scholarly journals Geochemical Characteristics of Sediment in Tropical Lake Sentani, Indonesia, Are Influenced by Spatial Differences in Catchment Geology and Water Column Stratification

2021 ◽  
Vol 9 ◽  
Author(s):  
Sulung Nomosatryo ◽  
Rik Tjallingii ◽  
Anja Maria Schleicher ◽  
Paulus Boli ◽  
Cynthia Henny ◽  
...  
Keyword(s):  
Water Chemistry ◽  
Water Column ◽  
Pore Water ◽  
Bottom Water ◽  
Geochemical Characteristics ◽  
Tropical Lake ◽  
Sediment Composition ◽  
Column Structure ◽  
Wide Range ◽  
Sediment Input

Physical and (bio)chemical processes in the catchment as well as internal lake processes influence the composition of lacustrine sediments. Lake internal processes are a consequence of reactions and fluxes between sediment, porewater and the water column. Due to its separation into four interconnected sub-basins, Lake Sentani, Papua Province, Indonesia, is a unique tropical lake that reveals a wide range of geochemical conditions. The highly diverse geological catchment causes mineralogical and chemical differentiation of the sediment input into each sub-basin. Also, strong morphological differences between the sub-basins result in a unique water column structure for each sub-basin, ranging from fully mixed to meromictic. Given the strong differences in sediment composition and bottom water chemistry among the four sub-basins, Lake Sentani offers a unique chance to study multiple lacustrine systems under identical climate conditions and with a common surface water chemistry. We used sediment cores and water samples and measured physicochemical water column profiles to reveal the geochemical characteristics of the water column, the sediment and pore water for all four sub-basins of Lake Sentani. The chemical composition of the sediment reveals differentiation among the sub-basins according to their sediment input and water column structure. Catchment lithology mainly affects overall sediment composition, whereas pore water chemistry is also affected by water column structure, which is related to basin morphology and water depth. In the meromictic sub-basins the bottom water and sediment pore water appear to form a single continuous system, whereas in those sub-basins with oxygenated bottom water the sediment-water interface forms a pronounced chemical barrier.

On the lack of widespread bottom simulating reflectors in the Mediterranean Basin

2021 ◽  
Author(s):  
Cristina Corradin ◽  
Angelo Camerlenghi ◽  
Michela Giustiniani ◽  
Umberta Tinivella ◽  
Claudia Bertoni
Keyword(s):  
Water Column ◽  
Pore Water ◽  
Mediterranean Basin ◽  
Stability Field ◽  
Hydrocarbon Gases ◽  
Wide Range ◽  
Bottom Simulating Reflectors ◽  
Messinian Evaporites ◽  
The Mediterranean ◽  
The Mediterranean Basin

<p>In the Mediterranean Basin, gas hydrate bottom simulating reflectors (BSR) are absent, with very few and spatially limited exceptions occurring in Eastern Mediterranean mud volcanoes and in the Nile deep sea fan. This is in spite of widespread occurrence of hydrocarbon gases in the subsurface, mainly biogenic methane, from a wide range of stratigraphic intervals.<br>In this study we model the methane hydrate stability field using all available information on DSDP and ODP boreholes in the Western Mediterranean and in the Levant Basin, including the downhole changes of pore water salinity. The models take into account the consequent pore water density changes and use known estimates of geothermal gradient. None of the drilled sites were located on seismic profiles in which a BSR is present.<br>The modelled base of the stability field of methane hydrates is located variably within, below, or even above the drilled sedimentary section (the latter case implies that it is located in the water column). We discuss the results in terms of geodynamic environments, areal distribution of Messinian evaporites, upward ion diffusion from Messinian evaporites, organic carbon content, and the peculiar thermal structure of the Mediterranean water column. <br>We conclude that the cumulative effects of geological and geochemical environments make the Mediterranean Basin a region that is unfavorable to the existence of BSRs in the seismic record, and most likely to the existence of natural gas hydrates below the seabed.<br><br></p>

scholarly journals The nitrogen isotope effect of benthic remineralization-nitrification-denitrification coupling in an estuarine environment

