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
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
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Modeling the export of DOC from large watersheds and its influence on the optical
ASLO Session SS54, New Orleans LAFebruary 19, 2013
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
DOC Quality- SUVA254
Little light passes through
sample
Aromatic DOC absorbs strongly
UV light at 254 nm
Image by K.W. Hanley
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
Chapter 1: Large Rivers
OrganicLayer
Mineral Layer
ForestWetlands
Weakly UV-absorbing,DOC-depleted
Strongly UV-absorbing,DOC-enriched
How do wetlands affect DOC quantity and quality?
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
HPOA Non-HPOA
River DOC
PhotoRespiration
GPP*
HPOA
Non-HPOA
Local Input
HPOA Non-HPOA
Downstream exports
HPOA Non-HPOA
Upstream inputs
1000 10000 100000 1000000 100000001000
10000
100000
1000000
10000000
f(x) = 0.743263268263621 x + 55788.3457527497R² = 0.961381000365854
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)
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
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.
Methods
• The fraction of DOC as hydrophobic organic acids (HPOA%) was determined according to Hanley et a. 2012: