What are the potential consequences of groundwater over-extraction on surface waters?

Groundwater over-extraction can have significant effects on surface waters, particularly in relation to the base flow of rivers and streams. Base flow refers to the portion of river flow that is sustained by groundwater discharge, often during periods of little to no precipitation. When groundwater is excessively withdrawn, the overall water table can decline, which, in turn, reduces the amount of water that naturally seeps into rivers and streams. This reduction in base flow can lead to lower water levels in these surface water bodies, impacting aquatic ecosystems, water availability for other uses, and potentially leading to negative effects on water quality.

The interplay between groundwater and surface water is crucial; when groundwater levels drop, there may be less water available to maintain the flow of rivers, especially during dry spells. This phenomenon highlights the relationship between groundwater resources and surface water levels, making the option of reduced base flow leading to lower water levels the most accurate consequence of over-extraction.