Aquatic Humic Substances: Ecology and Biogeochemistry

349 Pages·1998·10.95 MB·English

by  Dag O. Hessen

Ecological Studies, Vol. 133
Analysis and Synthesis
Edited by
M. M. Caldwell, Logan, USA
G. Heldmaier, Marburg, Germany
O. 1. Lange, Wiirzburg, Germany
H. A. Mooney, Stanford, USA
E.-D. Schulze, Bayreuth, Germany
U. Sommer, Kiel, Germany
Ecological Studies
Volumes published since 1992 are listed at the end of this book
Springer-Verlag Berlin Heidelberg GmbH
D. O. Hessen 1. J. Tranvik (Eds.)
Aquatic Humic
Substances
Ecology and Biogeochemistry
With 79 Figures and 14 Tables
, Springer
PROF. DR. DAG O. HESSEN
University of Oslo
Department of Biology
Div. Limnology
P.O. Box 1027, Blindern
0315 Oslo
Norway
J.
DR. LARS TRANVIK
Linkoping University
Department of Water and Environmental Studies
58183 Linkoping
Sweden
ISSN 0070-8356
ISBN 978-3-642-08362-4
Library of Congress Cataloging-in-Publication Data
Hessen, D. O. (Dag Olav), 1956-,Tranvik, L. J. (Lars J.), 1959-
Aquatic humic substances: ecology and biogeochemistry 1 D.O. Hessen, L.J. Tranvik, (eds.) p. cm. -
(Ecological studies / Analysis and synthesis, ISSN 0070-8356; vol. 133) Includes bibliographical refe
rences and index.
ISBN 978-3-642-08362-4 ISBN 978-3-662-03736-2 (eBook)
DOI 1O.1007/978-3-662-o3736-2
1. Freshwater ecology. 2. Humus -
Environmental aspects. H541.5.F7 A61998 577-6 dC21 97-048264
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Foreword
Understanding of the structure of aquatic ecosystems moved forward swiftly
during the past century. The basic premises of food-web structures and
feeding relationships among trophic levels have been studied in remarkable
detail, and consistent patterns of population and community relationships
are emerging for aquatic ecosystems of different physical and chemical envi
ronmental properties.
As the metabolism of community components was analyzed with in
creasing accuracy, however, flux pathways and rates of transfer of organic
carbon demonstrated a number of complexities and inconsistencies that
could not be explained within the conventional food-web paradigms. Six
pervading alterations of prevailing wisdom have arisen in the past two dec
ades. Firstly, the observed biotic productivity of most lakes and rivers cannot
possibly be supported by the autochthonous organic carbon generated by
pelagic primary productivity within these waters. The aquatic biotic produc
tivity must be supplemented by external quantities of allochthonous organic
matter imported from terrestrial and land-water interface regions. Only re
cently have a number of diverse and thorough studies demonstrated that
these external sources are often dominating, which indicates that most in
land aquatic ecosystems are largely heterotrophic ecosystems.
Secondly, a large portion (usually> 90%) of the organic matter imported
to these aquatic ecosystems is predominantly in dissolved or colloidal form.
Although a portion of the dissolved organic compounds may aggregate and
shift to a particulate and hence gravitoidal form that may sediment out of
the water, most of the imported dissolved organic matter is dispersed within
the water and moved about with the hydrodynamics of the water body.
Thirdly, much of the dissolved organic matter derives from lignin and re
lated structural precursor compounds of higher plants. These substances are
abundant, chemically complex, and relatively recalcitrant to rapid biological
degradation. These compounds are variously modified by microbial activities
during transport and partial decomposition in soils, wetlands, and littoral
areas before movement to the receiving lake or river. Because of limited ac
cessibility of large portions of these molecules to enzymatic hydrolysis, the
low degradation rates of many of these macromolecules, as well as their
common acidic properties, slow turnover times result in long residence
times. Dissolved macromolecules are often of considerable age (years) but
are mixed with variable and rapidly changing inputs of younger humic sub-
VI Foreword
stances. In addition, recent studies are demonstrating that humic substances,
particularly fulvic acids, are generated by algae and contribute to the multi
tude of diverse compounds that make up the dissolved humic substances. As
a result of the recalcitrance of all of these compounds, the dissolved organic
matter can reside within lakes and rivers for long periods of time (months,
years).
Despite the apparent chemical recalcitrance of humic substances and the
belief that these compounds were poorly used by microbiota, a fourth major
paradigm is emerging that these compounds can form major energy sources
in aquatic ecosystems. Physical processes, such as partial photochemical al
teration, can result in changes in availability of portions of the macromole
cules by cleavage of simple compounds that are readily degraded by mi
crobes. These photochemical changes can also alter enzymatic accessibility
to the residual macromolecules. Despite continued massive loading of dis
solved humic substances to aquatic ecosystems, accumulation does not occur
and large releases of excessive CO to the atmosphere indicate extensive bio
2
logical degradation of these compounds. The mechanisms of degradation of
these dissolved humic substances represent a major void in our understand
ing and a place where interdisciplinary collaboration among chemists and
biologists is essential in order to progress effectively.
