Biological controls on water chemistry

or

how microbes may one day control the earth

Richard Behr, Certified Maine Geologist

November 20, 2012

The “Take away”

• Chemical composition of ground water often results from microbial activity

• Human activities often enhance the microbial community’s influence

• Today’s examples are but a few that illustrate the human component

• Microbial activity often inferred from water quality data

Two great references

Microbes are the catalysts • Microbial mediated redox processes control solubility,

speciation, mobility, toxicity, bioavailability of many elements: – Fe, Mn, C, P, N, S, Cr, Cu, Co, As, Sb, Se, Hg …..

• Things were different in the 1960s and 70s….

• Microbial degradation of organic carbon is often the driving force • Organic carbon is both an energy and carbon source

• One microbe’s waste is another’s resource

Let’s begin with the basic

requirements for microbes

• Where do they obtain energy for cell growth and

reproduction?

• Source of carbon?

• What can they breath?

Terminology/Classification

• Metabolism, “denotes the complex series of energy-utilizing chemical reactions carried out by the cell” - Two general types….

• Catabolism – extracting energy from organic compounds by breaking

them down into component parts…thereby releasing energy

• Anabolism – using energy to build organic compounds by fitting the parts together.

To obtain energy from a substrate, the microbes remove electrons and transfer them to other chemicals (so-called terminal electron acceptors)

• Respiration - the use of inorganic chemicals as terminal electron acceptors (e.g., oxygen, iron, manganese or sulfate)

Terminology/Classification (cont.)

• Nutrition –

• Heterotrophs – organisms that use organic carbon as

energy and carbon source – humans too

• Lithotrophs – use inorganic carbon, such as CO2 or

HCO3- as carbon source and an external source of

energy

• Chemolithotrophs – energy from oxidizing reduced inorganic

chemicals…such as iron

• Photolithotrophs – obtain energy from light

Terminology/Classification (cont.)

• Aerobes – use oxygen as electron acceptor • Obligate aerobe – can only use oxygen

…. That’s what we are doing

• Anaerobes – respire using something other than oxygen as a terminal electron acceptor

• Obligate anaerobes – grow only in the absence of oxygen

• Falcultative anaerobes – use oxygen when available but may use other alternate electron acceptors or fermentation in absence of oxygen

Microbes alter geochemistry largely through oxidation (degradation) of organic carbon

• It’s really all about producing energy

• transferring electrons from a reduced species, often an organic carbon molecule, to an oxidized substrate, an electron acceptor (e.g., oxygen)

• Energy released depends on the electron acceptor

• It begins with aerobic respiration

Aerobic respiration or where it all begins

• Many microbes respire (or breathe) using oxygen in

ground water

• Under natural conditions the mass of organic carbon often does not exhaust the dissolved oxygen – Organic mass and flow paths

• But lots of human activities are capable of

overwhelming the natural system

Lots of human activities can overwhelm the natural system

Unlined Municipal Landfills – the old days

Closed Unlined Municipal Landfills

Septage spreading

Biosolids (waste water treatment sludge) for crop production

Gravel pit reclamation with manufactured topsoil

Petroleum releases

Unlined Construction and Demolition Debris Landfills

More sources of organic carbon

Dense residential development without public sewer

Some background

• Monitoring wells installed to provide a means to sample groundwater

• Groundwater sampling methods

• Characterize groundwater quality

Bedrock Bedrock

Glacial outwash sand

Marine clay Marine clay

Monitoring Well Detail

Bedrock core samples

Sediment samples Drilling underway

Monitoring well construction

Sample collection

Sometimes it’s obvious the water is contaminated

Field Parameters: Temperature Specific conductance pH Dissolved oxygen Turbidity

Laboratory Parameters: Metals (e.g., iron, manganese) Salts (e.g., chloride, sulfate) Volatile organic compounds

(e.g., diethyl ether, benzene, TCE)

Indicators (e.g., ammonia, nitrate, alkalinity)

Laboratory data is uploaded to a database for general use

Unlined Construction and Demolition Debris Landfills

0

2

4

6

8

January-93

October-95

July-98

April-01

January-04

October-06

TO

C (m

g/L

) Total Organic Carbon

Time Series Graph Unlined Construction and Demolition Debris Landfill

Groundwater Quality at MW-2

Unlined Construction and Demolition Debris Landfill

Groundwater Quality at MW-2

0

2

4

6

8

10

January-93

October-95

July-98

April-01

January-04

October-06

TO

C a

nd

DO

(m

g/L

)

Total Organic Carbon

Dissolved Oxygen

So, what happens after the oxygen disappears?

