Browsing by Subject "DISSOLVED ORGANIC-MATTER"

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    The biogeochemistry of carbon across a gradient of streams and rivers within the Congo Basin
    (Journal of Geophysical Research: Biogeosciences, 2014-04) Mann, PJ; Spencer, RGM; Dinga, BJ; Poulsen, JR; Hernes, PJ; Fiske, G; Salter, ME; Wang, ZA; Hoering, KA; Six, J; Holmes, RM
    Dissolved organic carbon (DOC) and inorganic carbon (DIC, pCO2), lignin biomarkers, and theoptical properties of dissolved organic matter (DOM) were measured in a gradient of streams and rivers within the Congo Basin, with the aim of examining how vegetation cover and hydrology influences the composition and concentration of fluvial carbon (C). Three sampling campaigns (February 2010, November 2010, and August 2011) spanning 56 sites are compared by subbasin watershed land cover type (savannah, tropical forest, and swamp) and hydrologic regime (high, intermediate, and low). Land cover properties predominately controlled the amount and quality of DOC, chromophoric DOM (CDOM) and lignin phenol concentrations (8) exported in streams and rivers throughout the Congo Basin. Higher DIC concentrations and changing DOM composition (lower molecular weight, less aromatic C) during periods of low hydrologic flow indicated shifting rapid overland supply pathways in wet conditions to deeper groundwater inputs during drier periods. Lower DOC concentrations in forest and swamp subbasins were apparent with increasing catchment area, indicating enhanced DOC loss with extended water residence time. Surface water pCO2in savannah and tropical forest catchments ranged between 2,600 and 11,922 μatm, with swamp regions exhibiting extremely high pCO2(10,598-15,802 μatm), highlighting their potential as significant pathways for water-air efflux. Our data suggest that the quantity and quality of DOM exported to streams and rivers are largely driven by terrestrial ecosystem structure and that anthropogenic land use or climate change may impact fluvial C composition and reactivity, with ramifications for regional C budgets and future climate scenarios. Key Points Vegetation cover predominately controls fluvial C concentration and composition Small streams (20 m wide) and wetlands are significant sources of aquatic CO2Changing vegetation cover, or hydrologic conditions impact regional carbon budgets ©2014. American Geophysical Union. All Rights Reserved.
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    ItemOpen Access
    Tropical peatland carbon storage linked to global latitudinal trends in peat recalcitrance.
    (Nature communications, 2018-09-07) Hodgkins, Suzanne B; Richardson, Curtis J; Dommain, René; Wang, Hongjun; Glaser, Paul H; Verbeke, Brittany; Winkler, B Rose; Cobb, Alexander R; Rich, Virginia I; Missilmani, Malak; Flanagan, Neal; Ho, Mengchi; Hoyt, Alison M; Harvey, Charles F; Vining, S Rose; Hough, Moira A; Moore, Tim R; Richard, Pierre JH; De La Cruz, Florentino B; Toufaily, Joumana; Hamdan, Rasha; Cooper, William T; Chanton, Jeffrey P
    Peatlands represent large terrestrial carbon banks. Given that most peat accumulates in boreal regions, where low temperatures and water saturation preserve organic matter, the existence of peat in (sub)tropical regions remains enigmatic. Here we examined peat and plant chemistry across a latitudinal transect from the Arctic to the tropics. Near-surface low-latitude peat has lower carbohydrate and greater aromatic content than near-surface high-latitude peat, creating a reduced oxidation state and resulting recalcitrance. This recalcitrance allows peat to persist in the (sub)tropics despite warm temperatures. Because we observed similar declines in carbohydrate content with depth in high-latitude peat, our data explain recent field-scale deep peat warming experiments in which catotelm (deeper) peat remained stable despite temperature increases up to 9 °C. We suggest that high-latitude deep peat reservoirs may be stabilized in the face of climate change by their ultimately lower carbohydrate and higher aromatic composition, similar to tropical peats.