Pilot assessment of depth related distribution of macrofauna in surf zone along Dutch coast and its implications for coastal management

Surf zones are highly dynamic, physically stressful parts of sandy beach ecosystems. The high wave energy of surf zones has in the past severely hampered ecological surveys of these systems. Here we used a novel technique to collect fauna from this environment along the Dutch coast. A large vehicle in the form a tripod that drives along the sandy seafloor and supports a sampling platform 11 m above the water line can collect both infaunal (grabs) samples and pull beam trawls for epibenthos. The distribution and diversity of macrofauna were studied at different depths in the surf zone along the Dutch coast. Species diversity and abundance increased with increasing depth of the water column. This increase was especially noticeable on the seaward side of the outer breaker bar. Within the surf zone, in the trough between the two breaker bars, there were spots of high diversity and abundance of macrobenthic infauna. Moreover, the area is also important for epibenthic and fish species, like the commercially important flatfish sole. Spatial patterns of species richness and abundance across an onshore-offshore gradient from the beach to seawards of the breakers suggest the presence of faunal zonation in this environment. The high abundance recorded in troughs was primarily caused by patches of juvenile Sand mason Lanice conchilega. The management implications of these results are that we suggest to protect the surf zone, including the trough between the two breaker bars, as a potential area of high diversity and abundance and to reconsider the objectives of the EU-Habitat Directive and the Water Framework Directive for the coastal area.     

Hydraulics of interrill overland flow on rough,bare soil surfaces

A set of laboratory experiments on bare, rough soil surfaces was carried out to study the relationship between soil surface roughness and its hydraulic resistance. Existing models relating roughness coefficients to a measure of surface roughness did not predict the hydraulic resistance well for these surfaces. Therefore, a new model is developed to predict the hydraulic resistance of the surface, based on detailed surface roughness data. Roughness profiles perpendicular to the flow are used to calculate the wet cross‐sectional area and hydraulic radius given a certain water level. The algorithm of Savat is then applied to calculate the hydraulic resistance. The value for the equivalent roughness, which is used in the algorithm of Savat, could be predicted from the roughness profiles. Here, the tortuosity of the submerged part of the surface was used, which means that the calculated roughness depends on flow depth. The roughness increased with discharge, due to the fact that rougher parts of the surface became submerged at higher discharges. Therefore, a single measure of surface roughness (e.g. random roughness) is not sufficient to predict the hydraulic resistance. The proposed model allows the extension of the flow over the surface with increasing discharge to be taken into account, as well as the roughness within the submerged part of the surface. Therefore, the model is able to predict flow velocities reasonably well from discharge and roughness data only. Copyright © 2000 John Wiley & Sons, Ltd.     

Species selection and assessment of eco-engineering effects of seedlings for biogeomorphological landscape experiments

Landscape experiments of fluvial environments such as rivers and deltas are often conducted with live seedlings to investigate effects of biogeomorphological interactions on morphology and stratigraphy. However, such experiments have been limited to a single species, usually alfalfa (Medicago sativa), whereas important environments in nature have many different vegetation types and eco-engineering effects. Landscape experimentation would therefore benefit from a larger choice of tested plant species. For the purpose of experimental design our objective was to identify fast-germinating and fast-growing species and determine their sensitivity to flow conditions during and after settling, their maximum growth, hydraulic resistance and added bank strength. We tested germination time and seedling growth rate of 18 candidate species with readily available seeds that are fast growing and occur at waterlines, plus Medicago sativa as a control. We selected five species that germinate and develop within days and measured properties and eco-engineering effects depending on plant age and density, targeting typical experimental conditions of 0–0.3 m/s flow velocity and 0–30 mm water depth. Tested eco-engineering effects include bank strength and flow resistance. We found that Rumex hydrolapathum can represent riparian trees. The much smaller Veronica beccabunga and Lotus pedunculatus can represent grass and saltmarsh species as they grow in dense patches with high flow resistance but are readily erodible. Sorghum bicolor grows into tall, straight shoots, which add significantly to bank strength, but adds little flow resistance and may represent sparse hardwood trees. Medicago sativa also grows densely under water, suggesting a use for mangroves and perhaps peat. In stronger and deeper flows the application of all species changes accordingly. These species can now be used in a range of landscape experiments to investigate combined effects on living landscape patterns and possible facilitation between species. The testing and treatment methodology can be applied to new species and other laboratory conditions. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd. © 2019 The Authors Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd © 2019 The Authors Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.     

Hydromagnetic stability of coronal arcade structures: The effects of photospheric line tying

A model is given of the magnetic-field equilibrium and possible dynamic excitations of a solar coronal arcade. Such structures are well observed in the spectral range from H to X-rays and often give rise to two-ribbon flares. However, the preflare state must be stable to ideal magnetohydrodynamic disturbances, and we treat this problem with particular attention to the necessary foot-point boundary conditions. Having devised a reasonably general perturbation set, we use an energy-principle analysis to show the strong stabilizing influence of inertial field-line tying at the photosphere.Address from October 1981: Tata Institute of Fundamental Research, Homi Bhabha Road, Bombay 400005, India.     

