Particulate Organic Carbon Transport Research Articles

Sources and Fluxes of Organic Carbon in Lake Malawi/Nyasa

Significant changes in land use of the watershed of Lake Malawi, one of the Great Lakes of East Africa, have occurred over the past 30 to 40 years and continue today. Deforestation and increasingly intensive agriculture have contributed to an increase in the mobilization of allochthonous organic material to the lake. Dissolved and particulate organic carbon transport by rivers as well as wet and dry atmospheric deposition were measured and used to construct an organic carbon budget for the lake. Although the concentrations of dissolved organic carbon (DOC) and particulate carbon (PC) in Lake Malawi are among the lowest measured in any large lake and approach oceanic concentrations, significant seasonal changes over the annual cycle were found. The lake had a mean mass of 62.6 × 10 10 moles of organic carbon and within the annual cycle of DOC the mass fluctuated by 35.5 × 10 10 moles of organic carbon from September 1997 (47.1 × 10 10 moles of organic carbon) to May 1998 (82.6 × 10 10 moles of organic carbon). The annual allochthonous organic carbon input to the whole lake from all sources was approximately 8 × 10 10 moles with 36% from atmospheric sources. Previous studies have estimated a mean annual phytoplankton production of 98.9 × 10 10 moles of carbon for the whole lake. Liberation of 20 to 40% of the algal production as DOC will account for the change in the mass of organic carbon. In this large tropical system, allochthonous particulate carbon may be an increasingly significant source of energy and nutrients to the food web. Due to the importance of primary production, land use changes that increase nutrient export the lake will also alter the organic carbon stores

Active transport of particulate organic carbon and nitrogen by vertically migrating zooplankton in the Sargasso Sea

Diel vertically migrating zooplankton can contribute significantly to dissolved carbon and nutrient export by respiring and excreting surface-ingested particulate organic matter below the mixed layer. Active export of particulate organic carbon (POC) and particulate organic nitrogen (PON) due to defecation at depth has rarely been considered in export budgets. We measured the gut passage time (GPT) of common migrant species at the Bermuda Atlantic Time-series Study (BATS) site, using the gut fluorescence method, to determine whether GPT is slow enough to allow active export of POC and PON to depth. Mean GPT for the copepods Pleuromamma xiphias and Euchirella messinensis was 191 and 114 min, respectively, and for the euphausiids Thysanopoda aequalis and Euphausia brevis (analyzed together) was 41 min, exceeding previously reported GPT for non- migrating zooplankton by a factor of 6. Between 18 and 81% of the initial gut pigment was retained in zooplankton guts upon descent below a mixed layer of 150 m. By comparing pigment ingestion rates (gut fluorescence technique) with total ingestion rates (CHN analysis of fecal material), we esti- mated that 71 to 85% of the migrant diet originated from non-plant material, which we included in our estimates of active POC/PON export. We applied the mean weight-specific active POC/PON export rate for the species examined to the total migratory zooplankton biomass using data from the BATS zooplankton time-series. Mean active POC (PON) flux at BATS was 0.94 mg C m -2 d -1 (0.18 mg N m -2 d -1 ) and the maximum was 5.27 mg C m -2 d -1 (1.02 mg N m -2 d -1 ), corresponding to a mean of 3% (4%) and a maximum of 18% (20%) of the mean gravitational POC (PON) flux measured by sediment traps at 150 m. Migrants also contributed significantly to passive flux via production of sinking fecal pellets during the night in surface waters. This passive flux exceeded active POC flux by ~10-fold. Freshly released feces by migrators at depth could be a valuable food source for mesopelagic organisms, in contrast to feces produced in surface waters which decompose while settling through the water column.

