Organic Matter In River Sediments Research Articles

Linking patterns of physical and chemical organic matter fractions to its lability in sediments of the tidal Elbe river

Degradability of organic matter in river sediments differs in relation to origin and age. In order to explain previously observed spatial patterns of organic matter degradability and stabilization, this study investigated sediment organic matter (SOM) properties along a tidal Elbe river transect using dissolved organic matter (DOM) fractions, density fractions, carbon stable isotopes and thermometric pyrolysis (Rock-Eval 6©). These properties were linked to SOM decay rates and biological indicators such as chlorophyll a and silicic acid in the water phase, and sediment-bound extracellular polymeric substances (EPS), microbial biomass and oxygen consumption. Sediment source gradients were established using the concentration of Zn in the fraction < 20 μm as proxy.The specific Zn concentration showed that the most upstream location was nourished primarily by upstream fluviatile sediments while the other locations carried a downstream signature. The upstream location was also characterised by the highest concentrations of chlorophyll a, microbial biomass, silicic acid, EPS, humic acids and hydrophilic DOM, the most negative δ13C signature and by the highest oxygen consumption rate, with decreasing trends towards downstream locations. This trend was also evident in the decreasing SOM lability from upstream to downstream, an increasing share of total SOM found in the acid-base-extractable fractions and a decreasing share of carbon in the light density fractions. Thermometric pyrolysis revealed the highest H-index (easily degradable SOM) for the most upstream location and the ratio of the I-index (immature SOM) to the R-index (refractory SOM) to correlate positively with measured SOM decay rates.This study suggests that spatial patterns of SOM degradability can be explained by a source gradient, with young organic matter entering the system from upstream from predominantly biogenic sources, while downstream sources (North Sea sediment) deliver more refractory SOM that is stabilized in organo-mineral associations to a higher extent. In the investigated sediments, dissolved organic matter represented 0.23–1.20% of the total organic carbon (TOC) from anaerobically degradable SOM, while 4.10–11.46% TOC was liberated as CO2 and CH4 after long-term incubation (250 days). Thermometric pyrolysis is shown to serve as a useful proxy for SOM degradability in river sediments, with the Hydrogen-Index (HI) correlating well with degradability and the relationship between the I-index and R-index changing consistently towards lower I-indices and higher R-indices with an increasing degree of SOM stabilization.

Riparian Cottonwood Trees and Adjacent River Sediments Have Different Microbial Communities and Produce Methane With Contrasting Carbon Isotope Compositions

AbstractRivers and their adjacent riparian forests are intimately linked by the exchange of water, nutrients, and organic matter. Both riparian cottonwood trees and adjacent river sediments host microbial communities including archeal methanogens, supporting methane production and emission to the atmosphere. Here we combine microbial community and in vitro stable isotope analyses to characterize the drivers of methane cycling in distinct anoxic habitats (river sediments vs. riparian cottonwood stems) associated with the Oldman River, southern Alberta (Canada). We demonstrate that, differences in the chemical characteristics of organic matter support divergent microbial communities that generate methane from distinct metabolic pathways. Organic matter in river sediments had C/N ratios approximately 50‐fold lower than in tree stems and had more diverse dissolved organic components. Contrasting substrate availability between river sediment and tree stems was likely the primary mechanism for the greater microbial diversity in river sediments than in tree stems, the significantly different bacterial communities, and the trend toward differing abundance of methanogen orders. The methane carbon isotope composition (δ13C values) differed for the tree stem (−103.6‰ to −70.6‰) and river sediment (−55.1‰ to −48.4‰) environments, suggesting that methane was primarily produced via CO2‐reduction in tree stems by Methanobacteriales, while river sediments produced more methane through acetate fermentation primarily by Methanosarcinales. This study demonstrates the importance of organic matter quality and microbial community composition in driving metabolic processes contributing to methane production and emission in rivers and adjacent riparian forests.

