Dissolved Carbon in Riverine Flow of Siberia
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Controls of dissolved inorganic and organic carbon discharge from permafrost ecosystems Prokushkin Anatoly S. V.N. Sukachev Institute of Forest SB RAS, Krasnoyarsk Siberian Federal University [email protected] ИЛ СО РАН: School of the young scientists on Biogeochemical 1 Matter Cycling In Permafrost Ecosystems Presentation structure: • Terms • Processes • Dissolved carbon in watersheds of Siberian rivers : interactions of hydrology, vegetation, permafrost, fires and C fluxes 2 • from Latin dissolvere : dis- + solvere, to release Physicochemical background: Wikipedia: Dissolution is the process by which a solute forms a solution in a solvent. The solute, in the case of solids, has its crystalline structure disintegrated as separate ions, atoms, and molecules form. For liquids and gases, the molecules must be adaptable with those of the solvent for a solution to form. The outcome of the process of dissolution (the amount dissolved at equilibrium, i.e., the solubility) is governed by the thermodynamic energies involved, such as the heat of solution and entropy of solution, but the dissolution itself (a kinetic process) is not. Overall the free energy must be negative for net dissolution to occur. In turn, those energies are controlled by the way in which different chemical bond types interact with those in the solvent. 3 Dissolved carbon species: • Dissolved inorganic carbon [CO2*] + [HCO3−] + [CO32−] • Dissolved organic carbon Complex mixture of organic volecules • Dissolved gases CO2, CH4 Other portion of C in waters is called particulate C: Particulate organic C Particulate inorganic C 4 Dissolved carbon: definitions and species Initially in hydrochemistry dissolved matter is operationally defined as matter which is passed through 0.45 um pore-size filter Wikipedia: …The "dissolved" fraction of organic carbon is an operational classification. Many researchers use the term "dissolved" for compounds below 0.45 micrometers, but 0.22 micrometers is also common... A practical definition of dissolved typically used in marine chemistry is all substances that pass through a GF/F filter (0.7 um pore size!). So, to work with dissolved carbon in a sample one need first to filter sample! 5 Advantages and disadvantages of filters: • 0.22 micrometers: to get rid of microbes… less loss during storage, but may contaminate with C (nitrocellulose, acetate cellulose matrix) • 0.7 um precombusted glass fiber filters (GF/F): miserable or no contamination by OC, but microbes… 6 How to measure? • DOC (TOC = TC-IC, NPOC – nonpurgeable OC) - The recommended measure technique is the high temperature catalytic oxidation (IR detection) - Previous technique (still in use by Roshydromet) Bichromate/permanganate oxidation 7 How to measure? • DIC - The recommended measure technique is acidification with further IR detection - Potentiometric titration with HCl for alkalinity + - H + HCO3 = H2CO3 = H2O + CO2 8 Why it is important? • DOC loss from terrestrial ecosystems to fresh waters constitutes 1-15% of NEP • DIC and specifically dissolved CO2/CH4 fluxes is not still well counted … • C exported from terrestrial ecosystems to rivers are rarely included in NEP estimates, causing its underestimation • DOM (DOC, DON, DOP etc…) is important driver of foodwebs in both terrestrial and aquatic systems 9 Dissolved organic C • To be microbially mineralized to CO2/CH4 all organic matter must be dissolved 10 Dissolved inorganic C Carbonate weathering… H2CO3 + CaCO3 → Ca(HCO3)2 Silicate weathering… 2 KAlSi3O8 + 2 H2CO3 + 9 H2O ⇌ Al2Si2O5(OH)4 + 4 H4SiO4 + 2 K+ + 2 HCO3− Temperature dependent process 11 high potential for sequestration of atmospheric CO2… • Weathering of basalts of Central Siberian Plateau may be important factor for atmospheric CO2 sequestration Illustration of the correlations between weathering fluxes and (A) thermal regimes and (B) hydrological regimes for 22 representative silicate sites around the world (excerpt from Beaulieu et al., 2010). Our study shows clear increase of DIC annual yield from 1.04 gC m−2 yr−1 for Tembenchi River (MAAT = −10.9 ◦C) to 2.77 gC m−2 yr−1 for Nizhnyaya Tunguska River (MAAT = −7.5 ◦C). The other basaltic boreal rivers such as Kamchatka River and its tributaries (MAAT = −2.5 ◦C) exhibit significantly higher annual fluxes of DIC: 4.8 gC m−2 yr−1 12 Dissolved organic C: dissolved or colloidal? 