Soil-Water-Solute Process Characterization: An Integrated Approach

SOIL-WATER￾SOLUTE PROCESS

CHARACTERIZATION

An Integrated Approach

CRC PRESS

Boca Raton London New York Washington, D.C.

SOIL-WATER￾SOLUTE PROCESS

CHARACTERIZATION

An Integrated Approach

Edited by

Javier álvarez-benedí

rafael munoz-carpena ~

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Library of Congress Cataloging-in-Publication Data

Soil-water-solute process characterization: an integrated approach / [edited by]

Javier A´ lvarez Benedı´ and Rafael Mun˜oz-Carpena.

p. cm.

Includes bibliographical references and index.

ISBN 1-56670-657-2 (alk. paper)

1. Soil moisture–Mathematical models. 2. Soils–Solute movement–Mathematical

models. 3. Soil permeability–Mathematical models. 4. Groundwater flow–

Mathematical models. I. A´ lvarez-Benedı´, Javier. II. Mun˜oz-Carpena, Rafael.

III. Title.

S594.S6935 2005

631.4'32'011–dc22 2004015853

Preface

The development and application of methods for monitoring and character￾izing soil-water-solute processes are among the most limiting factors in

understanding the soil environment. Experimental methods are a critical part

of scientific papers, and their design and implementation are usually the most

time-consuming tasks in research. When selecting a method to characterize a

property governing a soil process, the practitioner or researcher often faces

complex alternatives. In many cases these alternatives are bypassed in favor of

recommendations from colleagues on well-established methods that might not

be the most suitable for the specific conditions of a study.

Several factors add to the complexity of selecting the best characterization

method for a particular case:

The governing properties or parameters are referred to by similar names

although in fact their actual values depend greatly on the conceptual

model selected to explain the process (e.g., several empirical models of soil

infiltration have different parameters associated with saturated hydraulic

conductivity).

The ultimate goal of the characterization effort, whether it be general

classification of the soil, qualitative estimation of an output, exploratory

modeling to gain insight on a process, quantitative modeling prediction,

etc., may determine the method of choice.

Since many of the soil characteristics are intrinsically variable (spatially

and temporally), the most accurate method might not necessarily be the

best choice when compared with a simpler one that can provide a larger

number of samples with the same or lower investment.

An integrated approach for soil characterization is needed that combines

available methods with the analysis of the conceptual model used to identify

the governing property of a soil process, its intrinsic nature (variability), and

the ultimate use of the values obtained. This holistic approach should be

applied to the selection of methods to characterize energy and mass transfer

processes in the soil (i.e., water and solute flow), sorption, transformation,

and phase changes, including microbiological processes.

This book applies this integrated approach to present a comparative

discussion of alternative methods, their practical application for characteriza￾tion efforts, and an evaluation of strengths, weaknesses, and trade-offs. This

book is not a laboratory or field handbook. The authors present the

v

information with a critical spirit, showing benefits, limitations, and alternatives

to the methods when available. Numerous references to some of the excellent

handbooks and publications available are given for details on each of the

methods. Some nontraditional state-of-the-art characterization methods

(NMRI, x-ray tomography, fractals) and modeling techniques are also

presented as alternatives or as integral components.

The book is divided into six sections. (Fig. P.1) The first section defines the

basis for the integrated strategy that will be developed in the following sections

(i.e., need and use, issues of spatial and temporal variability, and modeling as

an integral part of the process). Sections II–IV present the critical evaluation of

methods available for energy and water transfer, chemical transport, and soil

microbiological processes. Different methods of characterization are presented

and compared using numerous tables and diagrams to help the users identify

the most suitable option for their application. Section V discusses tools and

applications to account for the intrinsic temporal and spatial variability and

scale of soil processes. The last section is devoted to modeling aspects including

uncertainty, inverse modeling, and practical recommendations.

Section I contains three chapters. In Chapter 1, Corwin and Loague discuss

the problem of subsurface non-point-source pollution and present the

application of an integrated array of multidisciplinary, advanced information

technologies useful in characterizing the process. This chapter introduces

FIGURE P.1. Book structure and contents roadmap.

vi Preface

the methods Sections II–IV. In Chapter 2, Campbell and Garrido explore the

role of deterministic and stochastic approaches to describe soil processes,

and how their intrinsic temporal and spatial variability affect method

selection in field studies. These issues remain the greatest challenges for

field research and limit the quantitative comparison of existing field

studies. This chapter provides the background for the chapters in Section V.

