Photobiogeochemistry of organic matter principles and practices in water environments

DOM in natural waters is composed of a heterogeneous ture of organic compounds with molecular weights ranging from less than 100 to humic acids of terrestrial origin are the dominant DOM

For further volumes:

Principles and Practices in Water Environments

Khan M G Mostofa · Takahito Yoshioka

M Abdul Mottaleb · Davide Vione

Editors

1 3

Photobiogeochemistry

of Organic Matter

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ISSN 1431-6250

ISBN 978-3-642-32222-8 ISBN 978-3-642-32223-5 (eBook)

DOI 10.1007/978-3-642-32223-5

Springer Heidelberg New York Dordrecht London

Library of Congress Control Number: 2012952610

M Abdul Mottaleb Department of Chemistry and Physics Northwest Missouri State University Missouri

USA Davide Vione Department of Analytical Chemistry University of Turin

Turin Italy

Dissolved Organic Matter in Natural Waters 1

Khan M G Mostofa, Cong-qiang Liu, M Abdul Mottaleb,

Guojiang Wan, Hiroshi Ogawa, Davide Vione, Takahito Yoshioka

and Fengchang Wu

Photoinduced and Microbial Generation of Hydrogen Peroxide

and Organic Peroxides in Natural Waters 139

Khan M G Mostofa, Cong-qiang Liu, Hiroshi Sakugawa,

Davide Vione, Daisuke Minakata and Fengchang Wu

Photoinduced Generation of Hydroxyl Radical

in Natural Waters 209

Khan M G Mostofa, Cong-qiang Liu, Hiroshi Sakugawa,

Davide Vione, Daisuke Minakata, M Saquib and M Abdul Mottaleb

Photoinduced and Microbial Degradation of Dissolved Organic Matter

in Natural Waters 273

Khan M G Mostofa, Cong-qiang Liu, Daisuke Minakata,

Fengchang Wu, Davide Vione, M Abdul Mottaleb,

Takahito Yoshioka and Hiroshi Sakugawa

Colored and Chromophoric Dissolved Organic Matter in Natural

Waters 365

Khan M G Mostofa, Cong-qiang Liu, Davide Vione,

M Abdul Mottaleb, Hiroshi Ogawa, Shafi M Tareq and

Takahito Yoshioka

Fluorescent Dissolved Organic Matter in Natural Waters 429

Khan M G Mostofa, Cong-qiang Liu, Takahito Yoshioka,

Davide Vione, Yunlin Zhang and Hiroshi Sakugawa

Contents

Photosynthesis in Nature: A New Look 561

Khan M G Mostofa, Cong-qiang Liu, Xiangliang Pan,

Takahito Yoshioka, Davide Vione, Daisuke Minakata, Kunshan Gao,

Hiroshi Sakugawa and Gennady G Komissarov

Chlorophylls and their Degradation in Nature 687

Khan M G Mostofa, Cong-qiang Liu, Xiangliang Pan, Davide Vione,

Kazuhide Hayakawa, Takahito Yoshioka

and Gennady G Komissarov

Complexation of Dissolved Organic Matter with Trace Metal

Ions in Natural Waters 769

Khan M G Mostofa, Cong-qiang Liu, Xinbin Feng,

Takahito Yoshioka, Davide Vione, Xiangliang Pan and Fengchang Wu

Impacts of Global Warming on Biogeochemical Cycles

in Natural Waters 851

Khan M G Mostofa, Cong-qiang Liu, Kunshan Gao, Shijie Li,

Davide Vione and M Abdul Mottaleb

Editors Biography 915

1 Introduction

Organic matter (OM) in water is composed of two major fractions: dissolved and non-dissolved, defined on the basis of the isolation technique using filters (0.1–0.7 μm) Dissolved organic matter (DOM) is the fraction of organic sub-stances that passes the filter, while particulate organic matter (POM) remains on

Dissolved Organic Matter in Natural Waters

K M G Mostofa et al (eds.), Photobiogeochemistry of Organic Matter,

Environmental Science and Engineering, DOI: 10.1007/978-3-642-32223-5_1,

© Springer-Verlag Berlin Heidelberg 2013

Khan M G Mostofa, Cong-qiang Liu, M Abdul Mottaleb, Guojiang Wan, Hiroshi Ogawa, Davide Vione, Takahito Yoshioka and Fengchang Wu

K M G Mostofa (*) · C Q Liu · G Wan

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry,

Chinese Academy of Sciences, Guiyang 550002, China

e-mail: mostofa@vip.gyig.ac.cn

M A Mottaleb

Center for Innovation and Entrepreneurship (CIE), Department of Chemistry/Physics,

Northwest Missouri State University, 800 University Drive, Maryville, MO 64468, USA

H Ogawa

Atmospheric and Ocean Research Institute, The University of Tokyo, 1-15-1, Minamidai, Nakano, 164-8639 Tokyo, Japan

D Vione

Dipartimento di Chimica Analitica, University of Turin, I-10125 Turin, Italy

Centro Interdipartimentale NatRisk, I-10095 Grugliasco (TO), Italy

or terrestrial material from soils, (ii) autochthonous or surface water-derived of algal or phytoplankton origin, and (iii) syhthetic organic substances of man-made

or industrial origin DOM in natural waters is composed of a heterogeneous ture of organic compounds with molecular weights ranging from less than 100 to

humic acids) of terrestrial origin are the dominant DOM fractions in freshwater

fulvic acids (or marine humic-like) of algal or phytoplankton and bacterial origin

addi-tion, among the major classes of DOM components there are carbohydrates, teins, amino acids, lipids, phenols, alcohols, organic acids and sterols (Mostofa

DOM can display physical properties such as the absorption of energy from

DOM can photolytically generate strong oxidants such as superoxide

play a role in its photoinduced decomposition in natural waters (Mostofa and

Correspondingly, DOM can undergo photoinduced and microbial degradation processes, which can produce a number of degradation products such as dis-

DOM, organic acids These compounds are very important in the aquatic

et al 2010; Ballaré et al 2011; Zepp et al 2011) DOM with its degradation ucts can extensively influence photosynthesis, thereby playing a key role in global

water quality, complexing behavior with metal ions, water photochemistry, ical activity, photosyhthesis, and finally global warming

biolog-This chapter will provide an overview on the origin of DOM, its contents and sources in natural waters, the contribution of organic substances to DOM, the bio-geochemical functions of DOM, its physical and chemical properties, as well as its molecular size distribution It comprehensively discusses the controlling fac-tors and their effects on the distribution of DOM in natural waters, the emerging contaminants and their sources, transportation and impacts, as well as methodol-ogies and techniques for the detection of pharmaceuticals in fish tissue Finally,

it is discussed how DOM acts as energy source for living organisms and aquatic ecosystems

