Study Motivations

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Modeling the export of DOC from large watersheds and its influence on the optical properties of coastal waters C.W. Hunt 1 , W.M. Wollheim 2,3 , J.S. Salisbury 1 , R.J. Stewart 3 , K.W. Hanley 4 and G.R. Aiken 4 ASLO Session SS54, New Orleans LA February 19, 2013

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Modeling the export of DOC from large watersheds and its influence on the optical properties of coastal waters. C.W. Hunt 1 , W.M. Wollheim 2,3 , J.S. Salisbury 1 , R.J. Stewart 3 , K.W. Hanley 4 and G.R. Aiken 4 ASLO Session SS54, New Orleans LA February 19, 2013. Study Motivations. - PowerPoint PPT Presentation

Transcript of Study Motivations

Page 1: Study Motivations

Modeling the export of DOC from large watersheds and its influence on the optical

properties of coastal waters

C.W. Hunt1, W.M. Wollheim2,3, J.S. Salisbury1, R.J. Stewart3, K.W. Hanley4 and G.R. Aiken4

ASLO Session SS54, New Orleans LAFebruary 19, 2013

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Study Motivations

River transport of DOC is a major component of global C cycle

River-borne DOC also influences the reactivity and optical properties of inland and coastal ocean aquatic systems

Recent studies* indicate that wetland abundance within small and large catchments is correlated with DOC quantity and quality at the catchment mouth

*Hanley et al. 2013 in review, Buffam et al. 2007

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DOC Quality- SUVA254

Little light passes through

sample

Aromatic DOC absorbs strongly

UV light at 254 nm

Image by K.W. Hanley

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Study Approach Couple a dynamic hydrological model (FrAMES, 6min) to a

process-based DOC quantity/quality model using parameters found in literature.

Simulate DOC loading as a function of land cover and runoff conditions. Partition DOC quality into Hydrophobic Organic Acids (HPOA, aromatic) and non-HPOA stocks. The %HPOA can be used to derive SUVA254.

Test model in 17 USA watersheds with processing (Respiration and photo-oxidation) turned on and off

Butman et al. 2012

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Chapter 1: Large Rivers

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OrganicLayer

Mineral Layer

ForestWetlands

Weakly UV-absorbing,DOC-depleted

Strongly UV-absorbing,DOC-enriched

How do wetlands affect DOC quantity and quality?

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0 10 20 30 40 50 60 70 800

2

4

6

8

10

12

14

16

18

20

Effect of Runoff on DOC

0mm Runoff4mm Runoff8mm Runoff

Wetland %

DOC

(mg/

l)

TransportLimited Source Limited

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HPOA Non-HPOA

River DOC

PhotoRespiration

GPP*

HPOA

Non-HPOA

Local Input

HPOA Non-HPOA

Downstream exports

HPOA Non-HPOA

Upstream inputs

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1000 10000 100000 1000000 100000001000

10000

100000

1000000

10000000

f(x) = 0.743263268263621 x + 55788.3457527497R² = 0.961381000365854

Observed Mean DOC flux (kg d-1)

Mod

el M

ean

DOC

flux

(kg

d-1)

Peno

bsco

t Riv

erKe

nneb

ec R

iver

Andr

osco

ggin

Riv

erSu

sque

hann

a Ri

ver

Poto

mac

Riv

erEd

isto

Rive

rAl

tam

aha

Rive

rSt

. Mar

y's

Sant

a Fe

Riv

erM

obile

Riv

erM

ississ

ippi

Riv

erRi

o Gr

ande

Colo

rado

Riv

erSa

n Jo

aqui

n Ri

ver

Sacr

amen

to R

iver

Colu

mbi

a Ri

ver

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

DOC IoASUVA IoA

Inde

x of

Agr

eem

ent

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0 5 10 15 20 25 30 35 400

10

20

30

40 DOC Concentration

ModelExponential (Model)ObservedExponential (Observed)

Wetland %

DOC

(mg/

l)

St Mary's River

0 2 4 6 8 10 12 14 16 18 200

10

20 DOC Concentration

ObservedLinear (Observed)ModelLinear (Model)

Wetland %

DOC

(mg/

l)

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0 5 10 15 20 25 30 35 400

5

10

15

20

25

30

35

40

f(x) = 0.679893936449303 x + 1.66231722458914R² = 0.951393659317006

DOC Concentration

Observed DOC (mg/l)

Mod

eled

DO

C (m

g/l)

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0 2 4 6 8 10 120

2

4

6

8

10

12

f(x) = 0.396646130953876 x + 3.11022498029868R² = 0.575714584837442

DOC Concentration

Without Process-ingLinear (With-out Process-ing)1:1

Observed DOC (mg/l)

Mod

el D

OC

(mg/

l)

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0 2 4 6 8 10 120

2

4

6

8

10

12

f(x) = 0.300959202639456 x + 1.36661260020991R² = 0.574656895655416

DOC Concentration

Without Process-ingWith Process-ingLinear (With Process-ing)1:1

Observed DOC (mg/l)

Mod

el D

OC

(mg/

l)

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0 1 2 3 4 5 6 7 80

1

2

3

4

5

6

7

8

f(x) = 0.521045105959255 x + 1.14955901270565R² = 0.812369639182967f(x) = 0.478368498350835 x + 1.10253900955503R² = 0.766650536893421

With ProcessingLinear (With Processing)Without ProcessingLinear (Without Processing)1:1

Observed HPOA (mg l-1)

Mod

el H

POA

(mg

l-1)

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0 3 250

0

2

10 SUVA254

ObservedPower (Observed)ModelPower (Model)

Wetland% - log scale

SUVA

254

(L*m

gC-1

m-1

) - lo

g sc

ale

Colorado River

St Lawrence River

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Conclusions and Future Work

The model shows promise for predicting bulk DOC loading and export at the catchment mouth

