Importance of intertidal sediment processes and porewater exchange on the water column biogeochemistry in a pristine mangrove creek (Ras Dege, Tanzania)

Abstract. We conducted diurnal sampling in a tidal creek (Ras Dege, Tanzania) to document the variations in a suite of creek water column characteristics and to determine the relative influence of tidal and biological driving forces. Since the creek has no upstream freshwater inputs, highest salinity was observed at low tide, due to evaporation effects and porewater seepage. Total suspended matter (TSM) and particulate organic carbon (POC) showed distinct maxima at periods of highest water flow, indicating that erosion of surface sediments and/or resuspension of bottom sediments were an important source of particulate material. Dissolved organic carbon (DOC), in contrast, followed the tidal variations and was highest at low tide. Stable isotope data of POC and DOC exhibit large variations in both pools, and followed tidal variations. Although the variation of δ13CDOC (−23.8 to −13.8‰) was higher than that of δ13CPOC (−26.2 to −20.5‰) due to the different end-member pool sizes, the δ13C signatures of both pools differed only slightly at low tide, but up to 9‰ at high tide. Thus, at low tide both DOC and POC originated from mangrove production. At high tide, on the other hand, the DOC pool had signatures consistent with a high contribution of seagrass-derived material, whereas the POC pool was dominated by marine phytoplankton. Daily variations in CH4, and partial pressure of CO2 (pCO2) were similarly governed by tidal influence and were up to 7- and 10-fold higher at low tide, which stresses the importance of exchange of porewater and diffusive fluxes to the water column. Furthermore, this illustrates that constraining an ecosystem-level budget of these greenhouse gases in tidal systems requires a careful appraisal of tidal variations. When assuming that the high dissolved inorganic carbon (DIC) levels in the upper parts of the creek (i.e. at low tide) are due to inputs from mineralization, δ13C data on DIC indicate that the source of the mineralized organic matter has a signature of −22.4‰, which shows that imported POC and DOC from the marine environment contributes strongly to overall mineralization within the mangrove system. Our data show a striking example of how biogeochemical processes in the intertidal zone appear to be prominent drivers of element concentrations and isotope signatures in the water column, and how pathways of dissolved and particulate matter exchange are fundamentally different. The estimated export of DIC through porewater exchange appears considerably larger than for DOC, suggesting that if this mechanism is indeed a major driver of solute exchange, benthic mineralization and subsequent export as DIC could represent a very significant and previously unaccounted fate of mangrove-derived C. Budgeting efforts should therefore pay attention to understanding the mechanisms and quantification of different pathways of exchange within and between both zones.

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Importance of intertidal sediment processes and porewater exchange on the water column biogeochemistry in a pristine mangrove creek (Ras Dege, Tanzania)

Biogeosciences ◽

10.5194/bg-4-311-2007 ◽

2007 ◽

Vol 4 (3) ◽

pp. 311-322 ◽

Cited By ~ 102

Author(s):

S. Bouillon ◽

J. J. Middelburg ◽

F. Dehairs ◽

A. V. Borges ◽

G. Abril ◽

...

Keyword(s):