Contribution of algal sinking and zooplankton grazing to downward flux in the Lazarev Sea (Southern Ocean) during the onset of phytoplankton bloom: a lagrangian study

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 233:73-88 (2002) - doi:10.3354/meps233073 Contribution of algal sinking and zooplankton grazing to downward flux in the Lazarev Sea (Southern Ocean) during the onset of phytoplankton bloom: a lagrangian study E. A. Pakhomov1,2,*, P. W. Froneman1, P. Wassmann3, T. Ratkova4, E. Arashkevich4 1Southern Ocean Group, Department of Zoology and Entomology, Rhodes University, PO Box 94, Grahamstown 6140, South Africa 2Department of Zoology, University of Fort Hare, Private Bag X1314, Alice 5700, South Africa 3Norwegian College of Fishery Science, University of Tromsø, 9037 Tromsø, Norway 4P. P. Shirshov Institute of Oceanology, Russian Academy of Sciences, Nakhimovsky Avenue 36, 117541 Moscow, Russia *Address for correspondence: University of Fort Hare. E-mail: epakhomov@ufh.ac.za ABSTRACT: Hydrography, chlorophyll a, phytoplankton and zooplankton dynamics and the vertical flux of particulate organic carbon (POC) and pigments in the upper 200 m were investigated for 12 consecutive days during a drogue study conducted in the open waters of the ice-edge zone of the Lazarev Sea during the austral summer (December/January) 1994/95. Results of the study indicate that during the experiment, primary production, although variable, increased from ~300 to ~800 mgC m-2d-1. This increase could likely be related to development of a shallow pycnocline. Analysis of sediment trap data showed that the vertical carbon flux resulting from sedimentation and grazing activity was greatest in the upper water column (<80 m). The importance of grazers to total POC flux was highest at the beginning and the end of the investigation and accounted for up to 15% of total carbon flux. The contribution of grazers to vertical flux was negligible (<2%) during the intermediate part of the Southern Ocean Drogue study. Lower contribution of grazers to sedimentation of POC at depth can likely be related to community composition of zooplankton. Sedimentation of phytoplankton cells from the upper water column increased during the study. Here, downward POC flux resulting from sedimentation of microphytoplankton was equivalent to 15-75% of the total. Increase in sedimentation of phytoplankton during the study can be related to an increase in the average size of phytoplankton cells. Transport of POC from surface waters to deeper depths resulting from sedimentation or grazing activity was equivalent to <48% of total daily primary production, measured at 50 m, while the same value for phytoplankton flux did not exceed 27% of the total. Zooplankton density was insufficient to exert either a positive (via faecal pellets) or negative (via reducing suspended phytoplankton concentration) effect on particulate carbon sedimentation. This resulted in algal sink being the most important mechanism in downward POC flux during the onset of the phytoplankton bloom period in the Marginal Ice Zone, even in the presence of pelagic tunicates. KEY WORDS: Seasonal ice zone · Antarctica · Lazarev Sea · Vertical flux · POC · Phytoplankton · Zooplankton · Grazing Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 233. Online publication date: May 21, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

Distribution of Particulate Organic Matter in the Southern East China Sea:Implications in Production and Transport

Repeated surveys in October, 1992 and May, 1993 in the southern East China Sea showed a high abundance of particulate organic carbon in the upwelling area around the shelf break northeast of Taiwan. Particulate nitrogen was well correlated with particulate organic carbon with a ∆C/∆N atomic ratio of 6.3-6.7. The vertical distribution of the particulate organic carbon had a surface maximum at many stations. Such distribution was not directly related to phytoplankton biomass but controlled by the primary production rate which also showed an eminent maximum close to the surface. The POC residence time in the upper water column varied from 2 tol9 days for different water types. For the coastal water and upwelling center, the residence time was calculated to be 3-8 days; for the nutrient-poor shelf and Kuroshio waters, 7-19 days. The sinking flux of particulate organic carbon at the bottom of the euphotic zone in the Kuroshio water was calculated from the standing stock and the particle residence time to be 3.3mmol C/m^2/d, which represents 18% of the potential primary productivity; the sinking flux of particulate nitrogen 0.29 mmol/m^2/d. Beneath the Kuroshio current in the Okinawa Trough, we found patches of relatively high particulate organic carbon concentration at depths between 500 and 750 m on both cruises. This was the first evidence of the lateral transport of particulate organic carbon across the shelf break to the deep sea off northeastern Taiwan. Such a process may have been responsible for the enrichment of organic carbon in the sediments on the slope.

