Academic journal article The American Midland Naturalist

Hydrologic Context and Macroinvertebrate Community Response to Floods in an Appalacian Headwater Stream

Academic journal article The American Midland Naturalist

Hydrologic Context and Macroinvertebrate Community Response to Floods in an Appalacian Headwater Stream

Article excerpt

ABSTRACT.-The response of aquatic macroinvertebrates to two floods was examined in a 2nd-order stream draining a 132-ha watershed on the Fernow Experimental Forest in West Virginia. Floods with recurrence intervals of 18 and 12 yr occurred in February and May 1994. Benthic organic matter and macroinvertebrate abundance and community structure were affected by the floods. Most of the common macroinvertebrate taxa decreased in abundance 70-95% immediately following the February flood. For most physical and biotic variables, recovery to preflood levels was complete before the May flood (42 days) based on preflood levels. Shifts in community structure following floods were small compared to seasonal variation. By August following the May flood, few differences could be detected from August of the previous year. Taxa associated with organic matter accumulations such as leaf packs and organic debris dams were affected less by the February flood than were most riffle taxa; one common leaf pack taxa, Pteronarcys, increased in abundance in riffles following the flood. I attribute the rapid recovery of the benthic community to abundant refugia, including organic debris dams, deep interstitial habitat, and lst-order tributaries. Analysis of the long-term flow record for the Fernow Experimental Forest suggests that a probabilitybased hydrologic criterion for a flow disturbance is inadequate for Appalachian headwater streams.

INTRODUCTION

Stream macroinvertebrate communities vary in their resistance and resilience to floods and spates (Hynes, 1970). The response of stream communities to floods is hypothesized to be linked to the historic pattern of spatiotemporal heterogeneity in stream flow (Resh et al., 1988; Poff and Ward, 1990), which is largely determined by the interaction among watershed climate, geology and terrestrial vegetation (Ward, 1992).

For the most part, hypotheses about geographic and other sources of variation in macroinvertebrate community response to floods (e.g., Cushing and Gaines, 1989; Wallace, 1990) have not been tested due to limited available data. Compared to the arid western United States (e.g., Moffett, 1936; Siegfried and Knight, 1977; Fisher et aL, 1982; Molles, 1985; Grimm and Fisher, 1989; McElravy et al., 1989) there are few published accounts of the effects of floods or spates on the benthic fauna of headwater streams in the Appalachian Mountains.

Case histories from flood-impacted streams generally cannot be used to test complex hypotheses about the influence of extreme flows on benthic communities because there is little opportunity to control aspects of flood frequency, magnitude or timing. Nevertheless, opportunistic studies are still necessary since experimental approaches to evaluating the role of flow disturbance on benthic communities usually are feasible at somewhat arbitrary spatial and temporal scales. For example, rock turning or substrate raking treatments are patch scale disturbances (Giller et al., 1991), whereas natural floods affect stream communities at patch through watershed scales. Case histories can reveal the scale of physical and biotic events occurring during floods and provide the context for experimentation (Townsend, 1989).

In this paper I report the results of an opportunistic study of macroinvertebrate community responses to a winter and a spring flood in a forested headwater stream within the Fernow Experimental Forest (U.S. Forest Service), West Virginia, for which there was recent preflood biotic and abiotic data. I will describe the hydrologic context of the floods, macroinvertebrate community responses and changes in some habitat variables following floods. I also consider potential flood recolonization sources, compare my findings to other flood case histories and relate my findings to a previous attempt to define a flow disturbance (Resh et al., 1988).

STUDY SITE

The Fernow Experimental Forest lies on the unglaciated Allegheny Plateau of the central Appalachian Mountains in N-central West Virginia (39deg3'N, 79deg41'W). …

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