2012 ◽  
Vol 9 (5) ◽  
pp. 1633-1646 ◽  
Author(s):  
M. Alkhatib ◽  
M. F. Lehmann ◽  
P. A. del Giorgio
Keyword(s):  
Organic Matter ◽  
Water Column ◽  
Pore Water ◽  
Bottom Water ◽  
Isotope Fractionation ◽  
N Loss ◽  
N Transformations ◽  
Lawrence Estuary ◽  
Water Oxygen ◽  
Oxygen Concentrations

Abstract. The nitrogen (N) stable isotopic composition of pore water nitrate and total dissolved N (TDN) was measured in sediments of the St. Lawrence Estuary and the Gulf of St. Lawrence. The study area is characterized by gradients in organic matter reactivity, bottom water oxygen concentrations, as well as benthic respiration rates. N isotope effects on the water column associated with the benthic exchange of nitrate (εapp) and TDN (εsed) during benthic nitrification-denitrification coupling were investigated. The sediments were a major sink for nitrate and a source of reduced dissolved N (RDN = DON + NH4+). We observed that both the pore water nitrate and RDN pools were enriched in 15N relative to the water column, with increasing δ15N downcore in the sediments. As in other marine environments, the biological nitrate isotope fractionation of net fixed N loss was barely expressed at the scale of sediment-water exchange, with &amp;varepsilon;app values <3‰. The strongest under-expression (i.e. lowest εapp) of the biological N isotope fractionation was observed at the most oxygenated sites with the least reactive organic matter, indicating that, through their control on the depth of the denitrification zone, bottom water oxygen concentrations and the organic matter reactivity can modulate εapp. For the first time, actual measurements of δ15N of pore water RDN were included in the calculations of εsed. We argue that large fractions of the sea-floor-derived DON are reactive and, hence, involved in the development of the δ15N of dissolved inorganic N (DIN) in the water column. In the St. Lawrence sediments, the combined benthic N transformations yield a flux of 15N-enriched RDN that can significantly elevate εsed above εapp. Calculated εsed values were within the range of 4.6 ± 2‰ and were related to organic matter reactivity and oxygen penetration depth in the sediments. &amp;varepsilon;sed reflects the δ15N of the N2 lost from marine sediments and thus best describes the isotopic impact of fixed N loss from sediments on the oceanic fixed N pool. Our mean value for εsed is larger than assumed by earlier work, questioning current ideas with regards to the state of balance of the modern N budget.

scholarly journals The nitrogen isotope effect of benthic remineralization-nitrification-denitrification coupling in an estuarine environment

2011 ◽  
Vol 8 (6) ◽  
pp. 11689-11723
Author(s):  
M. Alkhatib ◽  
M. F. Lehmann ◽  
P. A. del Giorgio
Keyword(s):  
Organic Matter ◽  
Water Column ◽  
Pore Water ◽  
Bottom Water ◽  
Isotope Fractionation ◽  
N Budget ◽  
N Transformations ◽  
Lawrence Estuary ◽  
Water Oxygen ◽  
Oxygen Concentrations

Abstract. The nitrogen (N) stable isotopic composition of pore water nitrate and total dissolved N (TDN) was measured in sediments of the St. Lawrence Estuary and the Gulf of St. Lawrence. The study area is characterized by gradients in organic matter reactivity, bottom water oxygen concentrations, as well as benthic respiration rates. Benthic N isotope exchange, as well as the nitrate and TDN isotope effects of benthic nitrification-denitrification coupling on the water column, &amp;varepsilon;app and &amp;varepsilon;sed, respectively, were investigated. The sediments were a major sink for nitrate and a source of reduced dissolved N (RDN = DON + NH4+). We observed that both the pore water nitrate and RDN pools were enriched in 15N relative to the water column, with increasing δ15N downcore in the sediments. As in other marine environments, the biological nitrate isotope fractionation of net nitrate elimination was barely expressed at the scale of sediment-water-exchange, with &amp;varepsilon;app values <3‰. The strongest under-expression of the biological N isotope fractionation was observed at the most oxygenated sites with the least reactive organic matter, indicating that, through their control on the depth of the denitrification zone, bottom water oxygen concentrations and the organic matter reactivity can modulate &amp;varepsilon;app. For the first time, actual measurements of δ15N of pore water RDN were included in the calculations of &amp;varepsilon;sed. We argue that large fractions of the sea-floor-derived DON are reactive and, hence, involved in the development of the δ15N of dissolved inorganic N (DIN) in the water column. In the St. Lawrence sediments, the combined benthic N transformations yield a flux of 15N-enriched RDN that can significantly enhance &amp;varepsilon;sed. Calculated &amp;varepsilon;sed values were within the range of 4.6 ± 2‰, and were related to organic matter reactivity and oxygen penetration depth in the sediments. &amp;varepsilon;sed reflects the δ15N of the N2 lost from marine sediments and thus best describes the isotopic impact of N elimination on the oceanic fixed N pool. Our mean value for &amp;varepsilon;sed is larger than assumed by earlier work, questioning current ideas with regards to the state of balance of the modern N budget.

