Which risk significantly increases in alluvial aquifers when over-extraction lowers the water table?

💡 Explanation

Over-extraction lowers the water table exposing arsenic-bearing minerals to oxidation via unsaturated flow processes. This is oxidation because oxidation reactions increase arsenic ion mobilization, therefore, arsenic concentrations rise rather than remaining stable due to saturation.

• Which consequence results when substantial airborne tephra reaches altitudes above freezing?
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