Biological Controls on Water Chemistry - November 21, 2012
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Transcript of Biological Controls on Water Chemistry - November 21, 2012
![Page 1: Biological Controls on Water Chemistry - November 21, 2012](https://reader030.fdocuments.us/reader030/viewer/2022032616/55a5fd681a28abc2738b47b3/html5/thumbnails/1.jpg)
Biological controls on water chemistry
or
how microbes may one day control the earth
Richard Behr, Certified Maine Geologist
November 20, 2012
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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
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Two great references
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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
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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?
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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)
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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
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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
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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
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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
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Lots of human activities can overwhelm the natural system
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Unlined Municipal Landfills – the old days
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Closed Unlined Municipal Landfills
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Septage spreading
Biosolids (waste water treatment sludge) for crop production
Gravel pit reclamation with manufactured topsoil
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Petroleum releases
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Unlined Construction and Demolition Debris Landfills
More sources of organic carbon
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Dense residential development without public sewer
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Some background
• Monitoring wells installed to provide a means to sample groundwater
• Groundwater sampling methods
• Characterize groundwater quality
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Bedrock Bedrock
Glacial outwash sand
Marine clay Marine clay
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Monitoring Well Detail
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Bedrock core samples
Sediment samples Drilling underway
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Monitoring well construction
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Sample collection
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Sometimes it’s obvious the water is contaminated
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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)
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Laboratory data is uploaded to a database for general use
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Unlined Construction and Demolition Debris Landfills
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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
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Unlined Construction and Demolition Debris Landfill
Groundwater Quality at MW-2
0
2
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8
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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?
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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
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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
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Oxidation is coupled with reduction
C6H6 (Benzene)
CO2
(Mn4+)
(Mn2+)
O2
H2O
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Gravel pit reclamation project in Sangerville, Maine
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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
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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
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Portion of the gravel pit reclaimed with a manufactured topsoil
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MW-104
Gravel pit reclamation with biosolids - 3 Acres of open pit
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Gravel Pit Reclamation Project – Barrett Pit MW-104
0
10
20
30
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
To
tal O
rgan
ic C
arb
on
(m
g/L
)
0
1
2
3
4
5
6
7
8
Dis
so
lved
Oxg
yen
(m
g/L
)
Total Organic Carbon
Dissolved Oxygen
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0
10
20
30
40
50
60
70
80
Iro
n a
nd
Man
gan
ese (
mg
/L)
iron
managnese
Initially we anticipated the generation of a nitrate plume …but
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0
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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
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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-
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Contaminated groundwater discharge
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0
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Iro
n a
nd
Man
gan
ese (
mg
/L)
iron
managnese
Mn and Fe oxidation
The oxidation often occurs in groundwater
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Visual evidence of the oxidation of reduced iron
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Petroleum spills & leaks contaminate groundwater
But microbes limit the size of the contaminant plume
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Petroleum UST And it’s leaking
Without attenuation (e.g., biodegradation) the plume would reach the stream
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Groundwater Flow Direction
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Components of Gasoline B – Benzene T – Toluene
E – Ethyl Benzene X - Xylene
Approximate Plume Boundary
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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
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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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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
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Just one last example of microbes in action
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Experimental Acidification of Lake 223
• Experimental Lakes Area
Research station in
northwestern Ontario
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Experimental lake acidification
Nitric (HNO3) and Sulfuric (H2SO4) acids added to reduce pH
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• 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
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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?
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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%
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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
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You made it…. Thanks very much