Stormwater contamination of urban estuaries. 2. Testing a predictive modelof the build-up of heavy metals in sediments

We describe the results of a sampling program to test a simple, management- oriented, predictive model of the build-up of contaminants (Cu, Pb, and Zn) in sediments in sheltered estuaries. The model described in detail in a co mpanion paper, is generally applicable to these environments but its develo pment and testing is described for two urban estuaries in Auckland, New Zea land. There was good agreement between observed concentrations of metals an d those predicted by the model. The model predicted larger concentrations w ithin a defined settling zone at the upper end of the estuary than outside this zone, and such a difference was detected for bad and zinc. Differences in concentrations of metals were detected among locations several hundreds of meters apart, with increasing concentrations from downstream to upstrea m locations. These patterns were apparent above smaller scale variation amo ng and within sites 10s of meters apart within each location. This small-sc ale variation did not conform to any obvious patterns. For example, there w ere no clear patterns in the metals distributions in sediments among differ ent shore heights. Patterns of contaminants distributions found in the pres ent study may be generalized to similar urban estuaries in other parts of t he world through their correspondence to those derived from the model, whic h is based on general assumptions and principles.