Sodium fluoride ion-pairs in seawater

Laboratory investigations were conducted on the formation of NaF° ion-pairs at the ionic strength of seawater using specific ion electrodes. Sodium and fluoride ion electrodes produced results which are consistent with the ion-pairing model for these ionic interactions. The stoichiometric association constant for NaF°, $\text{K}{}^1{}_{\mathrm{<mtext>NaF</mtext>}}$, was determined at 15, 25, and 35°C. It was assumed that $\text{K}{}^1{}_{\mathrm{<mtext>NaF</mtext>}}$ was a function of temperature, pressure, and ionic strength but not of solution composition. The value for $\text{K}{}^1{}_{\mathrm{<mtext>NaF</mtext>}}$ at 25°C and I = 0.7 m is 0.045 ± 0.006. $\text{K}{}^1{}_{\mathrm{<mtext>NaF</mtext>}}$ increased with decreasing temperature. This result was used to recompute values of $\text{K}{}^1{}_{\mathrm{<mtext>MgF</mtext>}}$ and $\text{K}{}^1{}_{\mathrm{<mtext>CaF</mtext>}}$ accounting for the presence of NaF° ion-pairs. The value for $\text{K}{}^1{}_{\mathrm{<mtext>NaF</mtext>}}$ indicates that 1.1% of the fluoride in seawater is ion-paired with sodium at 25°C and 35‰ salinity. This fraction increases to approximately 2% at the lower temperatures found in the deep ocean. The percentage of free fluoride in natural seawater was measured at 15, 25, and 35°C to verify the speciation calculated from equilibrium constants.     

The response of soil erosion and sediment export to land-use change in four areas of Europe: The importance of landscape pattern

The response of erosion and sediment export to past land-use change has been studied in four agricultural areas of Europe. Three of these areas were subject to land abandonment or de-intensification and one to intensification of land-use practices. Erosion and sediment yield were modeled using the WaTEM/SEDEM model, which combines the RUSLE equation with a sediment routing algorithm. Spatial relationships between the RUSLE C-factor (i.e. land-use) and other erosion and sediment export-determining factors (slope, soil erodibility and distance to rivers) were investigated, as these account for non-linearity in the response of erosion and sediment export to land-use change.Erosion and sediment export have decreased enormously in the de-intensified areas, but slightly increased in the intensively cultivated area. The spatial pattern of land-use change in relation to other erosion and sediment export-determining factors appears to have a large impact on the response of soil erosion and sediment export to land-use change. That the drivers of abandonment of arable land and erosion coincide indicates that de-intensification leads to a more favourable landscape pattern with respect to reduction of erosion and sediment export. This mechanism applies not only within the study areas, but also among the European study areas where the process of intensification of some areas and de-intensification of others might result in an overall decrease of erosion and sediment yield through time.     

Automated Analyte Separation by Ion Chromatography Using a Cobot Applied to Geological Reference Materials for Li Isotope Composition

The demand for large and reliable data sets on isotopic composition has increased in geochemistry and environmental sciences over recent years. We present an automated ion chromatographic separation method using a robotic pipetting arm, termed ‘ChemCobOne’, to reduce sample separation time. Its performance was tested for lithium isotope separation in geological reference materials using a single‐step separation with HCl (0.2 mol l^?1) and a 2 ml resin volume. This refined lithium purification method does not forfeit precision, accuracy or purity compared with manual sample processing. In addition, a δ⁷Li value for NASS‐6 of 30.99 ± 0.50‰ (2s) (95% CI = 0.14‰, n = 44) was determined and the first δ⁷Li values for the granite rock reference material GS‐N (?0.57 ± 0.25‰ (2s), 95% CI = 0.15‰, n = 15), and for the soil reference material NIST SRM 2709a (?0.37 ± 0.67‰ (2s), 95% CI = 0.15‰, n = 63) are proposed.     

Evaluating approximations for halo merging histories

We study the merging history of dark matter haloes in N -body simulations and semi-analytical 'merger trees' based on the extended Press–Schechter (EPS) formalism. The main focus of our study is the joint distribution of progenitor number and mass as a function of redshift and parent halo mass. We begin by investigating the mean quantities predicted directly by the Press–Schechter (PS) and EPS formalism, such as the halo mass and conditional mass functions, and compare these predictions with the results of the simulations. The higher moments of this distribution are not predicted by the EPS formalism alone and must be obtained from the merger trees. We find that the Press–Schechter model deviates from the simulations at the level of 30–50 per cent on certain mass scales, and that the sense of the discrepancy changes as a function of redshift. We show that this discrepancy is reflected in the higher moments of the distribution of progenitor mass and number. We investigate some related statistics such as the accretion rate and the mass ratio of the largest two progenitors. For galaxy sized haloes ( M ∼10¹² M_⊙), we find that the merging history of haloes, as represented by these statistics, is well reproduced in the merger trees compared with the simulations. The agreement deteriorates for larger mass haloes. We conclude that merger trees based on the extended Press–Schechter formalism provide a reasonably reliable framework for semi-analytical models of galaxy formation.     

Formation temperatures of clays from the volcaniclastic series of Site 841 ODP: an oxygen isotopic record of a paleothermal flux into the Tonga forearc

Oxygen isotopic compositions of clay minerals were determined on representative samples of the volcano-sedimentary series from Site 841 ODP (Tonga forearc). This isotopic study has demonstrated an abnormally high crystallisation temperature of the clay minerals with respect to temperature expected in burial diagenesis. Formation temperatures obtained using ¹⁸O reach up to 200 °C in a Fe-chlorite-corrensite paragenesis found in the vicinity of basaltic andesite sills intruded into the Miocene tuffs. The paleothermal flux resulting from the cooling of the sills has produced very low grade contact metamorphism in the Miocene Tonga forearc deposits. The consequence of this was the formation of a large amount of hydrous silicates characterised near the sills by a Fe-clays-analcime mineralogical association. Received: 26 September 1997 / Accepted: 22 September 1998