The in vitro influence of the burrowing polychaete Nereis diversicolor on the fate of petroleum hydrocarbons in marine sediments

The in vitro fate of the saturated hydrocarbon fraction (SF) of Arabian Light crude oil has been studied in PVC cores filled with a coastal marine sediment defaunated by sieving. Experiments were conducted in absence or presence of polychaetes Nereis diversicolor. The luminophore tracer technique was used to quantify the mixing of sediment by worms. Presence of crude oil reduced the building of burrows by polychaetes. This work demonstrates the ability of infaunal organisms to stimulate both downard and outward transfers of hydrocarbons from sediment reservoirs. In non-bioturbated sediment hydrocarbons were confined to the sediment surface. Introduction of polychaetes in sediment (1) induced the burying of SF in sediment (2.5 % and 13.5 % of the initial surface input after 15 and 45 days, respectively); (2) enhanced the exportation of SF in the overlying water (plus 59 % and 23.5 % compared to defaunated control sediment after 15 and 45 days, respectively). Buried hydrocarbons were submitted to biodegradation, from 2 cm to 10 cm depth in polychaete burrows, after 45 days

Analytical model for flux saturation in sediment transport

The transport of sediment by a fluid along the surface is responsible for dune formation, dust entrainment and for a rich diversity of patterns on the bottom of oceans, rivers, and planetary surfaces. Most previous models of sediment transport have focused on the equilibrium (or saturated) particle flux. However, the morphodynamics of sediment landscapes emerging due to surface transport of sediment is controlled by situations out-of-equilibrium. In particular, it is controlled by the saturation length characterizing the distance it takes for the particle flux to reach a new equilibrium after a change in flow conditions. The saturation of mass density of particles entrained into transport and the relaxation of particle and fluid velocities constitute the main relevant relaxation mechanisms leading to saturation of the sediment flux. Here we present a theoretical model for sediment transport which, for the first time, accounts for both these relaxation mechanisms and for the different types of sediment entrainment prevailing under different environmental conditions. Our analytical treatment allows us to derive a closed expression for the saturation length of sediment flux, which is general and can thus be applied under different physical conditions

Bioavailability of pesticides in freshwater sediments

In ecological risk assessment standardized sediment toxicity tests are used to predict the hazard of chemicals for sediment-living organisms. Feeding is a prerequisite in these long-term tests to avoid starvation of test organisms. Therefore, added food particles may act as vectors for the test compound. The importance of food particles as vectors, however, is dependent on several factors, for example, sorption and major uptake routes. In this thesis, laboratory experiments on the importance of pesticide sorption and uptake routes for the bioavailability to the midge Chironomus riparius in sediment toxicity test setups were performed. A feeding selectivity study showed that larvae almost exclusively fed on added food particles, and highly neglected sediment particles. Additionally, experiments on the sorption of the insecticide lindane, showed that food and peat particles (used in artificial sediment) efficiently sorbed lindane (>95% after 48 h). The binding strength of lindane was weak, facilitating particulate uptake. However, the uptake from dissolved lindane was higher than the uptake from particles. From this we concluded that toxicity may be underestimated in spiked-sediment scenarios, where hydrophobic pesticides sorb to the sediment and larvae to a large extent feed on uncontaminated food particles. Conversely, in a spiked-water scenario, the food particles may act as vector, resulting in a facilitated particulate uptake, in addition to the uptake from water. Sediment organic matter affects sorption, and thus bioavailability of pesticides. Pyrethroid toxicity was much higher in artificial sediment than in a natural sediment, indicating the simplicity and shortcomings of using artificial sediments. Interestingly, the sediment quality highly affected bioavailability in spiked-water. For example, C. riparus larvae in sediments with low organic matter content and exposed to spiked-water pyrethroids, showed lower survival, slower development, and increased adult size, than those in sediments with higher organic matter. The pyrethroid deltamethrin, showed an LC50-value (28 d) for C. riparius larvae in artificial sediment of 16 pg/L and 11 µg/kg for water- and sediment exposures, respectively, i.e. toxic effects occurred at concentrations lower than the detection limits for high-tech analytical methods. This thesis contributes to a wider understanding of processes affecting bioavailability in freshwater sediments, and in particular in standardized sediments used in toxicity testing. The understanding of test compound sorption and bioavailability is crucial for sound interpretations of toxicity tests and for the general credibility of such tests

