O l i g n i n M e O O l i - PowerPoint Presentation

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Dissolved

Organic

Matter

Slides and figures from Mark Williams, Diane McKnight, Bailey Simone, Rose Cory, Matt Miller, Rachel Gabor,

Eran

Hood

Slide2

Complex, heterogeneous mixture

Truly ubiquitous (ALL waters)

Colored (gives water its color)

Moderate molecular weight

Mass Distribution:

50% C

35-40% O

4-6% H

1-6% N

<1-3%S

Slide3

Why DOM Matters

Light absorbing DOM can act as sunscreen and control depth of

photic

zone

Some DOM is bio-available and contains nutrients

Organic acid portion of DOM can buffer pH

Some DOM can act as metal

complexing

agents (fate & transport and bioavailability of metals)

Hydrophobic organic pollutants can partition into some portion of DOM

Some DOM can act as electron acceptors and donors

Reducer

and oxidizer

Some DOM can “sensitize” the photochemical breakdown of pollutants

Reactions with some DOM can produce toxic disinfection byproducts during drinking water treatment

Slide4

Soluble Decomposition Products

PlantsMicrobes (bacteria, algae)

Man-made (organic pollutants)

Plant

DOM

Microbial

DOM

Sources of DOM

Slide5

DOM Pie

(sometimes called

hydrophobic)

So how do we learn anything from this complex mixture?

Slide6

CHEMISTRY!

Slide7

Chemistry is all about electrons

Slide8

Electrons have discrete energy levels

(characteristic of the substance)

Slide9

Electrons can move between energy levels

Slide10

Electrons

Orbitals have Specific Shapes

Slide11

Molecules can have conjugated bonds

(Molecular Orbital Theory!)

Slide12

Molecules can be aromatic

Slide13

So how does this awesome chemistry help us?

Spectroscopy!

Interaction of light and matter

Specifically….

UV-VIS

Fluorescence

Slide14

Grab

your sample

Filter

your sample

Run it on a DOC analyzer for Dissolved Organic Carbon (DOC) and Dissolved Organic Nitrogen (DON) concentrations

Spectroscopy!

Slide15

UV-VIS Spectroscopy and SUVA

254

Slide16

UV-VIS Spectroscopy and SUVA

254

Absorbance Spectra of a DOM sample

SUVA

254

is the absorbance at 254 nm normalized to the DOC concentration

Slide17

UV-VIS Spectroscopy and SUVA

254

Higher SUVA

254

means greater degree of

aromaticity!

Slide18

Fluorescence Spectroscopy

S

0

S

1

S

2

Absorbance

Δ

E =

λ

Fluorescence

Δ

E

≠

λ

Δ

E = Emission

λ

– Excitation

λ

= Stokes Shift

Geometry Rearrangements..Requires E!!

Internal conversion

vibrational relaxation

Slide19

Fluorescence Spectroscopy

Slide20

Quinones found in enzymes, e.g ubiquinone, and formed by lignin oxidation.

Forms of this complex are found throughout cells

Important in electron transfer reactions, such as the oxidation of NADH

Also known as coenzyme Q

“Q”

“HQ”

Ubiquinone

Brief

Interlude

For

More

Chemistry

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Quinones!

Slide22

What does

a DOM Fluorescence Spectrum Look Like?

Emission (nm)

Excitation (nm)

Protein-like

humic

Despite chemical diversity of DOM, similar

steady state

fluorescence spectra observed for ALL DOM

EEMs

; this strongly implies common pool of

fluorophores

Slide23

Fluorescence Index

Excitation (nm)

Emission (nm)

Ratio of emission intensity (470 nm / 520 nm) at 370 nm excitation

Slide24

Fluorescence Index

FI

Higher number = more microbial input

Lower number = more terrestrial (plant) input

Slide25

Excitation-emission matrix

(EEM)

Comp. 1

Comp. 2

Comp. 3

Fluorescence - PARAFAC

Part 2: Fluorescence Spectroscopy

Stedmon et al. 2003

Slide26

PARAFAC

Components

Oxidized

Quinone

-Like Components

Reduced

Quinone

-Like Components

Amino Acid-Like Components

Unknown Components

Slide27

Fluorescence Index

Redox Index

Component Ratio

Specific UV Absorbance (SUVA)

(254 nm)

UV-VIS Absorbance Scan

3-D Fluorescence Scan

UV-VIS Absorbance Scan

Dissolved Organic Carbon

Modeled in Cory + McKnight Parallel Factor Analysis (PARAFAC) Model yields..

+

+

Sample Processing - Analysis

Diagram: Bailey Simone

Slide28

DOM Fractionation

Slide29

Slide30

Fulvic Acid

Fulvic

acids make up a large fraction of aquatic DOM

Provide most of the colorChemically active - redox reactions

At pH = 2 HA precipitate, FA slightly hydrophobic

Slide31

Fulvic Acid Isolation

Whole Water

Sample

Filtered, pH< 2

XAD-8

0.1N NaOH

Fulvic Acid Portion

2

XAD-8

Forward

Back Elution

Effluent

1

200 ml

20 mL

FA portion

15 cm

column

Diagram: Bailey Simone

Slide32

XAD-8 Columns

Slide33

So We Can Know…

DOC & DON concentrations

SUVA254

Degree of Aromaticity Fluorescence

Fluorescence Index Microbial vs. Terrestrial Input

PARAFAC Component Ratio

Degree of oxidation/reductionAll for both whole water and fulvic acid fractions

….So What?

Slide34

Some DOM is Yummier to Microbes

Higher C:N is more recalcitrant and more aromatic

Slide35

Fe

3+

Fe

2+

NO

3

-

NO

2

-

+ DOM 

DOM-N

Humics act as electron shuttle

Photoreduction of Ferric to Ferrous Iron

Ferrous Wheel Hypothesis

CO

2

Acetate

Oxidized DOM

DOM reducing microorganism

Reduced DOM

e

-

e

-

Slide36

Fe

3+

Fe

2+

NO

3

-

NO

2

-

+ DOM 

DOM-N

Humics act as electron shuttle

Photoreduction of Ferric to Ferrous Iron

Ferrous Wheel Hypothesis

CO

2

Acetate

Oxidized DOM

DOM reducing microorganism

Reduced DOM

e

-

e

-

Electron shuttling affects:

Bioavailability of metals

Bioavailability of certain nutrients

Degradation of persistent organic pollutants

Microbial respiration rates

And the ability depends on reduced/oxidized nature of DOM as well as the source of the DOM.

Slide37

Hyporheic

Zone: “hotspot” of biogeochemical reactions driven by mixing across

redox gradient

DOM influences that gradient, thus influencing nitrogen transport

Slide38

How

does DOM behave in

a

watershed?

Most OM comes from top of soil (O and A horizons) which is more aromatic and more terrestrial-like than DOM from further down

Slide39

DOC Concentrations

DOC (mg/L)

Discharge (m

3

/day)

(

Eran

Hood’s work looking at DOC in Green Lakes Valley)

Slide40

DOC Concentrations

DOC (mg/L)

Slide41

Percent Fulvic Acid

Discharge (m

3

/day)

%

Fulvic

Acid

Slide42

Fluorescence Index

Fluorescence Index

Slide43

General Trends in an Alpine System

DOC peaks just before peak discharge

Fulvic acids highest on rising limb

Terrestrial production main source of DOM during snowmelt Terrestrial sources decrease on recession limb

On recession limb, alpine lakes have greater proportion of aquatic sources

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Dissolved

Organic

Matter