Collaborative Research: Arctic Stream Networks as Nutrient Sensors in Permafrost Ecosystems

永久冻土是指至少连续两年保持冻结状态的土地。它大约占北半球陆地表面的四分之一，含有大量的碳和氮、磷等营养物质。随着阿拉斯加北极变暖和永久冻土融化，这些营养物质被释放出来，支持植物生长，但也会加速温室气体的产生，影响当地栖息地并加强永久冻土气候反馈。由于融雪和雨水将一些营养物质从陆地转移到水中，北极河流网络中营养物质浓度的变化可以揭示永久冻土营养物质释放的位置，以及为什么一些地区释放的营养物质比其他地区多。这项研究极大地提高了对水流、植物生命、土壤和基岩条件如何受到野火、永久冻土退化和极端天气条件影响的理解。这些知识对于保护北极社区和预测永久冻土地区的环境变化如何破坏整个美国的气候和天气模式至关重要。该项目还通过创建一个由研究人员、作家、表演者和外展组织组成的网络，将对北极系统的更好理解直接传递给公众，该网络1)访问北极当地社区，2)创建一个儿童？这本书的灵感来自北极系统，3)将北极系统和气候科学直接带给大约3万名高中生，4)通过视频聊天与阿拉斯加农村和美国邻近地区的K-12教室远程连接。该项目采用新颖和传统的方法相结合，量化跨尺度和生物群系的营养动态。1)河流网络化学的高分辨率空间采样和流域出口的高频监测量化了生态系统梯度（如北极-北方和沿海-高地）和尺度（0.1至1000平方公里）的横向碳和养分通量。2)强大的营养限制测定和示踪剂注射方法估计了对流域尺度营养通量有强烈影响的地方的河流去除和释放营养的幅度。3)空间分析、统计建模和地球化学示踪剂将多尺度养分通量与生态水文特征联系起来，从而确定北极水化学变化的驱动因素。该项目收集的时空数据测试了一系列长期存在的和新兴的假设，即活动层厚度、植被群落、地形、水文、当前和过去的野火和永久冻土退化如何相互影响碳和养分通量。更一般地说，本研究为包含横向和纵向养分通量的地球系统模型提供了多尺度目标，减少了预测永久冻土区净生态系统碳平衡的最大不确定性来源之一。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Permafrost is ground that remains frozen for at least two consecutive years. It is found approximately one fourth of the northern hemisphere's land surface and contains large stores of carbon and nutrients such as nitrogen and phosphorus. As Arctic Alaska warms and permafrost thaws, these nutrients are released, which supports plant growth but also can accelerate the production of greenhouse gases, affecting local habitat and strengthening the permafrost climate feedback. Because snowmelt and rain transport some nutrients from land to water, variations in nutrient concentrations within Arctic stream networks can reveal where permafrost nutrients are released and why some areas release more than others. This research greatly improves understanding of how water flow, plant life, and conditions in the soil and bedrock are affected by wildfire, permafrost degradation, and extreme weather conditions. Such knowledge is crucial to protect Arctic communities and forecast how environmental change in the permafrost region could disrupt climate and weather patterns throughout the U.S. This project also transfers improved understanding of the Arctic system directly to the public by creating a network of researchers, writers, performers, and outreach organizations that 1) visits local communities in the Arctic, 2) creates a children?s book inspired by Arctic systems, 3) brings Arctic systems and climate science directly to about 30,000 high school students, and 4) connects remotely with K-12 classrooms in rural Alaska and the contiguous U.S. via video chats.The project applies a combination of novel and conventional approaches to quantify nutrient dynamics across scales and biomes. 1) High-resolution spatial sampling of stream network chemistry and high-frequency monitoring at watershed outlets quantify lateral carbon and nutrient flux across ecosystem gradients (e.g. Arctic-Boreal and coastal-upland) and scales (0.1 to 1,000 square kilometers). 2) Robust nutrient-limitation assays and tracer injection methods estimate the magnitude of instream removal and release of nutrients in locations that exert a strong influence on watershed-scale nutrient flux. 3) Spatial analysis, statistical modeling, and geochemical tracers link multi-scale nutrient fluxes with ecohydrological characteristics and thus identify drivers of hydrochemical change in the Arctic. The spatial and temporal data collected by the project test a series of long-standing and emerging hypotheses about how active-layer thickness, vegetation community, topography, hydrology, and current and past wildfire and permafrost degradation interactively influence carbon and nutrient flux. More generally, this research generates multi-scale targets for earth system models that incorporate lateral and longitudinal nutrient flux, reducing one of the largest sources of uncertainty in predicting net ecosystem carbon balance of the permafrost region.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.