A physical model for seismic noise generation from sediment transport in rivers

Measuring sediment flux in rivers remains a significant problem in studies of landscape evolution. Recent studies suggest that observations of seismic noise near rivers can help provide such measurements, but the lack of models linking observed seismic quantities to sediment flux has prevented the method from being used. Here, we develop a forward model to describe the seismic noise induced by the transport of sediment in rivers. The model provides an expression for the power spectral density (PSD) of the Rayleigh waves generated by impulsive impacts from saltating particles which scales linearly with the number of particles of a given size and the square of the linear momentum. After incorporating expressions for the impact velocity and rate of impacts for fluvially transported sediment, we observe that the seismic noise PSD is strongly dependent on the sediment size, such that good constraints on grain size distribution are needed for reliable estimates of sediment flux based on seismic noise observations. The model predictions for the PSD are consistent with recent measurements and, based on these data, a first attempt at inverting seismic noise for the sediment flux is provided

Soil carbon and nitrogen erosion in forested catchments: Implications for erosion-induced terrestrial carbon sequestration

Lateral movement of organic matter (OM) due to erosion is now considered an important flux term in terrestrial carbon (C) and nitrogen (N) budgets, yet most published studies on the role of erosion focus on agricultural or grassland ecosystems. To date, little information is available on the rate and nature of OM eroded from forest ecosystems. We present annual sediment composition and yield, for water years 2005-2011, from eight catchments in the southern part of the Sierra Nevada, California. Sediment was compared to soil at three different landform positions from the source slopes to determine if there is selective transport of organic matter or different mineral particle size classes. Sediment export varied from 0.4 to 177 kg ha-1, while export of C in sediment was between 0.025 and 4.2 kg C ha-1 and export of N in sediment was between 0.001 and 0.04 kg N ha-1. Sediment yield and composition showed high interannual variation. In our study catchments, erosion laterally mobilized OM-rich litter material and topsoil, some of which enters streams owing to the catchment topography where steep slopes border stream channels. Annual lateral sediment export was positively and strongly correlated with stream discharge, while C and N concentrations were both negatively correlated with stream discharge; hence, C: N ratios were not strongly correlated to sediment yield. Our results suggest that stream discharge, more than sediment source, is a primary factor controlling the magnitude of C and N export from upland forest catchments. The OM-rich nature of eroded sediment raises important questions about the fate of the eroded OM. If a large fraction of the soil organic matter (SOM) eroded from forest ecosystems is lost during transport or after deposition, the contribution of forest ecosystems to the erosion-induced C sink is likely to be small (compared to croplands and grasslands)

Application and evaluation of sediment fingerprinting techniques in the Manawatu River catchment, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Geography at Massey University, Palmerston North, New Zealand

Suspended sediment is an important component of the fluvial environment, contributing not only to the physical form, but also the chemical and ecological character of river channels and adjacent floodplains. Fluvial sediment flux reflects erosion of the contributing catchment, which when enhanced can lead to a reduction in agricultural productivity, effect morphological changes in the riparian environment and alter aquatic ecosystems by elevating turbidity levels and degrading water quality. It is therefore important to identify catchment-scale erosion processes and understand rates of sediment delivery, transport and deposition into the fluvial system to be able to mitigate such adverse effects. Sediment fingerprinting is a well-used tool for evaluating sediment sources, capable of directly quantifying sediment supply through differentiating sediment sources based on their inherent geochemical signatures and statistical modelling. Confluence-based sediment fingerprinting has achieved broad scale geochemical discrimination within the 5870 km2 Manawatu catchment, which drains terrain comprising soft-rock Tertiary and Quaternary sandstones, mudstones, limestones and more indurated greywacke. Multiple sediment samples were taken upstream and downstream of major river confluences, sieved to 40 and > 35 respectively. The revised mixing model estimated Mudstone terrain to contribute 59.3 % and 61.8 %, with significant contributions estimated from Mountain Range (12.0 % and 11.4 %) and Hill Surface (11.5 % and 11.3 %) respectively, indicating that Tm, Ni, Cu, Ca, P, Mn and Cr have an influence on these sediment source estimations

