An accurate representation of the particle organic matter (POM) footprint is necessary in order to effectively predict impacts upon benthic communities and the risk of excessive organic enrichment ...beneath aquaculture sea-cages. Consequently, bottom-related processes such as particle resuspension must be adequately parametrized and evaluated in the available numerical models. We implemented two approaches to model POM resuspension in a Lagrangian particle tracking model and compared their influence on footprint extension and gradients of depositional flux against a no-resuspension scenario. We performed simulations in both exposed and protected aquaculture locations, and at different stages of the Atlantic Salmon (Salmo salar) production cycle in Norway. Our results indicate that the use of sediment-dependent thresholds for resuspension has the potential to regulate the high levels of erosion produced when selecting a low critical value in constant-threshold approaches, particularly in dynamic environments with mixed sediment types.
•Resuspension influences the extent of the organic footprint in salmon fish farming.•Substrate type must be considered when defining resuspension thresholds.•Far-field effects can be obscured by the use of a unfitting resuspension approach.
The present work provides a literature survey of elastic scattering of exotic nuclei from
6He to
17F. It presents a set of definitions that allow different analyses to be put into a common language. ...A calculational approach is proposed that yields consistent results across different beams and targets so that conclusions concerning the influence of virtual and real breakup as well as transfer couplings on the elastic scattering may be drawn. Calculations of elastic scattering around the Coulomb barrier are emphasised, employing a Pb target whose large
Z
allows the interplay between nuclear and Coulomb forces to be exploited to maximise possible effects arising from proton or neutron haloes or skins. A series of test calculations is performed and where possible compared to data, demonstrating that there are instances where coupling to transfer channels can have a large effect on the elastic scattering angular distributions. By careful choice of target/beam combination, different aspects of the coupling effects may be emphasised.
Assessing the environmental impact of salmon farms on benthic systems is traditionally undertaken using biotic indices derived from microscopic analyses of macrobenthic infaunal (MI) communities. In ...this study, we tested the applicability of using foraminiferal-specific high-throughput sequencing (HTS) metabarcoding for monitoring these habitats. Sediment samples and physico-chemical data were collected along an enrichment gradient radiating out from three Chinook salmon (Oncorhynchus tshawytscha) farms in New Zealand. HTS of environmental DNA and RNA (eDNA/eRNA) resulted in 1,875,300 sequences that clustered into 349 Operational Taxonomic Units. Strong correlations were observed among various biotic indices calculated from MI data and normalized fourth-root transformed HTS data. Correlations were stronger using eRNA compared to eDNA data. Quantile regression spline analyses identified 12 key foraminiferal taxa that have potential to be used as bioindicator species. This study demonstrates the huge potential for using this method for biomonitoring of fish-farming and other marine industrial activities.
•Foraminiferal metabarcoding is a cost-effective tool for monitoring environmental impacts of fish farming.•Metabarcoding data correlate strongly with traditional biotic indices derived from macrobenthic infaunal community data.•Correlations are stronger using eRNA compared to eDNA data.•Quantile regression spline analysis identifies 12 key foraminiferal taxa that have potential to be used as bioindicator species.
A recent new expression for the Coulomb dipole polarization potential (CDPP) is applied to different cluster structures of
6
He and
8
He. The CDPPs are used to compare the effect of breakup coupling ...on the elastic scattering of these projectiles from a
208
Pb target at incident energies of 16 and 14 MeV, below the Coulomb barrier. None of the cluster structures investigated for
8
He gives a significant CDPP, supporting previous inferences that breakup coupling is much less important for
8
He than for
6
He at energies close to the Coulomb barrier, despite the significantly larger absorption observed in the measured
8
He elastic scattering at 16 MeV compared to that for
6
He. Coupled reaction channels calculations of the 1
n
stripping reaction indicate a much enhanced role for this reaction in the elastic scattering of
8
He compared to
6
He, alone sufficient to account for the observed significant deviation from Rutherford scattering for
8
He +
208
Pb elastic scattering even at this sub-barrier energy.
