Sources and transfers of particulate organic matter in a tropical reservoir (Petit Saut, French Guiana): a multi-tracers analysis using δ&lt;sup&gt;13&lt;/sup&gt;C, C/N ratio and pigments

Abstract. Carbon cycling and organic matter transfers in the tropical Sinnamary river system (French Guiana), including a mid-stream reservoir (Petit Saut) and its estuary on the Atlantic coast, were studied during the dry season by analyzing the organic carbon isotopic ratios (δ13C-OC), C/N ratios and pigments contents of suspended matter, sediments, sediments traps and epiphytic and epilithic biofilms. In the River upstream as well as in surface sediments at the entrance of the reservoir and at the littoral zone of the reservoir, particulate organic matter (POM) was in majority of terrestrial origin, with a δ13C-C/N signature close to the one of soil and litter collected in the surrounding forest and with high OC/total pigments ratios. High concentrations of Pheopigments a and b in these surface sediments showed that this terrestrial POM, either carried by the river and eolian transport or present in the soil before flooding, undergoes intense degradation. Deeper in the sediment, the δ13C profile showed a decreasing trend with depth typical of what is found in soils, showing that the flooded soil still remains present at the reservoir bottom 10 years after flooding. At the center of the reservoir, POM in the water column, in sediment traps and in surface sediments was in majority of aquatic origin with low C/N and OC/total pigments ratios. In the oxic epilimnion at 3 m depth, Chl a, Chl b and Lutein showed the predominance of Chlorophyceae to the phytoplankton community. At this depth, a C/N ratio of 21 suggests a large contribution of transparent exopolymeric particles to the bulk POM, which, in addition, was 13C-depleted due to a significant contribution of methanotrophic bacteria. At 7 m depth, below the oxicline, high concentrations of BChl d and occasionally BChl c revealed the presence of anoxygenic phototrophic bacteria, namely Chlorobiaceae. In the sediment traps, Chl a, Chl b, Lutein and BChl c and BChl d confirmed the contribution of plankton to the sedimentary POM. This material was undergoing intense degradation as revealed by high concentration of pheopigments and by an increase in C/N ratio and an increase in δ13C-OC with trap depth. Scytonemin was found in a biofilm developed on tree trunks at the reservoir surface and in all sediment traps. Other tracers showed however that the contribution of the biofilm to the sedimentary POM was minor compared to the planktonic source. In the Sinnamary downstream of the dam, POM became more 13C-depleted showing a larger contribution of methanotrophic bacteria. Chl b, Lutein and BChl c + BChl d originating from the reservoir progressively decreased downstream as the result of mineralization. At the estuarine mouth, fucoxanthin showed the presence of diatoms and the δ13C-C/N signature matched the one of POM carried by the Amazonian coastal mobile mud belt.

Download Full-text

A multi-tracers analysis of sources and transfers of particulate organic matter in a tropical reservoir (Petit Saut, French Guiana)

River Research and Applications ◽

10.1002/rra.1152 ◽

2009 ◽

Vol 25 (3) ◽

pp. 253-271 ◽

Cited By ~ 17

Author(s):

Alexis de Junet ◽

Gwenaël Abril ◽

Frédéric Guérin ◽

Isabelle Billy ◽

Rutger de Wit

Keyword(s):

Organic Matter ◽

Particulate Organic Matter ◽

French Guiana ◽

Tropical Reservoir ◽

Petit Saut

Download Full-text

Programmed cell death in diazotrophs and the fate of organic matter in the western tropical South Pacific Ocean during the OUTPACE cruise

Biogeosciences ◽

10.5194/bg-15-3893-2018 ◽

2018 ◽

Vol 15 (12) ◽

pp. 3893-3908 ◽

Cited By ~ 9

Author(s):

Dina Spungin ◽

Natalia Belkin ◽

Rachel A. Foster ◽

Marcus Stenegren ◽

Andrea Caputo ◽

...

