Monitoring the Influence of Acid Deposition On Soils in the Daniel Boone National Forest, Kentucky, USA.

Emissions of nitric and sulfuric acids began to exceed natural rates world-wide in the mid-20th century due to increased combustion of fossil fuels.  Today, emission rates are as high as eight times greater than natural rates.  Forest soils in many parts of the U.S. have become increasingly acidic during this time.  The Clean Air Act was enacted in 1970 to combat the problem of acid deposition, but air quality problems persisted. Between 1996 and 1998 a study was undertaken to examine the quality of water that infiltrated through forest soils found on the Daniel Boone National Forest (DBNF) of Kentucky to determine whether acid deposition is a problem in the Cumberland Plateau region. The study showed that deposition often exhibited low pHs which resulted in a shift in the mineral phase controlling the activity of Al and SO₄ in solution and an acceleration of base cation depletion. The study suggested that continued acidic inputs could, over time, become a major hindrance on forest productivity. A follow-up study was initiated in 2012 to reevaluate soils and water on the forest and document changes over the fifteen year period. Soil pits were excavated and sampled by horizon at four ridge-top locations within the DBNF. Pan lysimeters were installed at two depths (30 and 60-cm) in the wall of the pits and the pit was backfilled with native soil. Soil solution samples were collected from the lysimeters on a bi-weekly basis and analyzed for pH, conductivity, SO₄, NO₃, NH₄, Ca, Mg, K, Na, Al, Cl, and alkalinity.  pH results continue to show solution acidification over time, suggesting that base cations on soil exchange complexes and buffering ability of the system are still lacking.