Chapter 3, written by Alvarez-Benedı´ et al., proposes that modeling

(conceptual and mathematical) is at the core of the characterization effort,

affecting not only the method selection but also the final application of

the study. A review of the conceptual building blocks needed to construct

a soil-water-solute mathematical model is presented here to illustrate

current assumptions and limitations when modeling soil-water-solute phenom￾ena. This chapter leads into the final section (VI) of the book.

Section II, devoted to soil physical processes, opens with Chapter 4, in

which Polo et al. offer a review of water and energy exchange processes

between soil-plant and the atmosphere. A comparison of methods to account

for energy and water balance, with emphasis on evapotranspiration, is

presented. This chapter serves as background for the rest of the section, in

which water or energy are discussed. The authors reflect on how the selection

and success of the physically based methods presented require knowledge

of the relevant spatial and temporal scales and a determination of the

uncertainty associated with the variables of interest. In Chapter 5 Mun˜oz￾Carpena et al. present current field methods to monitor soil water status.

Soil water potential and soil water content devices are presented and

compared in terms of desired moisture range to measure, soil type, accuracy,

soil volume explored by the device, soil salinity levels, device maintenance

and installation issues, and cost. A criterion to select the most suitable

method for a given application is presented. Chapter 6, by Reynolds and

Elrick, introduces current methods to characterize soil hydraulic parameters

that control soil water redistribution and flow. They point out that in situ

measurements are essential for dealing with the extreme complexity of the

field, and that rather than using a single method, the correct approach

seems to use a ‘‘suite’’ of complementary methods. They propose the

infiltrometer, permeameter, and instantaneous profile methods as the core

of such a suite of methods. In Chapter 7, Deurer and Clothier give an in￾depth look at the complex soil topology using two state-of-the-art methods —

NMRI and x-ray tomography. These complementary techniques provide a

new look at the microscopic scale and topology of pore geometry and of

water and solute transport. Although for most practical applications

these methods are not yet cost-effective, they may be so in the near future.

Chapter 8, by Shirmohammadi et al., offers a critical assessment of one of the

most daunting problems encountered when describing flow and transport

processes in the soil: preferential flow. Preferential flow, probably more often

than not, presents a limit to our classical description of such processes.

Different experimental methods to quantify the presence of preferential

paths are compared. A detailed presentation of the theoretical representation

Preface vii

of the process and alternative models follows, with emphasis on their

limitations. It is concluded that our handling of the preferential flow either

fails to be properly represented mathematically, or fails in the parametrization

for proper representation of the system.

Within Section III, dedicated to solute processes, Tuller and Islam

present in Chapter 9 an exhaustive review of field methods for characterizing

solute transport. They conclude that our ability to measure and characterize

spatial distribution of chemicals and preferential migration pathways is

restricted due to the application of in situ point measurements with

limited volume and geophysical techniques that only work indirectly or

qualitatively. The authors present electrical methods such as time domain

reflectometry (TDR), electrical resistivity tomography (ERT), and magnetic

induction as the most promising for large-scale and real-time monitoring.

In Chapter 10, Vogeler et al. show the modern application of the TDR

technique to measure not only water content but also saline solute

concentration through soil electrical conductivity (ECa) changes. The method

can be applied reliably and successfully to study nonreactive and reactive

solutes. Although the estimation of ECa with TDR is well established, the

relation of that with solute concentration is soil specific, influenced by

soil texture/structure and bulk density, and not yet fully understood. Two

weaknesses of the method are the relatively small zone of influence and

inability to discriminate between different ionic species. The method should

not replace existing monitoring techniques, but rather complement them.

In Chapter 11, Alvarez-Benedı´ et al. build on Chapters 3, 5, 9, and 10 to discuss

the laboratory characterization of solute transport through miscible displace￾ment experiments. This method is presented as the most important for

characterizing solute transport at small to large lysimeter (column) scale,

especially if several experiments can be performed varying hydrodynamic

conditions and tracers in the same column. However, extending this

methodology to the field scale is usually not feasible, and field experiments

like the ones presented in Chapter 9 are preferred for validation purposes of the

parameters obtained in the column studies. Chapter 12, by Cornejo et al.,

compares methods to determine sorption of pesticides in the soil. This process

controls pesticide transport in different soils and conditions and has important

environmental implications. The selection of the method is governed by the

accuracy required for the intended use and regulatory environment. In Chapter

13, Rochette and McGinn take a critical look at state-of-the-art methods to

quantify another controlling factor in the distribution and degradation of

contaminants from the soil, volatilization. Three types of techniques are

compared: soil mass balance, chambers, and micrometeorology. Because of the

usually significant error associated with any one technique, the authors

recommend the use of two techniques when possible to increase confidence in

the gas flux estimates. Further research is recommended in all these techniques

to reduce current uncertainty in measurements. Chapter 14 completes Section

III. Li et al. present a critical and exhaustive look at one important aspect often

overlooked by field researchers and practitioners in soil solute characterization

