Interstitial Waters Of Marine Sediments Research Articles

Determination of Nitrate in Small Water Samples (100 µL) by the Cadmium-Copper Reduction Method: A Manual Technique with Application to the Interstitial Waters of Marine Sediments

The standard technique for the analysis of $ {\\rm NO}_3^ - $ in seawater and the interstitial waters of marine sediments is the cadmium-copper reduction method. The manual $ {\\rm NO}_3^ - $ method presented here provides a technique that is simple, cost-effective and capable of analysing small volumes (100 µL). The technique is also suitable for analysing $ {\\rm NO}_3^ - $ in DET (diffusive equilibration in thin films) gel samples. Reduction of $ {\\rm NO}_3^ - $ to $ {\\rm NO}_2^ - $ is achieved by drawing the sample into contact with a copper-coated cadmium wire using a micrometer burette. The reduced sample is then expelled and $ {\\rm NO}_2^ - $ is determined colorimetrically. The method has a concentration range of 0-100 µM $ {\\rm NO}_3^ - $ and a detection limit (2 s b ) of 0.4 µM $ {\\rm NO}_3^ - $ . Eight samples can be processed per hour.

Metal–colloid partitioning in artificial interstitial waters of marine sediments: Influences of salinity, pH, and colloidal organic carbon concentration

For decades, heavy metals have been deposited into marine sediments as a result of anthropogenic activities. Depending on their bioavailability, these metals may represent a risk to benthic organisms. Dissolved interstitial water metal concentrations have been shown to be better predictors of bioavailability than sediment metal concentrations. In order to improve our understanding of metals bioavailability in sediments, it is essential to fully comprehend metal speciation. Colloidal organic carbon is ubiquitous in marine interstitial water and readily forms complexes with numerous dissolved metals, greatly reducing their bioavailability. Methods were applied to isolate dissolved and colloidal cadmium, copper, nickel, lead, and zinc from interstitial waters using centrifugation and stirred cell ultrafiltration. Influences of salinity, pH, and colloidal carbon concentration on partitioning behavior were investigated. In the pH study, colloidal-dissolved partitioning of each metal (Kp) was observed to increase as pH rose. Conversely, in the salinity experiment, metal Kps declined as salinity increased. For the metal-organic colloid study, linear isotherms were calculated for each of the metals, resulting in log Kcocs ranging from 5.90 for zinc to 7.50 for copper. Kp values calculated from metal-spiked field sediments were in good agreement with those measured in the salinity study. These results provide insight into the behavior of metals associated with colloidal organic carbon in marine sediments under the conditions occurring in estuarine systems.

Anodic stripping voltammetry of copper in natural waters: A qualitative approach to the additional peak(s) occurrence

AbstractIn the presence of natural organic species, the electrochemical behavior of metals can be modified. Several authors have already noticed an extra peak or shoulder in the Cu peak during anodic stripping voltammetry (ASV) analysis, but the origin of this interference was generally not investigated and the experimental conditions were modified to make it disappear. In this article, this phenomenon alone was studied. The organic matter dissolved in interstitial waters of marine sediments was fractionated by ultrafiltration and gel permeation chromatography. The resulting fractions were qualitatively studied with respect to the complexity of the voltammograms they exhibit during an ASV analysis of Cu. Very similar electrochemical behaviors (multiple peaks) were found for interstitial waters and humic substances. The fractionation experiment suggests that particular families of molecules, which can be separated, are responsible for these extra peaks. Therefore, the “multipeak” phenomenon is related to the quality of the organic matter rather than to its quantity. This fact, supported by several experiments [DPASV, differential pulse polarography (DPP)], has led to a model which, although still somewhat speculative, describes well the usual observations: the extra peaks would originate from the oxidation of organic copper species [most likely as Cu(I)] adsorbed and stabilized on the mercury drop electrode.

Size separation of interstitial water in marine sediments.

Interstitial waters of marine sediments were separated into the two portions. A large interstitial water was extracted from sediment core samples by a centrifugation at 42×g for 30min, and then a small interstitial water was extracted at 1, 500×g from the residual sediment samples. The content of the large interstitial water was high in sandy sediment, while the small interstitial water was in silty and clayey sediment. Concentrations of polymeric carbohydrates were higher in the small interstitial water than in the large interstitial water, although no difference was found in monomeric carbohydrate. It was suggested that monomeric carbohydrates were uniformly distributed in marine sediments by diffusion, while polymeric carbohydrates were not.

