|Percent abundance of selected
pollen taxa and metal concentrations from a sediment core
the middle of Lake Pontchartrain. Near 120 cm (4ft) beneath the lake bottom
the pollen assemblages change from
pine/oak pollen (common Gulf coast) to
herbaceaous species that indicate human colonization and land clearing.
At this time the background concentrations of heavy metals jump to higher
levels, an indication of human influence.