Isotope Tracers in Catchment Hydrology

C. Kendall, J.J. McDonnell

• Publisher: Elsevier Science
• Year: 2012
• Print ISBN: 9780444815460
• eBook ISBN: 9780080929156
• Topic: Physical Sciences
• Subtopic: Geology & Earth Sciences

This book represents a new "earth systems" approach to catchments that encompasses the physical and biogeochemical interactions that control the hydrology and biogeochemistry of the system. The text provides a comprehensive treatment of the fundamentals of catchment hydrology, principles of isotope geochemistry, and the isotope variability in the hydrologic cycle -- but the main focus of the book is on case studies in isotope hydrology and isotope geochemistry that explore the applications of isotope techniques for investigating modern environmental problems.Isotope Tracers in Catchment Hydrology is the first synthesis of physical hydrology and isotope geochemistry with catchment focus, and is a valuable reference for professionals and students alike in the fields of hydrology, hydrochemistry, and environmental science. This important interdisciplinary text provides extensive guidelines for the application of isotope techniques for all investigatores facing the challenge of protecting precious water, soil, and ecological resources from the ever-increasing problems associated with population growth and environmental change, including those from urban development and agricultural land uses.

PART I

BASIC PRINCIPLES

Chapter 1

Fundamentals of Small Catchment Hydrology

James M. Buttle

Publisher Summary

This chapter provides an overview of hydrological processes relevant at the catchment scale, and it also identifies areas where environmental isotopes have assisted the study of such processes. It outlines the general components of the water balance equation and reviews the salient physical principles associated with each component. It discusses the related issue of spatial and temporal scale in small catchments. It reviews a survey of the use of isotopes in examining the nature of hydrological processes and discusses some suggested issues for future research. The chapter also highlights the dominant processes operating in small catchments, methods used to study these processes, and some of the ways in which isotopes have been used to improve the understanding of small catchment hydrology. Small catchments provide a convenient framework within which to examine hydrological processes, and the water balance equation forms the backdrop for the examination of most if not all of these processes. Many of the applications of isotopes to small catchment hydrology have assumed spatial and/or temporal homogeneity of the isotopic signature of water. The degree to which these assumptions hold, and the implications of these assumptions for the conclusions drawn from applications of isotopes to hydrological research need to be examined.

1.1 Introduction to Small Catchments

This chapter seeks to provide an overview of hydrological processes relevant at the catchment scale, and to identify areas where environmental isotopes have assisted the study of such processes. This will form the backdrop for subsequent chapters examining the use of environmental isotopes in specific hydrological subsystems (in particular Chapters 10 to 14). Beginning with an outline of the general components of the water balance equation, we will review the salient physical principles associated with each component. The related issue of spatial and temporal scale in small catchments will be examined. This will be followed by a survey of the use of isotopes in examining the nature of hydrological processes, and some suggested issues for future research.

We will concentrate on hydrological processes operating in small catchments. A glossary of terms relevant to hydrological processes discussed in this and subsequent chapters is presented in Table 1.1. An operational definition of “small” would encompass catchments ranging in size from 10⁻² to 10² km²; most isotopic hydrograph separations have been conducted in catchments < 10² km² (Buttle, 1994). Such catchments tend to be located in headwater areas and possess a number of attributes that distinguish them from “large” catchments, such as the Seine, the Potomac, and the Ottawa. Small catchments have relatively steep channel gradients and valley sideslopes, absent or minor floodplains, groundwater inputs from local or intermediate flow systems (cf. Tóth, 1963), and a comparatively uniform regional climate.

Table 1.1

Glossary of terms.

aerodynamic resistance	“The bulk meteorologic descriptor of the role of the atmospheric turbulence in the evaporation process” (Oke, 1978). It is dependent upon wind speed, surface roughness and atmospheric stability.
albedo	“The ratio of reflected solar radiation to the total incoming solar radiation where both streams are measured across the complete wavelength range of solar radiation (−0.3 – 4.0 µm)” (Henderson-Sellers and Robinson, 1986).
anisotropy	The condition of having different physical properties (e.g. KH) in different directions.
aquifer	“A saturated permeable geologic unit that can transmit significant quantities of water under ordinary hydraulic gradients” (Freeze and Cherry, 1979).
aquitard	“The less-permeable beds in a stratigraphic sequence” (Freeze and Cherry, 1979).
baseflow	Sustained runoff that is the sum of deep subsurface flow and delayed shallow subsurface flow; however, it is not synonymous with groundwater flow (Ward and Robinson, 1990).
Bowen Ratio	The ratio of the sensible and latent fluxes over a surface.
capillary fringe	The area between the vadose and phreatic zones; all pores are filled with water, but the water is held under slight matric tension, such that the addition of a small amount of water will convert this zone to saturated conditions (Gillham, 1984).
capillary rise	Movement of water from the saturated zone upward into the unsaturated zone due to surface tension (Dingman, 1993).
catchment	“A unit of land on which all the water that falls (or emanates from springs) collects by gravity and fails to evaporate and runs off via a common outlet” (Black, 1991).
channel precipitation	Direct precipitation onto a water surface.
depression storage	The volume of water contained in small surface depressions during or shortly after rainfall or melt, none of which runs off (Horton, 1933).
detention storage	Rainwater or snowmelt held in temporary storage on the surface as it moves downslope by overland flow, and which either runs off, is evaporated, or is infiltrated after rainfall or melt ceases (Horton, 1933).
dew point	Temperature at which an air parcel becomes saturated if cooled without a change in pressure or moisture content (Henderson-Sellers and Robinson, 1986).
emissivity	Degree to which a real body approaches a black body radiator (i.e. a perfect emitter of radiation) (Henderson-Sellers and Robinson, 1986).
evaporation	Diffusion of water vapor into the atmosphere from exposed water surfaces.
evapotranspiration	Diffusion of water vapor into the atmosphere from vegetated surfaces. It represents the combination of evaporation from soil and plant surfaces with plant transpiration (Goudie et al., 1985).
event water	Water that is added to a catchments surface as rainfall or snowmelt during a storm event.
exfiltration	The removal of water from the soil at the ground surface, together with the associated unsaturated upward flow (Freeze, 1974).
falling limb	That portion of the hydrograph where discharge is decreasing with time. Also known as the recession limb.
fractionation	“The separation of a mixture, usually of chemically related or otherwise similar components, into fractions of different properties” (Uvarov et al., 1979).
groundwater flow	That part of streamflow that has infiltrated the ground, has entered the phreatic zone, and has been discharged into a stream channel as spring or seepage water (Chorley, 1978b).
Horton flow	“Direct surface runoff across saturated soils where rainfall intensity exceeds infiltration plus depression storage” (Chorley 1978b).
hydraulic conductivity	The constant term in Darcy’s Law expressing the ability of a soil or rock to transmit water un...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• About the Editors
• Preface
• Acknowledgments
• List of Contributors
• PART I: BASIC PRINCIPLES
• PART II: PROCESSES AFFECTING ISOTOPIC COMPOSITIONS
• PART III: CASE STUDIES IN ISOTOPE HYDROLOGY
• PART IV: CASE STUDIES IN ISOTOPE GEOCHEMISTRY
• PART V: SYNTHESIS
• INDEX