Patrick Albéric

Amazon River carbon dioxide outgassing fuelled by wetlands

River systems connect the terrestrial biosphere, the atmosphere and the ocean in the global carbon cycle. A recent estimate suggests that up to 3 petagrams of carbon per year could be emitted as carbon dioxide (CO2) from global inland waters, offsetting the carbon uptake by terrestrial ecosystems. It is generally assumed that inland waters emit carbon that has been previously fixed upstream by land plant photosynthesis, then transferred to soils, and subsequently transported downstream in run-off. But at the scale of entire drainage basins, the lateral carbon fluxes carried by small rivers upstream do not account for all of the CO2 emitted from inundated areas downstream. Three-quarters of the world’s flooded land consists of temporary wetlands, but the contribution of these productive ecosystems to the inland water carbon budget has been largely overlooked. Here we show that wetlands pump large amounts of atmospheric CO2 into river waters in the floodplains of the central Amazon. Flooded forests and floating vegetation export large amounts of carbon to river waters and the dissolved CO2 can be transported dozens to hundreds of kilometres downstream before being emitted. We estimate that Amazonian wetlands export half of their gross primary production to river waters as dissolved CO2 and organic carbon, compared with only a few per cent of gross primary production exported in upland (not flooded) ecosystems. Moreover, we suggest that wetland carbon export is potentially large enough to account for at least the 0.21 petagrams of carbon emitted per year as CO2 from the central Amazon River and its floodplains. Global carbon budgets should explicitly address temporary or vegetated flooded areas, because these ecosystems combine high aerial primary production with large, fast carbon export, potentially supporting a substantial fraction of CO2 evasion from inland waters.

Geochernical study of a crater lake (Pavin Lake, France): Trace-element behaviour in the monimolimnion

Abstract Meromicticity of Pavin Lake leads to a consequential dissolved major-and trace-element enrichment of the lower layer (monimolimnion) of the lake. In a previous work, we showed that steady state is established within this permanently anoxic bottom layer and profiles for major species could be represented by an advection-diffusion model. In this paper, results concerning the contents of 16 trace; elements determined by ICP-MS are discussed in terms of variations through the redox interface and above the sediment-water interface. Trace alkalis and boron as expected are conservative. Arsenic, nickel and cobalt are dissolved below the redox interface from Mn-and/or Fe-oxyhydroxide precipitated in the mixolimnion. Results also show clearly that barium, aluminium, cerium, lead, uranium, lanthanum, vanadium, copper and molybdenum are first released into the solution from the sediment before being scavenged in the bottom water. Furthermore, common behaviour between trace metals and dissolved organic carbon may introduce to a better understanding of transfer mechanisms. Finally, dissolved element fluxes rising up in the monimolimnion are calculated.

Neutral carbohydrate geochemistry of particulate material (trap and core sediments) in an eutrophic lake (Aydat, France)

Carbohydrate compositions were determined on sinking particles and core samples from eutrophic lake Aydat. Carbohydrate fluxes indicate that phytoplanktonic production is the main organic matter (OM) source whereas the monosaccharides concentrations normalised to OC contents (TImage) mostly reflect degradation. The abundance of rhamnose in all samples, its increasing fluxes (together with fucose) with increasing water depth, and its strong decrease in the top 5 cm of the bottom sediments mark the intense activity of the microbiota. The almost complete removal of sugars in the water and top sediment indicates very little contribution to the preserved OM stock.

Identification of Sulfur-Cycle Prokaryotes in a Low-Sulfate Lake (Lake Pavin) Using aprA and 16S rRNA Gene Markers

Geochemical researches at Lake Pavin, a low-sulfate-containing freshwater lake, suggest that the dominant biogeochemical processes are iron and sulfate reduction, and methanogenesis. Although the sulfur cycle is one of the main active element cycles in this lake, little is known about the sulfate-reducer and sulfur-oxidizing bacteria. The aim of this study was to assess the vertical distribution of these microbes and their diversities and to test the hypothesis suggesting that only few SRP populations are involved in dissimilatory sulfate reduction and that Epsilonproteobacteria are the likely key players in the oxidative phase of sulfur cycle by using a PCR aprA gene-based approach in comparison with a 16S rRNA gene-based analysis. The results support this hypothesis. Finally, this preliminary work points strongly the likelihood of novel metabolic processes upon the availability of sulfate and other electron acceptors.

A portable infrared laser spectrometer for flux measurements of trace gases at the geosphere–atmosphere interface

A portable infrared laser absorption spectrometer named SPIRIT (SPectrometre Infra-Rouge In situ Tropospherique) has been set up for the simultaneous flux measurements of trace gases at the geosphere–atmosphere interface. It uses a continuous wave distributed feedback room temperature quantum cascade laser and a patented new optical multi-pass cell. The aim of SPIRIT field studies is to get a better understanding of land and water bodies to atmosphere exchange mechanisms of greenhouse gases (GHG). The analytical procedures to derive concentrations and fluxes are described, as well as the performances of the instrument under field conditions. The ability of SPIRIT to assess space and time dependence emissions of two GHG—nitrous oxide (N2O) and methane (CH4)—for different types of ecosystems is demonstrated through in situ measurements on peatland, on fertilized soil, and on water body systems. The objectives of these investigations and preliminary significant results are reported.