Organic Carbon ◽

Water Column ◽

Driving Forces ◽

Dissolved Inorganic Carbon ◽

High Tide ◽

Particulate Material ◽

Marine Phytoplankton ◽

Intertidal Sediment ◽

Matter Transport ◽

Water Height

Abstract. We sampled a tidal creek (Ras Dege, Tanzania) during a 24-h cycle to document the variations in a suite of creek water column characteristics and to determine the relative influence of tidal and biological driving forces. Since the creek has no upstream freshwater inputs, highest salinity was observed at low tide, due to evaporation effects and porewater seepage. Total suspended matter (TSM) and particulate organic carbon (POC) showed distinct maxima at periods of highest water flow, indicating that erosion of surface sediments and/or resuspension of bottom sediments were an important source of particulate material. Dissolved organic carbon (DOC), in contrast, varied in phase with water height and was highest at low tide. Stable isotope data of POC and DOC displayed large variations in both pools, and similarly followed the variations in water height. Although the variation of δ13CDOC (−23.8 to −13.8‰) was higher than that of δ13CPOC (−26.2 to −20.5‰), due to the different end-member pool sizes, the δ13C signatures of both pools differed only slightly at low tide, but up to 9‰ at high tide. Thus, at low tide both DOC and POC originated from mangrove production. At high tide, however, the DOC pool had signatures consistent with a high contribution of seagrass-derived material, whereas the POC pool was dominated by marine phytoplankton. Daily variations in CH4, and partial pressure of CO2 (pCO2) were similarly governed by tidal influence and were up to 7- and 10-fold higher at low tide, which stresses the importance of exchange of porewater and diffusive fluxes to the water column. When assuming that the high dissolved inorganic carbon (DIC) levels in the upper parts of the creek (i.e. at low tide) are due to inputs from mineralization, δ13C data on DIC indicate that the organic matter source for mineralization had a signature of −22.4‰. Hence, imported POC and DOC from the marine environment contributes strongly to overall mineralization within the mangrove system. Our data demonstrate how biogeochemical processes in the intertidal zone appear to be prominent drivers of element concentrations and isotope signatures in the water column, and how pathways of dissolved and particulate matter transport are fundamentally different.

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Coastal urbanization alters carbon cycling in Tokyo Bay

Scientific Reports ◽

10.1038/s41598-020-77385-4 ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Atsushi Kubo ◽

Jota Kanda

Keyword(s):

Organic Carbon ◽

Sedimentation Rate ◽

Dissolved Inorganic Carbon ◽

Sewage Treatment ◽

Tokyo Bay ◽

Net Community Production ◽

Labile Organic Carbon ◽

Treatment Facilities ◽

Coastal Urbanization ◽

Freshwater Inputs

AbstractThe carbon budget of Tokyo Bay, a highly urbanized coastal basin, was estimated using a box model that incorporated inorganic and organic carbon data over an annual cycle (2011–2012). The surface water represented net autotrophic system in which the annual net community production (NCP) was 19 × 1010 gC year−1. The annual loading of dissolved inorganic carbon and total organic carbon (TOC) from freshwater inputs was 11.2 × 1010 and 4.9 × 1010 gC year−1, respectively. The annual TOC sedimentation rate was 3.1 × 1010 gC year−1, similar to the annual air–sea CO2 uptake (5.0 × 1010 gC year−1). Although the NCP and TOC loading from freshwater inputs were respectively 3.0 and 2.7 times lower than those in the 1970s, the TOC sedimentation rate was similar. Therefore, a relatively high carbon efflux from Tokyo Bay likely occurred in the 1970s, including CO2 efflux to the atmosphere and/or export of labile organic carbon to the open ocean. The changes in carbon flow between the 1970s and 2011–2012 resulted from improved water quality due to increased sewage treatment facilities and improved sewage treatment efficiency in the catchment, which decreased the amount of labile organic carbon flowing into the bay.

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Sellafield-Derived Anthropogenic 14C in the Marine Intertidal Environment of the NE Irish Sea

Radiocarbon ◽

10.1017/s0033822200035918 ◽

2004 ◽

Vol 46 (2) ◽

pp. 877-883 ◽

Cited By ~ 21

Author(s):

G T Cook ◽

A B MacKenzie ◽

G K P Muir ◽

G Mackie ◽

P Gulliver

Keyword(s):

Organic Carbon ◽

Inorganic Carbon ◽

Dissolved Inorganic Carbon ◽

Specific Activity ◽

High Water ◽

Irish Sea ◽

Intertidal Sediment ◽

Intertidal Environment ◽

Natural Processes ◽

Nuclear Fuel Reprocessing Plant

The intertidal biota from Parton beach, close to the Sellafield nuclear fuel reprocessing plant, were all found to be enriched in radiocarbon relative to ambient background. The degree of enrichment appears to reflect the positions of the biota in the food chain once the dilution in seaweed from atmospheric uptake is taken into account. Close to the low-water mark, the order was mussels > limpets > anemones winkles > seaweed. The same order was observed close to the high-water mark, except that anemones were absent from this area. The activities in the biogeochemical fractions of the water column reflect the fact that discharges are primarily in the form of dissolved inorganic carbon (DIC), which is subsequently transferred to the particulate organic carbon (POC) and, to a lesser extent, the dissolved organic carbon (DOC), and finally, the particulate inorganic carbon (PIC). Analysis of intertidal sediment suggests that there is likely to be a gradual increase in the specific activity of 14C in the inorganic component of this material as Sellafield contaminated organisms die and their shells are ground down by natural processes.

