The effects of doubling limestone sand applications in two acidic southwestern Pennsylvania streams

Published source details Keener A.L. & Sharpe W.E. (2005) The effects of doubling limestone sand applications in two acidic southwestern Pennsylvania streams. Restoration Ecology, 13, 108-119.
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Summary

Acid deposition, a result of anthropogenic nitrate and sulphate emissions, is a serious form of pollution in aquatic habitats and is a prominent in many streams in industrial southwestern Pennsylvania, USA. Limestone sand application is considered a practical and relatively inexpensive acid water remediation technique, but questions remain about its effectiveness and potential negative effects on water quality and fauna. The effects of limestone sand additions in two chronically and episodically acidified streams in southwestern Pennsylvania was assessed. The main objectives were to evaluate the effects of doubling recommended limestone sand amounts on water quality and macroinvertebrates and to assess substrate changes resulting from limestone sand inundation.

Study sites: Two streams heavily affected by acid deposition, Bear Run and Rock Run in the Laurel Highlands of southwestern Pennsylvania were selected for limestone sand additions. Limestone sand remediation was initiated in June 1997 by annually applying limestone sand directly to the streams. In 2002 and 2003, limestone sand was applied twice per year (fall and winter), at rates twice the amount previously applied (see below). The Linn Run, a nearby episodically acidified stream, served as a reference stream.

Experimental design: Water quality (pH; total dissolved aluminum - TDA; and acid-neutralizing capacity -ANC) and macroinvertebrate data during the single application period (June 1999–January 2002) were compared to the data during the double application period (February 2002–March 2003). Three sites on Bear Run (located approximately 3,500 m downstream, 300 m downstream and 50 m upstream of the sand application, were sampled for water quality and macroinvertebrates. Two sites on Rock Run, one approximately 300 m downstream and one upstream of the sand application, were also sampled for water quality and macroinvertebrates. A site downstream of the confluence of Rock and Linn runs was sampled for water quality only.

Limestone addition: Approximately 23 and 6 tonnes of limestone sand were added annually to the headwaters of Bear and Rock runs, respectively, from 1999 to 2001. In 2002, amounts were doubled. Macroinvertebrate communities were assessed from 1999 to 2003 at points above and below the sand additions on Bear Run and Rock Run. Small, plastic substrate samplers were used to assess sand substrate effects.

Water quality: Doubling the quantity of annual limestone sand application resulted in significantly improved pH and acid-neutralizing capacity. However, total dissolved aluminum increased significantly downstream (α≤ 0.05).

Macroinvertebrates: Overall, there were no statistically significant differences at any site when comparing macroinvertebrate densities or diversities during the single application period to those from the double application period. There was however an increase in acid-sensitive taxa at the sampling site 3,500 m downstream in Bear Run, including eight genera of mayflies, Ephemeroptera. There was also a decrease in several acid-tolerant genera at all treated sites during the double application period. Substrate sampler data indicated a significant negative relationship between amount of sand deposited and density of macroinvertebrates.

Conclusions: In Bear and Rock Runs, a twice-annual application of limestone sand at double the recommended annual amount produced mixed water quality improvements. It significantly improved with respect to pH and ANC at Rock Run, but TDA concentrations downstream were generally higher compared to during the single application period in both streams. Sand addition had a negative effect on macroinvertebrate density 300 m downstream of application sites, with density appearing to be lowered by additional sand application. The presence of acid-sensitive species following limestone sand addition noted 3,500 m downstream on Bear Run was a positive result, although overall diversity did not improve. A twice-annual application of limestone sand at double the recommended amounts did not appear to consistently improve water quality or macroinvertebrate numbers, however, increased stream flow on Bear Run during the double application period may have influenced the results.

These mixed affects on water quality and macroinvertebrates were reasonably consistent with that found in earlier work, and call into question whether the use of limestone sand in the restoration of chronically and episodically acidified waters is worthwhile.

Note: If using or referring to this published study, please read and quote the original paper. Please do not quote as a www.conservationevidence.com case as this is for previously unpublished work only. The original paper can be viewed at: http://www.blackwell-synergy.com/journal.asp?ref=1061-2971