Biogenic gases and the oxidation and reduction of carbon in Amazon River and floodplain waters

Abstract

Concentrationsof COZ, 02, CH4, and N,O in the Amazon River system reflect an oxidationreduction sequence in combination with physical mixing between the floodplain and the mainstem. Concentrations of CO, ranged from 150 PM in the Amazon mainstem to 200-300 PM in aerobic environments and up to 1,000 PM in oxygen-depleted environments of the floodplain. Apparent oxygen utilization (AOU) ranged from 80 to 250 PM. Methane was highly supersaturated with respect to atmospheric equilibrium. Concentrations ranged from 0.06 PM in the mainstem to 100 PM on the floodplain. Concentrations of N,O were slightly supersaturated in the mainstem (-13 nM) but were undcrsaturated on the floodplain (averaging 9 nM). Fluxes calculated from these concentrations indicated decomposition of -1,600 g C m-2 yr-' of organic carbon in Amazon floodplain waters. Analysis of relationships between CH,, 02, and CO, concentrations indicated that about 50% of carbon mineralization on the floodplain is anaerobic, with 20% lost to the atmosphere as CH,. The predominance of anaerobic metabolism leads to consumption of N20 on the floodplain. Elevated concentrations of CH, in the mainstem probably reflect input from the floodplain, while high levels of CO, in the mainstem are derived from a combination of floodplain drainage and in situ respiration.-The rates of oxidation and reduction of carbon in rivers change dramatically with increasing river size (Vannote et al. 1980). Small, temperate streams are relatively well described; the sequence and extent of metabolic processes operating in very large rivers is essentially unknown. Many large river l To whom correspondence should be addressed.

Carbon source/sink function of a subtropical, eutrophic lake determined from an overall mass balance and a gas exchange and carbon burial balance

“…The gaseous carbon fluxes obtained by static chamber technique are somewhat higher than the values from thin boundary layer method, as ebullition is absent in the latter method (Richey et al, 1988;Devol et al, 1990;Bubier et al, 1993). Although there are some shortages of static chamber technique, the gas fluxes are relatively reliable as ebullition is included in this technique.…”

“…Research in two large reservoirs has shown that the static chamber technique contained fewer analytical biases whilst the thin boundary layer method underestimated CO 2 and CH 4 emission fluxes (Duchemin et al, 1999). Some researches showed that chamber technique overestimates the fluxes relative to the thin boundary layer technique, primarily because the latter only considers diffusion across the airewater interface (Richey et al, 1988;Devol et al, 1990). Similarly, Bubier et al (1993) also suggested the difference between chamber method and thin boundary layer technique results from the absence of ebullition, an important flux mechanism, especially to CH 4 , in the latter method.…”

Effects of agricultural land use on fluvial carbon dioxide, methane and nitrous oxide concentrations in a large European river, the Meuse (Belgium)

“…Pristine rivers are usually nitrogen poor and seem to be low sources or even sinks of N 2 O, related to sediment denitrification that removes N 2 O from the water column (Richey et al, 1988;Baulch et al, 2011;Borges et al, 2015a).…”

Longitudinal discontinuities in riverine greenhouse gas dynamics generated by dams and urban wastewater

“…A small number of studies that measured CO 2 , CH 4 , and N 2 O together in large rivers such as the Amazon and Congo have revealed some common longitudinal patterns of three GHGs driven by interrelated sources and production mechanisms (Richey et al, 1988;Borges et al, 2015). For instance, Richey et al (1988) found large increases in dissolved CO 2 and CH 4 and slight reductions in N 2 O in the Amazon mainstem downstream of large floodplains.…”

“…Above all, 40 recent global syntheses of CO 2 emissions from inland waters commonly emphasized the lack of reliable measurements of the surface water partial pressure of CO 2 (pCO 2 ) in many of large river systems across Asia and Africa Lauerwald et al, 2015). Furthermore, three major GHGs (CO 2 , CH 4 , and N 2 O) have rarely been measured simultaneously across different components of river systems except for a small number of large, 'natural' rivers such as the Amazon (Richey et al, 1988) and the Congo or highly human-impacted systems (Smith et al, 2017;Wang et al, 2017b). 45…”