Short-term response of physical habitat and fish to the addition of large woody debris in two Appalachian Mountain streams

Abstract

Large woody debris (LWD) was added to North Fork Stony Creek and North Prong Barbours Creek in southwest Virginia to inlprove fish habitat. The purposes of this study were to monitor stream channel response to the addition of LWD at a stream reach scale and at a local scale around individual logs, to evaluate changes in fish population parameters, and to observe microhabitat availability and use before and after L WD additions.

In low-gradient Stony Creek, LWD was effective in modifying fish habitat through the formation of pools, the structuring of poo1/riffle sequences, and the enhancement of channel complexity. New pools formed from the break up of continuous rime habitat, increasing the overall number of habitat units and decreasing mean surface areas. Total pool area increased for both treatment sections, while changing little in the reference section where no logs were added. Localized scour and fill was observed for crosssectional transects around individual logs, creating a more heterogenous environment than in areas without logs. In contrast, physical habitat changed little in moderate-gradient Barbours Creek after L WD was added.

An increase in the relative weight of brook trout in Barbours Creek suggested that although minimal channel changes were observed, logs may have increased channel complexity and cover, providing resting areas of lower velocities next to food pathways, which may have lead to decreased energy expenditure. Observations of microhabitat use revealed that unlike adult brook trout, juvenile brook trout used a limited range of depths and velocities. Adult brook trout shifted microhabitat use in response to changes in microhabitat available.

Low numbers of fish in Stony Creek may have been related to low pH, but numbers of adult brook trout found in each section increased in 1994. With improved water quality, I believe that fish abundance in Stony Creek would increase through time because of the improved habitat. Although few significant changes were observed for available microhabitat in Stony Creek, changes in physical habitat suggest that over time shifts in microhabitat would be apparent.