Transport of Particulate Organic Carbon by the Mississippi River and Its Fate in the Gulf of Mexico

This study was designed to determine the amount of particulate organic carbon (POC) introduced to the Gulf of Mexico by the Mississippi River and assess the influence of POC inputs on the development of hypoxia and burial of organic carbon on the Louisiana continental shelf. Samples of suspended sediment and supporting hydrographic data were collected from the river and >50 sites on the adjacent shelf. Suspended particles collected in the river averaged 1.8±0.3% organic carbon. Because of this uniformity, POC values (in μmol l−1) correlated well with concentrations of total suspended matter. Net transport of total organic carbon by the Mississippi-Atchafalaya River system averaged 0.48×1012 moles y−1 with 66% of the total organic carbon carried as POC. Concentrations of POC decreased from as high as 600 μmol l−1 in the river to 35% along the shelf at ≥10 km from the river mouth. River flow was a dominant factor in controlling particle and POC distributions; however, time-series data showed that tides and weather fronts can influence particle movement and POC concentrations. Values for apparent oxygen utilization (AOU) increased from ∼60 μmol l−1 to >200 μmol l−1 along the shelf on approach to the region of chronic hypoxia. Short-term increases in AOU were related to transport of more particle-rich waters. Sediments buried on the shelf contained less organic carbon than incoming river particles. Orgamic carbon and δ13C values for shelf sediments indicated 3 that large amounts of both terrigenous and marine organic carbon are being decomposed in shelf waters and sediments to fuel observed hypoxia.

Ecology of amorphous aggregations (marine snow) in the Northern Adriatic Sea. V. Role of fecal pellets in marine snow

Ecology of amorphous aggregations (marine snow) in the Northern Adriatic Sea. V. Role of fecal pellets in marine snow

Organic carbon dynamics in two regulated rivers in northwestern Montana, USA

We studied the transport of particulate organic carbon (POC) and dissolved organic carbon (DOC) in two regulated rivers during minimum and increasing discharges. Mean annual concentrations of total POC, measured monthly during conditions of minimum discharge from the dams, were twice as high at a station below a dam with a selective withdrawal system on the Kootenai River (KR, 0.15 mg 1−1), as at station below a dam with hypolimnetic water releases on the Flathead River (FR, 0.07 mg 1−1). Annual mean concentrations of DOC were similar below both dams (1.62 mg 1−1 FR; 1.71 KR). The percentage of POC in four size fractions differed in regulated and unregulated reaches of each river system; the smallest size fraction (0.45–10 smm) constituted a larger percentage of the total POC at the stations below the dams (50–93%), because POC in large size classes had settled out in the reservoir. The three largest size fractions (10–1000 µm) comprised a larger percentage of the total POC when samples were taken during conditions of full discharge from the dam. We measured large increases in all size classes of POC in samples collected during increasing discharges in a regulated reach, reflecting the component of sloughed periphyton and resuspended organic matter that were added during periods of hydropower generation at the dam. Seston (355 µm to 1 cm) collected in nets increased dramatically during increasing flows; concentrations of particulate organic matter (POM) in samples collected two and three hours after water levels began to rise were 572 and 1440 times higher than those collected during minimum discharge at the dam.

