Collaborative Research: Investigating Timescales of Hydrologic Transport in Catchments Using Natural Tracer Time Series, Theoretical Models, and Laboratory-Scale Simulations

水通过集水区的时间，即降雨到达河流所需的时间，是控制可溶性污染物持久性的基本水力参数，从而控制污染事件的下游后果。集水区的特征是流动时间的分布，反映了降雨可以进入溪流的不同流动路径。因此，量化集水区的行程时间分布将有助于阐明控制地下水流路径的水文机制。了解汇水区运输和储存的时间尺度对于预测降雨输入如何通过与汇水区土壤和基岩的反应而发生化学变化也很重要。但是，尽管流域旅行时间分布对流域水文和地球化学具有重要意义，但它们很少被量化，而且控制它们的机制也知之甚少。从降雨和水流中氯离子等惰性示踪剂的长期时间序列可以推断集水区的走时分布。最近有研究表明，集水区的移动时间分布可以有意想不到的长“尾巴”，这意味着它们可以比预期的更长时间地保留可溶性污染物[Kirchner， Feng, and Neal，分形流化学及其对集水区污染物运输的影响，Nature, 403, 524-527, 2000]。拟议的研究计划建立在最近的工作基础上，有四个主要组成部分：a)分析降雨的长期时间序列和氯化物（一种天然存在的非反应性示踪剂）浓度，这些浓度来自不同地质环境下潮湿的森林集水区，使用光谱、自相关、以及相互关联方法来推断每个流域的特征旅行时间分布，b)开发和测试观测到的旅行时间分布的替代概念模型，c)构建实验室规模的物理模型来模拟这些概念模型背后的假设机制，以及)分析反应性示踪剂数据，以补充被动示踪剂（氯）的研究。这个数据分析、概念建模和实验室规模物理模型的综合项目旨在阐明控制流域尺度水及其相关溶质的运输、储存和混合的机制。该项目预计将导致：a)提高对流域流动路径和旅行时间分布的理解，以及控制它们的因素；b)提高对流域流动路径和水固相之间的反应如何影响流域尺度上活性溶质流动性的理解；c)改进使用水文和地球化学时间序列探测流域内部工作的工具。通过与现场数据的比较，改进了测试集水区流量和路由模型的方法。

0125338Feng The travel time of water through a catchment -- that is, the time it takes for rainfall to reach the stream -- is a fundamental hydraulic parameter controlling the persistence of soluble contaminants, and thus the downstream consequences of pollution episodes. A catchment is characterized by a distribution of travel times, reflecting the diverse flow paths that rainfall can take to the stream. Thus, quantifying catchments' travel time distributions should help to clarify the hydrologic mechanisms controlling flow routing in the subsurface. Understanding the timescales of transport and storage in catchments is also important for predicting how rainfall inputs will be chemically modified by reactions with catchment soils and bedrock. But despite the importance of catchment travel time distributions for watershed hydrology and geochemistry, they have rarely been quantified and the mechanisms controlling them are poorly understood. Catchment travel time distributions can be inferred from long-term time series of inert tracers, such as chloride, in rainfall and streamflow. It has recently been shown that catchment travel-time distributions can have unexpectedly long "tails", implying that they can retain soluble contaminants for much longer than would otherwise be expected [Kirchner, Feng, and Neal, Fractal stream chemistry and its implications for contaminant transport in catchments, Nature, 403, 524-527, 2000]. The proposed research program builds on this recent work, and has four main components:a) analyses of long-term time series of rainfall and streamflow concentrations of chloride (a naturally occurring nonreactive tracer) from humid forested catchments in diverse geological settings, using spectral, autocorrelation, and cross-correlation methods to infer each catchment's characteristic travel time distribution,b) development and testing of alternative conceptual models for the observed travel-time distributions, c) construction of laboratory-scale physical models to simulate the hypothesized mechanisms underlying these conceptual models, andd) analyses of reactive tracer data, to complement the passive tracer (chloride) studies. This integrated program of data analysis, conceptual modeling, and laboratory-scale physical models is designed to clarify the mechanisms that control catchment-scale transport, storage, and mixing of waters and their associated solutes. This project is expected to lead to:a) improved understanding of catchment flowpaths and travel time distributions, and the factors controlling them,b) improved understanding of how catchment flowpaths, and reactions between aqueous and solid phases, affect the mobility of reactive solutes at catchment scale,c) improved tools for using hydrologic and geochemical time series to probe the internal workings of catchments, andd) improved methods for testing catchment flow and routing models through comparisons with field data.