The most likely reason why the pond does not greatly reduce downstream metal concentrations is the fact that many non-point sources of metals exist downstream of the pond. Any attenuation of metal concentrations by the pond is negated by sources downstream. In fact, the sediment contained in the pond does not have an abnormally high metal content. Another complication with sediment bound metal transport in South Creek is sediment residence times. Most sediment does not reside in the channel for long periods of time, thus reducing the absorption time of metals by the sediment.
South Creek is very flashy in nature and much of the channel is concrete.
This scenario creates an efficient conduit for material carried by the stream. Any sediment deposited in the channel is most likely completely washed from the system during the next flow event. It could be suggested, by looking at the trend charts, that metal enrichment in South Creek is nearly syngenetic in nature. The metals get deposited with the sediment and are washed out of system during the next event. The sediment does not remain in the channel where it has a chance to absorb metals from subsequent flow events.