A fifth revelation from continued intensive study of dissolved humic sub
stances in aquatic ecosystems consists of the many ways in which these di
verse compounds can interact with inorganic and other organic compounds,
associate with inert and living surfaces, alter chemical properties such as re
dox and pH, and change physical properties such as selective modifications
of light penetration. The result is a profound potential alteration of the
aquatic environment for biota and their growth and productivity. Examples
are many. The predominance of humic acids results in an organic acidity that
can influence and at times exceed inorganically derived acidity from natural
or anthropogenic ally induced sources. Humic substances can complex metals
and influence biotic availability and toxicity. Humic compounds can inhibit
free and surface-bound enzymes and materially alter nutrient recycling and
availabilities. Membrane properties, such as lipid hydrophobicity, can be al
tered by humic substances. Light is selectively attenuated by dissolved hufnic
substances and can change markedly the availability of spectral portions that
influence photosynthesis, hormonal activities, and migratory distribution
and reproductive behaviors. Absorption of ultraviolet irradiance by humic
substances can both protect organisms from genetic damage as well as mod
ify macromolecules and enhance bioavailability of organic substrates.
Lastly, for many years I have promulgated that the large amounts of dis
solved humic organic matter and their slow but collectively dominating utili
zation provide a thermodynamic stability to metabolism within lake and
river ecosystems that is essential for the maintenance of efficient nutrient re
cycling. As a result, most inland aquatic ecosystems are strongly detritus
dependent, and the trophic dynamics are likely predominantly controlled by
Foreword VII
the microbial interactions with humic compounds that can markedly influ
ence nutrient recycling rates. Despite great resistance to this idea, the same
mechanisms likely prevail in the oceans as well. Evidence presented in this
book enhances and strongly supports these viewpoints, at least for lakes, riv
ers, and coastal marine areas.
Aquatic Humic Substances: Ecology and Biogeochemistry is an excellent
synthesis of the state of the art of this complex subject regarding the many
interactive ways that humic compounds influence the properties, dynamics,
and metabolism of aquatic ecosystems. Every topic discussed above, as well
as other important facets, have been treated in appreciable detail. Three ma
jor aspects result from such a composite treatment. The coupling of the
sources of aquatic humic substances, produced both internally and exter
nally, to regulation of properties and metabolism within the waters provides
the important ecosystem perspectives that are essential to our understanding
as well as management of aquatic systems. The dominant pelagic influence
that has so strongly governed study and dogma in limnology and oceanog
raphy is gradually relaxing as we gain understanding of the coupled integra
tion of the land to the waters. Secondly, some of the analyses attempt to cou
ple the effects within drainage basins to larger global alterations of climate
on hydrology and nutrient cycling. Dissolved humic substances are a pri
mary vehicle of that coupling. Lastly, the messages of this synthesis empha
size the great complexities of the regulation of biological dynamics in aquatic
ecosystems. We are progressing beyond the important but simplistic ideas
that phosphorus and nitrogen are dominant regulators; it is rather aquatic
humic compounds that impose a multiplicity of dynamic controls of me
tabolism.
Tuscaloosa, Alabama, March 1998 Robert G. Wetzel
Bishop Professor of Biological Sciences
University of Alabama
Contents
Humic Substances as Ecosystem Modifiers - Introduction
D.O. Hessen and L.J. Tranvik ............................................................................. .