2 What is Dissolved Organic Matter?

DOM is conventionally defined as any organic material that passes through

a given filter (0.1–0.7 μm) The organic material that is retained on the filter is

from ultrafiltration (<10 kiloDaltons or kDa) is often defined as the truly solved organic carbon fraction and the filter-passing fraction between >10 kDa and

dis-<0.4 or 0.7 μm as the total dissolved organic carbon fraction in aqueous solution Colloids are operationally defined as particles between 1 nm and 1 μm in size, and

with pore sizes between 0.2 and 0.7 μm DOM can be in the size range of tens to hundreds of nm when they are associated with other colloidal materials in water

fraction, approximately 10–40 %, of the marine DOM pool

DOM in natural waters is composed of a heterogeneous mixture of numerous allochthonous and autochthonous organic compounds containing low molecu-lar weight substances (e.g organic acids) and macromolecules such as fulvic and humic acids (humic substances), with molecular weight ranging from less than

found in natural ground and surface waters are also referred as natural organic matter (NOM) The most common organic substances are humic substances

(fulvic and humic acids) of terrestrial origin, autochthonous fulvic acids of toplankton or algal origin, carbohydrates, sugars, amino acids, proteins, lipids, organic acids, phenols, alcohols, acetylated amino sugars, and so on On the other hand, POM includes plant debris, detritus, living organisms, bacteria, algae, phy-toplankton, corals, coral reefs, and so on DOM is considered as the larger pool of organic matter in a variety of waters, which can include more than 90 % of total

2.1 Biogeochemical Functions of OM (DOM and POM)

DOM of both allochthonous and autochthonous origin can play multiple functions

in photoinduced, chemical, microbial and geochemical processes in natural waters They can be classified as follows:

are involved in the photoinduced degradation of organic compounds (Vione

DOM undergoes rapid photoinduced decomposition by natural sunlight, and this process is less efficient in waters with high contents of DOM and more

can thus control redox and photo-Fenton reactions in natural waters (Voelker

(2) Microbial functions of OM (DOM and POM) DOM and POM are

for the maintenance of the microbial loop in natural waters (utilization of DOC by bacteria, consumption and decomposition of bacteria by protozo-

substrates produced from DOM and OM either photolytically or

bial degradation of DOM or POM can control the food-chains for

bio-geochemical functions of microbial processes are discussed in details in

“Photoinduced and Microbial Degradation of Dissolved Organic Matter in

(3) Optical (or physical) functions of DOM: a fraction of DOM is named as either colored and chromophoric dissolved organic matter (CDOM) based on the absorption of ultraviolet (UV) and photosynthetically available radiation (PAR), or fluorescent DOM (FDOM) based on the emission of fluorescence photons after radiation absorption DOM generally controls the downward irradiance flux through the water column of UV-B (280–320 nm), UV-A (320–400 nm), total UV (280–400 nm) as well as photosynthetically avail-

trans-parency, occurrence of the euphotic zone and thermal stratification in the surface waters of lakes and oceans because it affects (decreases) the pen-

Nutrients are produced by degradation of DOM and typically derive from dissolved organic nitrogen (DON) and dissolved organic phosphorus

mostly released during the photoinduced and microbial respiration (or assimilation) of POM (e.g algae or phytoplankton biomass), as shown

by in situ experiments conducted under light and dark incubations (Kim et

Kopáček et al 2004; Fu et al 2005; Mostofa KMG et al unpublished data)

Green 2004; Kopáček et al 2004; Lehmann et al 2004; Minero et al 2007) Nutrients produced by DOM and OM can fuel new primary and second-ary production in natural waters Total contents of DOM in lake waters are responsible for variation of the trophic level, due to eutrophication/oligotrophication processes The latter are a major driver of change for chemical vari-ables such as major ions, nutrients (phosphorus and nitrogen compounds, sil-ica) and the chemical nature of DOM.

(5) DOM can control photosynthesis in natural waters DOC can limit

Photoinduced and microbial oxidation of DOM is responsible for the

released by DOM and POM might also favor the occurrence of sis and subsequently enhance the cyanobacterial or algal blooms in natural

in waters with high contents of DOM, and the reverse happens in low-DOM

(6) Chemical functions of OM (DOM and POM) DOM and POM are posed of various functional groups in their molecular structures, which can form complexes with trace metal ions (M) in aqueous solution via

These studies imply that the M-DOM complexation is important for tion, bioavailability, transport and ultimate fate of trace metal ions in the water environment The detailed functions of M-DOM complexes are discussed in Complexation of Dissolved Organic Matter With Trace Metal Ions in Natural

(7) Maintenance of the drinking water quality by DOM and POM in waters

on the DOM contents in natural waters, and POM can produce new thonous DOM and nutrients under both irradiation and microbial respiration

autoch-or assimilation (Mostofa et al 2005a, 2009b; Zhang et al 2009; Kim

Kopáček et al 2004; Fu et al 2005) Simultaneously, DOM can release

the drinking water quality, but DOM can also balance acidity and alkalinity

(8) OM can maintain global carbon cycle processes through production, tion, transportation and decomposition of carbon compounds in the biosphere

house gases and contribute to the global carbon cycle (Davidson and Janssens

sup-ply, particularly in peat soils This is attributed to elevated net primary ductivity of plants and increased root exudation of DOC in soil environments,

(9) Character and energy functions of OM in the water ecosystem DOM and POM can provide a major source of energy, in the form of C and N, which

produced during the photoinduced and microbial degradation of DOM and organic matter, photoinduced redox reactions, microbial loop, as well as

for the growth of bacterial films on the surface of drinking-water pipes, a cess that involves also fulvic and humic acids (humic substances) depending

pro-on their occurrence in groundwater in developing and developed countries

3 Origin of DOM in Natural Waters

DOM is generally originated from three major sources in natural waters: (i) DOM derived from terrestrial soils, termed allochthonous DOM; (ii) DOM derived from

in situ production in natural surface waters, termed autochthonous DOM, and (iii) DOM derived from human activities (e.g industrial synthesis), termed anthropo-genic DOM

3.1 Origin of Allochthonous DOM in Soil Ecosystems

DOM including fulvic and humic acids (humic substances) originates from the decomposition of vascular plant material, root exudates and animal residues in ter-restrial soil Origin of allochthonous DOM from vascular plant materials or partic-ulate detrital pools is significantly varied in different regions (tropical, temperate and boreal), which is regulated by the occurrence of three key factors or functions

temperature and moisture; (ii) Chemical functions that include nutrient ability, amount of available free oxygen and redox activity, and (iii) Microbial processes that include microfloral succession patterns and availability of microor-ganisms (aerobic or anaerobic)

avail-It is suggested that microorganisms can alter sugars, starch, proteins, cellulose and other carbon compounds bound to organic matter of plant or animal origin during their metabolic processes These processes can transform the aromatic and lipid plant components into amphiphilic molecules including humic substances, i.e., molecules that consist of separate hydrophobic (non-polar) and hydrophilic

of relatively unaltered segments of plant polymers, while the polar parts include

organic matter at a faster rate than anaerobic ones, depending on the availability

of free oxygen Compositional changes of DOM occur with soil depth, leading to

a decrease of aromatic compounds and carbohydrates whilst alkyl, methoxy and

carboxylic C with depth are the result of biodegradation of forest litter and

The origin of allochthonous DOM from microbial processes can be judged from significant variations in respired organic carbon in different soil environ-

is lowest (1 year) in tropical forest soils (eastern Amazonia, Brazil), relatively

low (3 years) in temperate forest soils (central Massachusetts, USA), and

indicate that DOM, which is transported over decimetres or metres down into soil, mainly represents highly altered residues of organic matter processing (Schiff

that allochthonous DOM is mostly derived, in zero to a few decimeter depth from the decomposition of plant material by microbial processes in soils and shallow

DOC leached from soil is partly retained in the vadose zone before

partly discharged through hydrological processes directly into streams or riverbeds

or surrounding water bodies, which ultimately flux to lake or oceanic ments as final water reservoir

environ-3.2 Origin of Autochthonous DOM in Natural Waters

Production of autochthonous DOM is generally observed at the epilimnion (upper water layers) compared to the hypolimnion (deeper layers) during the sum-mer stratification period, particularly in lakes and oceans A rough estimation by comparing the upper with the deeper layers demonstrates that the contribution of autochthonous DOM is largely varied in lakes and oceans: it reaches 0–55 % in Lake Hongfeng (181–250 μM C at 0–6 m and 161–223 μM C at 22–25 m depth, respectively, during March–September), 3–47 % in Lake Baihua (183–264 μM C

at 0–3 m and 157–206 μM C at 14–15 m during March-September), 6–35 % in Lake Baikal (93–142 μM C at 0–100 m and 88–105 μM C at 600–720 m during August–September in 1995, 1998, 1999), 3–82 % in Lake Biwa (93–183 μM C

at 2.5–10 m and 78–101 μM C at 70 m during May–September in 1999–2002), 21–49 % in Lake Ashino in Japan (99–111 μM C at 0–10 m and 74–84 μM C at 30–38 m in September 1997), 81–102 % in Lake Ikeda in Japan (101–112 μM C

at 0–10 m and 55–56 μM C at 200–233 m for site I1; at 41 m for site I2 in October 1997), 52 % in Lake Suwa in Japan (216 μM C at 0 m in September and

142 μM C at 0 m in December 1997), 61–81 % in Lake Inawashiro in Japan (42–

47 μM C at 0–10 m and 26 μM C at 70 m), 13–29 % in Lake Fuxian (123–135

Hovsgol (95 μM C at 0 m and 80 μM C at 50–200 m in July 1999), 0–88 % in Lake Kinneret (270–485 μM C at 0–10 m and 258–368 μM C at 38 m during the summer period in 2004), 17–41 % in Lake Peter (data not shown), 11–29 % (bio-logical production) in Lake Bret, 0–104 % in Middle Atlantic Bight (82–98 μM C

at 0 m and 48–90 μM C at 90–2600 m in June 2001), 16–77 % in Western North Pacific (85–117 μM C at 0 m and 66–73 μM C at 150 m), 0–194 % in Atlantic Ocean (50–97 μM C at <100 m and 33–59 μM C at >1000 m), 0–165 % in Pacific Ocean (40–90 μM C at <100 m and 34–45 μM C at >1000 m), 28–121 %

in Indian Ocean and Arabian Sea (55–95 μM C at <100 m and 43 μM C at

>1000 m), 0–121 in Antarctic Ocean (38–75 μM C at <100 m and 34–60 μM C

at >1000 m), as well as 0–118 % in Arctic Ocean (34–107 μM C at <100 m and

The contribution of extracellular release of photosynthetically-derived DOM

a high water temperature (WT) than in those with a low water temperature, ticularly in the Arctic Ocean The key contributors to autochthonous DOM in natural waters as well as in sediment pore waters are considered to be phyto-plankton or algal biomass, bacteria, coral, coral reef, submerged aquatic vegeta-tion, krill (shrimp-like marine crustaceans), seagrass, and marsh- and mangrove

These studies demonstrate that autochthonous DOM is produced from POM by several processes such as photoinduced and microbial respiration (or assimilation), zooplankton grazing, bacterial release and uptake, viral interactions, and complex microbial processes in sediment pore waters

3.2.1 Respiration or Assimilation of Algae or Phytoplankton

Species and Bacteria

Algae or phytoplankton biomass and bacteria can release new DOM in ral waters by two key processes: first, photoinduced respiration or assimilation

natu-of algae or phytoplankton biomass and bacteria, which can produce new DOM

Second, microbial respiration or assimilation of algae or phytoplankton and

et al 2004; Yamashita and Tanoue 2004, 2008; Wada et al 2007; Hanamachi et al

Re-suspension of algae or phytoplankton in ultrapure water (Milli-Q), ficial sea water and natural waters can release new organic compounds, either under irradiation or under dark incubation These organic substances, produced

(excitation-emission matrix, EEM) properties The EEM spectra of

they are different from allochthonous humic acids that show more than two peaks

component of autochthonous fluorescent DOM is defined as “autochthonous

is defined as “autochthonous fulvic acid (M-like)” of algal or phytoplankton

Peak A

Peak C Peak M

(b) (a)

Ex wavelength (nm)

(e) (d)

Fig 1 Comparison of the fluorescent components of autochthonous fulvic acid (C-like)

pro-duced under microbial respiration of lake algae (a), autochthonous fulvic acid (C-like) under photorespiration or assimilation of algal biomass (b) and autochthonous fulvic acid (M-like) under microbial respiration of algae (c) with aqueous samples of standard Suwannee River Ful- vic Acid (d) and Suwannee River Humic Acid (e) identified using PARAFAC modeling on the

EEM spectra of their respective samples Data source Mostofa KMG et al., (unpublished data)

discussed extensively in the FDOM chapter (see chapter “Fluorescent Dissolved

algal or phytoplankton origin are newly termed in this study for mostly two sons: first, to distinguish and generalize between all freshwaters and marine waters; second, because of the confusion in different studies that use several