Bioavailability and remineralization of sediment-derived dissolved organic carbon from the Baltic Sea depositional area

2021 ◽  
Author(s):  
Monika Lengier
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Baltic Sea ◽  
Water Column ◽  
Pore Water ◽  
Half Life ◽  
Bottom Water ◽  
The Baltic Sea ◽  
Doc Concentration ◽  
The Baltic

&lt;p&gt;Sediment pore waters in the depositional areas of the Baltic Sea are enriched with the dissolved organic carbon (DOC), which results in a diffusive flux of DOC to the water column. It was found that up to 30% of OM deposited in the sediments returns to the water column and may alter processes occurring there e.g. increase the oxygen demand in the bottom waters. Still little is known about the bioavailability of sediment-derived DOC and its remineralization dynamics. Thus, the aim of this study was to assess the bioavailability, degradation rate constant and half-life time of sediment-derived DOC.&lt;/p&gt;&lt;p&gt;Bottom water and pore water, collected during r/v Oceania cruise in March 2018 in the Gda&amp;#324;sk Deep, have been mixed in a volume ratio of 4:1. To ensure oxic conditions in the experiment, the mixture was bubbled with the ambient air to reach 100% O&lt;sub&gt;2&lt;/sub&gt; saturation. Incubation of such prepared samples was conducted in 23&amp;#177;0.1&amp;#176;C for 126 days. At the beginning (t=0) and after 1, 2, 6, 18, 35, 73 and 126 days of the incubation the individual samples were analyzed for total dissolved organic carbon DOC. In parallel, untreated bottom water was incubated as a control, while the obtained results have been used to decouple the remineralization dynamics in the mixture.&lt;/p&gt;&lt;p&gt;The DOC decay had an exponential character. The highest dynamics of DOC remineralization was at the beginning of the experiment and it gradually decreased over time. During the incubation period pore water DOC concentration decreased from 1408 to 850 &amp;#181;mol l-&lt;sup&gt;1&lt;/sup&gt;&lt;sub&gt;,&lt;/sub&gt; which corresponds to almost 40% loss. In the control samples (bottom water) DOC concentration decreased from 304 to 260 &amp;#181;mol l&lt;sup&gt;-1&lt;/sup&gt; i.e. by ~14%.&lt;/p&gt;&lt;p&gt;In the experiment three different DOC fractions have been identified: labile DOC (DOC&lt;sub&gt;L&lt;/sub&gt;), semi-labile DOC (DOC&lt;sub&gt;SL&lt;/sub&gt;) and refractory DOC (DOC&lt;sub&gt;R&lt;/sub&gt;). To quantify the DOC remineralization rate constants (k) and half-life times (t&lt;sub&gt;1/2&lt;/sub&gt;) the first order kinetics was used. The total bioavailable fraction of pore water DOC (DOC&lt;sub&gt;L&lt;/sub&gt;+DOC&lt;sub&gt;SL&lt;/sub&gt;) amounted to 54%, while k and t&lt;sub&gt;1/2&lt;/sub&gt; were 0.0958 d&lt;sup&gt;-1&lt;/sup&gt; and 7.24 d for DOC&lt;sub&gt;L&lt;/sub&gt; and 0.0082 d&lt;sup&gt;-1&lt;/sup&gt; and 84.53 d for DOC&lt;sub&gt;SL&lt;/sub&gt;, respectively.&lt;/p&gt;&lt;p&gt;This study shows that about half of sediment-derived DOC is bioavailable, which gives a new insight on the Baltic Sea carbon cycle and O&amp;#173;&lt;sub&gt;2&lt;/sub&gt; consumption in deeper water layers.&lt;/p&gt;