I Biogeochemical Aspects ............................................................................ 7
1 Sources and Age of Aquatic Humus
D. M. McKnight and G.R. Aiken ............................................................. 9
1.1 Introduction ............................................................................................. 9
1.2 Isolation and Characterization of Aquatic Humus ............................... 13
1.3 Formation Pathways of Aquatic Humus ................................................ 19
1.4 Sources of Aquatic Humus in Aquatic Ecosystems ............................... 25
1.4.1 The Microbial End Member .................................................................... 28
1.4.2 The Plant/Soil End Member ................................................................... 29
1.5 The Age of Aquatic Humus ..................................................................... 30
1.5.1 Fulvic Acid Production and Transport in the Snake River
and Deer Creek Watershed ...................................................................... 32
1.5.2 Fulvic Acid Production and Transport in Lake Fryxell ........................ 34
1.6 Conclusions .............................................................................................. 36
1.7 Summary .................................................................................................. 36
References ............................................................................................................ 37
2 Chemical Composition, Structure, and Metal Binding Properties
E.M. Perdue ............................................................................................... 41
2.1 Introduction ............................................................................................. 41
2.2 Elemental Composition, Structural Features, and Bioavailability ...... 42
2.2.1 Analytical Constraints Calculations ...................................................... 43
2.2.2 Compositional Variability and Uncertainty .......................................... 44
2.2.3 Structural Variability ............................................................................... 45
2.2.4 Bioavailability ........................................................................................... 47
2.3 Mathematical Models of Cation Binding ............................................... 50
2.3.1 Modeling Objectives ................................................................................ 51
x Contents
2.3.2 Competitive Gaussian Distribution Model......................................... 51
2.3.3 Model V ................................................................................................... 53
2.3.4 The NICA Model.................................................................................. 55
2.3.5 Summary Comparison of Models ...................................................... 57
2.4 Summary............................................................................................... 58
References ........... ............... ............ ................................ ................................ .... 59
3 Humus and Acidification
E. Lydersen ................................................................ ............................ 63
3.1 Introduction ......................................................................................... 63
3.2 Water pH and Acid Neutralising Capacity........................................ 64
3.3 Quality and Quantity of Organic Acids of DOC............................... 65
3.4 Dissolution of Organic Acids with pH ............................................... 70
3.5 Effects of DOC on pH of Norwegian Lakes ....................................... 73
3.6 Cation Exchange Reactions with Humic Matter ............................... 80
3.7 Aluminium Toxicity to Biota and Effects of DOC ............................ 81
3.8 Summary............................................................................................... 85
References. ...................... .............. ...................... ................... ............................ 86
4 Climatic and Hydrologic Control of DOM Concentration
and Quality in Lakes
P.]. Curtis .... ......................................................................................... 93
4.1 Introduction ......................................................................................... 93
4.2 DOM Concentration ............................................................................ 94
4.3 DOM Quality ........................................................................................ 99
4.4 Effects of Climate Change on DOM in Lakes .................................... 100
4.5 Sensitivity of Aquatic Systems to Changes
in DOM Quantity and Quality ............................................................ 102
4.6 Summary. .............................................................................................. 103
References .......................................................................................................... 104
II Humus, Light Regimes and Primary Production ......................... 107
5 Attenuation of Solar Radiation in Humic Waters
D. Lean ................................................................................................... 109
5.1 Introduction ......................................................................................... 109
5.2 Measurements of Attenuation Coefficients for UV-B and UV-A .... 109
5.3 Relationship Between Attenuation and DOC
and DOC Fluorescence ........................................................................ 113
Contents XI
5.4 Relationship Between DOC and DOC Fluorescence (DOCFL) ....... 116
5.5 Using Absorbance Values to Predict UV Attenuation in Lakes ....... 117
5.6 Influence of Climate Change and Lake Acidification
on DOC Levels ...................................................................................... 118
5.7 Surface Water Photochemistry ........................................................... 119
5.7.1 Interaction of UV Radiation and Humic Materials
in Controlling Lake Mercury Levels ................................................... 119
5.7.2 Interaction of UV Radiation and Humic Materials
on Toxic Chemicals .............................................................................. 120
5.7.3 Photochemical reactions ..................................................................... 120
5.8 Summary. .............................................................................................. 122
References .......................................................................................................... 123
6 Effects of UV Radiation on Aquatic Humus:
Photochemical Principles and Experimental Considerations
W.L. Miller ............................................................................................. 125
6.1 Introduction ......................................................................................... 125
6.2 Some Fundamentals of Aquatic Photochemistry ............................. 126
6.2.1 Absorption of Light ............................................................................. 126
6.2.2 Photochemical Efficiency .................................................................... 128
6.2.3 Reaction Rates ...................................................................................... 131
6.3 Evaluating Photochemical Rates for Natural Waters ........................ 133
6.3.1 Apparent Quantum Yield .................................................................... 134
6.3.2 Spectral Irradiance ............................................................................... 137
6.3.3 Absorptivity .......................................................................................... 138
6.3.3.1 Self-Shading .......................................................................................... 139
6.3.3.2 Photochemical Fading ......................................................................... 139
6.4 Summary ............................................................................................... 140
References .......................................................................................................... 141
7 Phytoplankton, Primary Production and Nutrient Cycling
R.I. Jones ............................................................................................... 145
7.1 Introduction ......................................................................................... 145
7.2 Physical Effects ..................................................................................... 146
7.3 Chemical Effects ................................................................................... 154
7.4 Adaptations by Phytoplankton in Humic Lakes ............................... 162
7.5 Phytoplankton Community Structure in Humic Lakes ................... 165
7.6 Summary. .............................................................................................. 168
References .......................................................................................................... 169