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Carbon Cycling and Organic Radiocarbon Reservoir Effect in a Meromictic Crater Lake (Lac Pavin, Puy-de-Dôme, France)

Radiocarbon ◽

10.1017/s0033822200058161 ◽

2013 ◽

Vol 55 (2) ◽

pp. 1029-1042 ◽

Cited By ~ 14

Author(s):

Patrick Albéric ◽

Didier Jézéquel ◽

Laurent Bergonzini ◽

Emmanuel Chapron ◽

Eric Viollier ◽

...

Keyword(s):

Organic Carbon ◽

Water Column ◽

Surface Waters ◽

Crater Lake ◽

Dissolved Inorganic Carbon ◽

Organic Production ◽

Data Set ◽

Radiocarbon Dates ◽

Reservoir Effect ◽

Sediment Layers

Lac Pavin is a meromictic maar lake for which the interpretation of sediment radiocarbon dates is complicated by the existence of a largely undefined reservoir effect resulting from degradation of carbon stored in the bottom layer of the water column. A data set of the contemporary 14C distribution of dissolved and particulate organic pools in the water column is presented to address this issue. Dissolved inorganic carbon (DIC) and organic carbon (DOC), plankton, suspended particulate organic carbon (POCsusp), sinking POC (POCsink), and bottom sediment organic carbon (SOC) were analyzed. Present-day Δ14C values of DIC were measured ranging from −750′ in the monimolimnion to atmospheric values in lake surface waters and in spring inlet waters. A range of Δ14C values between −200 and −300′ was observed for superficial POCsusp, POCsink, SOC, and DOC. This relatively uniform 14C offset of the exported organic production from the surface waters to the bottom represents a contemporary reservoir effect of ∼2500 yr. Laminated buried sediment samples and terrestrial vegetal macro-remains were used to evaluate temporal reservoir effect variations since the formation of the crater lake (7 ka cal BP). Buried sediment layers presented a similar offset or showed larger differences between Δ14C values of bulk sediment and terrestrial plant remains (–400 to −500′). Furthermore, an almost 0-yr reservoir effect was inferred from the sediment layers deposited just above the volcanic bedrock at the early flooding of the crater, and increasing slightly within the first centuries of the lake's history. A second objective was to tentatively model a defined scenario of the cycling of carbon in the lake capable of predicting a modern reservoir effect. Alternative scenarios were then tested for which a larger contribution of deeper DIC would provide a model compatible with larger past reservoir effects. It is concluded that using Δ14C SOC variation in laminated lake sediments as a proxy of paleolimnological conditions may be valuable provided that more data on the dynamics of the 14C composition of plankton and more detailed sampling of laminated sediment layers are available.

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Variability of ocean stratification, sea ice coverage and bioproduction off NE Greenland in the Late Glacial to Holocene reconstructed from planktic foraminifer morphotypes

10.5194/egusphere-egu2020-4818 ◽

2020 ◽

Author(s):

Robert F. Spielhagen ◽

Andreas Mackensen

Keyword(s):

