Collaborative Research: Forest Water Use and the Influence of Acid Deposition

森林水分利用效率（WUE）是指单位蒸腾损失的水蒸气所吸收的碳的比率。微气象测量表明，森林WUE在过去二十年中急剧增加，超过了大气二氧化碳浓度增加的预期。与观测到的森林WUE趋势相一致的是，北美和欧洲大部分地区的酸沉降显著减少。有证据表明，酸沉降可能会影响森林水分利用效率，无论是通过改变森林土壤中的养分的可用性或直接影响叶片生理。 WUE的变化也可能导致森林集水区的流量变化。 森林对酸沉降水平变化的假设反应目前尚未在全球气候模式的陆地表面组成部分中考虑。由于二氧化碳和水蒸气是两种最重要的温室气体，因此精确模拟它们的陆地-大气交换至关重要。拟议的研究采用集水区为基础的方法来调查变化的酸沉降对森林WUE的影响。树轮碳同位素将被用来重建历史WUE时间序列内的六个集水区，已差异化的影响，由于其底层基岩矿物学和地质历史之间的区别，酸沉积。该研究还将利用在成对集水区设计（Bear Brook，ME; Hubbard Brook，NH;和Fernow Experimental Forest，WV）中改变土壤地球化学的实验处理。河流流量分析和基于模型的方法将用于检测酸沉降对森林WUE的影响。该项目将支持一个博士学位。学生，谁将接受培训，在广泛的领域，实验室和建模技术，和至少八名本科生。高中学生也将通过既定的计划参与，并将包括他们在现场和实验室活动的参与。项目小组的所有高级成员都有从代表性不足的群体中招收学生的记录。研究结果将通过期刊出版物和会议报告传达给更广泛的科学界，并将组织一次特别会议，目的是与建模界分享研究成果。

Forest Water Use Efficiency (WUE) is defined as the ratio of carbon uptake per unit water vapor loss via transpiration. Micrometeorological measurements suggest that forest WUE has dramatically increased over the last two decades, in excess of what would be expected from increases in atmospheric carbon dioxide concentrations. Coinciding with observed trends in forest WUE have been marked decreases in acid deposition throughout much of North America and Europe. There is evidence that acid deposition may impact forest WUE, either by altering the availability of nutrients in forest soils or by directly affecting foliar physiology. Changes in WUE could also lead to changes in stream discharge from forested catchments. The hypothesized response of forests to changing levels of acid deposition is not currently considered in the land surface components of global climate models (GCMs). Since carbon dioxide and water vapor are the two most important greenhouse gases, it is vital to accurately model their land-atmosphere exchange. The proposed research uses a catchment-based approach to investigate the effects of changing acid deposition on forest WUE. Tree ring carbon isotopes will be used to reconstruct historical WUE time series within six catchments that have been differentially impacted by acid deposition due to distinctions between their underlying bedrock mineralogy and geological histories. The research will also capitalize on experimental treatments that have altered soil biogeochemistry in paired catchment designs (Bear Brook, ME; Hubbard Brook, NH; and Fernow Experimental Forest, WV). Stream discharge analysis and model-based approaches will be applied to detect the impact of acid deposition on forest WUE. The project will support a Ph.D. student, who will receive training in a wide range of field, laboratory, and modeling techniques, and at least eight undergraduate students. High school students will also be involved through established programs, and will include their participation in both field and lab activities. All senior members of the project team have track records of recruiting students from underrepresented groups. Results will be communicated to the broader scientific community through journal publications and conference presentations, and a special conference session will be organized with an objective of sharing research findings with the modeling community.