X-ray Computed Tomography as a Tool for Screening Sediment Cores: An Application to the Lagoons of the Po River Delta (Italy)

Lagoon sediments have heterogeneous structure and texture, contain shells and plants and are often highly bioturbated and disturbed by human activities. In such sediments, the selection of representative cores and the choice of a subsampling strategy are important but difficult. In this study, we examine the usefulness of X-ray computed tomography (CT) for inferring sediment features that will help in making optimal decisions prior to core opening (24 cores from seven lagoons). Various algorithms (intensity projections, slice thickness, axial and sagittal images, CT number profiles and volumetric region of interest) are tested to visualise low- and high-density volumes or objects and to quantify the relations between the average volumetric CT number and the bulk density of the sediment matrix. The CT number is related mainly to water content and indirectly to total nitrogen and <16-μm grain-size fraction (model R2 = 0.94). The outliers are attributed to a weak correspondence between the fraction of sediment sampled for water content determination and the volume of sediment matrix used for CT number measurements in highly heterogeneous sediment slices. In conclusion, CT is a powerful tool for the initial screening of cores recovered from heterogeneous lagoon sediments. The adequate use of available algorithms may provide quantitative information on various sediment features, allowing the purposeful selection of cores and subsamples for further investigation.

A novel multi-parameter approach to assess the effects of river restoration measures on the sediment matrix

&lt;p&gt;Clogging of riverbeds, also referred to colmation, has been frequently reported in residual flow river reaches. In such river reaches, colmation occurs mostly due to regulated (minimum) flow conditions without significant flood events that drive morphodynamics. Consequently, incoming fine sediments continuously deposit, infiltrate, and accumulate in the gravel matrix of the riverbed. The negative effect of such clogged layers on river ecology is well-known, especially with respect to the hyporheic interstitial leading to reduced porosity and hydraulic conductivity. These limitations results in a reduced supply of dissolved oxygen for aquatic species living in the hyporheic interstitial. However, no standardized quantitative measuring technique exists to determine the vertical location and the degree of colmation. Most available measuring methods involve a variety of mapping methods or single-parameter approaches. While mapping methods enable only qualitative assessments, single-parameter approaches are insufficient to describe the complexity of colmation.&lt;/p&gt;&lt;p&gt;The objective of this study is to test a novel multi-parameter approach in a residual flow river reach to assess the effect of river restoration measures on colmation. The multi-parameter approach includes four key parameters to describe colmation: i) the grain size distribution of the riverbed using freeze core sampling and sieving, ii) the hydraulic conductivity using a newly developed double packer system, iii) the porosity identified with a photogrammetric approach, and iv) the interstitial dissolved oxygen content (DOC) using optodes. This novel approach enables a quantitative description of colmation and an identification of clogged layers in stratified riverbeds as the hydraulic conductivity and the DOC are measured in vertical profiles. The entire measuring concept is applied before and after the implementation of river restoration measures to detect the intervention&amp;#8217;s effects on colmation.&lt;/p&gt;&lt;p&gt;The first analyses of the measurement show clearly the effects of dredging with an artificial alteration of the riverbed on the sediment matrix. The vertical profiles of hydraulic conductivity and dissolved oxygen show typically high values in the permeable upper sediment layer and significant reductions in deeper sediment layers. The thickness range of the permeable upper layer is between 5 and 15&amp;#160;cm before the intervention and increased up to 30 and 50&amp;#160;cm after the interventions. The analyses of a coarsened grain size distribution and porosity support the observation of this declogging effect, although a direct correlation is challenging because both parameters are not detected in the form of vertical profiles, but rather as a bulk information for every measurement point.&lt;/p&gt;&lt;p&gt;These very first results provide the conclusion that the measured vertical profiles of hydraulic conductivity and DOC are promising data to assess the location and degree of colmation and their modification as a result of river restoration action. Yet, grain size and porosity analyses provide only little evidence because those represent bulk information only. In summary, the multi-parameter approach represents an innovative and quantitative approach to objectively assess the degree and vertical location of clogged layers in gravel riverbed, which is a major advantage over existing methods for assessing colmation.&lt;/p&gt;