Characteristics and significance of dissolved organic matter in river sediments of extremely water-deficient basins: A Beiyun River case study

The characteristics of dissolved organic matter in river sediments, affected by microorganisms, are of great significance to water management strategies. Based on three-dimensional excitation and emission matrix fluorescence, ultraviolet–visible spectroscopy, and high-throughput sequencing technology, this study jointly analyzed the composition and transformation mechanisms of dissolved organic matter as well as the microbial community structure in sediments of the Beiyun River, the main river within a basin with extreme water shortages. Moreover, we evaluated N and P contents in sediments to identify parameters to reflect potential eutrophication risks. Our results demonstrated that the content of dissolved organic matter in sediments was between 30.2 and 49.9 g/kg in the Tongzhou area of the Beiyun River. Humic substances were the largest components of dissolved organic matter in the sediments, followed by protein-like substances and soluble microbial byproducts. Furthermore, the proportion of humic matter decreased from upstream to downstream. The proportion of carbonyl, carboxyl, hydroxyl, and ester substituents on the aromatic structures of dissolved organic matter was significantly higher in the upstream, whereas the proportion of substances with aliphatic chain substituents on their aromatic structures was relatively low. The variation in downstream sediment microbial communities was much greater than that in the upstream (analyzed at the phylum level). Proteobacteria was the most abundant phylum (47.97%), which was closely related to the aromaticity of the dissolved organic matter in sediments. The N and P contents in the sediments of the Beiyun River were high and exhibited active transformation. The maximum fluorescence intensity of fulvic-acid-like components in the sediments [Fmax(C4)] can indirectly reflect the potential risk of eutrophication in the Beiyun River. Therefore, our results provide a theoretical basis for the assessment of water quality and pollution control in the Beiyun River and other water-deficient regions worldwide.

Material Composition and Geochemical Characteristics of Technogenic River Silts

Abstract—The paper discusses the results of many years of studying the material composition and geochemical characteristics, conditions, and processes in the formation of technogenic river silts: a new type of modern river sediments formed in riverbeds within the boundaries and zones of influence of industrial–urbanized areas. The article examines the main sources and most important characteristics of technogenic sedimentary material flowing into rivers, as well as the geochemical conditions of technogenic alluvial sedimentation, the morphology and structure of technogenic silts, the extent of their spatial distribution in riverbeds, their grain size characteristics, and mineral and chemical composition. Special attention is paid to analyzing the group composition of organic matter in river sediments and the features of its transformation in pollution zones. The study analyzes the technogenic geochemical associations that form in silts in zones of influence of various impact sources, the features of the concentration and distribution of chemical elements, heavy metal speciation, the composition of exchangeable cations in technogenic silts and natural (background) alluvium, and the composition of silt water. Possible secondary transformations of technogenic silts and their significance as a long-term source of pollution of the water mass and hydrobionts are substantiated.

Geochemical indicators of technogenic pollution of bottom sediments of small rivers in an urbanized environment

We have explored the possibility of using the geochemical characteristics of migration and accumulation of alkali metals (lithium, rubidium, and caesium) as the indicators of anthropogenic status of heavy metals in bottom sediments of small rivers of a technogenically disturbed (urbanized) environment. A study was made of the behavior of the above elements in bottom sediments of the rivers of Petrozavodsk (Republic of Karelia). The chemical composition of the sediments used in the study was determined with X-ray fluorescence spectrometer ARL ADVANT’X and mass spectrometer XSeries-2 ICP-MS; the content of organic matter in bottom sediments (from the LOI index) was estimated by the weighing method upon heating the samples under investigation to the temperature of 1100°C. As a result of the investigations, it was found that among the heavy metals, Co, Ni, Cu, Zn, Mo, Sb, W and Pb are of predominantly technogenic origin in river sediments, which Cr and Cs are of predominantly natural origin due to a high background of these elements in Quaternary formations of the study area. We determined a close association of the trace elements of technogenic status as well as of Li, Rb and Cs with content levels of iron-manganese formations and organic matter in river sediments, which does indicate a commonalty of the processes promoting their input into the urban water stream. It is established that the commonalty of accumulation of a number of heavy metals in bottom sediments with lithophylic elements (Li, Rb and Cs), due to the high chemical activity of these latter, makes it possible to use the geochemical characteristics of the alkali metals as the indicator of technogenic status of the main pollutants of the urban environment.