Adding two compartments (HPOA and nHPOA) is helpful, but…

There is information we are not capturing in DOC quality (SUVA)

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Amazon River Study

From Salisbury et al. 2011

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From Salisbury et al. 2011

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Model Parameter Values- after Monte Carlo

Parameter Original Monte Carlo test

DOC vs. Wetland% Intercept at low runoff (mg/l) 2.36 2.36

DOC vs. Wetland% Slope at low runoff 0.374 0.55

DOC vs. Runoff asymptote at high flow (mg/l) 6.7 13.5

HPOA% vs. Wetland% .0084*%wet + 0.390 .0084*%wet + 0.390

Photo degredation constant (m-1) 0.001 0.0034

Resp degredation constant (at Tref=30, m/d) 1.47 1.31

Resp degredation constant Q10 2.0 2.0

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Monte Carlo Results

0 2 4 6 8 10 120

2

4

6

8

10

12

f(x) = 0.435620690687397 x + 1.83354725243794R² = 0.432048895717466

f(x) = 0.484626433273438 x + 4.94643337362162R² = 0.532170639851622

DOC Concentration- Monte Carlo Params

Without Processing

Linear (Without Process-ing)

With Process-ing

Observed DOC (mg/l)

Mod

el D

OC

(mg/

l)

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Monte Carlo Results

1 2 3 4 52

3

4

5

6

7

8

f(x) = − 0.0616244411795221 x + 5.52961375451189R² = 0.00479866938491946

f(x) = 0.538341295194449 x + 3.78355831281822R² = 0.205120734254932

SUVA - Monte Carlo Params

Monte Carlo ParamsLinear (Monte Carlo Params)Lit ParamsLinear (Lit Params)1:1

Observed SUVA

Mod

el S

UVA

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ReferencesButman, D., Raymond, P.A., Butler, K. and G. Aiken. 2012. Relationships between Δ14C and the molecular quality of dissolved organic carbon in rivers draining to the coast from the conterminous United States. Global Biogeochemical Cycles, 26: GB4014.

Hanley, K.W., Wolheim, W.M., Salisbury, J., Huntington, T., and G. Aiken. 2013. Controls on dissolved organic carbon quantity and quality in large North American rivers. Global Biogeochemical Cycles, in review.

Raymond, P.A. and J.E. Saiers. 2010. Event controlled DOC export from forested watersheds. Biogeochemistry dio 10.1007/s10533-010-9416-7.

Salisbury, J., Vandemark, D., Campbell, J., Hunt, C.W., Wisser, D., Reul, N., and B. Chapron. 2011. Spatial and temporal coherence between Amazon River discharge, salinity, and light absorption by colored organic carbon in western tropical Atlantic surface waters. J. Geophys. Res. 116: COOHO2.

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Methods

• The fraction of DOC as hydrophobic organic acids (HPOA%) was determined according to Hanley et a. 2012:

• HPOA% = ((1.19 * log10(wetlands%)) + 3.762) / 8.792

• Finally, the specific ultraviolet absorbance of DOC at 254 nm, an indicator of DOC aromaticity, was estimated:

• SUVA-254=(HPOA% * 8.792) - 1.126

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*from Hanley et al. 2013 in press

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Processing and DOC Quality

DOC (HPOA) DOC (non-HPOA)

Upstream DOC

(HPOA)

Upstream DOC (non-

HPOA)

Photodegradation

GPP* Resp

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Water Balance Model (WBM)

Vorosmarty et al. 1998 (Appendix B)

FrAMES

Water Transport Model (WTM, STN)

Vorosmarty et al. 2000

Other functions*

“Vertical” movement of water (precip, ET, etc.)

Wollheim et al. 2008Wisser et al. 2009Stewart et al. 2011

“Horizontal” movement of water (river network routing

using STN or Simulated Topological Network)

Nitrogen, Reservoirs, Transient Storage

* These are often embedded within WBM, WTM

1. 2.

1.

2.

Grid Cell

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SnowmeltET

Rooting Zone

Shallow Groundwater Detention Pool

Snowpack

Recharge

Precipitation

WBM Grid Cell

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Parameter Value or formula Source

DOC vs. Wetland% Intercept at low runoff (mg/l) 2.36 Raymond and Saiers 2010

DOC vs. Wetland% Slope at low runoff 0.374

Composite of Eckhardt and Moore 1990, Buffam et al 2007, and Raymond and Hopkinson 2003

DOC vs. Runoff asymptote at high flow (mg/l) 6.7 Raymond and Saiers 2010, at peak flow of 8 mm/d

HPOA% vs. Wetland% .0084*%wet + 0.390 Wollheim (Ipswich-Parker river data)

Photo degredation constant (m-1) 0.001 Literature composite

Resp degredation constant (at Tref=30, m/d) 1.47 Literature composite

Resp degredation constant Q10 2.0 Literature composite

Model Parameter Values

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Soil Organic Matter

Riverine DOC

Sources of DOC in Rivers

Image by K.W. Hanley

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Without wetlands, DOC removal and fractionation can occur in the subsurface…

Organic HorizonMineral Horizon

DOC added to new groundwater

1.

DOC transported out of organic horizon

2.

Preferential sorption of humic and fulvic acids to mineral soils

and extensive microbial processing

3.

Weakly UV-absorbing, DOC-depleted

groundwater enters stream

4.

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With wetlands, DOC depletion and fractionation are less likely…

Organic Horizon

Mineral Horizon

DOC added to new groundwater

1.

Subsurface flow through deep and often anaerobic organic horizon -

little sorption or microbial processing

2.

Strongly UV-absorbing, DOC-rich groundwater

enters stream

3.