Keyword(s):

Cell Death ◽

Organic Matter ◽

Pacific Ocean ◽

Programmed Cell Death ◽

South Pacific ◽

Sediment Traps ◽

Vertical Flux ◽

Filamentous Cyanobacterium ◽

Chl A ◽

South Pacific Ocean

Abstract. The fate of diazotroph (N2 fixers) derived carbon (C) and nitrogen (N) and their contribution to vertical export of C and N in the western tropical South Pacific Ocean was studied during OUTPACE (Oligotrophy to UlTra-oligotrophy PACific Experiment). Our specific objective during OUTPACE was to determine whether autocatalytic programmed cell death (PCD), occurring in some diazotrophs, is an important mechanism affecting diazotroph mortality and a factor regulating the vertical flux of organic matter and, thus, the fate of the blooms. We sampled at three long duration (LD) stations of 5 days each (LDA, LDB and LDC) where drifting sediment traps were deployed at 150, 325 and 500 m depth. LDA and LDB were characterized by high chlorophyll a (Chl a) concentrations (0.2–0.6 µg L−1) and dominated by dense biomass of the filamentous cyanobacterium Trichodesmium as well as UCYN-B and diatom–diazotroph associations (Rhizosolenia with Richelia-detected by microscopy and het-1 nifH copies). Station LDC was located at an ultra-oligotrophic area of the South Pacific gyre with extremely low Chl a concentration (∼ 0.02 µg L−1) with limited biomass of diazotrophs predominantly the unicellular UCYN-B. Our measurements of biomass from LDA and LDB yielded high activities of caspase-like and metacaspase proteases that are indicative of PCD in Trichodesmium and other phytoplankton. Metacaspase activity, reported here for the first time from oceanic populations, was highest at the surface of both LDA and LDB, where we also obtained high concentrations of transparent exopolymeric particles (TEP). TEP were negatively correlated with dissolved inorganic phosphorus and positively coupled to both the dissolved and particulate organic carbon pools. Our results reflect the increase in TEP production under nutrient stress and its role as a source of sticky carbon facilitating aggregation and rapid vertical sinking. Evidence for bloom decline was observed at both LDA and LDB. However, the physiological status and rates of decline of the blooms differed between the stations, influencing the amount of accumulated diazotrophic organic matter and mass flux observed in the traps during our experimental time frame. At LDA sediment traps contained the greatest export of particulate matter and significant numbers of both intact and decaying Trichodesmium, UCYN-B and het-1 compared to LDB where the bloom decline began only 2 days prior to leaving the station and to LDC where no evidence for bloom or bloom decline was seen. Substantiating previous findings from laboratory cultures linking PCD to carbon export in Trichodesmium, our results from OUTPACE indicate that nutrient limitation may induce PCD in high biomass blooms such as displayed by Trichodesmium or diatom–diazotroph associations. Furthermore, PCD combined with high TEP production will tend to facilitate cellular aggregation and bloom termination and will expedite vertical flux to depth.

Download Full-text

Influence of Light Intensity on Methanotrophic Bacterial Activity in Petit Saut Reservoir, French Guiana

Applied and Environmental Microbiology ◽

10.1128/aem.65.2.534-539.1999 ◽

1999 ◽

Vol 65 (2) ◽

pp. 534-539 ◽

Cited By ~ 39

Author(s):

J. F. Dumestre ◽

J. Guézennec ◽

C. Galy-Lacaux ◽

R. Delmas ◽

S. Richard ◽

...

Keyword(s):

