Calcium isotopic response to disturbance at Hubbard Brook: acidification, deforestation, and recovery

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This study evaluates changes in Calcium (Ca) cycling at the Hubbard Brook Experimental Forest in New Hampshire based on measurements of Ca stable isotope ratios on a unique sample archive dating to as early as 1963. Like other Northeast U.S. forests, the Ca cycle was significantly perturbed by acid deposition beginning in the early 1950's resulting in increased Ca loss from bio-available soil pools and detrimental effects on forest growth. Additionally, several of the first order watersheds at HBEF have been experimentally logged allowing examination of the relationship between harvesting, Ca cycling and forest ecology. Research will address the following questions: How do the Ca isotope ratios of streamwater and soil change in response to disturbances including acidification and deforestation? What can such data tell us about the mechanisms of Ca loss from forest ecosystems and changes in Ca cycling resulting from disturbance? An isotope-tracer box model indicates that soil and streamwater Ca isotopes reflect the relative magnitudes of important fluxes in the forest Ca cycle (external supply, plant uptake, and recycling to soil), leading to a series of testable hypotheses related to the ecosystem-level response to these perturbations. The main hypothesis is that forest growth will take up Ca, limiting it's input to streamwater, while deforestation will increase streamwater Ca as runoff from soil. To address questions and hypotheses, Ca isotope ratios and elemental concentrations will be determined on a carefully selected group of archived soil parent material, precipitation, streamwater, soil, and vegetation samples.Ca biogeochemistry has important implications for forest sustainability, both in the NE US, Northern Europe, and China. Ca isotopes, like other tracers of Ca cycling, has the potential to resolve some of the uncertainties in the sources of Ca loss from forests that are not apparent from mass balance studies alone. This information is important beyond biogeochemical research, with implications for forest management and regionally important agribusiness, such as maple syrup production. This project will primarily support a graduate student in Boston University's new Terrestrial Biogeosciences PhD program. The graduate student and the PI will create modules for use by a future year's cohort of GLACIER graduate students that introduce middle school students to New England biogeochemistry, acid rain, and forest sustainability. The results of this project will further be communicated to the about 300 students at Boston University and Tufts that the PI teaches annually.