Sterols in interstitial waters of marine sediments

In order to attempt to elucidate the nature of biogeochemical processes occurring at the water-sediment interface, sterols have been analysed in near bottom sea and interstitial waters collected in the eastern and western intertropical Atlantic ocean. Free and esterified sterol concentrations range from 0.2 to 82 μg l −1 and are much higher than those found in overlying sea water, which range from 0.2 to 1.7 μg l −1 for the dissolved fraction and from 0.01 to 0.07 μg l −1 for the particulate fraction. Cholest-5-en-3β-ol and 24-ethylcholest-5-en-3β-ol are the dominant sterols in sea and interstitial waters. The variability encountered for the relative importance of minor sterols such as 24-methylcholesta-5,24(28)-dien-3β-ol and stanols, 5α-cholest-22(E)-en-3β-ol, 5α-cholestan-3β-ol and 24-ethyl-5α-cholestan-3β-ol in interstitial water and their variation with depth is discussed in terms of diversity of inputs and bacterial activity. For sediments cored off the Mauritanian coast, a productive area characterized by an intense upwelling, the chemical signatures observed in interstitial water through stanol/stenol ratios occur at levels of very high heterotrophic aerobic bacterial biomass estimations. The study of the sterol composition of interstitial water could constitute a valuable tool in appreciating the intensity of chemical and biological processes occurring in the first few metres of recent marine sediments.

Sr isotopes in interstitial waters of marine sediments from Deep Sea Drilling Project cores

Sr isotopes in interstitial waters of marine sediments from Deep Sea Drilling Project cores

Sr isotopes in interstitial waters of marine sediments from Deep Sea Drilling Project cores

Sr isotopic compositions of interstitial sea waters have been documented in detail with cores from 37 Deep Sea Drilling Project sites. The 87Sr/86Sr ratios are sensitive indicators of diagenetic reactions involving alteration of volcanic matter dispersed in sediments and recrystallization of carbonates. Effects of basalt alteration reactions, except possibly for hydrothermal signals, and of alteration of continental debris are minimal. Carbonate recrystallization has a significant effect on the geochemical mass balance of Sr but diffusion of unradiogenic strontium from interstitial waters has only a small effect on the 87Sr/86Sr ratio of ocean water.

Amino acids in interstitial waters of marine sediments: a comparison of results from varied sedimentary environments

High concentrations of dissolved free amino acids, ranging from 2 to 95 μM, have been measured in interstitial waters of marine sediments from Buzzards Bay (Massachusetts), the northwestern Atlantic, and the Peru upwelling region. Amino acid concentrations were highest in the interstitial water at or near the sediment-water interface, and decreased with depth in the sediment. The amino acid composition varied systematically with depth in the sediment and with depositional environment. Glutamic and β-aminoglutaric acids were important constituents of most samples, especially those from anoxic sediments.

Amino acids in interstitial waters of marine sediments

DISEQUILIBRIA within the mixture of organic matter, mineral particles and seawater in near-surface sediments result in extensive reaction, often biologically mediated. Variations in interstitial water composition are very sensitive indicators of the chemical and biological reactions in this zone of transition and the interaction between the water column and the permanent deposit1,2. Although most studies have been confined to inorganic ions, the few measurements of pore water DOC in marine sediments3–6 show large gradients in dissolved organic matter concentration within sediments and across the sediment–water interface. We describe here our study of dissolved amino acids in interstitial waters, which were used to trace some of the biogeochemical processes affecting organic matter in marine sediments. We have analysed the dissolved free amino acids in 15 interstitial water samples from four cores obtained in Buzzards Bay, Massachusetts; the Gulf of Maine; and the North-west Atlantic continental rise. These pore waters have very high amino acid concentrations, of the order of 1 mg l−1. In addition, the distribution of individual amino acids differs substantially from that reported for seawater7,8, particularly in the large relative abundance of glutamic acid and β-aminoglutaric acid. β-aminoglutaric acid (HOOCCH2CH(NH2)CH2COOH) is an isomer of glutamic acid which, to our knowledge, has not been previously reported in the marine environment.

Nature and reactions of dissolved organic matter in the interstitial waters of marine sediments

Two organic rich sediments, an oxic muddy sand and a silty mud containing sulphate reducing and methane producing metabolic zones, were sampled from Loch Duich, a fjord type estuary in the N.W. coast of Scotland. Dissolved organic carbon (DOC), as measured by dry combustion and UV absorption, remained constant (8.3–15.8 mg C/l) with depth in the oxic pore waters at a concentration at least twice that of the overlying seawater. DOC in the anoxic pore waters increased linearly with depth from 13.6 at the surface to 55.9–70.5 mg C/l at 80cm. Most of the DOC was present in the high molecular weight (HMW) fraction as separated by ultrafiltration; the low molecular weight (LMW) fraction remained constant (10.0 mg C/l) in both oxic and anoxic pore waters. Spectroscopic data showed the ‘humic’ fraction of the HMW dissolved organic matter was mainly fulvic acid, a small proportion (approx 1%) of humic acid, and a third fraction, possibly melanoidins, which increased relative to fulvic acid with depth. These data confirm the pathway of humification (NissenBaum et al, 1971; nissenbaum and Kaplan, 1972) where HMW organic matter accumulates in pore waters as condensation products of LMW organic substances.