Organic Carbon ◽

Water Column ◽

Dissolved Inorganic Carbon ◽

Greenland Ice Sheet ◽

Late Glacial ◽

Laminated Sediments ◽

The Arctic ◽

Migration Activity ◽

Near Surface ◽

Ice Coverage

We use stable isotope data from different morphotypes of the polar species Neogloboquadrina pachyderma in a sediment core from the NE Greenland continental margin (79&#176;N) as proxies for the variability of salinity, ice coverage, and bioproductivity/carbon fluxes. Stable oxygen and carbon isotopes (d18O, d13C) were measured on both thin- and thick shelled specimens of planktic foraminifers N. pachyderma. Since this species is known to attain the thick carbonate crust of adult specimens in deeper water, the isotopic difference between thick-shelled (morphotypes 1 and 2, according to Eynaud, 2011) and thin-shelled specimens (morphotypes 4 and 5) is proposed to reflect the salinity difference between subsurface and near-surface waters. In Late Glacial sediments only minor d18O differences between the morphotypes suggest an upper water mass structure with only minor salinity differences. The high d13C difference of >0.5&#8240; is ascribed to strong quantitative differences in the decomposition of isotopically light organic carbon within the upper water column (likely from intense ice coverage and reduced bioproductivity) which precludes that the d18O similarities merely result from a reduced vertical migration activity of the foraminifers. After 13 ka, a series of d18O spikes (amplitudes >1.5&#8240; in morphotypes 4/5) preserved in laminated sediments reflects a strong freshwater event at the NE Greenland margin, likely related to the export of freshwater from the Arctic Ocean and/or the decay of the nearby outer Greenland Ice Sheet. Within these spikes, d18O and d13C differences of N. pachyderma morphotypes reach maximum values, pointing at extreme salinity differences in the upper few hundred meters of the water column and likely high portions of isotopically light dissolved inorganic carbon from terrestrial sources (meltwater). In the Holocene, d18O differences are reduced to ca. 0.5&#8240; and relatively low d13C differences may indicate an activity of organic carbon decomposition reaching significantly deeper in the water column than in the glacial and deglacial, possibly related to a more open ice cover, enhanced bioproduction and higher C fluxes.ReferenceEynaud, F., 2011. Planktonic foraminifera in the Arctic: potentials and issues regarding modern and quaternary populations. IOP Conf. Series, Earth and Environmental Science 14, 012005, doi:10.1088/1755-1315/14/1/012005

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Organic carbon production, mineralization and preservation on the Peruvian margin

Biogeosciences Discussions ◽

10.5194/bgd-11-13067-2014 ◽

2014 ◽

Vol 11 (9) ◽

pp. 13067-13126 ◽

Cited By ~ 4

Author(s):

A. W. Dale ◽

S. Sommer ◽

U. Lomnitz ◽

I. Montes ◽

T. Treude ◽

...

Keyword(s):

Organic Matter ◽

Organic Carbon ◽

Water Column ◽

Water Depth ◽

Dissolved Inorganic Carbon ◽

Sediment Accumulation ◽

Inner Shelf ◽

Global Database ◽

Carbon Burial ◽

Organic Carbon Burial

Abstract. Carbon cycling in Peruvian margin sediments (11° S and 12° S) was examined at 16 stations from 74 m on the inner shelf down to 1024 m water depth by means of in situ flux measurements, sedimentary geochemistry and modeling. Bottom water oxygen was below detection limit down to ca. 400 m and increased to 53 μM at the deepest station. Sediment accumulation rates and benthic dissolved inorganic carbon fluxes decreased rapidly with water depth. Particulate organic carbon (POC) content was lowest on the inner shelf and at the deep oxygenated stations (< 5%) and highest between 200 and 400 m in the oxygen minimum zone (OMZ, 15–20%). The organic carbon burial efficiency (CBE) was unexpectedly low on the inner shelf (< 20%) when compared to a global database, for reasons which may be linked to the frequent ventilation of the shelf by oceanographic anomalies. CBE at the deeper oxygenated sites was much higher than expected (max. 81%). Elsewhere, CBEs were mostly above the range expected for sediments underlying normal oxic bottom waters, with an average of 51 and 58% for the 11° S and 12° S transects, respectively. Organic carbon rain rates calculated from the benthic fluxes alluded to a very efficient mineralization of organic matter in the water column, with a Martin curve exponent typical of normal oxic waters (0.88 ± 0.09). Yet, mean POC burial rates were 2–5 times higher than the global average for continental margins. The observations at the Peruvian margin suggest that a lack of oxygen does not affect the degradation of organic matter in the water column but promotes the preservation of organic matter in marine sediments.

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Recycling and fluxes of carbon gases in a stratified boreal lake following experimental carbon addition

Biogeosciences Discussions ◽

10.5194/bgd-11-16447-2014 ◽

2014 ◽

Vol 11 (11) ◽

pp. 16447-16495 ◽

Cited By ~ 3

Author(s):

H. Nykänen ◽

S. Peura ◽

P. Kankaala ◽

R. I. Jones

Keyword(s):