Methane Emission ◽

French Guiana ◽

Methanotrophic Bacteria ◽

Phospholipid Analysis ◽

In Situ Conditions ◽

The Mean ◽

One Year ◽

Petit Saut ◽

Potential Inhibitors

ABSTRACT One year after impoundment in January 1994, methanotrophic bacteria in Petit Saut Reservoir (French Guiana) were active at the oxic-anoxic interface. This activity was revealed by the sudden extinction of diffusive methane emission (600 metric tons of CH4 · day−1 for the whole lake surface area, i.e., 360 km2). Lifting of inhibition was suspected. After reviewing the potential inhibitors of this physiological guild (O2, NH4 +, sulfides) and considering the similarities with nitrifiers, we suggest that sunlight influenced the methanotrophic bacteria. On the basis of phospholipid analysis, only a type II methanotrophic community was identified in the lake. Both growth and methanotrophic activity of an enriched culture, obtained in the laboratory, were largely inhibited by illumination over 150 microeinsteins · m−2 · s−1. These results were confirmed on a pure culture of Methylosinus trichosporium OB3B. In situ conditions showed that water transparency was quite stable in 1994 and 1995 and that the oxycline moved steadily deeper until January 1995. Considering the mean illumination profile during this period, we showed that removal of methanotrophic growth inhibition could only occur below a 2-m depth. The oxycline reached this level in October 1994, allowing methanotrophic bacteria to develop and to consume the entire methane emission 4 months later.

Download Full-text

Effects of tributary size on the resource supply and physical habitat at tributary junctions along two mainstem rivers

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/cjfas-2019-0435 ◽

2020 ◽

Vol 77 (8) ◽

pp. 1393-1408

Author(s):

David A. Tavernini ◽

John S. Richardson

Keyword(s):

Organic Matter ◽

Particulate Organic Matter ◽

Main Stem ◽

Spatiotemporal Variability ◽

Physical Habitat ◽

Resource Concentration ◽

Coarse Particulate Organic Matter ◽

Substrate Size ◽

High Concentrations ◽

Diel Period

Tributary junctions are regarded as ecologically important due to unique habitat present; however, there is limited understanding of the drivers of habitat attributes at these locations. Using six sites across two mainstem rivers, we tested whether tributary size relative to main stem governs the strength and direction of response of substrate size, stream temperature, and nutrient and coarse particulate organic matter (CPOM) concentration. We found that only phosphorus and CPOM concentration showed a significant relationship with relative tributary size. Small tributaries contributed high concentrations, whereas concentrations in larger tributaries resembled the main stem. Often, tributary exports were enough to increase the resource concentration in the main stem by 40%. Substrate coarsened by ∼60% downstream of tributaries. Temperature asynchrony was observed, where tributaries contributed water between 2.8 °C cooler to 1.9 °C warmer than the main stem within one diel period. Our results highlight the importance of small tributaries for whole network functioning. However, large spatiotemporal variability revealed how habitat attributes are highly context-dependent in these locations and may be difficult to predict in both scientific and management settings.

Download Full-text

Carbon Isotope Ratios of Particulate Organic Matter in the Gulf of St. Lawrence

Journal of the Fisheries Research Board of Canada ◽

10.1139/f79-099 ◽

1979 ◽

Vol 36 (6) ◽

pp. 678-682 ◽

Cited By ~ 20

Author(s):

F. C. Tan ◽

P. M. Strain

Keyword(s):

Organic Matter ◽

Surface Water ◽

Organic Carbon ◽

Carbon Isotope ◽

Particulate Organic Matter ◽

Surface Sediments ◽

Isotope Ratios ◽

Lawrence Estuary ◽

Carbon Isotope Ratios ◽

Surface Samples

Sixteen offshore surface samples within the Gulf of St. Lawrence show low δ13C values and are similar to eight offshore surface samples collected seaward of the Gulf of St. Lawrence. The δ13C surface values are consistent with δ13C values in plankton produced at the temperature found in the euphotic zone in the study area. Higher values are observed in four surface samples from the mouth of the St. Lawrence Estuary and probably result from high carbon demand during periods of high biological productivity. Lower values found in seven deep POC samples indicate changes in the nature of the POC caused by biological degradation of the organic matter. Significant differences (2–6‰) between the uniformly high δ13C values of the organic carbon in surface sediments and the low values of near-bottom water POC have been observed. The similarity between the δ13C values of surface water POC and the surface sediments suggest that surface water POC is an important source of organic carbon in surface sediments. Several observations of large vertical δ13C gradients in deep water POC suggest the presence of resuspended sediments 30–60 m above the sediment–water interface. Key words: particulate organic matter, carbon isotope ratios, isotope fractionation, sediment resuspension, sediment sources, Gulf of St. Lawrence

Download Full-text

Biological composition and microbial dynamics of sinking particulate organic matter at abyssal depths in the oligotrophic open ocean

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1903080116 ◽

2019 ◽

pp. 201903080 ◽

Cited By ~ 19

Author(s):

Dominique Boeuf ◽

Bethanie R. Edwards ◽

John M. Eppley ◽

Sarah K. Hu ◽

Kirsten E. Poff ◽

...