Chemistry of Interstitial Waters of Marine Sediments

In recen t years muc h in terest has developed in the processes that have l ed to the present chemical composi tion of the oceans. A mong the pioneering efforts were those o f Gol dschm idt 1933) and Conway 1943). These authors made up approxi­ mate mass balances and calculated the amounts of primary rocks that mus t have weathered to account for the chemical composition of the o cean and the sediments. This work was l ater amplified by Horn & A dams 1966). In the m ass bal ances considered by these various authors, no ser ious attention was given to the possible recycling of materials, nor to the o cean as just one geochemical reservoir through which the elemen ts pass on to a subsequ ent reservoir, namely the s ediments . Considerat ions of t his type were introduced by Barth (1952) and Gol dber g & Arrhenius 1958). The latter authors found good agreemen t between measured rates o f i nput o f some element s into the o cean, vi a the ri vers and the atmosphere, and the ratc of output into thc s edimcn ts. Such balanccs suggest that a stcady state exists in the overall geochemical cycle. In a different approach Sil len ( 967) used a simple chemical equi l ibrium model to account for the composition of sea water. He assumed an e quil ibrium between the ocean an d the m arine sediments, part icul arly w ith the alumino-sil icate and the carbonate phases. Broecker (1971) cri ticized this model , especially because i t tends to discourage any i nquiry into the reactions that m ay t ake place in the various geochemical reservoirs. Broeck er specifical ly ci tes examples that could impl y variatio ns in the i onic compositi on of sea water wi th time, an d he advocates a kinetic approach to the problem, which wou ld then l ead to a search for the processes that control the apparent s teady s tate as i t exists today. Garrels & Mackenzie (1971) developed a steady-state model based on the concept of chemical uniformi tarianism, in w hich the to tal mass and the chemical com­ pos ition of s edimen tary rocks, as well as the c h emical compos ition of the depos ited materials , have remained constan t wi th time, that is, at l east during the las t two b il l ion years. These authors (Garrel s & M ackenzie 1972, Garrels & Perry 1974) have developed this concept i nt o a quantitat ive model i nvolvi ng both estimates of overall fluxes and residen ce times of chemi cal el ements in various geochemical

Alkalinity Determination in Interstitial Waters of Marine Sediments

ABSTRACT The titration alkalinity of interstitial water is defined in terms of the ionic species that contribute to the alkalinity and the significance and the magnitude of these contributions is estimated from available analytical data. Also a method for the potentiometric titration of the alkalinity is described with special reference to the various techniques available for the evaluation of the equivalence point. Special attention is given to the possible effect of the sulfate content of the samples on the mathematical evaluation of the end point. The accuracy of the method is estimated to be 0.5%.

Diffusion of sea water ions—I. Diffusion of sea water into a dilute solution

Derivations of Vinograd and McBain (1941) were applied to explain ionic diffusion out of sea water and into dilute solution. Models so constructed were found to be compatible with experimental data obtained from Cl −, K +, Mg 2+ and Ca 2+ diffusion studies. The present investigation suggests that ionic interaction—resulting from the electroneutrality requirement—may extensively modify fluxes of diffusing ions and may also affect the relative distribution of both migrating and non-migrating ions. It is suggested that a change in the ratio ion Cl in interstitial waters of marine sediments does not necessarily imply that the ion is involved in a chemical reaction or that it migrates.

Composition of Interstitial Waters of Marine Sediments: Temperature of Squeezing Effect

Warmeling of samples of marine sediments to room temperatures prior to the extraction of interstitial water accounts for the apparent enrichments of potassium ion (13.3 percent) and chloride ion (1.4 percent) and depletions of magnesium ion (2.5 percent) and calcium ion (4.9 percent). These differences are the result of changes in ion-exchange selectivity as a function of temperature.

Trace elements in the interstitial waters of marine sediments

Phosphate and eleven elements were determined in the interstitial waters of four piston cores from the continental borderland area off the coast of Southern California. Calcium, magnesium, potassium, sodium and strontium were determined directly by atomic absorption spectrophotometry. Phosphate was determined colorimetrically and the trace elements: cadmium, cobalt, copper, iron, nickel and zinc, were determined by extraction of the chelate complexes with ammonium pyrollidine dithiocarbamate into methylisobutyl ketone and subsequent analysis by atomic absorption spectrophotometry. Correlation coefficients for various pairs of variables are given. Decrease of Eh and increase of phosphate with depth was attributed mainly to bacterial activity and in the case of phosphate, partly due to release from metal phosphates. Calcium and strontium showed decreases with depth probably due partly to precipitation of carbonate by excess bicarbonate ions produced as a result of bacterial activity and partly to precipitation as phosphate. Potassium levels were higher and magnesium values were slightly lower than in sea water, probably due to interaction with the solid phase of the sediments. Copper showed no overall trends, but zinc showed moderate decrease with depth and correlated well with cadmium. Enrichment of cobalt, zinc, cadmium and copper at the surface of the sediments was attributed to biological concentration, and release, since there is more than sufficient organic matter present to account for such a source. Iron and nickel concentrations were greater in reducing sediments and showed an overall trend to increase with depth.