Transition from Aerobic to Anaerobic respiration

• After oxygen disappears, degradation continues…. – lots of microbes continue to degrade the organic carbon

• Microbes use a series of so-called alternate terminal electron acceptors – There is an order to their use

• The order dictated by energy released (and/or thermodynamics and kinetics)

• Energy released/available depends on the electron acceptor

Nitrate reduction - NO3- ⇄ N2 or NO2

Manganese reduction - MnO2 ⇄ Mn2+

(insoluble species ⇄ soluble species)

Iron reduction - Fe2O3 ⇄ Fe2+

(insoluble species ⇄ soluble and insoluble species)

Sulfate reduction - SO42- ⇄ H2S

Carbon dioxide reduction - CO2 or CH2O ⇄ CH4

(Methanogenesis)

Alternate terminal electron acceptors The order after oxygen is depleted

Oxidation is coupled with reduction

C6H6 (Benzene)

CO2

(Mn4+)

(Mn2+)

O2

H2O

Gravel pit reclamation project in Sangerville, Maine

GRAVEL PIT RECLAMATION

• Affected land must be restored: Establish

a vegetative layer to reduce erosion

• 3 Acre portion of a working gravel pit

• Reclaimed with a manufactured topsoil

rather than natural topsoil

• Monitor groundwater • Evaluate groundwater impacts

• Establish acceptable level and duration of impact,

if any

MANUFACTURED TOPSOIL

WHAT IS IT? Yds/Acre Lb Nitrogen/Yd

• Short Paper Fiber 1200 2.2

• Municipal WW Sludge 120 56

• Sand 1200 0

• Nitrogen primarily organic

• Metals, organic carbon and other nutrients

• Final thickness: 12 - 15 inches

Portion of the gravel pit reclaimed with a manufactured topsoil

MW-104

Gravel pit reclamation with biosolids - 3 Acres of open pit

Gravel Pit Reclamation Project – Barrett Pit MW-104

0

10

20

30

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50

60

70

80

5/20/1999

10/1/2000

2/13/2002

6/28/2003

11/9/2004

3/24/2006

8/6/2007

12/18/2008

To

tal O

rgan

ic C

arb

on

(m

g/L

)

0

1

2

3

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6

7

8

Dis

so

lved

Oxg

yen

(m

g/L

)

Total Organic Carbon

Dissolved Oxygen

0

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60

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80

Iro

n a

nd

Man

gan

ese (

mg

/L)

iron

managnese

Initially we anticipated the generation of a nitrate plume …but

0

10

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40

50

60

70

80

5/20/1999

10/1/2000

2/13/2002

6/28/2003

11/9/2004

3/24/2006

8/6/2007

12/18/2008

Iro

n a

nd

Man

gan

ese (

mg

/L)

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

Ars

en

ic (

mg

/L)

iron

managnese

Arsenic

Take home – In addition to producing an iron and manganese plume, we produced an arsenic plume without adding arsenic

Full Circle

• The reduced iron and manganese represents an energy source, if conditions are right

– In the presence of oxygen, some microbes obtain energy from the oxidation of iron and manganese

Fe 2+ (aq) Fe3+ (s) + e-

Contaminated groundwater discharge

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60

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80

Iro

n a

nd

Man

gan

ese (

mg

/L)

iron

managnese

Mn and Fe oxidation

The oxidation often occurs in groundwater

Visual evidence of the oxidation of reduced iron

Petroleum spills & leaks contaminate groundwater

But microbes limit the size of the contaminant plume

Petroleum UST And it’s leaking

Without attenuation (e.g., biodegradation) the plume would reach the stream

Groundwater Flow Direction

Components of Gasoline B – Benzene T – Toluene

E – Ethyl Benzene X - Xylene

Approximate Plume Boundary

1

10

100

1000

10000

0 200 400 600 800 1000 1200

Distance from Source (feet)

To

tal

BT

EX

(u

g/L

)

BTEX

Pete’s Garage – North Fryeburg

The microbes are responsible for the natural attenuation of the petroleum components…..otherwise the plume would be significantly larger

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0 200 400 600 800 1000 1200

Distance from Source (feet)

Iro

n (

mg

/L)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Dis

so

lved

Oxyg

en

(m

g/L

)

Iron

Dissolved Oxygen

Pete’s Garage – North Fryeburg

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50

0 200 400 600 800 1000 1200

Distance from Source (feet)

Iro

n &

Man

gan

ese (

mg

/L)

Iron

Manganese

0

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0 200 400 600 800 1000 1200

Distance from Source (feet)

Iro

n &

Man

gan

ese (

mg

/L)

Iron

Manganese

Zone of Mn & Fe Reduction

Zone of Mn & Fe Oxidation

Just one last example of microbes in action

Experimental Acidification of Lake 223

• Experimental Lakes Area

Research station in

northwestern Ontario

Experimental lake acidification

Nitric (HNO3) and Sulfuric (H2SO4) acids added to reduce pH

• Typical lake cross-section after stratification

• Experimental acidification is nothing more than a large titration

• If one estimates volume of lake, pH and alkalinity

• Should be able to estimate the amount of acid needed to reduce pH

Lake 223 – 1976 to 1978 • pH progressively lowered during 3 year period

– pH in 1976 reduced to 7.0

pH in 1977 reduced to 6.2

pH in 1978 reduced to 5.9

• But there was a big surprise…. – Original experimental design expected to focus on

biological changes (e.g., fish, algae and macro-invertebrates)

– Majority of buffering capacity from watershed?

• Added more acid than calculated to reduce pH

• Why?

Microbial activity increased

• The lake sediments were already home to lots of microbes, including… anaerobic bacteria capable of reducing the added sulfate and nitrate

• Sulfate and nitrate “fueled” an unexpected increase in sulfate and nitrate reduction

• Reduced the effectiveness of acidification by more than 60%

Micro-organisms provide internal lake buffering system

• Sulfate reduction

– CH2O + H2SO4 2- H2S + HCO3 -

– Sulfate reduction consumes hydrogen ions and produces alkalinity

• Nitrate reduction (aka denitrification)

Also produces alkalinity and consumes hydrogen ions

You made it…. Thanks very much