Keyword(s):

Organic Matter ◽

Particulate Organic Matter ◽

Deep Sea ◽

Deep Ocean ◽

Sediment Traps ◽

Rrna Gene ◽

North Pacific Subtropical Gyre ◽

Near Surface ◽

The North ◽

Sinking Particles

Sinking particles are a critical conduit for the export of organic material from surface waters to the deep ocean. Despite their importance in oceanic carbon cycling and export, little is known about the biotic composition, origins, and variability of sinking particles reaching abyssal depths. Here, we analyzed particle-associated nucleic acids captured and preserved in sediment traps at 4,000-m depth in the North Pacific Subtropical Gyre. Over the 9-month time-series, Bacteria dominated both the rRNA-gene and rRNA pools, followed by eukaryotes (protists and animals) and trace amounts of Archaea. Deep-sea piezophile-like Gammaproteobacteria, along with Epsilonproteobacteria, comprised >80% of the bacterial inventory. Protists (mostly Rhizaria, Syndinales, and ciliates) and metazoa (predominantly pelagic mollusks and cnidarians) were the most common sinking particle-associated eukaryotes. Some near-surface water-derived eukaryotes, especially Foraminifera, Radiolaria, and pteropods, varied greatly in their abundance patterns, presumably due to sporadic export events. The dominance of piezophile-like Gammaproteobacteria and Epsilonproteobacteria, along with the prevalence of their nitrogen cycling-associated gene transcripts, suggested a central role for these bacteria in the mineralization and biogeochemical transformation of sinking particulate organic matter in the deep ocean. Our data also reflected several different modes of particle export dynamics, including summer export, more stochastic inputs from the upper water column by protists and pteropods, and contributions from sinking mid- and deep-water organisms. In total, our observations revealed the variable and heterogeneous biological origins and microbial activities of sinking particles that connect their downward transport, transformation, and degradation to deep-sea biogeochemical processes.

Download Full-text

Calibration of in situ chlorophyll fluorometers for organic matter

Hydrobiologia ◽

10.1007/s10750-019-04086-z ◽

2019 ◽

Vol 847 (21) ◽

pp. 4377-4387 ◽

Cited By ~ 1

Author(s):

Jonna Kuha ◽

Marko Järvinen ◽

Pauliina Salmi ◽

Juha Karjalainen

Keyword(s):

Organic Matter ◽

Water Quality Monitoring ◽

Quality Monitoring ◽

Calibration Model ◽

Humic Lakes ◽

Water Colour ◽

Chl A ◽

The One ◽

Chl Fluorescence

AbstractOrganic matter (OM) other than living phytoplankton is known to affect fluorometric in situ assessments of chlorophyll in lakes. For this reason, calibrating fluorometric measurements for OM error is important. In this study, chlorophyll (Chl) fluorescence was measured in situ in multiple Finnish lakes using two sondes equipped with Chl fluorometers (ex.470/em.650–700 nm). OM absorbance (A420) was measured from water samples, and one of the two sondes was also equipped with in situ fluorometer for OM (ex.350/em.430 nm). The sonde with Chl and OM fluorometers was also deployed continuously on an automated water quality monitoring station on Lake Konnevesi. For data from multiple lakes, inclusion of water colour estimates into the calibration model improved the predictability of Chl assessments markedly. When OM absorbance or in situ OM fluorescence was used in the calibration model, predictability between the in situ Chl and laboratory Chl a assessments was also enhanced. However, correction was not superior to the one done with the water colour estimate. Our results demonstrated that correction with water colour assessments or in situ measurements of OM fluorescence offers practical means to overcome the variation due to OM when assessing Chl in humic lakes in situ.

Download Full-text