DOM is produced significantly by eleven species of intertidal and sub-tidal macroalgae when they are illuminated, providing evidence for a light-driven exu-

has been detected as 6.4 and 17.3 % of the total organic carbon in cultures of

Chlorella vulgaris and Dunaliella tertiolecta, respectively, upon light exposure

bio-mass, representing a further loss of algal assimilated carbon in water (Hulatt and

particu-late amino acids and non-protein amino acids are often decreased in downstream rivers, which is likely the result of photoinduced degradation of DOM and algae

On the other hand, the key processes of autochthonous DOM release by bial respiration of algae or phytoplankton biomass in waters are presumably the extracellular release by living cells, cell death and lysis, or herbivore grazing that may occur in the deeper waters of rivers, lakes and oceans (Mostofa et al

a specific role in subsequent processing of the DOM released by algae in

kinds of phytoplankton (green algae Microcystis aeruginosa and Staurastrum

dor-cidentiferum and dark-brown whip-hair algae Cryptomonas ovata collected from

lake waters) shows that fulvic acid-like and protein-like fluorescent components are released when they are cultivated under a 12:12 h light/dark cycle in a MA

implies that the increase of the refractory organic matter in lake waters may be attributed to a change of the predominant phytoplankton Similarly, cultivation of

three kinds of phytoplankton (Prorocentrum donghaiense, Heterosigma akashiwo and Skeletonema costatum collected from sea water) can produce visible humic-

like (C-like and M-like) and protein-like or tyrosine-like components in waters

Releases of DOM by eleven species of intertidal and sub-tidal gae in the dark account for 63.7 % of that in the light in the UV-B band (Hulatt

canaliculata), which are more comparable to the green and red species (Hulatt

the plume during the highly stratified summer period but are absent in the spring,

which is the strong evidence of significant in situ biological production of CDOM

Incubation of coastal seawater in the presence of model (DON: amino ars and amino acids) and DIN compounds shows that net biological DOM for-mation occurs upon addition of amino sugars (formation of fluorescent, mostly labile DOM) and tryptophan (formation of non-fluorescent, refractory DOM)

rap-idly produce refractory material (in <48 h) utilizing labile compounds (glucose,

other hand, photoinduced formation of DOM is only detected when tryptophan

excitation-emission matrices (EEMs) resembling those of terrestrial, humic-like

dur-ing the decomposition process of freshwater or marine algae and ton is significantly decreased during the first few days It subsequently remains

con-tents of both the particulate and dissolved pools are increased during the toplankton growth cycle, accounting for 18–45 % and 26–80 % of total organic

Photoreactions driven by UV-B can reduce the microbial availability of certain organic substrates such as peptone and algal exudates (Morris and Hargreaves

caused by light-induced cross-linking between DOM and algal exudates (Morris

LMW organic acids are presumably formed by four major processes (Lovley

pho-toinduced decomposition of allochthonous and autochthonous DOM in surface waters; second, photoinduced and microbial respiration or assimilation of algae or phytoplankton biomass in natural waters; third, conversion of anaerobic organic

soil ecosystems; and fourth, root exudations of plants or plant–microbe tions (e.g Rhizobium symbiosis with leguminous roots)

associa-A number of factors can influence the DOC release by algae or ton and bacteria in waters, which can be distinguished as: (i) occurrence of the phytoplankton species and their contents; (ii) water quality; (iii) presence of nutrients; (iv) effect of UV and PAR; (v) water temperature; (vi) occurrence of

3.2.2 Photosynthesis

Photosynthesis is the key process for the formation of organic carbon or OM (e.g algae or cyanobacteria, phytoplankton, etc.) through light-stimulated inor-

then able to produce autochthonous DOM via photoinduced respiration (or toinduced assimilation) and microbial respiration or assimilation in natural waters

be involved in the occurrence of oxygenic photosynthesis in both higher plants

includes two facts: the first is the generation of numerous chemical species from DOM, which may proceed as follows: (i) photoinduced degradation of DOM can

photosynthe-sis either directly or indirectly and lead to fixation of organic carbon or OM from

microbial degradation of DOM and POM can take part to photosynthesis, to form

where Cx(H2O)y represents a generic carbohydrate (Eq 3.3) According to this

and the atmosphere (see the photosynthesis chapter for detailed description for

produced during photosynthesis

Currently, model results imply that the progressive release of DON in the ocean’s upper layer during summer increases the primary production by 30–300 % This will in turn enhance the DOC production mostly from phyto-plankton exudation in the upper layer and the solubilization of POM deeper in

quantity and the spectral quality of DOM produced by bacteria can be influenced

Photosynthetically produced POM (algae or phytoplankton) and their photo- and microbial respirations are significantly influenced by several key factors, such as

high transport of DOC from catchments to adjacent surface waters (Worrall et al

3.3 DOM Derived from Anthropogenic and Human Activities

Organic pollutants derived from sewerage and from domestic, agricultural and industrial effluents significantly contribute to increase the concentration levels

problem in both developed and developing countries through input of untreated sewerage and industrial effluents into natural waters However, its impacts may be much worse in developing countries due to the lack of sewerage treatment and of industrial effluent treatment plants The occurrence of DOM derived from anthro-pogenic and human activities is gradually increasing because of the increasing dif-fusion of domestic, agricultural and industrial activities Some components of sewerage-impacted DOM are made up of detergents or fluorescent whitening agents (FWAs), including mostly diaminostilbene type (DAS1) and distyryl biphe-nyl (DSBP), protein-like components, sterols, and unknown organics (McCalley

pesti-cides, herbipesti-cides, dichlorodiphenyltrichloroethane (DDT) and their degradation

Recent studies show that emerging organic contaminants such as cals and personal care products (PPCPs) are a ubiquitous class of organic chemi-cals of considerable concern for natural waters, and will be discussed in details later Wastewater-derived organic compounds can produce three major types

pharmaceuti-of toxic byproducts such as trihalomethanes (THMs), N-nitrosodimethylamine (NDMA) and organic chloramines These compounds may be formed either upon

chlorination or in conventional and advanced wastewater treatment plants (Scully

4 Contribution of Organic Substances to DOM

in Natural Water

The contributions of major organic substances in streams and rivers to the total DOM pool are 20–85 % of humic substances, of which 15–80 % fulvic acid and 5–29 % humic acid (the ratio of fulvic acid to humic acid is 9:1 for lower stream DOC and it decreases to 4:1 or less for higher stream DOC), 10–30 % of carbo-hydrates, 2–48 % of dissolved amino acids, organic acids or hydrophilic acids (9–25 %), autochthonous fulvic acids of phytoplankton or algal origin (or marine

acids, organic peroxides (ROOHs), sterols; organic contaminants of

gener-ally include amino acids, proteins, carbohydrates and free sugars The tion of humic substances (hydrophobic acids) in groundwater is approximately 12–98 % (1–80 % of fulvic acid and 2–97 % of humic acid), and the contribu-

studies observe high variation in the contribution of humic substances from stream (source) to the end of river mouths The main reasons are the mixing up of vari-ous sources of water in the downstream locations as well as the photoinduced and microbial changes during transportation

