The Buffering Balance: Modeling Arctic river total-, inorganic- and organic-alkalinity fluxes C.W. Hunt, J.E. Salisbury, W. Wollheim, M. Mineau, and R.J. Stewart. University of New Hampshire

Alkalinity Background River Estuary Total alkalinity (T-Alk): Org- Potential effects: CO2 degassing estimates Decreased pH Overestimated Ω Reduced estuary buffering Total alkalinity (T-Alk): The buffering capacity of an aqueous solution. OR The capacity of an aqueous solution to neutralize acid. CO2 River Estuary Carbonic Acid CO2 (aq) H2CO3 Alkalinity HCO3- + H+ Bicarbonate Org- OH- H3PO4 SiO(OH)3- CO32- + H+ Carbonate -Alkalinity measured for 100+years, one of the most robust water-quality datasets we have -Important link between terrestrial and oceanic aquatic system -BUT some components of alkalinity system are still relatively poorly understood B(OH)4- NH3 HPO42- PO43-

How is alkalinity defined? Acid-Neutralizing Definition: T-Alk = [HCO3−] + 2[CO3−2] + [B(OH)4−] + 2[PO4−3] + [HPO4−2] + [SiO(OH)3−] …+ [Organic-] Ion Balance Definition [HCO3−] + 2[CO3−2] +[OH-]- [H+ ] = [Na+]+[K+]+ 2[Ca+2] + 2[Mg+2] - [Cl-] - 2[SO4-2] - [Organic-] Working Definitions: C-Alk = [HCO3−] + 2[CO3−2] ≈ [HCO3−] NC-Alk = [B(OH)4−] + 2[PO4−3] + [HPO4−2] + [SiO(OH)3−] + [Organic-] Org-Alk = [Organic-] ≈ NC-Alk Org-Alk% = [Org-Alk] / [Total Alk] -Full definition is sum of all potentially acid-neutralizing species in solution -Ion balance definition is sum of all common cations and anions, requires complete analysis of species composition -Carbonte alkalinity sometimes treated as equivalent to total alkalinity -Non carbonate alkalinity composed of minor species, or which organics can sometimes be the most consequential -Working assumption for this work is all non-carbonate alkalinity comprised of organic species

Where has Org-Alk been documented? Hunt et al. 2011, 2014 Wang et al. 2012 De Kluijver et al. 2014 Cai et al. 1998, Cai and Wang 1998 Abril et al. 2014

How is Org-Alk measured? It’s not! (directly, at least) -Method 1: Difference between measured and calculated T-Alk Org-Alk = T-Alkmeas - T-AlkDIC,pH,pCO2 -Method 2: Re-titration Org-Alk = T-Alk (second titration) -Method 3: Estimation Org-Alk = f(DOC, pH) Oliver 1983 Requires 3 carbonate measurements Poor precision, hysteresis,time-consuming -I’m going to start by presenting data from Gulf of Maine, then extend trends from this region to the Arctic -Better tools are needed, especially for carbonate data-sparse areas, such as the Arctic Small n, possible errors at higher Alk/pH BETTER TOOLS ARE NEEDED!

A B C D E Gulf of Maine Org-Alk A B C D E -Higher proportions of Org-Alk are found in acidic rivers in the Gulf of Maine -Similar results are found in the Congo as well. -In the Gulf of Maine higher proportions of organic alkalinity associated with higher DOC, a trend we can try to apply to the Arctic -Does NC-Alk promote increased acidity, or are they co-occuring? A B D E C

FrAMES 1. 2. Water Balance Model (WBM) Water Transport Model Vorosmarty et al. 1998 (Appendix B) Water Transport Model (WTM, STN) Vorosmarty et al. 2000 Other functions* Wollheim et al. 2008 Wisser et al. 2009 Stewart et al. 2011 “Vertical” movement of water (precip, ET, etc.) “Horizontal” movement of water (river network routing using STN or Simulated Topological Network) Nitrogen, Reservoirs, Transient Storage , HCO3-,(lithology) Org-Alk (DOC) Couple an established process-based hydrological model with process-based HCO3 and semi-empirical DOC loading models * These are often embedded within WBM, WTM

Model Results- Gulf of Maine -10 Gulf of Maine rivers with 2013 T-Alk, I-Alk and Org-Alk measurements -Model was able to retrieve gross HCO3 well in the Gulf of Maine -Model DOC was not nearly as dynamic as observations -Model estimate of Gulf of Maine Org-Alk did not do well, since DOC was underestimated in most rivers -Oliver estimation of Org-Alk did quite well in Gulf of Maine, compared to observations, although it apparently overestimates Org-Alk in very acidic organic rivers (high points)

Arctic Great Rivers Observatory (GRO)/PARTNERS Arctic data -GRO HCO3 calculated as alkalinity left over after Oliver Org-Alk subtracted (next slide) Image from Tank et al. 2012

[Org-Alk] = (10-pH )(DOC*10) (10-pH ) + K Oliver 1983: [Org-Alk] = (10-pH )(DOC*10) (10-pH ) + K - Kolyma Yenisey Lena Ob Yukon Mackenzie

