Karst Landscapes: These regions are characterized by rapid subsurface drainage through limestone and cave systems. They account for approximately 20% of the Earth's land surface, 25% of the continental United States and 45% of the area east of the Mississippi River. Approximately 40% of the U.S. population relies upon karst aquifers for drinking water.

Karst Topography

Formed by solution of limestone; usually in humid areas where groundwater is slightly

acidic and undersaturated with respect to calcite.

Generalized equation:

CaCO₃ + (H+ + HCO₃-) ---à Ca²⁺ + 2HCO₃ ----à H₂O + CO₂

Calcite + carbonic acid Calcium ion + bicarbonate ion

Development of Karst Landscape

Groundwater percolates through limestone along joints and bedding planes.

Solution activity creates caverns at or below water table.

Joints act as conduits for water in cave networks.

So, caves and passageways lie along joints.

Features of Karst Topography include:

Caves, Sinkholes, Springs, Karst Valleys, Solution Valleys, Disappearing Streams, Deeply Entrenched Permanent Streams

Groundwater Contamination in Karst Regions

Surface waters get into karst aquifers very quickly along joints, fractures, sinkholes, etc.

Once in the caves, water travels very quickly underground in cave streams.

Karst regions typically have thin soil cover, so contaminants are not filtered out before percolating water gets to the water table.

Groundwater in regions with thick soil cover (e.g. western Oregon, Pennsylvania) generally have better quality groundwater:

Microbes in the soil “eat” some of the petrochemical wastes and other chemicals

Silt and other material gets filtered out as groundwater moves through pore spaces in sediments.

Groundwater moves more slowly, allowing more filtration