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Harvard Forest REU Symposium Abstract 2006

  • Title: Do increases in light intensity following the hemlock woolly adelgid invasion alter stream temperature and periphyton growth?
  • Author: ()
  • Abstract:

    Hemlock woolly adelgid (HWA), an invasive insect from Asia that infests and kills eastern hemlock, continues to spread throughout the eastern United States causing hemlock forests to be replaced by deciduous forests. Many streams in the northeastern United States have riparian forests that are dominated by hemlock and may be impacted by the HWA. Previous research has documented low light levels reaching hemlock dominated streams, and these stream light regimes will likely be augmented following the HWA invasion. The primary objective of this study was to quantify differences in photosynthetically active radiation (PAR) reaching streams with healthy hemlock, infested hemlock, dead hemlock, and deciduous riparian zones. The secondary objective was to relate changes in stream light regimes to changes in stream temperature and periphyton (i.e., benthic algae) growth. PAR measurements were taken along stream reaches with riparian zones of healthy hemlock, infested hemlock, dead hemlock, and deciduous trees in Massachusetts and Connecticut. Stream temperature was recorded every thirty minutes for several weeks, and ceramic tiles were incubated in stream for periphyton colonization. PAR levels reaching the streams were found to be highest in streams with riparian zones of dead hemlock, followed by deciduous trees, infested hemlock, and finally healthy hemlock. Daily water temperature fluctuations were higher in deciduous stream reaches than in hemlock stream reaches, while temperature patterns in recently infested hemlock streams were not greatly altered. Periphyton biomass in a deciduous stream reach and an infested hemlock stream reach was markedly higher than in a healthy hemlock stream reach, however variation in periphyton biomass among streams implies that there are other factors besides PAR limiting periphyton growth in headwater streams. Changes in stream thermal regimes and periphyton biomass following the HWA infestation may significantly affect important stream functions such as nutrient retention and food availability.

  • Research Category: Invasive Plants, Pests & Pathogens; Watershed Ecology