Carbon isotope geochemistry of the Changjiang estuary

Stable carbon isotope ratios have been used to study the sources and transport of particulate organic carbon (POC) in the Changjiang estuary and the East China Sea. δ 13C values of POC collected during the period of high water discharge (June 1980) show a range of −25·4 to −19·7 ppt, suggesting mixing of riverine and marine organic carbon. Samples collected during the low water discharge period (November 1981) have a δ 13C range of −26·6 to −23·7 ppt, indicative of dominant terrestrial organic carbon contribution. The sedimentary organic carbon in the East China Sea exhibits a relatively narrow δ 13C range (−22·9 to −20·8 ppt) suggesting a dominant marine source.

Nature of POC transport in a mangrove ecosystem: A carbon stable isotopic study

The isotopic composition of particulate organic carbon (POC) was studied during five tidal cycles in a mangrove creek of Sepetiba Bay, Rio de Janeiro, Brazil. The results show that a mixture of organic carbon from mangrove and marine origins is always present in the creek. Mean mangrove contribution to the POC varied from 16% to 100% and was dependent on tidal amplitude. The results suggest that oceanic carbon can be an important component of carbon balance in mangrove ecosystems. Therefore, earlier carbon balance studies from mangroves which did not include measurements of carbon isotopic composition should be interpreted with care.

Sources and transport of particulate organic carbon in the Amazon River and estuary

Stable carbon isotope ratios have been used to study the sources of particulate organic carbon (POC) in the Amazon River and its tributaries as well as to examine the transport of the riverine POC into the oceanic environment. POC in the upper reaches of the Amazon River has more positive δ 13C values (−24·5 to −28·0‰) than that in the middle and lower reaches (−27·9 to −30·1‰). The δ 13C content of POC from the tributaries is generally more negative than that observed in the Amazon main channel. This δ 13C evidence shows that the POC in the Amazon main channel is predominantly of terrestrial origin rather than a result of in situ production. A large range of δ 13C values (−17·5 to −28·4‰) is observed in the Amazon estuary and plume and is attributed to the mixing of riverine and marine POC. POC δ 13C measurements detect riverine organic detritus as far as 290 km offshore in a direction parallel to the river channel; the isotopic signal of riverine POC can be seen as far as 1100 km to the north-west of the river mouth in the Amazon River plume.

Sedimentation, Resuspension, and Oxygen Depletion in Lake Erie (1979)

Oxygen depletion in Lake Erie's central basin hypolimnion is ultimately sustained by the respiration rate of organisms using organic matter which is produced in the trophogenic zone. Although other transformations are certainly important, they are nevertheless driven by the decomposition of organic carbon both in the water column and in the sediments. Rates of transport of particulate organic carbon to the hypolimnion and sediments were estimated using sediment traps. Corrections for sediment resuspension were necessary even during the summer period when the lake is stratified. Particulate organic carbon concentrations in the hypolimnion were partially independent of short-term variations in chlorophyll concentration. The net downflux of carbon to the hypolimnion appeared less than that required to support the observed oxygen depletion. Sediment resuspension accounted for much of the particulate material caught by the sediment traps in the central basin. It is concluded that organic material stored in the surficial sediments is made available to the water column through frequent resuspension. Of total phosphorus in the trap samples, an average of 42% was potentially bioavailable (NaOH extraction).

Concentration of particulate trace metals and particulate organic carbon in marine surface waters by a bubble flotation mechanism

The transport of particulate organic carbon (POC) and particulate trace metals (PTM) to the sea surface by rising bubbles in samples of surface water collected in Narragansett Bay was examined using an adsorptive bubble separation technique. Recoveries of POC ranged from 30 to 59% while those of the particulate form of the trace metals, Al, Mn, Fe, V, Cu, Zn, Ni, Pb, Cr and Cd were generally greater than 50%. The recovery data were used to arrive at a rough order of magnitude estimate of the bubble transport of POC and PTM under open-ocean conditions. While transport rates of the trace metals to the sea surface by both bubble transport and atmospheric deposition varied over approximately 3 orders of magnitude, the ratio of bubble transport to atmospheric deposition for most metals varied over approximately one order of magnitude, perhaps suggesting some degree of coupling between atmospheric PTM and bubble-transported PTM.