Model Results- Arctic

Model Results- Arctic -Model probably way overestimates O-Alk. But considering underestimate of Oliver relationship of Org-Alk for the de Kluijver et al data, the true result may be somewhere between the model and Oliver numbers

Model Results- Arctic

Model Results- Arctic

Conclusions and future goals Data data data, especially DIC, pCO2 DOC quality- remote sensing opportunities Calibrating model coefficients for Arctic setting Including a permafrost parameter

Arctic - COLORS Arctic-Coastal Land Ocean Interactions A NASA Scoping Study History: 2012 Processes (particularly rates) within and near the world’s largest river plumes. Grants NASA NNX14AD75G and NNX09AU89G

Questions? I have many, such as: What factors are missing in the model for DOC, HCO3? Need quality to understand DOC color signature. Can SUVA get us there? What data are needed to improve understanding of Artic O-Alk? Strategies for modeling Arctic river pH? How can we simulate the potential release of DOC from thawing permafrost?

References Abril, G., S. Bouillon, F. Darchambeau, C.R. Teodoru, T.R. Marwick, F. Tamooh, F. Ochieng Omengo, N. Geeraert, L. Deirmendjian, P. Polsenaere, and A.V. Borges. 2014. Technical Note: Large overestimation of pCO2 calculated from pH and alkalinity in acidic, organic-rich freshwaters. Biogeosciences bg-2014-341 Amiotte-Suchet, P., J.-L. Probst, and W. Ludwig (2003), Worldwide distribution of continental rock lithology: Implications for the atmospheric/soil CO2 uptake by continental weathering and alkalinity river transport to the oceans, Global Biogeochem. Cycles, 17(2), 1038, doi:10.1029/2002GB001891. Cai, W.-J. and Wang, Y.: The chemistry, fluxes and sources of carbon dioxide in the estuarine waters of the Satilla and Altamaha Rivers, Georgia, Limnol. Oceanogr., 43, 657–668, 1998. Cai, W.-J., Wang, Y., and Hodson, R. E.: Acid-base properties of dissolved organic matter in the estuarine waters of Georgia, USA, Geochim. Cosmochim. Ac., 62, 473–483, 1998.  de Kluijver, A., Schoon, P. L., Downing, J. A., Schouten, S., and Middelburg, J. J.: Stable carbon isotope biogeochemistry of lakes along a trophic gradient, Biogeosciences, 11, 6265-6276, doi:10.5194/bg-11-6265-2014, 2014. Hartmann, Jörg; Moosdorf, Nils (2012): Global Lithological Map Database v1.0 (gridded to 0.5° spatial resolution). doi:10.1594/PANGAEA.788537, Supplement to: Hartmann, Jens; Moosdorf, Nils (2012): The new global lithological map database GLiM: A representation of rock properties at the Earth surface. Geochemistry, Geophysics, Geosystems, 13, Q12004, doi:10.1029/2012GC004370 Hunt, C.W., J.E. Salisbury and D. Vandemark. (2013) CO2 Input Dynamics and Air-Sea Exchange in a Large New England Estuary. Estuaries and Coasts 37(5): 1078-1091 C.W. Hunt, J.E. Salisbury, D. Vandemark. (2011) Contribution of non-carbonate anions to total alkalinity and overestimation of pCO2 in New England and New Brunswick rivers. Biogeosciences, doi:10.5194/bg-8-3069-2011 Kicklighter, DW, Hayes, DJ, McClelland, JW, Peterson, BJ, McGuire, AD and JM Melillo. 2013. Insights and issues with simulating terrestrial DOC loading of Arctic river networks. Ecological Applications 23(8): 1817-1836. Tank, S. E., P. A. Raymond, R. G. Striegl, J. W. McClelland, R. M. Holmes, G. J. Fiske, and B. J. Peterson (2012), A land-to-ocean perspective on the magnitude, source and implication of DIC flux from major Arctic rivers to the Arctic Ocean, Global Biogeochem. Cycles, 26, GB4018, doi:10.1029/2011GB004192. Wang, Z. A., D. J. Bienvenu, P. J. Mann, K. A. Hoering, J. R. Poulsen, R. G. M. Spencer, and R. M. Holmes (2013), Inorganic carbon speciation and fluxes in the Congo River, Geophys. Res. Lett., 40,511–516, doi:10.1002/grl.50160.

PhotoVf (m/d) = KPhoto * PAR * (PhotoDepth * ChannelDepth) Loading equation: DOC (µmol/l) = Constant * ROSlope Slope =1 - (0.0001WL2 – 0.0193*WL + 1.4237) Constant = -0.002WL2 + 0.4552*WL + 7.275 RO=Runoff (mm/d), WL=Wetland% HCO3 (µmol/l) = Lithological HCO3- load (Amiotte-Suchet et al. 2003) Global 1° lithology (Hartmann and Moosdorf 2012) Respiration Removal of DOC: RespVf (m/d) = KResp * RespQ10(waterT - Resp_Tref) / 10 RespRemoval = DOC * (1 - 10(-RespVf / HL)) HL=Hydraulic Load (m/d) Photolysis Removal of DOC: PhotoVf (m/d) = KPhoto * PAR * (PhotoDepth * ChannelDepth) PhotoRemoval = HPOA * (1 - 10(-PhotoVf / HL))