Cary Institute of Ecosystem Studies
Date of Award
Master of Environmental Management (MEM)
Environmental Science and Management
Soils -- Nitrogen content -- New Hampshire -- Hubbard Brook Experimental Forest -- Case studies, Calcium, Watershed management
A watershed-scale calcium addition experiment at Hubbard Brook Experimental Forest, New Hampshire, was performed in 1999 to better understand how forest ecosystem function and biogeochemistry are affected by changes in pH. Significant increases in forest growth and acid neutralizing capacity of the soil and stream water were reported in the six years following the calcium addition, but the expected stimulation of the nitrogen cycle was not observed. The aims of this study were to 1) examine the 20-year dataset of soil nitrogen dynamics following the experimental calcium addition in the treated watershed and paired reference area to understand longer term trends and effects, and 2) explore connections between soil nitrogen processes and watershed nitrogen export in stream water observed in the calcium-treated watershed since 2013. Since 2002, soil pH was higher in the calcium-treated watershed than the reference, with stronger differences seen in surface horizons, but declined over time and converged toward the reference conditions by 2018, throughout the soil profile. Soil nitrogen cycling measurements were not consistent with the changes in soil pH, and temporal trends were different depending on the variable in question. Differences in temporal trends in nitrogen cycling variables were often more pronounced as a function of soil horizon than Ca treatment. However, interesting trends were seen in certain variables, with effects of Ca treatment diverging from long term trends in the reference area for some variables while converging toward reference conditions for others. There was no strong evidence from microbial nitrogen transformations at the plot scale to explain the nitrate export from the calcium treated watershed observed by other researchers (Rosi-Marshall et al. 2016). Because pathways in soil nitrogen cycling did not show consistent trajectories over time in response to the calcium treatment, understanding how changes in pH and other environmental variables, along with competition for nitrogen between plants and soil microbes, differentially affect these various processes remains a challenge in forest ecosystem science.
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Uribe, Angelina, "Soil Nitrogen Cycling Over Two Decades Following Calcium Treatment in Hubbard Brook Experimental Forest, NH" (2020). Environmental Science and Management Professional Master's Project Reports. 78.