At Powdermill Nature Reserve, differences in stream quality between unpolluted Powdermill Run and acidified Laurel Run adjacent to it have provided an excellent opportunity to study the possible effects of acid mine drainage pollution (AMD) of headwater streams on the demographics, behavioral ecology, productivity, and survivorship of populations of an obligate riparian songbird, the Louisiana Waterthrush (Seiurus motacilla; LOWA).

The LOWA feeds mostly on aquatic macroinvertebrates, many of which cannot survive or reproduce in acid-polluted streams. Powdermill Run is a pH-neutral stream, has abundant macroinvertebrates, and supports diverse fish populations. Laurel Run, which is impacted by drainage from two abandoned coal mines, is acidic (pH 4.0-5.0), with high levels of dissolved aluminum and iron, has reduced macroinvertebrate diversity and density, and supports no fish.

Studies were begun in 1996 by Robert S. Mulvihill, Field Ornithology Projects Coordinator to determine whether or not pollution of Laurel Run affects the breeding density, reproductive success, foraging behavior, and/or survivorship of Louisiana Waterthrushes by reducing the diversity, abundance, and/or biomass of invertebrate prey available to them during the breeding season. Preliminary results of the study showed that the number of territories, pairing success, and nesting densities of LOWAs nesting along the acidified stream were lower. In the first year, we found only four territories and 50% pairing success in Laurel Run compared to 11 territories and 91% pairing success for the same reach length of Powdermill Run (see Mulvihill, R. S., 1997, The Louisiana Waterthrush and Our Mountain Streams, Carnegie Magazine May/June:62-65).

The study was continued in 1997 with partial funding from Pennsylvania's Wild Resource Conservation Fund (WRCF). At the end of 1997, two sources of AMD on Laurel Run were partially remediated using passive treatment technologies (see Gangewere, R. J., 1998, Saving Our Mountain Streams, Carnegie Magazine January/February:8-12, 36-39). Funding from WRCF for fieldwork in 1998 enabled us to continue to monitor changes in the Laurel Run LOWA and macroinvertebrate populations in response to anticipated improvement in stream quality resulting from these treatments. Additional funding for the LOWA study in 1999 and 2000 came from the Loyalhanna Watershed Association and the Rea Research Fund of Carnegie Musuem of Natural History.

Remediation of Laurel Run is ongoing and before long we expect to see LOWA numbers there increase to levels similar to those observed on Laurel's unimpacted sister stream, Powdermill Run, signalling that the ecological balance of this picturesque stream has been substantially restored after more than 50 years of degradation.