The isotope geochemistry of calcium and strontium in tree tissues as a monitor of calcium sources and cycling in a base-poor forested ecosystem, New Hampshire, United States

Calcium is leached from soil exchange pools by acid deposition, potentially impacting forest productivity, soil fertility, and water quality. This dissertation examines the biogeochemistry and cycling of Ca in terrestrial ecosystems and includes studies conducted in base-poor northeastern forests. In the Hubbard Brook Experimental Forest, a whole-watershed Ca addition with Ca/Sr and 87Sr/86Sr distinct from natural sources within the watershed, permits tracking of Sr, and by proxy Ca, as it cycles through the ecosystem.; Incorporation of Ca and Sr into plant tissue was examined, and it was determined that relative to the exchange pool of plant-available nutrients, Ca is preferentially allocated to foliage formation, whereas Sr is sequestered in wood. A discrimination factor (DF) was defined, with values greater than unity indicating preferential uptake of Ca over Sr. Foliar DFs estimated for dominant species include 1.14 for sugar maple, 1.31 for yellow birch, 1.33 for white birch, 1.43 for pin cherry, 1.78 for American beech, and 1.93 for red maple. Understanding the degree to which Ca is fractionated from Sr in different species allows for refinement in the use of 87Sr/ 86Sr and Ca/Sr ratios to trace Ca sources to foliage.; The fidelity of tree ring chemistry in sugar maple and red spruce was investigated as a potential biomonitor of past soil chemistry using Sr isotopes. It was found that Sr, and by proxy Ca, are laterally re-equilibrated in a >30 year window in both sugar maple and red spruce, demonstrating that tree rings cannot be used as a precise chronometer of soil chemistry.; A watershed-scale investigation of Ca isotopic compositions was carried out and delta44/42Ca values were found to vary by >2‰ in ecosystem pools. American beech and sugar maple bark have a delta 44/42Ca of -1.62 (+/-0.08)‰, which is significantly different from wood, which has a value of delta44/42Ca (1.14 +/-0.14‰). delta 44/42 Ca values of lysimeter water (-0.66‰) and stream water (0.32‰) are significantly different from each other and from bark and wood. No change in Ca isotopic composition was observed with increasing height in trees in either wood or bark.