Summary

The chemical principles governing iron dissolution in groundwaters are reviewed. In the upper River Bure catchment in Norfolk the Chalk aquifer is covered by sand and gravel drift aquifers and a leaky till aquiclude. Iron contents of groundwaters are several mgl−1 beneath till, but less beneath valleys where the till is not present. The iron contents and redox potentials of chalk waters are related to groundwater flow in two separate circulation cells. In the larger cell, chalk beneath the higher parts of the catchment receives recharge which has high Fe and low Eh due to oxidation of pyrite in the drift formations. Iron contents in the chalk groundwater decrease with depth and towards discharge areas, probably reflecting precipitation of iron carbonate. Iron content decreases further where ground-waters discharge upwards beneath the Bure valley and mix with waters of the second circulation cell which occurs where the till has been removed by erosion. Oxygenated, iron-poor waters recharge the chalk beneath the upper parts of the valley sides and discharge through the valley floor. Mixing between waters in the two cells may cause precipitation of iron oxides. Similar flow patterns have been demonstrated elsewhere in East Anglia and it is likely that iron contents will generally be lowest where active groundwater circulation occurs beneath till-free valley floors.

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