In lakes the contributions of humic substances (fulvic and humic acids) account for 14–90 % of total DOM (14–70 % of fulvic acid and 0–22 % of humic acid); the DOM pool is also made up of ~12–60 % of autochthonous fulvic acids (see FDOM chapter for detailed description) of algal or phytoplankton origin; of car-bohydrates for 1–65 %; of amino acids, proteins and organic acids that together account for 10–33 % of total DOM; of organic acids (2.5–7.5 %, but 0–11 %

in pore water); sterols; algal toxins, organic contaminants of anthropogenic

and Handa 1987; Baron et al 1991; Søndergaard and Middelboe 1995; Reitner et

carbohydrates and proteins) as well as organic acids account for approximately

70 % of high molecular weight (HMW) DOM, and only for approximately 2 %

that allochthonous fulvic acids in lakes are largely varied during the summer and winter season, with winter maxima and summer minima Their total content is also low in algal-dominated lakes

The percentages of major organic substances in bulk DOM in shelf, coastal and open ocean are: 1–75 % of allochthonous fulvic acids of terrestrial origin;

also FDOM chapter for detailed description) of algal or phytoplankton origin; 10–80 % of carbohydrates (~25 % in deeper layers); 10–28 % of amino acids, proteins and lipids taken together (amino acids alone account for 7 %); organic acids; organic peroxides (ROOH); sterols; algal toxins, and so on (Mostofa et al

con-tributions of allochthonous humic substances in shelf seawater are 11–75 %, of which around 38 % of marsh origin and 62 % of river origin (Moran and Hodson

col-umn by algae or phytoplankton under photo- and microbial respiration (Mostofa

and lipids are vital biochemical organic groups that together constitute mately 10–80 % of organic carbon and 15–50 % of the nitrogen assimilated dur-

including organic acids (~14–40 %) such as acetic and formic acid, dicarboxylic acids (~<6 %, including oxalic, succinic, malonic and maleic acids), pyruvic acid (~<1 %), amino acids (~2 %) including tryptophan-like and tyrosine-like compo-nents, formaldehyde (~2–8 %), acetaldehyde (~5 %), organic peroxides (ROOHs:

rainwa-ter mostly consists of low molecular weight organic substances, having MW < 1000 Dalton Note that factors such as wind speed, storm trajectory and rainwater volume can influence DOM contents in rainwater The relative importance of these factors

The contribution of allochthonous fulvic and humic acids is significantly high

in source waters (streams and rivers), then their contributions decrease during the flow into the downward water ecosystem (lakes, estuaries and oceans) because of three major processes: first, photoinduced and microbial degradation; second, dilu-tion of the source waters with other water bodies; third, high contents of autoch-thonous DOM can decrease the relative contribution of allochthonous fulvic and humic acids in stagnant waters, particularly in lakes, estuaries and oceans

On the other hand, the contribution of autochthonous DOM including thonous fulvic acids of algal or phytoplankton origin, carbohydrates, proteins, amino acids, lipids, organic acids etc is relatively low in source waters, but sig-nificantly high in lakes and oceans Autochthonous production of DOM is typi-cally detected in the epilimnion of lake and ocean during the stratification period

autoch-A rough estimate shows that the contribution of autochthonous DOM is 0–102 %

in lakes and 0–194 % in oceans, which has been discussed in earlier section

The sterol biomarkers used for identifying DOM sources in water are terrestrial (b-sitosterol and ergosterol), sewage (5b-coprostanol and epi-coprostanol), phy-toplankton (cholest-5,22-dien-ol, brassicasterol, dinosterol), and marine markers

con-sidered to originate from terrestrial plants, while short-chain alkanols have

of waters, it is evidenced that, on average, approximately 80–90 % of bulk DOM

in streams, rivers, lakes and oceans is specifically identified as allochthonous vic and humic acids, autochthonous fulvic acids, carbohydrates, proteins, lipids, amino acids, fatty acids, sterols, and organic acids

ful-4.1 Physical and Chemical Properties of DOM

Naturally-originated organic compounds such as humic substances (fulvic and humic acids) of terrestrial plant origin, autochthonous DOM of algal or phyto-plankton origin, proteins, amino acids, peptides and polysaccharides exhibit,

heterogeneous; (ii) polyfunctional, due to the existence of a variety of functional groups and the presence of a broad range of functional reactivity; (iii) polyelec-trolytical, with high electric charge density due to the presence of a large number

of dissociated functional groups; (iv) structurally labile, because of their capacity

to associate intermolecularly and to change molecular conformation in response

to changes in pH, pE, ionic strength, trace metal binding, and so on; (v) perse in size

polydis-Water Color:

The yellow color in natural waters is due to the occurrence of humic stances (fulvic and humic acid) and of autochthonous fulvic acids (C- and M-like) of algal or phytoplankton origin, which absorb light in the blue

color is an important feature of water that was recently determined using

phytoplankton origin as well as partly to allochthonous fulvic and humic acids (humic substances) A recent study has shown that autochthonous fulvic acids (C-like and M-like) of lake algal origin under dark incubation can exhibit yel-

and M-like) are characterized based on their similar fluorescence properties

to allochthonous fulvic acids (C-like and M-like), which will be discussed

Attenuation of Spectral UV Irradiance

DOM is the key factor that controls the downward irradiance flux through the water column of UV-B (280–320 nm), UV-A (320–400 nm), total UV (280–

400 nm) and photosynthetically available radiation (PAR, 400–700 nm) (Kirk

and Sugiyama 2008; Effler et al 2010) These studies show that UV-B penetration depths vary from only a few centimeters in highly humic lakes to dozens of meters

in the oceans, due to variation in DOM contents It is also observed that 99 % of the UV-B radiation is attenuated in an approximately 0.5-m water column in the

clearest lake for DOC ranging from 408 to 725 μM C and for chlorophyll a

the corresponding attenuation is limited to the upper one meter

The absorption coefficients predict that, in a small humic lake (DOC 1100–

1242 μM C), UV-B radiation is attenuated to 1 % of the subsurface ance within the top 10 cm water column, whereas UV-A radiation (at 380 nm)