8000 7000 450 6000 400 5000 350 4000 300 [Na], ppb [Na], 3000 250 LMW = 1 kDa 2000 [Fe], ppb [Fe], 200 150 (Dialysis) 1000 0 100 18.0 20 um 10 um 5 um 1.2 um 0.22 um 1 kDa 50 LMW 16.0 HMW Pore diamter 0 14.0 20 um 10 um 5 um 1.2 um 0.22 um 1 kDa 700 Pore diamter 12.0 600 300 10.0 8.0 500 250 NPOC [mgC/l]NPOC 6.0 400 200 4.0 [K], ppb [K], 300 2.0 150 200 [Al], ppb [Al], 0.0 100 100 December March April May June July September Month 0 50 20 um 10 um 5 um 1.2 um 0.22 um 1 kDa Pore diamter 30 0 LMW 20 um 10 um 5 um 1.2 um 0.22 um 1 kDa Pore diamter 25 HMW 12000 0.025 20 10000 15 0.02 8000 10 6000 0.015 [Ca], ppb [Ca], NPOC [mgC/L] NPOC 5 4000 [Tb], ppb [Tb], 0.01 0 2000 07.06.2013 07.06.2013 20.06.2013 20.06.2013 05.08.2013 05.08.2013 0.005 NT KO NT KO NT KO 0 20 um 10 um 5 um 1.2 um 0.22 um 1 kDa River/sampling date 0 Pore diamter 20 um 10 um 5 um 1.2 um 0.22 um 1 kDa 13 Pore diamter What is DOC? How to investigate the composition? • Complex mixture of organic molecules • Fulvic acids (dissolved at pH 2) • Hydrophobic acid (by XAD fractionation) • Spectral characteristics (e.g. SUVA, spectral slope) • Fluorescence (chromatophoric groups) • Biomarkers (e.g. lignin, sugars etc.) • Isotopic composition (i.e. 13C) • Radiocarbon age (compound specific) • Pyr-GC/MS-IRMS, 13C NMR CP MAS, electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI- FT-ICR-MS) • etc. 14 Dissolved organic carbon in terrestrial systems Rainfall 0.9-4.5 mgC/l (< 0.5 gC/m2/a) Throughfall/stemflow 0 6-70 mgC/l 20 (ca 1.0 gC/m2/a) 40 60 Jun Soil Depth, cm Depth, Soil Jul 80 Aug Sept O 20-120 mgC/l 100 (2-18 gC/m2/a) 0 10 20 30 40 NPOC, mgC/l Ah 15-40 mgC/l ALT B 5-15 mgC/l C 2-5 mgC/l Time Export to 5-31 mgC/l stream 2-10 gC/m2/a 15 moss O layer 5 cm 20 cm 40 cm 35 30 5 cm 25 20 15 20 cm NPOC,mgC/l Active layer 10 5 0 1-Jun 15-Jun 29-Jun 13-Jul 27-Jul 10-Aug 24-Aug 7-Sep 21-Sep 40 cm Sampling date 15 60 cm 10 5 Permafrost 0 5.8.09 19.9.09 3.11.09 18.12.09 1.2.10 18.3.10 2.5.10 16.6.10 31.7.10 May September -5 Nfs 5 cm -10 Soil solution sampling and Nfs 20 cm Nfs 4016 cm temperature monitoring -15 Terrestrial C links to aquatic moss O layer 0 10 20 30 40 Depth, cm Depth, 50 Sfs 60 Nfs 70 0 20 40 60 80 Active layer DOC Permafrost 17 Dissolved organic carbon in aquatic systems 18.0 LMW 16.0 HMW 14.0 • Authochtonous12.0 10.0 15 8.0 low C:N, high N, [mgC/l]NPOC 6.0 LMW, specific biomarkers 4.0 2.0 0.0 • Allochtonous (terrigenic)December March April May June July September Month High C:N, low 15N, low 13C, HMW, specific biomarkers 18 DOC production • Biological - Exudates - Cell lysis - Microbial breakdown of SOM DOM • Physical Freeze-thaw cycles SOM DOM 19 Terrestrial controls over C export: soil C stocks and C:N ratio Frey and Smith 2005, GRL 20 DOC “consumption” • Microbial mineralization 20 DOC = CO2/CH4 + H2O y = 0.6295x - 5.5604 10 -1 0 y = 0.6365x - 18.041 y = 0.6484x - 19.44 -10 y = 0.612x - 26.517 -20 • Sorption to mineral matrix y = 0.5812x - 32.144 -30 DOC released or retained, mmol kg mmol retained, or DOCreleased -40 Ah (05CP) Ah (05BP) B (05CP) B (05BP) Bf (05BP) -50 0 10 20 30 40 50 DOC added, mmol kg-1 0.80 0.80 50 • Precipitation y = 0.0138x + 0.3777 y = 0.0466x - 0.2044 0.70 0.70 2 y = 5.8368x + 5.4781 2 R = 0.9391 R = 0.8213 R2 = 0.7657 0.60 0.60 40 0.50 0.50 30 0.40 0.40 0.30 0.30 20 b, mmol DOC/kg 0.20 0.20 10 partition coefficient (m) partition coefficient 0.10 (m) partition coefficient 0.10 0.00 0.00 0 0 5 10 15 20 0 10 20 30 0.0 2.0 4.0 6.0 8.0 Fe(d) SSA, m2/g OC, mol C/kg soil 21 Permafrost and dissolved C: A Органический слой СТС СТС Periodic forest fires ? мерзлота мерзлота Июнь Октябрь Июнь Октябрь Пожар Послепожарная восстановительная сукцессия B Органический слой СТС мерзлота Permafrost degradation СТС мерзлота Деградация мерзлоты DOC DIC 22 Arctic and subarctic ecosystems: why dissolved carbon is important • Largest amount of carbon (of which 1-2% is dissolved) locked in soils and particularly conserved within the frozen ground (SOC = 1672 PgC, Tarnocai et al 2009) • Dissolved carbon is most labile and indicative component of soil C reservoir • Highest rates of warming and permafrost degradation • Highest sensitivity of ecosystem processes to ongoing climate change • Little is known about behavior of dissolved carbon in arctic and subarctic watersheds 23 Global change: permafrost degradation and an increase of active layer thickness Monitoring sites Positive trend in ALT depth By 2091-2100, permafrost extent will be decreased 30- 75% and active layer thickness increased about 55-125 cm, compared to 1991-2010 (Park and Walsh 2013, EGU General Assembly) Implications for C export: Higher retention times in soil (DOC negative) Negative trend in freezing depth Higher mineralization rates (DIC, pCO2 positive) IPCC 2007, 24 Higher weathering rates (DIC positive) from Frauenfeld et al 2004 Global change: hydrology Eurasian river annual runoff to the Arctic Ocean tends to increase for ca.