Organic Carbon ◽

Water Column ◽

Dissolved Inorganic Carbon ◽

Stable Carbon Isotope ◽

Boreal Lakes ◽

Co2 Production ◽

Strength Increase ◽

Humic Lakes ◽

Ch4 Oxidation ◽

Anoxic Layer

Abstract. Partly anoxic stratified humic lakes are important sources of methane (CH4) and carbon dioxide (CO2) to the atmosphere. We followed the fate of CH4 and CO2 in a small boreal stratified lake, Alinen Mustajärvi, during 2007–2009. In 2008 and 2009 the lake received additions of dissolved organic carbon (DOC) with stable carbon isotope ratio (δ13C) around 16‰ higher than that of local allochthonous DOC. Carbon transformations in the water column were studied by measurements of δ13C of CH4 and of the dissolved inorganic carbon (DIC). Furthermore, CH4 and CO2 production, consumption and emissions were estimated. Methane oxidation was estimated by a diffusion gradient method. The amount, location and δ13C of CH4-derived biomass and CO2 in the water column were estimated from the CH4 oxidation pattern and from measured δ13C of CH4. Release of CH4 and CO2 to the atmosphere increased during the study. Methane production and almost total consumption of CH4 mostly in the anoxic water layers, was equivalent to the input from primary production (PP). δ13C of CH4 and DIC showed that hydrogenotrophic methanogenesis was the main source of CH4 to the water column, and methanogenic processes in general were the reasons for the 13C-enriched DIC at the lake bottom. CH4 and DIC became further 13C-enriched in the anoxic layer of the water column during the years of DOC addition. Even gradient diffusion measurements showed active CH4 oxidation in the anoxic portion of the water column; there was no clear 13C-enrichment of CH4 as generally used to estimate CH4 oxidation strength. Increase in δ13C-CH4 was clear between the metalimnion and epilimnion where the concentration of dissolved CH4 and the oxidation of CH4 were small. Thus, 13C-enrichment of CH4 does not reveal the main location of methanotrophy in a lake having simultaneous anaerobic and aerobic oxidation of CH4. Overall the results show that organic carbon is processed efficiently to CH4 and CO2 and recycled in the anoxic layer of stratified boreal lakes by CH4 oxidation. In spite of this, increased DOC input led to increased greenhouse gas release, mainly as CO2 but also as CH4. Due to the predominantly anaerobic CH4 oxidation, a relatively small amount of CH4-derived biomass was produced, while a large amount of CH4-derived CO2 was produced in the anoxic bottom zone of the lake.

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The Carbon:²³⁴Thorium ratios of sinking particles in the California Current Ecosystem 2: Examination of a thorium sorption, desorption, and particle transport model

10.26434/chemrxiv.7803698 ◽

2019 ◽

Author(s):

Michael Stukel ◽

Thomas Kelly

Keyword(s):

Organic Carbon ◽

Water Column ◽

Particulate Organic Carbon ◽

Transport Model ◽

California Current ◽

In Situ Measurements ◽

Power Law Distribution ◽

Sinking Particles ◽

Organic Carbon Concentration

Thorium-234 (234Th) is a powerful tracer of particle dynamics and the biological pump in the surface ocean; however, variability in carbon:thorium ratios of sinking particles adds substantial uncertainty to estimates of organic carbon export. We coupled a mechanistic thorium sorption and desorption model to a one-dimensional particle sinking model that uses realistic particle settling velocity spectra. The model generates estimates of 238U-234Th disequilibrium, particulate organic carbon concentration, and the C:234Th ratio of sinking particles, which are then compared to in situ measurements from quasi-Lagrangian studies conducted on six cruises in the California Current Ecosystem. Broad patterns observed in in situ measurements, including decreasing C:234Th ratios with depth and a strong correlation between sinking C:234Th and the ratio of vertically-integrated particulate organic carbon (POC) to vertically-integrated total water column 234Th, were accurately recovered by models assuming either a power law distribution of sinking speeds or a double log normal distribution of sinking speeds. Simulations suggested that the observed decrease in C:234Th with depth may be driven by preferential remineralization of carbon by particle-attached microbes. However, an alternate model structure featuring complete consumption and/or disaggregation of particles by mesozooplankton (e.g. no preferential remineralization of carbon) was also able to simulate decreasing C:234Th with depth (although the decrease was weaker), driven by 234Th adsorption onto slowly sinking particles. Model results also suggest that during bloom decays C:234Th ratios of sinking particles should be higher than expected (based on contemporaneous water column POC), because high settling velocities minimize carbon remineralization during sinking.

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