CZO: Critical Zone Observatory--Snowline Processes in the Southern Sierra Nevada

CZO：关键区域观测站——内华达山脉南部的雪线过程

• 批准号: 1239521
• 负责人: Roger Bales
• 金额: $ 100万
• 依托单位: University of California - Merced
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-09-01 至 2014-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1239521&HistoricalAwards=false
• 关键词: CZO; Critical; Zone; Observatory; Snowline

The Southern Sierra Critical Zone Observatory (CZO), located at 1700-2100 m elevation, crosses the rain-snow transition, an area that is particularly vulnerable to large changes in climate and landcover. Rapid seasonal changes and steep gradients in precipitation make this zone an excellent natural laboratory for studying how critical-zone processes respond to perturbations and how the water cycle drives critical-zone processes. In particular, differences along locally pronounced altitudinal and aspect-related gradients in climate offer the opportunity to substitute space for time in a rich cross-disciplinary array of process-oriented studies. Collocated with the USFS Kings River Experimental Watersheds, the CZO takes advantage of multiple, well-instrumented and characterized catchments and long-term data sets to provide a community platform for research. Four key findings from the CZO have helped shape the current research agenda. First is closing the water budget at headwater catchment and larger scales using a rich set of water-balance, flux-tower and sap-flow measurements of evapotranspiration (ET). Second, multiple lines of evidence are consistent with a year-round growing season at mid elevation, with mid-montane forests exhibiting cold tolerance in winter and avoiding late-summer drought stress through deep rooting. Third, rates of ET at mid-elevation are high relative to nearby lower-elevation water-limited and higher-elevation cold-limited ecosystems. Fourth, deep rooting and soil development are important for sustaining high rates of net primary productivity (NPP), with over one-third of ET coming from depths below 1m. Together these results provide a unifying theme for the current research, which addresses: i) how soil moisture and topographic variability interact to influence soil-formation and weathering, ii) how the response of soil moisture, ET and streamflow, to snowmelt and rainfall is controlled by landscape variability, iii) how and why vegetation and ecosystem distribution and function vary with climate, iv) and how landscape heterogeneity and vegetation interact to influence cycling of water, energy, nutrients, and NPP. The foundation of CZO research is a rich field measurement program, with geochemical analyses and a well-integrated modeling effort that will provide a fundamental understanding of the links among climatic, hydrologic, (bio)geochemical, ecosystem and landscape processes. The Southern Sierra CZO is a data-rich community platform for process-level research that enhances the science of multiple individuals and research groups. It is located in an elevation range that has characteristically rapid seasonal changes, going from snowcover to wet soil to dry soil over a 1-2 month period. Regional climate warming will make such changes occur earlier or eliminate them entirely if snow is largely replaced by rain at the current rain-snow transition. This will lead to major water- related changes in seasonal-to-interannual critical-zone processes involving weathering, regolith formation, nutrient cycling, and vegetation/ecosystem distribution and function. Forest density of the largely mixed-conifer forest and the threat of catastrophic fire are very high, raising the chances of major changes in longer-term critical-zone processes. Research at the CZO is providing an unprecedented predictive ability for how the linked hydrologic, (bio)geochemical, ecosystem and landscape processes will respond to perturbations, i.e. changes in temperature, precipitation patterns, and human management of forests. It is providing a solid foundation for science-based vegetation and water management in the Sierra Nevada and other seasonally snow-covered mountain forests. Further, the CZO provides a basis for the design and evaluation of broader observation networks for both research and applications. Finally, the research team uses CZO data and knowledge to enhance the science experience of thousands of middle and high school students and also many undergraduate students at the participating universities.

南塞拉关键区观测站（CZO）位于海拔1700-2100米，横跨雨雪过渡区，该地区特别容易受到气候和土地覆盖的大变化的影响。快速的季节变化和陡峭的降水梯度使该区域成为研究关键区域过程如何响应扰动以及水循环如何驱动关键区域过程的绝佳天然实验室。特别是，气候在当地显著的海拔和方向相关梯度上的差异，为丰富的面向过程的跨学科研究提供了用空间代替时间的机会。CZO与USFS Kings River实验流域相结合，利用多个仪器完备的特征集水区和长期数据集，为研究提供社区平台。CZO的四个关键发现帮助塑造了当前的研究议程。首先是利用一套丰富的水平衡、通量塔和蒸发蒸腾（ET）的水流量测量来关闭源头集水区和更大尺度的水收支。其次，多种证据都与中海拔地区全年的生长季节相一致，中山地森林在冬季表现出耐寒性，并通过深生根避免夏末的干旱胁迫。第三，相对于附近低海拔限水生态系统和高海拔限冷生态系统，中海拔的ET速率较高。第四，深层生根和土壤发育对于维持高净初级生产力（NPP）非常重要，超过三分之一的ET来自1米以下的深度。这些结果为当前的研究提供了一个统一的主题，即：i)土壤湿度和地形变异性如何相互作用影响土壤形成和风化；ii)土壤湿度、蒸散发和河流流量对融雪和降雨的响应如何受到景观变异性的控制；iii)植被和生态系统分布和功能如何以及为什么随气候变化而变化；iv)景观异质性和植被如何相互作用影响水、能量、养分和NPP的循环。CZO研究的基础是丰富的实地测量计划，地球化学分析和良好整合的建模工作，将提供对气候，水文，（生物）地球化学，生态系统和景观过程之间联系的基本理解。南塞拉CZO是一个数据丰富的社区平台，用于过程级研究，增强了多个个人和研究小组的科学。它所处的海拔高度具有季节性快速变化的特点，在1-2个月的时间内从积雪到潮湿的土壤再到干燥的土壤。区域气候变暖将使这种变化发生得更早，或者如果在当前的雨雪转换中，雪大部分被雨所取代，则这种变化将完全消除。这将导致涉及风化、风化层形成、养分循环以及植被/生态系统分布和功能的季节性至年际临界带过程中与水有关的重大变化。大部分混合针叶林的森林密度和灾难性火灾的威胁非常高，增加了在长期关键地带过程中发生重大变化的可能性。CZO的研究为水文、（生物）地球化学、生态系统和景观过程如何响应扰动（即温度、降水模式和人类对森林管理的变化）提供了前所未有的预测能力。它为内华达山脉和其他季节性积雪覆盖的山地森林的科学植被和水管理提供了坚实的基础。此外，CZO为设计和评估更广泛的研究和应用观测网络提供了基础。最后，研究团队利用CZO的数据和知识，增强了参与大学的数千名初高中学生和许多本科生的科学体验。