viii Preface

studies, i.e., the chemical analysis of the samples. There is a multitude of

available techniques to analyze any given element or compound. The selection

of the appropriate method is often complex, since new methods and techniques

are continuously entering the market. In addition, the intrinsic uncertainty,

interferences, and method detection limit (MDL) are not always taken into

account when interpreting the results, although these can vary greatly across

methods. Comparison of results obtained with a standard method is the

important criterion in the selection of an appropriate method. Laboratory

accreditation is discussed as a growing trend that will benefit the scientist and

clientele of analyses.

Section V (and Chapter 15) is devoted to the emerging area of soil

microbiological processes. Pell and Stenstro¨m discuss the fact that, although

soil quality is closely related to soil microbiology, the latter has received little

attention. This common oversight is at the root of many of the difficulties

found in measuring or predicting reactive solute transport of important

contaminants such us pesticides and fertilizers. The authors describe how

microbial respiration and nitrification/denitrification processes affect soil

sample handling, soil reactive behavior, and how microbial parameters can

be used in soil function description and assessment of special variability at

different scales. The authors conclude that cooperation between soil physicists,

chemists, and microbiologists is needed to advance our understanding of

soil processes.

Section VI reviews available techniques that could be incorporated in

methods to address the intrinsic soil variability. In Chapter 16, Van Meirvenne

et al. give a comprehensive review of available geostatistical techniques and

how to incorporate them in field and laboratory methods. Despite its promise,

there is no single solution for all situations, and the user must understand the

underlying hypotheses and limitations before embarking on a geostatistical

analysis. In Chapter 17, Kravchenko and Pachepsky present the use of fractals

as an innovative technique to address scaling issues in soil processes. Fractal

and multifractal techniques show promise in identifying scaling laws in soil

science. Although soils are not ideal fractals and because fractal scaling is only

applicable within a range of scales, these models present limitations. One

important advantage of fractal models of variability is their ability to better

simulate ‘‘rare’’ occurrences in soils (i.e., large pores, preferential pathways,

very high conductivities, localized bacteria habitats, etc.). These rare

occurrences often define soil behavior at scales coarser than observational

ones. Corwin provides in Chapter 18 an overview of the characterization of soil

spatial variability using ECa-directed soil sampling for three different

landscape-scale applications: (1) solute transport modeling in the vadose

zone, (2) site-specific crop management, and (3) soil quality assessment.

Guidelines, methodology, and strengths and limitations are presented for

characterizing spatial and temporal variation in soil physicochemical proper￾ties using ECa-directed soil sampling. Fast geospatial ECa measurements can

be made with available mobile electrical resistivity (ER) or electromagnetic

induction (EMI) equipment coupled with GPS. The author stresses that

Preface ix

without ground-truthing with soil samples, the interpretation of measurements

is questionable and is not advised.

Section VI is devoted to modeling tools. In Chapter 19, Trevisan and

Vischetti present the issue of modeling uncertainty across different scales.

Uncertainty analysis techniques are presented as well as sources of errors. Data

availability, choice of model, parameter estimation error, error propagation

in model linkages, and upscaling are presented as significant sources of error

that must be controlled in the modeling application. Chapter 20, by Lambot

et al., examines the utility of inverse modeling (IM) techniques to obtain

parameters for characterizing a soil process. Although IM is attractive, since it

can reduce the cost associated with experimental measurement of model

parameters, the success of the procedure depends on the suitability of the

forward model, objective function, identifiability of parameters, uniqueness

and stability of the inverse solution, and robustness of the IM algorithm.

A comparison of available techniques and possible pitfalls of this promising

technique are presented. Finally, Chapter 21 by Jantunen et al. discusses

the practical aspects of choosing a suitable model for a given purpose and how

to use it correctly and also reviews recent pesticide-fate models and their

practical applications.

In the words of D. Hillel (1971, Soil and Water, Physical Principles and

Processes), ‘‘No particular book by one or even several authors is likely to

suffice. The field [...] is too important, too complex and too active to be

encapsulated in any one book, which necessarily represents a particular point

of view.’’ We hope that the views presented herein by the excellent group of

authors will spark a critical sense in the reader when discussing methods for

soil process characterization.