EARLY–MIDDLE ORDOVICIAN SEASCAPE-SCALE AGGREGATION PATTERN OF SPONGE-RICH REEFS ACROSS THE LAURENTIA PALEOCONTINENT

ABSTRACT During the late Cambrian–Early Ordovician interval the predominant non-microbial reef builders were sponges or sponge-like metazoans. The lithological and faunal composition of Cambro-Ordovician sponge-dominated reefs have previously been analyzed and reviewed. Here we take the relationship between reef aggregation pattern at reef to seascape scale into account, and look for changes during the Early–Middle Ordovician interval, in which metazoans became dominant reef builders. In a comparison of sponge-rich reefs from eight sites of the Laurentia paleocontinent three different seascape level reef growth patterns can be distinguished: (1) mosaic mode of reef growth, where reefs form a complex spatial mosaic dependent on hard substrate; (2) episodic mode, where patch reefs grew exclusively in distinct unconformity bounded horizons within non-reefal lithological units that have a much larger thickness; and (3) belt-and-bank mode, where reefs and reef complexes grew vertically and laterally as dispersed patches largely independent from truncation surfaces. The distinct modes of growth likely represent specific reef forming paleocommunities, because they differ in content and abundance of skeletal metazoan framebuilders, bioturbation intensity of non-skeletal reef sediment matrix, and in association of reef growth with underlying hard substrate. We suggest, based on a review of Laurentian reef occurrences, that the mosaic mode dominated in Early Ordovician strata and that the dominance shifted toward the belt and bank mode from Middle Ordovician strata onward.

Inducing the Attachment of Cable Bacteria on Oxidizing Electrodes

The scope of the present study is to introduce electrochemical reactors as a tool for investigating the growth of novel filamentous cable bacteria and their unique extracellular electron transfer ability. New evidence that cable bacteria are widely distributed in sediments throughout an estuarine system connected to the NE Pacific Ocean is also presented. Cable bacteria found within Yaquina Bay, Oregon, USA, appear to cluster with the genus, Candidatus Electrothrix. Results of a 135-day bioelectrochemical reactor experiment confirm a previous observation that cable bacteria can grow on oxidatively poised electrodes suspended in anaerobic seawater above reducing sediments. However, several diverse morphologies of Desulfobulbaceae filaments, cells, and colonies were observed on the carbon fibers of the suspended electrodes including encrusted chains of cells. These observations provide new information to suggest what conditions will induce cable bacteria to perform electron donation to an electrode surface, further informing future experiments to culture cable bacteria apart from a sediment matrix.

The Radiocarbon Ages of Different Organic Components in the Mires of Eastern Australia

ABSTRACTRadiocarbon (14C) dating is widely used to determine the age of organic material in palaeoenvironmental research. Here we compare 14C dates (n=17) resulting from macro-charcoal (>250 μm), short-lived plant macrofossils and pollen-rich residues isolated from two mire environments in eastern Australia. In most samples we found that short-lived plant macrofossils were the youngest organic component, the charcoal samples most often fell into the middle and the pollen-rich residues consistently returned older dates than the other samples. Although pollen-rich residues have been widely used for 14C dating in Australasia we suggest some caution in their use, perhaps because in our fire-prone environments these samples often also contain fine charcoal and other oxidative resistant organic matter that is older than the surrounding sediment matrix. The macro-charcoal samples also often returned older calibrated ages compared to short-lived plant macrofossils from the same depth, although this difference was relatively small (<245 years). Our results demonstrate that 14C dating of short-lived plant macrofossils are likely to yield more accurate chronologies and we advocate their routine use in palaeoenvironmental research when they are available.

Distribution of butyltin species in sediment samples collected from Saigon habours in Ho Chi Minh city

In this study, the distribution of tributyltin (TBT) and its degradation products, dibutyltin –DBT and monobutyltin – MBT in sediment sample collected adjacent Saigon habours was studied using gas chromatographic separation/ mass spectrometric detection. Sediment samples at 12 sites along the Saigon river were taken during dry and raining seasons in 2014 and 2015. Butyltin species were extracted from sediment matrix using HBr-tropolone into dichloromethane followed by ethylation with NaB(C2H5)4 in hexane. The reliability of the analytical method for butyltin species was evaluated by the use of the certified reference BCR-646 material. The concentrations of TBT, DBT and MBT in sediment samples were <0.1–2.81 ng/g, <0.1–4.3 ng/g and <0.2–8.4 ng/g (as Sn, dw). Butyltin species in sediment samples at sites within the habour area were higher than those at sites far upstreams or down-streams of the habours. Low values in TBT/(DBT+MBT) ratios revealed that the discharge of TBT from fouling paint was low at recent years.