The use of sedimentary metal data in predictive modelling of estuarine contamination, assessment of environmental condition and pollutant source identification (Narrabeen Lagoon, Sydney, Australia)

Narrabeen Lagoon is recognized as an Intermittently Closed and Open Lake or Lagoon (ICOLL) and is the largest coastal lagoon (2.2 km(2)) in the Sydney metropolitan region. The catchment (53 km(2)) supports five major river systems, and land use comprises of 56% residential, 42% parkland and 2% light industry, commercial, hospital and education. An initial screening environmental assessment was undertaken using sedimentary metals to determine the magnitude of anthropogenic change and level of ecological risk posed by these contaminants. Results illustrated an unusual example of an estuary significantly influenced by human-induced change, but exhibiting minimal ecological risk. This anomaly was due to high anthropogenic metal concentrations in the fine fraction of surficial sediment, which was considerably diluted by abundant metal-poor coarse material resulting in reduced adverse ecological impact for total sediment. Predictive modelling to 2020 suggested that Pb concentrations will decline and Cu and Zn levels will increase slightly. Modelling of river discharge and analyses of fluvial sedimentary metals suggested stormwater derived from the most urbanized catchments and a major roadway combined with poor flushing explained surficial sediment metal distributions in the lagoon.