Low cost limestone treatment of acid sensitive trout streams in the appalachian mountains of Virginia

Abstract

The method of single point, single application liming has been studied as a means of mitigating anthropogenic acid in trout streams in Virginia. Three critically acid sensitive streams were dosed with a total of five applications of limestone sand and monitored before, during and after the treatments to assess changes in water chemistry and biota. Limestone treatments of 8 to 50 tons (particle sizes 150–1000 μm), with the amounts based on sulfate deposition loading and existent stream water chemistry, were used to restore ‘lost’ acid neutralizing capacity (ANC). Contact time between the limestone bed in the stream bottom and the water was the limiting factor affecting the degree of treatment with bed length primarily controlled by the gradient of the stream at the dosing site. A single site application was able to restore approximately 2/3 of the ANC. Exponential fits of limestone consumption data were used to predict that treaments of similar streams would last from two five years before reliming was necessary. Both total and monomeric aluminum levels were reduced up to 50%, and aquatic biota increased below the treatment sites. Post-liming average values for the three streams were pH 6.66, 82.7 μeq L−1 ANC and 2.63 mg L−1 Ca. The average ANC improvement suggests that some 88% of the native trout streams in Virginia, which average 29 μeq L−1 ANC reduction from acid deposition, could be temporarily restored using single application liming.