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Harvard Forest REU Symposium Abstract 2006

  • Title: Summer Organic Matter Budget for a Hemlock Dominated Stream
  • Author: ()
  • Abstract:

    Construction of stream organic matter budgets allows: 1) comparison of streams having different carbon dynamics and watershed characteristics; 2) calculation of losses of carbon from watershed to downstream ecosystems; 3) additional carbon loss terms to be incorporated into forest carbon budgets; and 4) quantification of ecosystem impacts following forest disturbances (e.g., hemlock woolly adelgid invasion). The objectives of the study were to construct a summer carbon budget for a hemlock dominated stream, and to explore relationships between physical variables, such as stream discharge, and water chemistry. The study was conducted in a headwater stream (Bigelow Brook West) located on the Prospect Hill Tract of Harvard Forest in Petersham, Massachusetts. We constructed an organic matter budget for a 400 m stream reach that is dominated by hemlock and has a well characterized hydrological regime. A stream survey was conducted to assess important physical characteristics including stream area, habitat types, substrate types and surrounding riparian conditions. Water temperature, dissolved oxygen, pH, dissolved carbon dioxide, colored dissolved organic matter, stream depth and turbidity were measured continuously in situ. In addition, water samples were collected for analysis of nitrate (NO3-), ammonium (NH4+) and phosphate (PO4+) ions; and dissolved organic and inorganic carbon. Stream discharge was estimated using continuous depth measurements, and it was incorporated into existing hydrological model. Summer data collection enabled us to estimate many important organic carbon inputs (e.g., gross primary production), standing stocks (e.g., wood), and exports (e.g., dissolved organic matter). Some important findings were: 1) marked diurnal variation in discharge (Figure 1); 2) rapid storm response of stream discharge (Figure 1); 3) dissolved organic matter increases with storm events; 4) low primary production; 5) respiration (23.5 g C m-2 day-1) greatly exceeds primary production (6.9 g C m-2 day-1); and 6) dissolved organic matter (590 g C day-1) dominates organic matter export. In order to produce an annual stream organic matter budget similar seasonal budgets must be constructed for the fall, winter and spring seasons.

  • Research Category: Watershed Ecology