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

美国西部山区的雨雪过渡地带特别容易受到气候和土地覆盖的大规模和潜在的快速变化的影响。虽然这一地区的季节变化非常迅速，在1-2个月的时间里从积雪到湿土再到干土，但气候变暖将提前或完全消除这一过渡期。其结果将是在雨雪过渡带发现的主要混合针叶林的涉及水、养分和生态系统响应的季节性到年际临界区过程的重大变化。降水模式沿海拔和坡向的陡峭梯度，加上快速的季节变化，使该地区成为研究临界区过程如何响应扰动，特别是水循环如何驱动临界区过程的优秀自然实验室。拟建的临界区观测站(CZO)将通过建立雪线CZO作为社区资源来利用这些特征，为来自多个学科的研究人员提供研究平台和一个强有力的研究计划，旨在获得一般知识和工具，以了解临界区水、大气、生态系统和地形之间的相互作用。CZO的数据和知识还将增强数千名初中生和多名大学生的科学体验。CZO将设在国王河实验分水岭(KREW)，这是一个分水岭级别的综合生态系统项目，用于塞拉利昂国家森林的源头流域的长期研究；它利用KREW(北纬37.053oN，海拔119.194oW，海拔1400-2000米)的多个经过良好测量和特征的集水区和长期数据集。首要目标是了解关键地带过程如何控制整个地貌中的水的通量和储存，以及水循环如何调节关键地带的(生物)地球化学、生物、地貌和土壤学过程。五个迫在眉睫的研究问题将定义和聚焦核心测量和研究计划：i)耦合的水文和生物地球化学通量如何在雨雪过渡期间变化，ii)极端水文事件在水文和生物地球化学平衡中的作用是什么，iii)植被在多大程度上调节或主动控制水和营养物质的初级地下通量，而不是起被动作用，iv)在什么时间和空间尺度上，以及在什么季节，大孔隙和其他短路路径在临界区占主导地位，以及v)季节性积雪的存在如何影响次表层、临界区、土壤、地貌、关于塞拉利昂分水岭和山坡的生物地球化学和水文学，以及随着气候变暖和积雪消退，相关过程和水库将如何应对。

The rain-snow transition zone in mountains of the Western United States is particularly vulnerable to large and potentially rapid changes in climate and landcover. While this zone has characteristically rapid seasonal changes, going from snowcover to wet soil to dry soil over a 1-2 month period, climate warming will shift this transition period earlier or eliminate it entirely. The result will be major changes in seasonal-to-interannual critical zone processes involving water, nutrients and ecosystem response of the largely mixed conifer forest found in the rain-snow transition zone. Steep gradients in precipitation patterns, along both elevation and aspect, plus rapid seasonal changes, make this zone an excellent natural laboratory for studying how critical zone processes respond to perturbations, and particularly how the water cycle drives critical zone processes.The proposed Critical Zone Observatory (CZO) will take advantage of these features by establishing a snowline CZO as a community resource, providing both a platform for research by investigators from multiple disciplines and a vigorous research program aimed at yielding general knowledge and tools for understanding the interactions between water, atmosphere, ecosystems and landforms in the critical zone. CZO data and knowledge will also enhance the science experience of thousands of middle and high school students, and multiple university students. The CZO will be located in the Kings River Experimental Watershed (KREW), a watershed-level, integrated ecosystem project for long-term research in headwater catchments in the Sierra National Forest; it takes advantage of multiple well-instrumented and characterized catchments and long-term data sets at KREW (37.053oN, 119.194oW, 1,400-2,000 m elevation). A primary, overarching goal is to understand how critical zone processes control fluxes and stores of water across the landscape, and how the water cycle modulates (bio)geochemical, biological, geomorphological and pedological processes in the critical zone. Five immediate research questions will define and focus the core measurement and research program: i) how do coupled hydrologic and biogeochemical fluxes vary across the rain-snow transition, ii) what is the role of extreme hydrologic events in hydrologic and biogeochemical balances, iii) to what extent does vegetation modulate or actively control the primary subsurface fluxes of water and nutrients, versus act as passive agents, iv) over what time and space scales, and during what seasons, are macropores and other short-circuit pathways dominant in the critical zone, and v) how does the presence of a seasonal snowpack affect the subsurface, critical zone, soils, geomorphology, biogeochemistry and hydrology in Sierra watersheds and hillslopes, and how will the relevant processes and reservoirs respond as the climate warms and snowpacks recede.