However, in clear lakes with low DOC concentration the contribution of

Any enhancement of photoinduced degradation of DOC by UV radiation and acidification can substantially increase the UV transparency in lakes (Morris and

water column, which can significantly damage aquatic biota DOM is thus sible for UV attenuation in the water column and for the related protection of aquatic organisms in natural waters

respon-Aggregation of DOM

Aggregation of fulvic and humic acid (humic substances) can occur at the molecular (involving a single polymer molecule) or intermolecular (involving

aggre-gates is relatively hydrophobic, whilst the exterior is more hydrophilic They can exist in a pseudomicellar form or as micelle-like aggregates in solution,

humic acids isolated from natural environments (water, soil, peat, sediments, and sludge from wastewater treatment facilities) demonstrate that the per-centage elemental composition, the contents of carboxylic groups and of aro-matic phenolic groups is very variable They range from 33.2 (river) to 60.7 % (Aldrich) of C; 2.25 (river) to 5.4 % (soil) of H; 0.65 (river) to 3.7 % (peat) of N; 34.1 (Aldrich) to 63.8 (river) of O; 0.06 (soil) to 0.10 % (sewage sludge) of

Humic acids behave like surface-active substances when they are added to solutions, which depend on their origin and molecular properties Therefore, their

functional groups such as the benzene ring in phenolic structures with the tion of hydrophilic sulfonic, hydroxyl or trimethylammonium functional groups

thus modifying autotrophic primary production and the dependent food chains; and (ii) By acting as a direct carbon/energy source for food chains

4.1.1 Redox Behavior of Fulvic and Humic Acids

Fulvic and humic acids (humic substances) can act as reductants and oxidants in

oxi-dation states of the redox-sensitive actinides (e.g Pa, Np, U, Pu) are stabilized by complexation with fulvic and humic acids Fulvic and humic acids are thus capable

of detoxifying surface water and soils contaminated with toxic organic and inorganic chemicals Some examples are (i) reduction of metals from toxic valence states to

reductive cleavage of halogenated hydrocarbons such as trichloroethylene, a common pollutant in soil and groundwater, which can be degraded to ethylene and hydrochlo-

com-peting ion as well as methylation of the carboxylic groups of humic and fulvic acids,

organic nitro groups to amines For instance, trinitrotoluene (TNT) is reduced to pounds such as aminodinitrotoluene that can form complexes with fulvic and humic

groundwater

On the other hand, it has also been observed that the functional groups in vic and humic acids can be oxidized, as is the case of catechol moieties (oxidized

ful-to quinones), aldehydes (ful-to carboxylic acids), alcohols (ful-to aldehydes or

pres-ence of intermediates such as semiquinones in fulvic and humic acids A typical redox process involving fulvic acids (FA) and humic acids (HA) can be depicted

For instance, SRHA has standard reduction potential E° = 760 ± 6 at pH

(2.1)

Skogerboe and Wilson 1981; Matthiesen 1994; Struyk and Sposito 2001) Some studies also suggest that functional groups such as quinone or quinone-like moie-ties in fulvic and humic acids are largely responsible for the observed reversible

donate electrons photolytically in aqueous media, which can induce the

The presence of diverse functional groups in the molecular structure of vic and humic acids is responsible for their redox behavior in waters The redox behavior of humic acids depends on the redox potential of the aqueous solu-tions as well as on the complexation capacity with multicharged cations in water

4.1.2 Definition and Chemical Nature of Allochthonous Fulvic

and Humic Acids

Allochthonous DOM of vascular plant origin is primarily composed of humic substances (fulvic and humic acids), which are also termed as hydrophobic acids Stream fulvic and humic acid are therefore vital to understand the nature of the allochthonous DOM, because the chemical composition and optical properties of these substances are greatly altered photolytically and microbially during their transportation after leaching from soil into rivers, lakes or oceans

Allochthonous Fulvic Acids

Allochthonous fulvic acids can be defined as molecularly heterogeneous and supramolecular, with molecular weight ranging from less than 100 to over 300,000 Daltons and with the largest fractions ranging less than 50,000 They are opti-cally active, typically refractory to microbial degradation, photolytically reac-tive, biogenic, and yellow-colored They are also soluble under all pH conditions

contents of organic N compared to organic C, i.e a high C:N ratio This ratio is

in the range ~45–202, and standard SRFA (1S101F and 2S101F) have values of 73–78 Allochthonous fulvic acids also have relatively high contents of O and organic P, low contents of S, relatively low aromaticity (17–30 % of total C) and

Meyers-Schulte and Hedges 1986; Ma et al 2001; McIntyre et al 2005; Frimmel

Allochthonous fulvic acids are supramolecular structures composed of a variety of functional groups or components such as benzene-containing car-boxyl groups, ketones, methoxylate and phenolic groups (catechol-type), carboxylic and di-carboxylic groups, ethers, esters, amides, aliphatic OH, car-bohydrate OH, –C = C–, hydroxycoumarin-like structures, chromone, xan-thone, quinones, flavones, O, N, S, and P-atom-containing functional groups attached to aromatic and aliphatic C, indole groups, degraded lignins, and so on

phenylpropanoid biopolymers including only C, H, and O atoms in their ular structure They are mostly found in wood cells, whereas the main build-ing blocks for the phenyl portion of lignins are coumaryl, coniferyl, and sinapyl

is degraded by fungi and eventually bacteria through different pathways that include depolymerization, demethylation, side-chain oxidation, and aromatic

In humic substances, 60–90 % of the acid groups are carboxylic and the

is present in humic substances in many different oxidation states: organic sulfides (R–S–R), thiol (–SH), di– and polysulfides (R–S–S–R), sulfoxide (R–SO–R), sul-

Depending on the major elemental composition of C, H, O and N disregarding

on accurate mass measurements, molecular formulas have been assigned to 4626 individual Suwannee River fulvic acids with molecular masses between 316 and 1098 Da, which led to plausible structures consistent with degraded lignin

on average 5.5 mmoles of carboxyl groups per gram, which corresponds to one carboxylic group per six carbon atoms, or one group per aromatic ring if distrib-uted evenly; (ii) has an average phenolic group content of 1.2 mol per gram, which means one phenolic group per 30 carbon atoms, or only two phenolic groups per

fulvic molecule; and (iii) has hydroxyl and carbonyl groups that, put together,

hydroxyl or carbonyl group every three carbon atoms Amino acids, amino

–27.6 ‰, while other isolated allochthonous fulvic acids in rivers have [–(25.6–26.4 ‰)] and in lakes have [−(23.02–33.13) ‰] These data indicate that SRFA

