≤21% of total phosphorus were contributed to annual loading by dry weather base-flow conditions. All flow conditions posed an in-stream ecological threat because contaminant concentrations exceeded water quality guidelines for all analytes measured, except Pb. Irregular, temporal variability in contaminant concentrations associated with base-flow (within day and amongst days), high-flow (amongst events) and irregular discharges indicated that contaminant contributions in stormwater were strongly controlled by human activity in the three catchments. Significant variation in contaminant concentrations under all flow conditions revealed unique chemical signatures for each catchment despite similarities in land uses, location and geology amongst catchments. These characteristics indicate that assessment and management of stormwater pollution needs to be conducted on an individual-catchment basis for highly urbanised regions of Sydney estuary catchment.