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

本研究评估了新罕布什尔州哈伯德布鲁克实验森林中钙（Ca）循环的变化，该研究基于可追溯到1963年的独特样本档案中Ca稳定同位素比率的测量。与美国东北部其他森林一样，从20世纪50年代初开始，酸沉降显著干扰了钙循环，导致生物有效土壤库中的钙流失增加，对森林生长产生不利影响。此外，对HBEF的几个一级流域进行了实验记录，以便检查采伐、钙循环和森林生态之间的关系。研究将解决以下问题：河流和土壤的Ca同位素比率如何随着酸化和森林砍伐等干扰而变化？这些数据能告诉我们森林生态系统中钙流失的机制和干扰导致的钙循环变化吗？同位素示踪箱模型表明，土壤和河流中的钙同位素反映了森林钙循环（外部供应、植物吸收和再循环到土壤）中重要通量的相对大小，从而产生了一系列与生态系统对这些扰动的响应相关的可验证假设。主要的假设是，森林生长将吸收钙，限制其输入到河流中，而森林砍伐将增加河流中的钙作为土壤径流。为了解决问题和假设，Ca同位素比率和元素浓度将在一组精心挑选的存档土壤母质、降水、河流、土壤和植被样本上进行测定。钙生物地球化学对美国东北部、北欧和中国的森林可持续性具有重要意义。钙同位素与钙循环的其他示踪剂一样，有可能解决森林中钙流失来源的一些不确定性，这些不确定性在单独的质量平衡研究中并不明显。这些信息的重要性超出了生物地球化学研究，对森林管理和区域性重要的农业综合企业，如枫糖浆生产具有影响。该项目将主要支持波士顿大学陆地生物地球科学博士项目的一名研究生。研究生和PI将创建模块，供未来一年的冰川研究生群体使用，向中学生介绍新英格兰生物地球化学、酸雨和森林可持续性。该项目的结果将进一步传达给PI每年在波士顿大学和塔夫茨大学授课的约300名学生。

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.