Dissolved CO2 in Waters of the Amazon : Deconvolving Signals of Land-Water Coupling and In-Stream Processes as Indicative of Ecosystem Dynamics
Richey, Univ. of Washington, email@example.com
Krusche, CENA, firstname.lastname@example.org
Ballester, CENA, email@example.com
BeijaRio, Tudos, firstname.lastname@example.org
What controls regional differences in the pCO2 of Amazonian waters?” By analyzing results across the multiple water types sampled through the sampling network Rede Beija Rio, we see that variability in the predictable annual regime of pCO2 (essentially, increasing and decreasing in synchrony with the hydrograph) at any point in a river network across regions is functionally governed by the relative distributions of the ecosystem state variables controlling pH, water movement (infiltration and runoff on land, current velocity in channels), production and mobilization of LMW DOC fractions, and suspended sediment loads:
(1) With rising water, the primary source term for pCO2 in small streams is groundwater, but as that source degasses, in-river mineralization of (near-) contemporary low molecular weight (<5kDa) dissolved organic compounds derived from the local mix of terrestrial C3 and, preferentially, C4 plants becomes the dominant source. DOC export amount and composition by region is determined by soil type and flushing (which also drives pH). With falling water, depletion of terrestrial sources and reduction in sediment load promotes a higher ratio of aquatic primary productivity to respiration (to a greater extent than previously thought), leading to a sink of pCO2 (but subsequent export of labile organic matter from in situ sources). pCO2 during rising water is more aged and depleted in 13C than during falling water, reflecting the greater terrestrial sources
(2) pH, responding to the stage of the hydrograph and set initially by weathering and then with feedbacks from biological processes, affects not only the distribution of dissolved inorganic carbon among carbonate system species, but also the bioavailability of dissolved substrates for respiration.
(3) The primary pCO2 sink term in flowing waters is outgassing, where scale of habitat and river current-induced turbulence are the primary controlling factors, and weather factors (wind speed, air-water temperature gradients) are secondary.