Zinc and cadmium effects on growth and ion distribution in Populus tremula × Populus alba

The effects of cadmium and zinc on growth and mineral distribution in Populus tremula × P. alba genotype 717-1B4 were investigated. Exposure to 360 mg(Cd) kg−1(soil) resulted in accumulation of Cd in all organs and inhibition of primary and secondary growth as well as of the net photosynthetic rate. No growth inhibition occurred under zinc exposure. Cd was mainly stored in the woody parts of stem, whereas zinc was preferentially localized in the leaves. Cd treatment also altered distribution of Zn2+, Ca2+, Mg2+, K+, and Fe2+ in different organs.

Cadmium and Zinc are differentially distributed in Populus tremula x P. alba exposed to metal excess

Abstract Poplar plants were exposed during 61 days to a soil added with heavy metals so as to contain 300 mg Zn2+.kg−1 soil dry weight (SDW) (Zinc) or 50 mg Cd2+.kg−1 SDW (Cadmium). The Cd treatment induced a delayed growth of poplar, whereas Zn induced no change in physiological parameters. Both treatments resulted in a significant metal accumulation in plants. Zn2+ and Cd2+ exhibited contrasting distribution within tissues, indicating dissimilar handling by the plant. The main difference was the efficient compartmentalisation of Zn2+ in specific organ parts: old leaves and bark, while Cd2+ did not exhibit such a compartmentalisation. Results were also compared with a previous work where plants were exposed to 360 mg Cd2+.kg−1 SDW.

Relationships between organo-mineral supply and early diagenesis in the lacustrine environment: A study of surficial sediments from the Lac du Bouchet (Haute Loire, France)

The relationships between organo-mineral composition and early diagenetic processes in surface (< 50 cm) sediments from the Lac du Bouchet (Haute Loire, France) are presented. Parallel pore-water studies reveal downcore increases in dissolved organic carbon, inorganic carbon and CH4, illustrating the dominant methanogenetic degradation, but also highlighting regions of enhanced degradation due to sulphate reduction (confirmed by solid phase sulphur and pyrite distributions). Three sedimentary facies are observed: IA (0–25 cm) where the majority of compaction and degradation of the organic matter by diagenesis occurs in the absence of any significant change in the type of organic material or sedimentation rate; IB (25–40 cm) characterised by an increased grain size and diatom abundance; II (below 40 cm), whose base dates at 2500 ± 350 BP (i.e. within the Sub-Atlantic) shows high organic carbon contents and large grain size. Autochthonous amorphous organic matter is the dominant petrographical organic component, whereas pedogenetic (allochthonous) amorphous organic matter is slightly enriched in facies II and IA. This is coincident with the disappearance of the spores and pollen and suggests a greater continental runoff from the surrounding basin at these times. Proportions of kaolinite, chlorite and illite content do not vary greatly, indicating that the detrital input has not changed significantly over the last 2500 years. Downcore decreases in the SiAl curve (proxy for biogenic silica) parallel those of total organic carbon suggesting the dissolution of solid phase silica over time. The anthropogenic deforestation and consequent greater nutrient runoff into the oligotrophic lake encouraged an increased production of diatoms around 30 cm. The increased sedimentation rate at the beginning of the Sub-Atlantic (facies II), as a result of greater continental runoff due to installation of present climatic conditions, enhanced the preservation of the organic material by reducing the dia-genetic effects and by increasing the proportion of diagenetically inert and relatively resistant organic matter. These findings underline the critical role that bulk sedimentation rate and the nature of organic matter play in the final determination of sediment composition, both in terms of input and in post-depositional degradation.

Liquid chromatography/mass spectrometry stable isotope analysis of dissolved organic carbon in stream and soil waters

A commercial interface coupling liquid chromatography (LC) to a continuous-flow isotope ratio mass spectrometry (CF-IRMS) instrument was used to determine the δ(13) C of dissolved organic carbon (DOC) in natural waters. Stream and soil waters from a farmland plot in a hedgerow landscape were studied. Based on wet chemical oxidation of dissolved organics the LC/IRMS interface allows the on-line injection of small volumes of water samples, an oxidation reaction to produce CO(2) and gas transfer to the isotope ratio mass spectrometer. In flow injection analysis (FIA) mode, bulk DOC δ(13)C analysis was performed on aqueous samples of up to 100 μL in volume in the range of DOC concentration in fresh waters (1-10 mg C.L(-1)). Mapping the DOC δ(13)C spatial distribution at the plot scale was made possible by this fairly quick method (10 min for triplicate analyses) with little sample manipulation. The relative contributions of different plot sectors to the DOC pool in the stream draining the plot were tentatively inferred on the basis of δ(13)C differences between the hydrophilic and hydrophobic components.

New Evidence of Holocene Mass Wasting Events in Recent Volcanic Lakes from the French Massif Central (Lakes Pavin, Montcineyre and Chauvet) and Implications for Natural Hazards

High-resolution seismic profiling (12 kHz) surveys combined with sediment cores, radiocarbon dating, tephrochronology and multibeam bathymetry (when available) allow documentation of a range of Holocene mass wasting events in nearby contrasting lakes of volcanic origin in the French Massif Central (45°N, 2°E): two deep maar lakes (Pavin and Chauvet) and a shallow lake (Montcineyre) dammed by the growth of a volcano. In these lacustrine environments dominated by authigenic sedimentation, recent slide scars, acoustically transparent to chaotic lens-shaped bodies, slump deposits or reworked regional tephra layers suggest that subaqueous mass wasting processes may have been favoured by gas content in the sediments and lake level changes. While these events may have had a limited impact in both lakes Chauvet and Montcineyre, they apparently favoured the development of lacustrine meromicticity in maar Lake Pavin along with possible subaerial debris flows resulting from crater outburst events.