R. Mun˜oz-Carpena

J. A´ lvarez-Benedı´

x Preface

Editors

Javier A´ lvarez-Benedı´ obtained his Science and Doctoral

Degrees at the University of Valladolid (Spain) in 1988

and 1992. His doctoral work was related to the

characterization and modeling of soil heat flux and

heat balance at the soil surface in greenhouses with

energy support at a fixed soil depth. After completing his

Ph.D. degree, he worked as a researcher at the Servicio

de Investigacio´n Agraria in Valladolid (Spain). In this

research center, he was involved in the characterization

of soil–solute processes such as sorption, transport, and

volatilization of soil applied pesticides at different work￾ing scales. The focus of his research has been modeling

and characterization as close-coupled topics. In 2003,

Dr. A´ lvarez-Benedı´ joined Instituto Tecnolo´gico

Agrario de Castilla y Leo´n, Valladolid, Spain, where he

provides technical oversight and program management.

Dr. A´ lvarez-Benedı´ has been an active member of the

Scientific Committee of the Spanish Vadose Zone Group

‘‘Zona no Saturada,’’ and he was the president of the

organizing committee at the biannual meeting held at

Valladolid in November 2003. He is a member of the Soil

Science Society of America and the International

Association of Hydrogeologists.

Rafael Mun˜oz-Carpena is an assistant professor in

hydrology and water quality at the University of

Florida’s IFAS/TREC and Department of Agricultural

and Biological Engineering (United States), and tenured

researcher on leave at the Instituto Canario de Investi￾gaciones Agrarias (Spain). He obtained his profes￾sional engineering degree at Universidad Polite´cnica de

Madrid (Spain) and his Ph.D. at North Carolina State

University (United States), where he developed and

tested a surface water quality numerical model,

VFSMOD. He has taught courses internationally in

hydrology, soil physics for irrigation, and instrumenta￾tion for hydrological research. Currently his work is

focused in hydrological and water quality issues

xi

surrounding the Everglades restoration effort in Florida (United States), one of

the most expensive and ambitious environmental projects in history. His work

involves field and computer modeling activities to understand water flow and

quality in the area, including solute transport in the soil. He has been an active

member of the Scientific Committee of the Spanish Vadose Zone Group for the

last 10 years, where soil characterization research has been a central issue. Dr.

Mun˜oz-Carpena serves as Associate Editor for Transactions of ASAE and

Applied Engineering in Agriculture and is a member of the American Society of

Agricultural Engineers and the American Geophysical Union.

xii The Editors

Contributors

Javier A´ lvarez-Benedı´

Instituto Tecnolo´gico Agrario de Castilla y Leo´n

Valladolid, Spain

Lars Bergstro¨m

Division of Water Quality Management

Swedish University of Agricultural Sciences

Uppsala, Sweden

S. Bolado

Departamento de Ingenierı´a Quı´mica

Universidad de Valladolid

Valladolid, Spain

David Bosch

Research Hydraulic Engineer

USDA-ARS, SEWRL

Tifton, Georgia

Moira Callens

Laboratory of Hydrology and Water Management

Ghent University

Gent, Belgium

Chris G. Campbell

Earth Sciences Division

Lawrence Livermore National Laboratory

Livermore, California

Ettore Capri

Istituto di Chimica Agraria ed Ambientale

Universita` Cattolica del Sacro Cuore

Piacenza, Italy

Rafael Celis

Instituto de Recursos Naturales y Agrobiologı´a

de Sevilla, CSIC

Sevilla, Spain

xiii

Brent E. Clothier

Environment and Risk Management Group

HortResearch Institute

Palmerston North, New Zealand

Juan Cornejo

Instituto de Recursos Naturales y Agrobiologı´a

de Sevilla, CSIC

Sevilla, Spain

Dennis L. Corwin

USDA-ARS

George E. Brown, Jr. Salinity Laboratory

Riverside, California

Lucı´a Cox

Instituto de Recursos Naturales y Agrobiologı´a

de Sevilla, Sevilla

CSIC

Spain

Markus Deurer

Institute for Soil Science

University of Hannover

Hannover, Germany

Ahmed Douaik

Department of Soil Management and Soil Care

Ghent University

Gent, Belgium

Marı´a P. Gonza´lez-Dugo

Department of Soils and Irrigation

CIFA, Alameda del Obispo, IFAPA

Co´rdoba, Spain

David E. Elrick

Department of Land Resource Science

University of Guelph

Guelph, Ontario, Canada

Fernando Garrido

Department of Soils

Centro de Ciencias Medioambientales, CSIC

Madrid, Spain

Juan Vicente Gira´ldez

Department of Agronomy

University of Co´rdoba

Co´rdoba, Spain

xiv Contributors