COLLABORATIVE RESEARCH: COUPLED HYDROLOGICAL AND GEOCHEMICAL PROCESS EVOLUTION AT THE LANDSCAPE EVOLUTION OBSERVATORY

自然景观中控制生物地球化学反应、流动和运输的物理、化学和生物结构和过程在多个空间和时间尺度上相互作用，难以量化。水文和生物地球化学理论的当前范例是，只要能够确定尺度相关参数的一些有效值，从小尺度观测中得出的过程描述就可以应用于更大尺度的预测。然而，这种模式被认为是有缺陷的，人们越来越频繁地呼吁建立新的理论，以更好地将小规模过程的理解与大规模的预测联系起来。此外，自然系统以一种难以在短期实验室实验或具有未知初始条件和时变强迫的自然景观中观察到的方式随时间演变。该项目将使用精心设计的湿润和干燥实验，在山坡尺度上使用稳定的水同位素示踪剂来确定流道的结构，并量化沿这些流道的水传输时间分布。孔隙水和山坡流出水的化学分析将决定这些干湿循环过程中的矿物风化动力学，这将与观测到的水传递时间有关。采用耦合系统模型进行详细的数值模拟，通过数据同化和反演模拟，模拟多孔介质的流动、反应输运和演化过程。这个项目将观察水、岩石和生命相互作用的方式，并创造有组织的土壤结构。这些观测将利用生物圈2号的景观演变观测站（LEO）以前所未有的空间和时间分辨率进行。LEO由三个大型人工景观组成，这些景观建在一个气候可控的环境中，其中包含1800多个传感器，用于测量水如何流经这些景观以及与土壤矿物质和微生物生态系统的相互作用。研究成果将有助于新一代的建模工具，量化污染物在不断变化的环境中迁移。结果将调和在实验室和野外尺度上观察到的流动和输运现象之间的差异。两名博士生和几名本科生将接受新的水文地球化学实验和地球系统建模方面的培训，他们的研究成果将与每年参观生物圈2号的10万人分享。

The physical, chemical and biological structures and processes controlling biogeochemical reaction, flow and transport in natural landscapes interact at multiple space and time scales and are difficult to quantify. The current paradigm of hydrological and biogeochemical theory is that process descriptions derived from observations at small scales can be applied to predict at much larger scales, as long as some effective values of the scale dependent parameters can be identified. However, this paradigm is known to be flawed and increasingly frequent calls have been made for new theories that will better link small-scale process understanding with large-scale predictions. Furthermore, natural systems evolve in time in a way that is hard to observe in short-run laboratory experiments or in natural landscapes with unknown initial conditions and time-variant forcing. This project will use carefully designed wetting and drying experiments using stable water isotope tracers at the hillslope scale to determine the structure of flow paths, as well as to quantify water transit time distributions along those flow paths. Chemical analysis of pore waters and hillslope outflow will determine mineral weathering kinetics during these wetting-drying cycles which will be related to observed water transit times. Detailed numerical modeling with a coupled systems model will be used to simulate the flow and reactive transport and the evolution of the porous medium through data assimilation and inverse modeling. This project will observe the way water, rock and life interact and create the organized structure of the soil. These observations will be made at an unprecedented spatial and temporal resolution using the Landscape Evolution Observatory (LEO) at Biosphere 2. LEO consists of three large artificial landscapes built in a climate controlled environment that contain over 1,800 sensors to measure how water flows through these landscapes and interacts with the soil minerals and microbiological ecosystems. The research outcome will contribute to a new generation of modeling tools for quantifying contaminant transport in a changing environment. The result will reconcile the discrepancies between observations of flow and transport phenomena at lab and field scales. Two PhD students and several undergraduate students will be trained in novel hydrologic-geochemical experimentation and Earth systems modeling, and their research will be shared with the 100,000 people that visit Biosphere 2 each year.