The present understanding of reaction processes involving light unstable nuclei at energies around the Coulomb barrier is reviewed. The effect of coupling to direct reaction channels on elastic ...scattering and fusion is investigated, with the focus on halo nuclei, for which such effects are expected to be most important. With the aim of resolving possible ambiguities in the terminology a short list of definitions for the relevant processes and quantities is proposed. This is followed by a review of the experimental and theoretical tools and information presently available. The effect of breakup couplings on elastic scattering and of transfer couplings on fusion is investigated with a series of model calculations within the coupled-channels framework. The experimental data on fusion are then compared to ‘bare’ no-coupling one-dimensional barrier penetration model calculations employing reasonably realistic double-folded potentials. On the basis of these model calculations and comparisons with experimental data, conclusions are drawn from the observation of recurring features. The total fusion cross-sections for halo nuclei show a suppression with respect to the ‘bare’ calculations at energies just above the barrier that is probably due to single neutron transfer reactions. The data for total fusion are also consistent with a possible sub-barrier enhancement; however, this observation is not conclusive and other couplings besides the single-neutron channels would be needed in order to explain any actual enhancement. We find that a characteristic feature of halo nuclei is the dominance of direct reactions over fusion at near and sub-barrier energies; the main part of the cross-section is related to neutron transfers, while calculations indicate only a modest contribution from the breakup process.
A recent comparison of the average fusion cross section,
σ
F
, for energies just above the Coulomb barrier for the
12
-
15
C +
12
C systems found that the behaviour as a function of projectile ...neutron excess could not be satisfactorily explained by static barrier penetration model calculations and suggested that the neutron dynamics plays an important rôle. In this work we demonstrate that the (
15
C,
14
C) single neutron transfer has a significant influence on the above barrier
15
C +
12
C total fusion, although not quite in the way expected since it leads to a reduction in the cross section, contrary to the trend in the measured
σ
F
. However, this result underlines the danger of ignoring the effect of neutron transfer reactions on fusion in systems involving neutron halo nuclei.
While it is well established that the ground state reorientation coupling can have a significant influence on the elastic scattering of deformed nuclei, the effect of such couplings on transfer ...channels has been much less well investigated. In this letter we demonstrate that the
208
Pb
(
7
Li
,
6
He
)
209
Bi
proton stripping reaction at an incident energy of 52 MeV can be well described by the inclusion of the
7
Li
ground state reorientation coupling within the coupled channels Born approximation formalism. Full finite-range distorted wave Born approximation calculations were previously found to be unable to describe these data. Addition of coupling to the 0.478-MeV
1
/
2
-
excited state of
7
Li
, together with the associated two-step transfer path, has little or no influence on the shape of the angular distributions (except that for stripping leading to the 1.61-MeV
13
/
2
+
level of
209
Bi
which is significantly improved) but does affect appreciably the values of the
209
Bi
→
208
Pb
+
p
spectroscopic factors. Implications for experiments with weakly-bound light radioactive beams are discussed.
A modern variation of the Rutherford experiment to probe the tunneling of exotic nuclear matter from the measurement of the residues formed in the bombardment of (197)Au by extremely neutron-rich ...(8)He nuclei is presented. Using a novel off-beam technique the most precise and accurate measurements of fusion and neutron transfer involving reaccelerated unstable beams are reported. The results show unusual behavior of the tunneling of (8)He compared to that for lighter helium isotopes, highlighting the role of the intrinsic structure of composite many-body quantum systems and pairing correlations.
Accurate elastic scattering angular distribution data measured at bombarding energies just above the Coulomb barrier have shapes that can markedly differ from or be the same as the expected classical ...Fresnel scattering pattern depending on the structure of the projectile, the target or both. Examples are given such as
18
O +
184
W and
16
O +
148, 152
Sm, where the expected rise above Rutherford scattering due to Coulomb-nuclear interference is damped by coupling to the target excited states, and the extreme case of
11
Li scattering, where coupling to the
9
Li +
n
+
n
continuum leads to an elastic scattering shape that cannot be reproduced by any standard optical model parameter set. An early indication that the projectile structure can modify the elastic scattering angular distribution was the large vector analyzing powers observed in polarised
6
Li scattering. The recent availability of high-quality
6
He,
11
Li and
11
Be data provides further examples of the influence that coupling effects can have on elastic scattering. Conditions for strong projectile-target coupling effects are presented with special emphasis on the importance of the beam-target charge combination being large enough to bring about the strong coupling effects. Several measurements are proposed that can lead to further understanding of strong coupling effects by both inelastic excitation and nucleon transfer on near-barrier elastic scattering. A final note on the anomalous nature of
8
B elastic scattering is presented as it possesses a more or less normal Fresnel scattering shape whereas one would
a priori
not expect this due to the very low breakup threshold of
8
B . The special nature of
11
Li is presented as it is predicted that no matter how far above the Coulomb barrier the elastic scattering is measured, its shape will not appear as Fresnel like whereas the elastic scattering of all other loosely bound nuclei studied to date should eventually do so as the incident energy is increased, making both
8
B and
11
Li truly “exotic”.
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