The use of sediments to detect human impact on the fluvial system

Sediments have been used to detect sources of contamination in a catchment of the Port Jackson (Sydney Harbour) estuary and to evaluate the effects of different land-use practices on the fluvial environment. Mean enrichment (mean concentrations over pre-anthropogenic background) of size-normalized (<62.5 pm) aquatic sediment is 10 x for Cu, 20 x for Pb and 90 x for Zn adjacent to industrialized areas and 2 x, 7 x and 7 x, respectively for these metals in highly urbanized subcatchments. Diffuse sources contribute minor metals to fluvial sediment even in the most underdeveloped subcatchment (2 ×, 3 x and 3 x for Cu, Pb and Zn respectively). Organochlor- ine pesticide residue concentrations parallel heavy-metal trends due to a common mixed industrial base. Effects-based sediment criteria suggest that some adverse biological impacts are probably occurring in streams flowing through the industrial areas. This interpretation is supported by sequential extraction data which show that a moderate proportion of total heavy metals, especially Zn, is associated with the more bioavailable exchangeable/ adsorbed phases in these aquatic sediments. High total suspended solid loads in water downstream of one of the industrial centers, and high particle-bound Cu and Pb concentrat- ions, suggest that most contaminants exiting the catchment do so in association with the solid phase.