Abstract
We assessed physicochemical and biological continuity in an 800-m reach of a small (<2 m wide) headwater stream during 2010 and 2012 in the northcentral U.S. Dense riparian canopy covered the first 600 m of stream reach, was lacking in an approximately 100-m portion due to historical (>10 years previously) agriculture, and returned in the last 100 m of the study area. Reflecting this difference, the forested area had less sunlight penetration to the water level and greater volume of woody debris in the stream. There was no difference in specific conductance or pH among sites. Water temperature was lower in the upstream forested sites and higher in the non-forested site and those downstream of it. Dissolved oxygen exhibited a reciprocal trend with temperature. The non-forested site exhibited an abrupt change in biological continuity as indicated by a decrease in benthic macroinvertebrate and adult caddisfly shredder abundance, an increase in filtering collector and scraper abundance, a decrease in trout abundance, and an increase in both total and warm-water fish species. The stream returned to its previous state when canopy returned downstream. Both years of the study yielded similar results. Our results indicate that abrupt changes in riparian canopy can lead to similarly abrupt changes in biological continuity, often within a relatively short (100 m) distance.