Discharge and turbidity of the regulated River Tees. Variance spectrum analysis

High suspended sediment loads may be deleterious to adult salmonids and invertebrates in gravel-bedded streams. Further, the accumulation of fine material in the interstices of the gravel may have an adverse impact on the recruitment of the young stages of salmonids. It is important therefore not only to quantify the rates and degrees of silting but also to identify sediment sources and to determine both, the frequency of sediment inputs to the system and the duration of high sediment concentrations. This report explores the application of variance spectrum analysis to the isolation of sediment periodicities. For the particular river chosen for examination the method demonstrated the essentially undisturbed nature of the catchment. The regulated river chosen for examination is the River Tees in Northern England. Variance spectrum analysis was applied to a series of over 4000 paired daily turbidity and discharge readings

Hydraulic and mechanical properties of glacial sediments beneath Unteraargletscher, Switzerland: implications for glacier basal motion

The force on a ‘ploughmeter’ and subglacial water pressure have been measured in the same borehole at Unteraargletscher, Switzerland, in order to investigate ice–sediment coupling and the motion at the base of a soft-bedded glacier. A strong inverse correlation of the recorded pressure and force fluctuations, in conjunction with a significant time lag between the two signals, suggests that pore-water pressures directly affect the strength of the subglacial sediment. The lag is interpreted to reflect the time required for the water-pressure wave to propagate through the pores of the sediment to the depth of the ploughmeter. Analysis of the propagation velocity of this pressure wave yielded an estimate of the hydraulic diffusivity, a key parameter necessary to characterize transient pore-water flow. Furthermore, the inferred inverse relationship between pore-water pressure and sediment strength implies that Coulomb-plastic deformation is an appropriate rheological model for the sediment underlying Unteraargletscher. However, the sediment strength as derived from the ploughmeter data was found to be one order of magnitude smaller than that calculated for a Coulomb-frictional material using the water-pressure measurements. This significant discrepancy might result from pore-water pressures in excess of hydrostatic down-glacier from the ploughmeter. As the ploughmeter is dragged through the sediment, sediment is compressed. If the rate of this compression is large relative to the rate at which pore water can drain away, excess pore-water pressures will develop that have the potential to weaken the sediment. The same process could lead to highly fluid sediment down-glacier from clasts that protrude into the glacier sole and thus would otherwise provide the roughness to couple the glacier to its bed (Iverson, 1999). Rapidly sliding glaciers overlying sediments might therefore move predominantly by ‘ploughing’, which tends to focus basal motion near the glacier sole rather than at depth in the bed

Seismic characteristics of sediment drifts: An example from the Agulhas Plateau, southwest Indian Ocean

Sediment drifts provide information on the palaeoceanographic development of a region. Additionally, they may represent hydrocarbon reservoirs. Because of this, sediment drift investigation has increased over the last few years. Nevertheless, a number of problems remain regarding the processes controlling their shape, the characteristic lithological and seismic patterns and the diagnostic criteria.As an example, sediment drifts from the Agulhas Plateau, southwest Indian Ocean, are presented here. They show a variety of seismic features and facies including an asymmetric mounded geometry, changes in internal reflection pattern, truncation of internal reflectors at the seafloor and discontinuities. This collection of observations in combination with the local oceanography appears to comprise a diagnostic tool for sediment drifts

Physical and biological controls on fine sediment transport and storage in rivers

Excess fine sediment, comprising particles <2 mm in diameter, is a major cause of ecological degradation in rivers. The erosion of fine sediment from terrestrial or aquatic sources, its delivery to the river, and its storage and transport in the fluvial environment are controlled by a complex interplay of physical, biological and anthropogenic factors. Whilst the physical controls exerted on fine sediment dynamics are relatively well-documented, the role of biological processes and their interactions with hydraulic and physico-chemical phenomena has been largely overlooked. The activities of biota, from primary producers to predators, exert strong controls on fine sediment deposition, infiltration and resuspension. For example, extracellular polymeric substances (EPS) associated with biofilms increase deposition and decrease resuspension. In lower energy rivers, aquatic macrophyte growth and senescence are intimately linked to sediment retention and loss, whereas riparian trees are dominant ecosystem engineers in high energy systems. Fish and invertebrates also have profound effects on fine sediment dynamics through activities that drive both particle deposition and erosion depending on species composition and abiotic conditions. The functional traits of species present will determine not only these biotic effects but also the responses of river ecosystems to excess fine sediment. We discuss which traits are involved and put them into context with spatial processes that occur throughout the river network. Whilst strides towards better understanding of the impacts of excess fine sediment have been made, further progress to identify the most effective management approaches is urgently required through close communication between authorities and scientists