Organic matter flux and reactivity on a South Carolina sandflat: The impacts of porewater advection and macrobiological structures

In this study, we presented a high-resolution benthic foraminiferal assemblage record from the western Bay of Bengal (BoB) (off Krishna–Godavari Basin) showing millennial-scale variations during the last 45 ka. We studied temporal variations in benthic foraminiferal assemblages (relative abundances of ecologically sensitive groups/species, microhabitat categories, and morphogroups) to infer past changes in sea bottom environment and to understand how monsoon induced primary productivity-driven organic matter export flux and externally sourced deep-water masses impacted the deep-sea environment at the core site. Our records reveal a strong coupling between surface productivity and benthic environment on glacial/interglacial and millennial scale in concert with Northern Hemisphere climate events. Faunal data suggest a relatively oxic environment when the organic matter flux to the sea floor was low due to low primary production during intensified summer monsoon attributing surface water stratification and less nutrient availability in the mixed layer. Furthermore, records of oxygen-sensitive benthic taxa (low-oxygen vs. high-oxygen benthics) indicate that changes in deep-water circulation combined with the primary productivity-driven organic matter flux modulated the sea bottom oxygen condition over the last 45 ka. We suggest that the bottom water at the core site was well-ventilated during the Holocene (except for the period since 3 ka) compared with the late glacial period. At the millennial timescale, our faunal proxy records suggest relatively oxygen-poor condition at the sea floor during the intervals corresponding to the cold stadials and North Atlantic Heinrich events (H1, H2, H3, and H4) compared with the Dansgaard/Oeschger (D-O) warm interstadials. The study further reveals oxygen-poor bottom waters during the last glacial maximum (LGM, 19–22 ka) which is more pronounced during 21–22 ka. A major shift in sea bottom condition from an oxygenated bottom water during the warm Bølling–Allerød (B/A) (between 13 and 15 ka) to the oxygen-depleted condition during the cold Younger Dryas (YD) period (between 10.5 and 13 ka) is noticed. It is likely that the enhanced inflow of North Atlantic Deep Water (NADW) to BoB would have ventilated bottom waters at the core site during the Holocene, B/A event, and probably during the D-O interstadials of marine isotope stage (MIS) 3.

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Long-term watershed management is an effective strategy to reduce organic matter export and disinfection by-product precursors in source water

International Journal of Wildland Fire ◽

10.1071/wf18174 ◽

2019 ◽

Vol 28 (10) ◽

pp. 804 ◽

Cited By ~ 2

Author(s):

Hamed Majidzadeh ◽

Huan Chen ◽

T. Adam Coates ◽

Kuo-Pei Tsai ◽

Christopher I. Olivares ◽

...

Keyword(s):

Organic Matter ◽

South Carolina ◽

Watershed Management ◽

Management Practices ◽

Mass Spectrometry Analysis ◽

Gas Chromatography Mass Spectrometry ◽

Long Term Effects ◽

Pyrolysis Gas ◽

Water Extracts

Watershed management practices such as prescribed fire, harvesting and understory mastication can alter the chemical composition and thickness of forest detritus, thus affecting the quantity and quality of riverine dissolved organic matter (DOM). Long-term effects of watershed management on DOM composition were examined through parallel field and extraction-based laboratory studies. The laboratory study was conducted using detritus samples collected from a pair of managed and unmanaged watersheds in South Carolina, USA. Results showed that dissolved organic carbon (DOC), total dissolved nitrogen (TDN) and ammonium (NH4+-N) concentrations were higher in water extracts from the unmanaged watershed than from the managed watershed (P<0.01). Pyrolysis gas chromatography–mass spectrometry analysis showed that water extracts from the unmanaged watershed contained more aromatic compounds than extracts from the managed watershed. For the field study, monthly water samples were collected for 1 year (2015) from the paired watersheds. DOC and TDN concentrations, as well as DOM aromaticity, were significantly higher in the unmanaged watershed than in the managed watershed for most of the year (P<0.05) and were linked to detrital thickness, precipitation and flow patterns. The formation potential of two regulated disinfection by-products was lower in the unmanaged watershed for most of 2015 (P<0.05). From this study, it appears that long-term watershed management practices may alter detrital mass and chemistry in ways that improve water quality.

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Summer rainfall dissolved organic carbon, solute, and sediment fluxes in a small Arctic coastal catchment on Herschel Island (Yukon Territory, Canada)

Arctic Science ◽

10.1139/as-2018-0010 ◽

2018 ◽

Vol 4 (4) ◽

pp. 750-780 ◽

Cited By ~ 5

Author(s):

Caroline Coch ◽

Scott F. Lamoureux ◽

Christian Knoblauch ◽

Isabell Eischeid ◽

Michael Fritz ◽

...