Comparison of digestion methods for determination of total phosphorus in river sediments

AbstractIn this study, four digestion methods used to determine total phosphorus in river sediments, including Na2CO3 fusion, the H2SO4 and H2SO4 + H2O2 methods and the SMT protocol were investigated. Interference effects of iron, calcium and organic matter in river sediments, and the substances contained in the digestion agents on the photometric determination of the phosphates were analysed. The digestion methods were tested on ten river sediment samples. Statistical analysis of the results showed significant differences between sample treatments relating to the mean total phosphorus concentration.

Natural, anthropogenic and fossil organic matter in river sediments and suspended particulate matter: A multi-molecular marker approach

Different classes of organic matter (OM) have been systematically investigated in sediments and suspended particulate matter (SPM) along the Danube River in order to understand causes of compositional changes. Analytical pyrolysis revealed the dominance of natural organic matter (NOM) in most of the samples. The predominance of aquatic biomass is evident mainly from the abundance of organonitrogen compounds and phenol distributions. As the river enters a forested gorge, the terrestrial component of the NOM in sediments is more significant. This is reflected in abundant methoxyphenols and a very high carbon preference index. SPM sample from a tributary shows a unique geochemical signature. It contains abundant carboxylic acids, amines, isoprenoids in the pyrolyzate, and is dominated by phytol and 24-methyl-cholesta-5,24(28)-dien-3β-ol in the extract, produced by a diatom bloom. Wax esters with a relatively high proportion of short, methyl-branched alkyl-chains appear together with abundant phytadienes and n-C 17 alkane in some samples, suggesting a microbial origin. Anthropogenic OM from runoff and atmospheric deposition was evident from a minor input of polycyclic aromatic hydrocarbons (PAHs) originating from mixed combustion sources. Multivariate analysis using PAH data led us to define simple molecular ratios to distinguish the PAH composition in sand and silty sediments. The newly defined ratios are the alkylated phenanthrenes and anthracenes ratio (APA; C 1-C 3/C 0–C 3 phenanthrenes and anthracenes) and the PAH ring number ratio (RN; 5–6 ring parent PAHs/all parent PAHs). This demonstrates that alkylated, as well as 5–6 ring PAHs are better preserved in the finer than in coarser grained sediments. A ubiquitous, but minor input of petroleum-related contamination with a uniform composition was evident in all samples as revealed by the analysis of petroleum biomarkers. This study demonstrates that the investigation of different classes of riverine OM requires a detailed molecular analysis, applying a series of analytical techniques and adequate statistical data treatment.

Molecular studies of insoluble organic matter in river sediments from Alsace-Lorraine (France)

Insoluble organic matter (IOM) from river sediments of Alsace-Lorraine (France) was examined by semi-quantitative pyrolysis-gas chromatography–mass spectrometry (Py-GC–MS). IOM in rivers can play a role in the production of noxious metabolites and mobilization of pollutants by complexation. The relative abundance of aliphatic hydrocarbons, aromatic hydrocarbons and heteroatomic compounds was determined in IOM from natural and pollutant sources and small and large rivers. A ternary plot of these compound classes allowed the natural and pollutant end members to be distinguished. The IOM of the small rivers was similar to the pollutant end member whilst that of the large rivers was similar to the natural sources. This semi-quantitative Py-GC–MS approach constitutes a promising tool for IOM characterization.