Terrestrial DOM from groundwater, streams, rivers, lakes and sea water

deciduous leaves (–30.4 ‰), it increases in the top soil (–28.9 ‰) and then from –27.8 to –26.4 ‰ in soil Plant leaves with C3 photosynthesis have

has lower values in litter-rich soil DOC [−(26.6–27.7 ‰)] than in ing soil DOC [approximately −(23–27 ‰)] or terrigenous soil with surface/forest litter [−(23–27 ‰)], terrestrial leaf OM (−27 ‰), terrigenous vascular plant [−(26–30 ‰)], yellow soil profile [−(21.1–24.8 ‰)] or limestone soil

significantly dependent on the types and nature of terrestrial vegetation in soil environments

the DOC pool is carried to the stream by discharging groundwater This DOC

proba-bly has a low proportion of labile functional groups Although groundwater tributions to stream flow are high even during storm events, groundwater DOC concentrations are low The relative contribution of this older recalcitrant pool

con-is limited by the amount of soluble carbon which elutes through the overlying soil column The second pool is composed of recently fixed and potentially more microbially labile DOC leached from the A horizon or litter layer The potential contribution of this second pool is very high especially after leaffall

Allochthonous Humic Acids

Allochthonous humic acids in surface waters can be defined as molecularly erogeneous and supramolecular, with molecular weight ranging from less than

het-500 to over 300,000 Daltons The largest fraction is found in the range larger than 300,000 Daltons They are optically active, typically refractory to microbial degradation, photolytically reactive, biogenic, and yellow-colored organic acids

of various origin (soil, bog peat, sewerage sludge) have relatively high contents

of organic N to organic C, i.e they have relatively low C:N atomic ratio (8–51) Standard SRHA (1S1011H and 2S101H) have C:N = 44–45 Allochthonous humic acids also have relatively low contents of O and organic P, high contents

of S, relatively high aromaticity (30–40 % of total C) and relatively low contents

the contents of aromatic and other functional groups are very variable depending

on the different sources of humic acids and their photobiogeochemical changes

in natural waters The aromaticity of humic acids is very low (~15 %) in marine

Allochthonous humic acids have a supramolecular structure composed of a variety of functional groups (or fluorophores), such as aromatic carboxylic and di- carboxylic acids, aromatic OH groups including phenols (or catechols) and phe-nolic acids, aliphatic or carbohydrate OH, aldehyde or aliphatic ketones, amide/amino groups, peptides, esters (COOR) or benzene-containing methoxylates, poly-

qui-none, O, N, S, and P-atom-containing functional groups attached to aromatic and aliphatic carbon, methylated forms of para-coumaric, ferrulic, vanillic and syringic

on the elemental compositions of C, H, O, and N, an empirical formula for humic

C72H72O30N4·8H2O (Steelink 2002; Schnitzer and Khan 1978; Paciolla et al 1998)

which indicates that they are most likely derived from higher plant matter (IHSS

2011) Note that Standard HAs of Elliot Soil have δ13C = −22.6 ‰; Pahikee peat

average values are −170 ± 79 ‰ for humic acid and −44 ± 73 ‰ for fulvic

4.1.3 Definition of Autochthonous Fulvic Acids and Chemical

Nature of Autochthonous DOM

The key autochthonously produced biochemical organic groups or substances

autoch-thonous fulvic acids (C-like and M-like) of algal (cyanobacteriam) or toplankton origin; carbohydrates such as uranic acids, amino sugars and neutral sugars including free mono-, oligo- lipopoly-, exopoly-, homopoly-, and heteropolysaccharides; nitrogen-containing organic compounds including amino acids, proteins, amines, amides, urea, purines, pyrimidines, peptides, polypep-tides, pyrrole, and indole; lipids, including saturated, monounsaturated, polyun-saturated, branched-chain and odd-chain fatty acids (mostly composed of oleic acid, arachidonic acid, eicosapentanoic acid, linoleic acid, docosahexaenoic acid,

fatty acids; organic acids including mono-, di- and tri-carboxylic acids, late, and hydroxamate; allelopathic compounds There are also steroidal alcohols

glycol-(sterols) such as 24-methyl-cholesta-5,24(28)-dien-3ß-ol, 3ß-ol, cholesta-5,22E-dien-3ß-ol, cholest-5-en-3ß-ol, cholesta-5,22-dien-3ß-ol, 27-Nor-24-methylcholesta-5,22-dien-3ß-ol, 4α,23,24-trimethyl-5α-cholest-22E- en-3ß-ol (dinosterol), 24-methylcholesta-5,22-dien-3ß-ol, 24-ethylcholesta-5,22E- dien-3ß-ol, 24-ethylcholesta-5-en-3ß-ol, 24-ethylcholesta-5,24(28)E-dien-3ß-ol, 24-n-propylcholesta-5,24(28)E-dien-3ß-ol, 3-methyllidene-7,11,15-trimethylhexa-

24-ethylcholest-5-en-decan-1,2-diol (phytyldiol); vanillyl and syringyl phenols including vanillin, tovanillone, vanillic acid, syringaldehyde, acetosyringone and syringic acid from lignin-derived oxidation products; bisnorhopane and various alkenones such as

6,10,14-trimeth-ylpentadecan-2-one; pigments including melanin, mycosporine-like amino acids (shinorine, palythine, porphyra-334, palythene and usujirene); carotenoids (dia-dinoxanthin, zeaxanthin, myxoxanthophyll, and echinenone); algal toxins (mostly cyanobacterial toxins produced from blue–green algae) including microccystins, nodularins, anatoxins, cylindrospermopsin, and saxitoxins; red tide toxins includ-

Richardson 2007; Singh and Singa 2002; Miller et al 2002; Hama et al 2004;

“Autochthonous fulvic acids” of algal or phytoplankton origin are molecularly heterogeneous, with molecular weight ranging from less than 100 to over 1,898 Daltons They are optically active, biogenic, highly photoreactive, microbially

seawa-ter have relatively high contents of dissolved organic N compared to organic C, i.e low C:N atomic ratios (ca 8–36, but lower in surface waters and higher in deeper waters) They are rich in S, highly aliphatic in nature and have low contents of

(C:N = 8–36) than allochthonous standard fulvic and humic acids (C:N = 44–78) This may indicate that autochthonous fulvic acids are less refractory than alloch-thonous fulvic and humic acids, probably because autochthonous DOM has fewer aromatic compounds and relatively more proteins and lipids, which decreases its carbon to nitrogen ratio compared to allochthonous DOM (McCallister et al

which are esters of fatty acids and alcohols that comprise a large group of turally distinct organic compounds including fats, waxes, phospholipids, glycolip-

components of the diet of humans and animals and are becoming important feed

Spectroscopic studies of isolated autochthonous fulvic acids show that they are composed of methylated isomers of hydroxy-benzenes and hydroxy-benzoic acids, aliphatic acids, carbohydrate OH, protein amide and amine groups; they also contain Schiff-base derivatives (–N = C–C = C–N–), fatty acid methyl esters (heptanedioic acid, octanedioic acid, nonanedioic acid, methyl tetradecanoate, 12-methyl-tetradecanoic acid, 7-hexadecenoic acid, and hexadecanoic acid), N- and S-containing amino and sulfidic functional groups The latter include 3-(methylthio)-propanoic acid; dimethyl sulfone; N,N-dimethyl-2-butanamine, N-methyl pro-line; N-methyl aniline; 3-piperidinemethanol; 1-methyl-2,5-pyrrolidinedione; 1-methyl-2-piperidinone; caprolactam; 3-ethyl-1,3-dimethyl-2,5-pyrrolidinedione; 2-amino-5,6-dihydro-4,4,6-trimethyl-4 H-1,3-oxazine; 3-ethyl-2,6-piperidinedi-

