Answer based on context:

The iron concentration in the Lackawanna River near Coxton Road ranged from less than 1.21 to 10.5 milligrams per liter, with an average of 3.98 milligrams per liter. The amount of manganese ranged from less than 0.199 to 1.35 milligrams per liter, with an average of 0.67 milligrams per liter. The aluminum concentration ranged from less than 0.5 to 0.664 milligrams per liter. The pH ranged between 6.5 and 6.7, with an average of 6.58. The acidity concentration was typically 0, but once reached 15.4 milligrams per liter. The alkalinity concentration ranged from 24 to 68 milligrams per liter (with an average of 44.37 milligrams per liter). The sulfate concentration ranged from 30.2 to 221 milligrams per liter, with an average of 104.78 milligrams per liter.

Which does the Lackawanna River near Coxton Road have a lower average concentration of, iron or manganese?
manganese