TIME TO THE END OF PRIMARY CONSOLIDATION (EOP) OF SOFT CLAYEY SOILS: CONCERNING THE EFFECT OF ATTERBERG’S LIMIT AND CYCLIC LOADING HISTORY

2019 ◽  
Vol 128 (2B) ◽  
pp. 29-41
Author(s):  
Trần Thanh Nhàn
Keyword(s):  
Cyclic Loading ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Clayey Soils ◽  
Loading History ◽  
Cyclic Shear ◽  
Wide Range ◽  
Primary Consolidation ◽  
Time Required

In order to observe the end of primary consolidation (EOP) of cohesive soils with and without subjecting to cyclic loading, reconstituted specimens of clayey soils at various Atterberg’s limits were used for oedometer test at different loading increments and undrained cyclic shear test followed by drainage with various cyclic shear directions and a wide range of shear strain amplitudes. The pore water pressure and settlement of the soils were measured with time and the time to EOP was then determined by different methods. It is shown from observed results that the time to EOP determined by 3-t method agrees well with the time required for full dissipation of the pore water pressure and being considerably larger than those determined by Log Time method. These observations were then further evaluated in connection with effects of the Atterberg’s limit and the cyclic loading history.

scholarly journals Water column structure and statistics of Denmark Strait Overflow Water cyclones

2014 ◽  
Vol 84 ◽  
pp. 110-126 ◽  
Author(s):  
Wilken-Jon von Appen ◽  
Robert S. Pickart ◽  
Kenneth H. Brink ◽  
Thomas W.N. Haine
Keyword(s):  
Water Column ◽  
Column Structure ◽  
Denmark Strait

scholarly journals Biogeochemical processes and buffering capacity concurrently affect acidification in a seasonally hypoxic coastal marine basin

2015 ◽  
Vol 12 (5) ◽  
pp. 1561-1583 ◽  
Author(s):  
M. Hagens ◽  
C. P. Slomp ◽  
F. J. R. Meysman ◽  
D. Seitaj ◽  
J. Harlay ◽  
...  
Keyword(s):  
Seasonal Variation ◽  
Primary Production ◽  
Water Column ◽  
Bottom Water ◽  
Substantial Reduction ◽  
Buffering Capacity ◽  
Total Alkalinity ◽  
Acid Base ◽  
Data Set ◽  
Ph Fluctuations

Abstract. Coastal areas are impacted by multiple natural and anthropogenic processes and experience stronger pH fluctuations than the open ocean. These variations can weaken or intensify the ocean acidification signal induced by increasing atmospheric pCO2. The development of eutrophication-induced hypoxia intensifies coastal acidification, since the CO2 produced during respiration decreases the buffering capacity in any hypoxic bottom water. To assess the combined ecosystem impacts of acidification and hypoxia, we quantified the seasonal variation in pH and oxygen dynamics in the water column of a seasonally stratified coastal basin (Lake Grevelingen, the Netherlands). Monthly water-column chemistry measurements were complemented with estimates of primary production and respiration using O2 light–dark incubations, in addition to sediment–water fluxes of dissolved inorganic carbon (DIC) and total alkalinity (TA). The resulting data set was used to set up a proton budget on a seasonal scale. Temperature-induced seasonal stratification combined with a high community respiration was responsible for the depletion of oxygen in the bottom water in summer. The surface water showed strong seasonal variation in process rates (primary production, CO2 air–sea exchange), but relatively small seasonal pH fluctuations (0.46 units on the total hydrogen ion scale). In contrast, the bottom water showed less seasonality in biogeochemical rates (respiration, sediment–water exchange), but stronger pH fluctuations (0.60 units). This marked difference in pH dynamics could be attributed to a substantial reduction in the acid–base buffering capacity of the hypoxic bottom water in the summer period. Our results highlight the importance of acid–base buffering in the pH dynamics of coastal systems and illustrate the increasing vulnerability of hypoxic, CO2-rich waters to any acidifying process.

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