PW15 Environmental Toxicology, Environmental Assessment
Exhibit Hall
8:00 AM - Wednesday
(PW249) Mortality of brook trout in response to timber-harvest induced acidification in streams of the Catskill Mountains, NY, USA.
Baldigo, B.1, Burns, D.2, Murdoch, P.3, 1 U.S. Geological Survey, Troy, NY, USA2 U.S. Geological Survey, Troy, NY, USA3 U.S. Geological Survey, Troy, NY, USA
ABSTRACT- The effects of clearcut and partial-forest harvest on the toxicity of surface waters were evaluated by assessing water quality and mortality of caged brook trout from 1994 to 2000 in three small streams of the Catskill Mountains of New York State. Harvests in two subbasins of one stream removed 73% of tree basal area (BA) in a clearcut watershed during winter 1996-97, and 5% of tree BA in a timber-stand-improvement watershed during winter 1995-96 and fall 1996. A stream site below the confluence of the two subbasins had 14% reduction in tree BA within its watershed. Another stream in an uncut watershed served as a control. Water quality and trout mortality were significantly affected only at the stream in the clearcut watershed following tree harvest. Acidity and concentrations of nitrate and inorganic monomeric aluminum (Alim) increased sharply at the site during high flows after the first growing season -- during fall 1997 and spring 1998. Acid- Alim episodes were most severe during this period and decreased steadily in magnitude and duration thereafter. Stormflow chemistry generally returned to preharvest conditions by spring 2000. At the clear-cut site, all trout died within seven days during spring 1998, 85% died during 30 days in spring 1999, and none died in 30 days during spring 2000. Only background levels of mortality (<15%) were observed at the other three sites during all test periods. The lack of increased mortality in partially harvested watersheds indicates that TSIs are unlikely to harm fisheries of the region if harvests are limited in intensity or extent. The effects of clear cuts on stream ecosystems, however, are of great concern because many species of fish are more sensitive to acid and aluminum than brook trout, and both can increase severely following tree harvest.
Key words: acidification, clear-cut, trout, aluminum