Influence of Acid Precipitation and Liming on Leaf Breakdown in Virginia Streams

Acid precipitation has long been a problem in the eastern United States. We evaluated the impact of acid precipitation and the efficacy of liming on leaf breakdown in 4 streams in western Virginia. These streams have been chronically acidic and each stream has been limed for nearly a decade. At 10 sites distributed above and below liming stations on each stream and in 2 additional sites in a naturally buffered stream we incubated 18 packs containing 8g of Chestnut Oak leaves. Packs were collected in triplicate from each site at monthly intervals from November 2003 to May 2004. Mean pH ranged from 4.9 upstream of liming stations to 6.8 in the naturally buffered stream. Liming raised pH of the streams by 0.1-0.6 units. Leaf breakdown rates ranged from 0.0015 day-1 upstream of liming stations to 0.0058 day-1 in the naturally buffered stream. Breakdown rate was generally faster downstream of liming sites and differences in breakdown rate among sites was largely explained by variation in pH (r = 0.67, p = 0.001). Slower breakdown was at least partly due to reduced microbial respiration on leaves in acidic sites. Overall, liming was moderately effective in restoring leaf breakdown in acidified streams.