Collaborative Research: MRA: Particulates in canopy flowpaths: A missing mass flux at the macrosystem scale?

森林覆盖了地球上三分之一的土地。雨水要穿过森林树冠层，必须沿着两条“水文公路”：雨水（从树叶或树皮的缝隙中滴下的水）；还有茎流（顺着茎流的水）。随着雨水和茎流的流失，它们冲走了树叶和树皮上的颗粒。虽然很小，但这些水文高速公路从树冠上冲刷下来的颗粒可以构成对土壤的重要化学输入，并代表从营养物质到污染物的各种物质。尽管如此，还没有大规模的努力来测量、衡量和预测沿着这些水文公路下降的颗粒的数量和质量。在目前关于森林元素循环的生态理论中，这些颗粒通常是“缺失的”。这项研究试图通过监测风暴条件、穿透、干流和这些水文高速公路中的颗粒来填补这一空白，这些水文高速公路横跨北美主要森林类型的地点。研究结果将把贯通流和茎流与用于为淡水和森林管理提供信息的通用模型联系起来。结果将为推广工作提供信息，包括科学漫画和插图展览，为小学生和中学生写的开放获取的文章，以及由MinuteEarth（一个拥有数百万国际观众的频道）制作的YouTube视频。该项目还将向代表性不足的群体成员提供研究经验，以扩大对科学的参与。对于北美大陆40%的土地和全球三分之一的地表来说，雨水必须穿过森林才能到达土壤表面。这种降雨被森林冠层划分为两种净降雨通量：一种是称为通流（TF）的滴流通量，另一种是称为茎流（SF）的沿茎流下的水流。沿着这些水文高速公路的降雨量可以改变20-50%的供水，它们从树冠上携带的物质每年可以向每公顷土壤表面提供100公斤的各种物质。这些冠层生态水文过程处于气候和土地利用变化的前沿，因为森林-降雨相互作用启动了陆地水文途径并向地表提供养分/污染物，是受水文强化影响的第一个生态系统要素。忽略这些通量及其颗粒流量，会在陆地生物地球化学和水文循环交织的第一个点给水和养分通量模型带来误差，并可能通过下降梯度过程将这些误差串联起来。该项目旨在扩展目前对宏观系统生物学的理解，包括穿透和茎流颗粒浓度、通量和组成，具体解决3个主要目标：(1)估算森林类型的净降雨量（TF+SF）水和颗粒质量通量；(2)表征TF和SF的颗粒组成（C:N:P，包括总C、有机C、黑C和微塑料C等C组分）；(3)确定净降雨颗粒通量和组成宏观系统变率的主要驱动因素。对代表美国主要森林域的国家生态观测站网络的11个站点的上述变量进行现场监测，可以测试现有功能特征与将穿透和干流动力学实际整合到大陆到全球尺度的生物地球物理模型之间的联系。本项目还将支持1名博士后、1名硕士生和1名博士生、1名技术人员的科研培训。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。

Forests cover one-third of the land on Earth. For rainfall to pass through the forest canopy, it must drain along two “hydrologic highways”: throughfall (water that drips through gaps and from leaves or bark); and stemflow (water that runs down stems). As throughfall and stemflow drain, they wash particles from leaves and bark. Although tiny, particles washed from the canopy by these hydrologic highways can constitute a significant chemical input to the soil, and represent a wide range of materials, from nutrients to pollutants. Despite this, no large-scale effort has sought to measure, scale, and predict the amount and quality of particles descending down these hydrologic highways. These particles are generally “missing” from current ecological theory of how forests cycle elements. This study seeks to fill this gap by monitoring storm conditions, throughfall, stemflow, and the particles in these hydrologic highways across sites representing major forest types in North America. Results will link throughfall and stemflow to common models used to inform freshwater and forest management. Outcomes will inform outreach efforts, including science comics and illustration exhibits, open-access articles written for (and reviewed by) primary and secondary school children with Frontiers for Young Minds, and YouTube videos with MinuteEarth, a channel with an international viewership of millions. The project will also provide research experiences to members of underrepresented groups to broaden participation in science.For 40% of the North American continent and one-third of global land surface, rainfall must pass through forests to reach the soil surface. This rainfall is partitioned by the forest canopy into two net rainfall fluxes: a drip flux called throughfall (TF), and a flow of water down stems, called stemflow (SF). How much rain travels along these hydrologic highways can alter water supply by 20-50%, and what they carry from the canopy can supply 100 kg per hectare of various materials to the soil surface each year. These canopy ecohydrological processes are on the front line of climate and land use change, being that the forest-rainfall interactions that initiate terrestrial hydrological pathways and supply nutrients/pollutants to the surface are the first ecosystem elements impacted by hydrologic intensification. Ignoring these fluxes, and their particulate traffic, introduces error in water and nutrient flux models at the first point where terrestrial biogeochemistry and hydrological cycles entwine, and which may cascade those errors through downgradient processes. This project aims to extend current macrosystem biological understanding to include throughfall and stemflow particulate concentrations, fluxes and composition, specifically addressing 3 major objectives: (1) estimate the net rainfall (TF+SF) water and particulate mass flux across forest types; (2) characterize the particulate composition (C:N:P, including C components like total C, organic C, black C, and microplastic C) of TF and SF; and (3) identify major drivers of macrosystem variability in net rainfall particulate flux and composition. Field monitoring of the above variables across 11 sites of the National Ecological Observatory Network representing the major US forest domains allows links to be tested between existing functional characteristics and the practical integration of throughfall and stemflow dynamics into continental-to-global scale biogeophysical models. The project will also support research training of a postdoctoral researcher, masters and doctoral students, and a technician.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.