The relationship between adsorption of heavy metal and organic matter in river sediments

Sediment samples of eight sites in two rivers located in northern Taiwan, the Tao-Chen River and the Lau-Che River, were collected to investigate the influences of organic matter on adsorbabilities of heavy metals in dry and wet periods. A batch scale adsorption study was conducted to examine the adsorbabilities of heavy metals of sediments. In the less polluted river (Tao-Chen River), pH, organic matter, cation exchange capacity (CEC), and heavy metals of sediments were independent of the changes of the flow of the river. In contrast, they would be related to those of the more polluted river (Lau-Che River). Metal concentrations and CEC in sediments were positively correlated with organic matter content. On the other hand, there was significantly positive correlation between the adsorbabilities of heavy metals of sediments and organic matter content. The adsorbabilities of sediments to heavy metals increased in the order Zn < Pb < Cu < Cr. The amount of adsorbed Cr in sediments was much greater than that of the other metals, and Zn was adsorbed much less than others.

δ13C composition of sediments from the Sanaga River, Cameroon

The Sanaga River basin in Cameroon represents an ideal system for investigating the relationship between the carbon-isotope composition of organic matter in river sediments, and the type of vegetation in the river catchment. The headwaters of the river and its tributaries are located on a savannah-covered plateau in central Cameroon, with abundant Ca grasses (813 C = _ 12°/oo). The river then flows through transitional forest /savannah regions and finally through tropical rainforest (comprising only C3 vegetation with 813 C = _ 29%o) before discharging into the Gulf of Guinea. 8t3C values in the headwaters of the river are as high as 19%0 consistent with the presence of abundant C4 carbon derived from extensive savannah and montane regions. As the Sanaga River descends into the zone of transitional vegetation and into the forested regions, the 8~3C value of carbon in the samples decreases progressively to -26.9%0 due to the addit ion of forest-derived C 3 carbon. Below its confluence with the Mbam River, the ~13C value of the sediments increase to ~ 24%o, due to the addition of organic carbon with a ~3C value of -23%o derived from the Mbam River, which has extensive savanna and agricultural regions in its catchment. The 8~3C value again decreases downstream of the confluence to around -25%o at the mouth of the river. The trends in the ~3C data can be duplicated using a simple box model which assumes that the observed ~3C values are the result of mixing of carbon derived from C3and C4dominated vegetation types within the catchment. This suggests that the carbon-isotope composit ion of riverine organic carbon can provide information on catchment vegetation, and that ancient sediments can provide information on changes in catchment vegetation in the past.

Breakdown and Invertebrate Colonization of Leaf Litter in Two Contrasting Streams, Significance of Oligochaetes in a Large River

The breakdown of willow (Salix alba) and beech (Fagus silvatica) leaves and their colonization by invertebrates were studied in a third-order mountain stream (breakdown rate k = 0.0147 and 0.0052∙d−1, respectively) and a seventh-order lowland river (k = 0.0094 and 0.0027∙d−1). Willow leaves broke down three times faster than beech leaves; this difference was twice that between streams. Total invertebrate densities and biomass and the proportion of shredders were higher in the large river; therefore, differences in breakdown capacities between streams cannot be attributed to differences in invertebrate community structure. Instead, microbial processing and abiotic fragmentation are suggested as factors controlling breakdown rates. Owing to the abundance of naidids, up to 2000 invertebrates per leaf bag were recorded in the large river. These oligochaetes appeared to use litter accumulations as a microhabitat that provided shelter and a rich supply of food in the form of fine particulate organic matter. Tubificid oligochaetes accounted for 55% of total biomass on partly degraded leaves at this site. Their abundance and regular occurrence inside willow leaves suggest that tubificids enhance leaf fragmentation and possibly mediate the incorporation of organic matter in river sediments once the plant tissue is sufficiently macerated.

The determination of organic matter in river sediments

The determination of organic matter in river sediments