Stream Response to Hemlock Decline in Southern New England
HF099 Overview Data EML Archive- Investigators: Elizabeth Colburn, David Orwig
- Contact: Elizabeth Colburn
- Start date: 2003-05-01
- End date: ongoing
- Location: Central Connecticut and Central Massachusetts
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- Taxa: Caudata, Diptera, Ephemeroptera, Megaloptera, Plecoptera, Trichoptera
- Keywords: biodiversity, functional feeding group, headwater streams, stream order, trophic dynamics, watershed
- Abstract:
Stream flora and fauna, as well as ecosystem processes such as carbon processing and transport, are tightly coupled to plant community composition and structure in the watershed. Changes in watershed land use or plant communities can affect hydrology, water temperatures, and water chemistry, and through them, the stream biota. Hemlock (Tsuga canadensis (L.) Carriere), one of the longest-lived and most shade-tolerant forest trees, is an important riparian species in cool, shaded ravines, and it is found commonly in wooded swamps and in mid-slope communities. In New England, where many small streams are surrounded by hemlock, the potential loss of hemlock forests to invasion by an introduced insect, the hemlock woolly adelgid (HWA), has the potential to alter radically the physical, chemical, and biological conditions in streams.
Preliminary research by the US Geological Survey in the Delaware Water Gap National Recreation Area suggests significant differences in water quality and biota of streams draining hemlock and hardwood-dominated stands. We are initiating studies in which we compare small, headwater streams in hemlock-dominated catchments with streams in deciduous forests. This research is complementary to ongoing studies on forest community composition and ecosystem function in relation to HWA and should further promote our understanding of potential regional-scale impacts of hemlock decline.
Streams in hemlock-dominated watersheds tend to have higher levels of dissolved organic carbon (DOC) and lower levels of dissolved nutrients than streams in hardwood catchments, due to soils under conifers tending to be acidic, high in organic carbon, and low in nitrogen and phosphorus. We predict that watershed-level changes associated with woolly adelgid-induced hemlock decline will alter stream habitat (hydrology; chemistry, including color, DOC, pH, alkalinity, and dissolved nutrients; temperature; and physical structure) and will produce reorganization of food webs including distribution of functional feeding groups and dominance of top predators.
- Methods:
We will compare aquatic invertebrate and salamander communities in up to 50 streams along a space-time continuum of hemlock decline and replacement by hardwoods, in undisturbed hemlock and hardwood stands, and in stands that have been pre-emptively logged in advance of hemlock decline. Physical habitat will be evaluated through stream surveys characterizing gradient and substrate, continuous monitoring of air and water temperatures, hydrologic studies in intensively monitored stands, and chemical analysis of pH, alkalinity, DOC, color, and total nitrogen. Stratified random sampling by dipnetting, with leaf packs, and, where stream conditions permit, with electroshocking, will survey fauna in streams along the space-time continuum, in intensively monitored stands, and in manipulated sites with stream reaches. Coverboard transects perpendicular to the channel will assess headwater streams as refugia for terrestrial salamanders (woodland salamanders, Plethodon cinereus, and red efts, Notophthalamus viridescens) in relation to hemlock decline. Salamanders will be identified, measured, and returned immediately to the sample location; invertebrates will be preserved in 70 percent ethanol and returned to the laboratory for sorting, identification, and classification into functional feeding groups. We will evaluate functional feeding group composition, taxa richness in the Trichoptera, Plecoptera, and Ephemeroptera, presence and absence of fishes, and distribution and abundance of Desmognathus fuscus, Gyrinophilus porphyriticus, and Eurycea bislineata, to identify trends in community composition and trophic structure and patterns in community reorganization.
- Related datasets: HF095