Collaborative Research: Landform controls on hydrologic flowpaths and pedogenesis explain solute retention and export from pedon to catchment scales

源头集水区本质上是复杂的。土壤、底土和地貌属性在不同的尺度上表现出异质性，排水这些地区的河流化学通常在空间和时间上从一个流域到另一个流域不同。然而，这些水源集水区构成了大部分景观，并负责在区域范围内设定水质。该项目的目的是利用水文土壤学框架，即水文学和土壤发展的综合研究，解释源头集水尺度上溪流水化学的时空变化。该框架为将集水区划分为类似区域提供了功能基础，这些区域可以整合起来解释集水区的径流和水质。与成壤作用(土壤发育)有关的化学反应在从泥土到山坡的尺度上进行，记录了反映主要水文径流路径的地球化学特征，并调节了排水山坡土壤序列的化学质量，最终决定了溪流化学。水在流向溪流的过程中，沿着水流路径的化学演化方式受到水流流经的土壤的强烈影响。在哈伯德布鲁克实验森林的一个小源头集水区，将对代表整个新英格兰北部森林溪流的四个具有对比的溪流化学的子集水区进行研究，以考察如何使用不同的土壤发育模式来解释溪水中的溶质来源。根据地貌形态、底土类型(水文限制带)和土壤提取化学确定的土壤发育序列来预测水流路径。沿着这些路径，将使用人工示踪实验、地球化学模式和同位素地球化学示踪剂来预测溶质运移的模式和过程，这些运移在每个子流域中产生径流，并形成整个流域的综合反应。该项目的总体目标是开发一个关于水文径流和成壤作用的地貌控制的预测模型，解释溶质的保留和从泥土到山坡再到集水区尺度的输出。该项目将展示水文学如何强烈影响土壤发育和土壤化学，进而控制源头集水区的溪流水质。了解水文学和土壤开发之间的联系可以为管理森林和溪水水质提供有价值的信息。土壤和水文学之间的反馈导致土壤化学的可预测景观格局，这对于理解立地生产力的空间梯度和对不同栖息地要求或化学敏感性的物种的适宜性具有重要意义。需要工具来确定和预测这些梯度，最终为土地管理和营林决策提供指导。土壤科学、水文学和生物地球化学之间的更好结合将提供水文界所需的概念飞跃，以便能够更好地预测和解释溪流水质的时空变异性，并了解促成溪流的水源。

Headwater catchments are inherently complex. The soils, subsoils, and geomorphic properties exhibit heterogeneity at different scales and stream chemistry draining these areas typically varies from one catchment to another in space and time. Yet these headwater catchments comprise the majority of the landscape and are responsible for setting the quality of water at a regional scale. The project is aimed at explaining the spatial and temporal variation in stream water chemistry at the headwater catchment scale using a hydropedological framework, i.e. the combined study of hydrology and soil development. This framework provides a functional basis for discretizing the catchment into similar regions that can be integrated to explain catchment runoff and water quality. Chemical reactions related to pedogenesis (soil development) that operate at scales from the pedon to hillslope record the geochemical signature reflective of the dominant hydrologic flowpaths and regulate the chemical quality of water draining hillslope soil sequences, ultimately setting stream chemistry. The way water chemically evolves along flowpaths in the landscape as it travels to the stream is strongly influenced by the soils through which it passes. In a small headwater catchment at the Hubbard Brook Experimental Forest, four subcatchments that have contrasting stream chemistry representative of forested streams throughout northern New England will be studied to examine how distinct patterns of soil development can be used to interpret sources of solutes in stream water. Flow pathways are predicted from landform shape, subsoil type (hydrologic restriction zones) and soil development sequences determined by soil extraction chemistry. Along these pathways, artificial tracer experiments, geochemical patterns, and isotopic geochemical tracers will be used to predict the patterns and processes of solute transport that generates streamflow in each subcatchment and forms the integrated response of the entire catchment. The overall goal of the project is to develop a predictive model of landform control on hydrologic flowpaths and pedogensis that explains solute retention and export from pedon to hillslope to catchment scales. The project will demonstrate how hydrology strongly influences soil development and soil chemistry, and in turn, controls stream water quality in headwater catchments. Understanding the linkages between hydrology and soil development can provide valuable information for managing forests and stream water quality. Feedbacks between soils and hydrology that lead to predictable landscape patterns of soil chemistry have implications for understanding spatial gradients in site productivity and suitability for species with differing habitat requirements or chemical sensitivity. Tools are needed that identify and predict these gradients that can ultimately provide guidance for land management and silvicultural decision making. Better integration among soil science, hydrology, and biogeochemistry will provide the conceptual leap needed by the hydrologic community to be able to better predict and explain temporal and spatial variability of stream water quality and understand water sources contributing to streamflow.