Leaf Litter Decomposition in a Reservoir Affected by Acid Mine Drainage

Abstract

The effects of acid mine drainage on the decomposition of vascular plant material in a reservoir were compared at 3 sites: a control site with no acid mine drainage (average pH = 6.3), an experimental site with dilute acid mine drainage (average pH = 5.7) and an experimental site near the acid mine drainage source (average pH = 3.7). The decomposition rate (loss of ash-free dry weight from litter bags) of leaves from 3 types of trees [Cornus florida, Quercus alba, Betula lutea] and a rush [Juncus effusus] differed significantly between leaf species and between sites. For all leaf species, the decay rate coefficients (k) for the control site were at least twice those for the most severely affected experimental site. Heterotrophic activity, measured with 14C glucose, was depressed at both experimental sites as compared to the control site. Numbers of bacteria were about 1010 cells per gram dry detritus, and did not differ significantly between control and experimental sites. Both microbial activity and the process of leaf decomposition were inhibited in a region close to the source of contamination although the degree of inhibition decreased as the acid mine drainage was diluted within the reservoir.