Seasonal variability in concentration, composition, age, and fluxes of particulate organic carbon exchanged between the floodplain and Amazon River

Abstract

[1] The composition, sources, and age of particulate organic matter were determined in an Amazonian river-floodplain system during rising, high, falling, and low water periods over 7 yr (1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006), and a mass balance for total organic carbon (dissolved and particulate) was estimated. The Curuai floodplain, composed of several temporally interconnected lakes, is permanently connected to the Amazon River via channels. Organic matter (OM) is imported to the floodplain from the Amazon River mainly during the rising water period and produced in the floodplain and exported to the river during high and falling water periods. No significant exchanges occurred during low water periods. The OM produced in the floodplain is characterized by low C/N ratios and by high chlorophyll a concentrations (Chl-a). The d 13 C signature has a seasonal trend, with more negative d 13 C values during the high water period than other periods. Δ 14 C results indicate that the bulk OM present in floodplain lakes is predominantly post-bomb (i.e., post-1950). Particulate organic carbon (POC) and dissolved organic carbon (DOC) fluxes exported by the Curuai floodplain represent 1.3% and 0.1%, respectively, of the POC and DOC annual fluxes in the mainstem Amazon River at Óbidos but may reach up to 3.3% and 0.8% during falling water. Based on Δ 14 C, d 13 C, Chl-a, and elemental analysis of the particulate organic matter, we demonstrate that floodplain lakes have intense phytoplankton and macrophyte primary production, which is partly exported to the main river channel. Floodplains are thus a significant source of modern and labile organic carbon to the river mainstem, where it can be rapidly degraded and recycled back to the atmosphere.Citation: Moreira-Turcq, P., M.-P. Bonnet, M. Amorim, M. Bernardes, C. Lagane, L. Maurice, M. Perez, and P. Seyler (2013), Seasonal variability in concentration, composition, age, and fluxes of particulate organic carbon exchanged between the floodplain and Amazon River, Global Biogeochem. Cycles, 27,[119][120][121][122][123][124][125][126][127][128][129][130]

Novel analytical strategies for tracing the organic carbon cycle in marine and riverine particles

“…plants (Moreira-Turcq et al, 2013). By contrast, the data imply that main stem POC in April, during rising waters, is influenced by a greater proportion of POC from the upstream tributaries, including POC transported by the Solimões and Madiera Rivers to the main stem, which are more 13 C-enriched and N-enriched (Table 3; Fig.…”

“…Particle transport studies have reported significant geographical and temporal variations in the fraction of marine and terrestrial primary productivity exported (export efficiency) and sequestered (transfer efficiency) in the deep ocean (Hedges and Oades, 1997;Moreira-Turcq et al, 2013). The following chapters of this dissertation aim to expand mechanistic understanding of this variation in POC export and transfer efficiency by (1) comparing multiple factors that govern the fraction of primary productivity transferred to the deep ocean and (2) assessing different empirical approaches to sampling and analyzing the dynamics of POC exported from the water column and through rivers.…”

“…Finally, seasonality presents another challenge to measuring fluxes. Water levels in the Amazon River alone fluctuate by at least a factor of two between the rainy and dry seasons (Moreira-Turcq et al, 2013), which manifests in variability in POC flux and composition as well (Richey et al, 1990;Kim et al, 2012;Ward et al, 2015).…”

Spatial and seasonal contrasts of sedimentary organic matter in floodplain lakes of the central Amazon basin

“…The periodic floods intensify the exchange of organic compounds, nutrients and minerals between rivers, lakes and flooded soils (Junk, 1997). Although only 10-20 % of the organic matter (OM) produced in the water column reaches the sediment and is finally buried (Devol et al, 1984), the sediments in these lakes are important sinks of carbon (Moreira-Turcq et al, 2004). Most of the sedimentary organic matter (SOM) in freshwater systems is derived from terrestrial vascular plants (Goñi and Hedges, 1992;Moreira-Turcq et al, 2004;Mortillaro et al, 2011).…”

“…Although only 10-20 % of the organic matter (OM) produced in the water column reaches the sediment and is finally buried (Devol et al, 1984), the sediments in these lakes are important sinks of carbon (Moreira-Turcq et al, 2004). Most of the sedimentary organic matter (SOM) in freshwater systems is derived from terrestrial vascular plants (Goñi and Hedges, 1992;Moreira-Turcq et al, 2004;Mortillaro et al, 2011). In the Amazon basin, many studies have characterized the suspended particulate organic matter (SPOM) in the rivers and the floodplain lakes and concluded that the main sources of OM to the aquatic system are the forests and the upstream Andean soils (e.g., Hedges et al, 1986Hedges et al, , 1994Quay et al, 1992;Victoria et al, 1992;Moreira-Turcq et al, 2004Aufdenkampe et al, 2007;Mortillaro et al, 2011;Zell et al, 2013b).…”