one; 1,3,5-trimethyl-1,3,5-triazine-2,4,6-trione; 1,3-dimethyl-2,4-pyrimidinedione; 2-methyl-isoindole-1,3-dione; 5-methoxy-2-methyl-indole; 1,3,5-trimethyl-2,4-py-rimidinedione; and 3,3-dimethyl-4-[(2-methoxycarbonyl)ethyl]-2,5-dione-pyrro-

pre-sent in autochthonous DOM originate from intracellular quinones in the chloroplasts

Algal toxins such as as microcystins and nodularins have high molecular weight and cyclic peptide structures and are hepatotoxic; anatoxins, cylindrosper-mopsin and saxitoxins have heterocyclic alkaloid structures Anatoxins and saxi-

On the other hand, red tide toxins such as brevetoxins have heterocyclic polyether structures and are neurotoxic Note that bacteria, algae and their exudates also consist of a mosaic of functional groups such as amino, phosphoryl, sulfhydryl and carboxylic groups The net charge on the cell wall depends on the pH of the

Algal- or phytoplankton-derived autochthonous fulvic acids can absorb light to

a lesser extent (by approximately 3–5 times) than allochthonous fulvic acids They show a progressive increase in absorbance with decreasing wavelength that is typi-

ful-vic acids (C-like and M-like) of algae or phytoplankton origin can exhibit higher fluorescence intensity at peak C-region than at peak A-region, which is an opposite behavior compared to allochthonous fulvic acids (C-like and M-like) of terrestrial

fulvic acids can persist with ages up to 3,000 yr in the desert lakes in Antarctica

or phytoplankton origin ranges from −17.2 to 23.7 ‰ in lake and marine

fresh-water [−(18.3–34.6 ‰)] and sea fresh-water [−(18–24.2 ‰)] (Mostofa KMG et al.,

high variations between benthic microalgae [−(12–18 ‰)]; benthic marsh algae [−(23.7–27.7 ‰)]; C-4 salt marsh plants [−(12–14 ‰)]; C-3 freshwater/brackish marsh plants [−(23–26 ‰)]; submerged macrophytes [−(21.7–22.2 ‰)]; emergent macrophytes (−26 ‰); marsh macrophytes [−(23.3–28.9 ‰)]; marsh

micro-OM [−(22.3–26.4 ‰)]; and freshwater grass leachate such as Peltandra

et al 1998; Fry and Sherr 1984; Currin et al 1995; Sullivan and Moncreiff 1990) Depending on the origin of DOM from these algae and plants, there can be found variable carbon isotope ratios for DOM in natural waters.

The autochthonous DOM of algal or phytoplankton origin is usually very able for bacterial use, as suggested by the pattern of increased bacterial produc-

However, autochthonously derived DOC may become persistent over time (Ogawa

shown that natural assemblages of marine bacteria become rapidly able (in <48 h)

to utilize labile compounds (glucose, glutamate) and produce refractory DOM that

only 10–15 % of the bacterially derived DOM is identified as hydrolysable amino acids and sugars, which is a characteristic nature of marine DOM (Ogawa et al

most likely accounted for by the produced autochthonous DOM in natural waters

4.2 Molecular Size Distribution of DOM

The molecular size distribution of DOM is significantly variable in natural waters

tangen-tial flow ultrafiltration (also called cross-flow ultrafiltration) The results show that the contributions of the various fractions to total DOC are 21–65 % for the frac-tion <1 kDa, 44–68 % for <5 kDa, 57–65 % for <10–12 kDa Moreover, they are

41 % for 1–30 kDa, 32–56 % for 1 kDa–0.1 μm, 67–84 % for 1 kDa–0.45 μm,

various DOM fractions are 42–73 % for <1 kDa, 54–79 % for <5 kDa, 21–43 %

for 1–3 kDa, 63–75 % for <10 kDa, 25–31 % for 1–30 kDa, 2–45 % for 1 kDa–0.2 μm, 22–48 % for 3 kDa–0.2 μm, 14–20 % for 30 kDa–0.2 μm, and 1–2 %

and open oceans, the contributions of the relative DOM fractions are 30–85 % for

<1 kDa (30–70 % in coastal waters, 49–85 % in the open ocean), 23–53 % for the fraction between 1 kDa and 10 kDa, 3–19 % for the fraction between 10 kDa and 0.1–0.2 μm, 15–70 % for the fraction between 1 kDa and 0.2 μm, 85 % for

Table

et al 2010; Midorikawa and Tanoue 1998; Carlson et al 1985; Sugimura and

of the lower MW fraction (<1–10 kDa) is relatively low in rivers and that it nificantly increases in lakes, coastal waters and the open ocean Comparison of molecular fractions between surface (epilimnion) and deep (hypolimnion) waters shows that the molecular size fraction of <1–5 kDa in deep water is often more

that either microbial degradation of DOM or new releases of DOM from bial respiration of organic matter in deeper waters are responsible for the high contents of the low molecular size fractions of DOM in natural waters An addi-tional implication is that significant microbial or biological degradation of DOM and organic matter occurs in deep waters The high percentage of colloidal DOC

micro-or colloidal micro-organic carbon included in the >1 kDa to 0.45 μm range suggests that colloids are the predominant phase in bulk DOC transported by rivers (Guéguen

fractions of sedimentary fulvic acid extracted from Tokyo Bay sediment samples are 44.8 % for <1 kDa, 3.5 % for 10 kDa, 31.8 % for 50 kDa, 14.6 % for 100 kDa and 5.3 % for 300 kDa The corresponding contributions of humic acid are 2.4 % for <1 kDa, 0.8 % for 10 kDa, 5.3 % for 50 kDa, 16.1 % for 100 kDa and 75.4 %

fulvic acid is mostly composed of low molecular size fractions (<1–10 kDa) whilst allochthonous humic acid is mostly composed of high molecular size fractions,

distin-guish between fulvic and humic acids in DOM in a variety of natural waters.These results also imply that allochthonous fulvic acid of terrestrial origin or the autochthonous fulvic acid (C-like) of algal or phytoplankton origin can primar-ily undergo photoinduced and microbial in situ degradation, which can decrease the molecular size and increase as a consequence the low molecular size fraction