Keyword(s):

Organic Matter ◽

Organic Carbon ◽

Dissolved Organic Carbon ◽

Suspended Sediment ◽

Summer Rainfall ◽

Yukon Territory ◽

The Arctic ◽

Rainfall Frequency ◽

The Future ◽

Matter Flux

Coastal ecosystems in the Arctic are affected by climate change. As summer rainfall frequency and intensity are projected to increase in the future, more organic matter, nutrients and sediment could be mobilized and transported into the coastal nearshore zones. However, knowledge of current processes and future changes is limited. We investigated streamflow dynamics and the impacts of summer rainfall on lateral fluxes in a small coastal catchment on Herschel Island in the western Canadian Arctic. For the summer monitoring periods of 2014–2016, mean dissolved organic matter flux over 17 days amounted to 82.7 ± 30.7 kg km−2 and mean total dissolved solids flux to 5252 ± 1224 kg km−2. Flux of suspended sediment was 7245 kg km−2 in 2015, and 369 kg km−2 in 2016. We found that 2.0% of suspended sediment was composed of particulate organic carbon. Data and hysteresis analysis suggest a limited supply of sediments; their interannual variability is most likely caused by short-lived localized disturbances. In contrast, our results imply that dissolved organic carbon is widely available throughout the catchment and exhibits positive linear relationship with runoff. We hypothesize that increased projected rainfall in the future will result in a similar increase of dissolved organic carbon fluxes.

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Benthic foraminifera as proxies of organic matter flux and bottom water oxygenation? A case history from the northern Arabian Sea

Palaeogeography Palaeoclimatology Palaeoecology ◽

10.1016/s0031-0182(00)00074-2 ◽

2000 ◽

Vol 161 (3-4) ◽

pp. 337-359 ◽

Cited By ~ 111

Author(s):

M den Dulk ◽

G.J Reichart ◽

S van Heyst ◽

W.J Zachariasse ◽

G.J Van der Zwaan

Keyword(s):

Organic Matter ◽

Case History ◽

Benthic Foraminifera ◽

Arabian Sea ◽

Bottom Water ◽

Northern Arabian Sea ◽

Matter Flux

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Spatial distribution of benthic foraminiferal stable isotopes and dinocyst assemblages in surface sediments of the Trondheimsfjord, central Norway

Biogeosciences ◽

10.5194/bg-10-4433-2013 ◽

2013 ◽

Vol 10 (7) ◽

pp. 4433-4448 ◽

Cited By ~ 9

Author(s):

G. Milzer ◽

J. Giraudeau ◽

J. Faust ◽

J. Knies ◽

F. Eynaud ◽

...

Keyword(s):

Organic Matter ◽

Climatic Variability ◽

Intermediate Water ◽

North Atlantic Current ◽

Local Conditions ◽

Bottom Water Temperature ◽

The North ◽

Show Evidence ◽

Matter Flux ◽

Instrumental Records

Abstract. Instrumental records from the Norwegian Sea and the Trondheimsfjord show evidence that changes of bottom water temperature and salinity in the fjord are linked to the salinity and temperature variability of the North Atlantic Current (NAC). Changes in primary productivity and salinity in the surface and intermediate water masses in the Trondheimsfjord as well as the fjord sedimentary budget are mainly driven by changes in riverine input. In this study we use 59 surface sediment samples that are evenly distributed in the fjord to examine whether dinocyst assemblages and stable isotope ratios of benthic foraminifera reflect the present-day hydrology and can be used as palaeoceanographic proxies. In general, modern benthic δ18O and δ13C values decrease from the fjord entrance towards the fjord head with lowest values close to river inlets. This is essentially explained by gradients in the amounts of fresh water and terrigenous organic matter delivered from the hinterland. The distribution of benthic δ13C ratios across the fjord is controlled by the origin (terrigenous vs. marine) of organic matter, local topography-induced variability in organic matter flux at the water–sediment interface, and organic matter degradation. The dinocyst assemblages display the variations in hydrography with respect to the prevailing currents, the topography, and the freshwater and nutrient supply from rivers. The strength and depth of the pycnocline in the fjord strongly vary seasonally and thereby affect water mass characteristics as well as nutrient availability, temporally creating local conditions that explain the observed species distribution. Our results prove that dinocyst assemblages and benthic foraminiferal isotopes reliably mirror the complex fjord hydrology and can be used as proxies of Holocene climatic variability.

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Role of Naturally Occurring Organic Matter on Thorium Transport in a Wetland

MRS Proceedings ◽

10.1557/proc-757-ii7.2 ◽

2002 ◽

Vol 757 ◽

Cited By ~ 1

Author(s):

Daniel I. Kaplan ◽

A. S. Knox

Keyword(s):

Organic Matter ◽

South Carolina ◽

Transport Model ◽

Indirect Evidence ◽

Pilot Scale ◽

Test Facility ◽

Savannah River ◽

Particle Size Fractionation ◽

Enhanced Mobility

ABSTRACTA wetland located on the Savannah River Site in Aiken, South Carolina has become contaminated by a number of radionuclides as a result of operating a pilot-scale nuclear test facility. Sediment Th-232 concentration at the site exceed 700 mg/kg, whereas background concentrations are ∼7 mg/kg. The Th is relatively mobile, having moved >300-m since 1958 and greatly exceeding contaminant transport model predictions. Studies were initiated to determine the chemical cause for the enhanced transport of Th. Particle-size fractionation studies showed that colloids alone were not likely responsible for all of the enhanced transport of Th. Sediment sequential extraction data showed that >80% of the Th was associated with the sediment organic fraction. In an experiment in which varying soil amendments resulted in the release of dissolved organic carbon (DOC) to the aqueous phase, a significant correlation (r = 0.91; p ≤ 0.01, n = 8) was calculated between aqueous Th and DOC. Pore water Th partitioning to hydrophobic resins suggested that 33% of the aqueous Th was associated with organic matter. Together, these results provide indirect evidence support the notion that enhanced mobility of Th at the site may in part be due to the presence of Th-DOC complexes.

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