Post-fire soil erosion mitigation at the scale of swales using forest logging residues at a reduced application rate

Mulching with forest residues has proved to be highly effective in reducing post-fire soil losses at the plot scale. However, its effectiveness has not been quantified at the application rates that are typically used in operational post-fire land management (2–3 Mg ha^-1 using straw), as well as at scales larger than 100 m². The present study compared post-fire erosion rates for six convergent hillslopes or swales of 500 to 800 m², three of which were left untreated while the other three were mulched immediately after the fire with shredded eucalypt bark at a rate of 2.4 Mg ha^-1. Erosion rates were monitored at irregular intervals during the first three post-fire years, whilst ground cover was assessed yearly. Selected topsoil properties (0–2 cm) such as organic matter content and aggregate stability were determined at a single occasion – two years after the wildfire, for three micro-environments separately: bare soil, and under mulch/litter and vegetation. Soil losses on the untreated swales decreased with post-fire year from 2.2 to 0.4 and 0.11 Mg ha^-1 yr^-1 (respectively for the first, second and third post-fire years), while the mulched swales produced 84%, 77% and 38% less soil losses than the untreated swales. Soil losses also depended on slope aspect, with the north-facing swales producing less erosion than the west-facing ones. This could be linked to their significant differences in bare soil, vegetation and stone cover, or a combination thereof. The type of micro-environment also played a significant role in topsoil properties (stone content, bulk density, resistance to penetration/shear stress, porosity and organic matter content). The present results add to the increasing evidence that forest residues should be duly considered for operational post-fire land management. Forest residues were highly effective in reducing erosion from swales at application rates as low as the typical 2 Mg ha^-1 of post-fire straw mulch. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.     

Seafloor change detection using multibeam echosounder backscatter: case study on the Belgian part of the North Sea

To characterize seafloor substrate type, seabed mapping and particularly multibeam echosounding are increasingly used. Yet, the utilisation of repetitive MBES-borne backscatter surveys to monitor the environmental status of the seafloor remains limited. Often methodological frameworks are missing, and should comprise of a suite of change detection procedures, similarly to those developed in the terrestrial sciences. In this study, pre-, ensemble and post-classification approaches were tested on an eight km² study site within a Habitat Directive Area in the Belgian part of the North Sea. In this area, gravel beds with epifaunal assemblages were observed. Flourishing of the fauna is constrained by overtopping with sand or increased turbidity levels, which could result from anthropogenic activities. Monitoring of the gravel to sand ratio was hence put forward as an indicator of good environmental status. Seven acoustic surveys were undertaken from 2004 to 2015. The methods allowed quantifying temporal trends and patterns of change of the main substrate classes identified in the study area; namely fine to medium homogenous sand, medium sand with bioclastic detritus and medium to coarse sand with gravel. Results indicated that by considering the entire study area and the entire time series, the gravel to sand ratio fluctuated, but was overall stable. Nonetheless, when only the biodiversity hotspots were considered, net losses and a gradual trend, indicative of potential smothering, was captured by ensemble and post-classification approaches respectively. Additionally, a two-dimensional morphological analysis, based on the bathymetric data, suggested a loss of profile complexity from 2004 to 2015. Causal relationships with natural and anthropogenic stressors are yet to be established. The methodologies presented and discussed are repeatable and can be applied to broad-scale geographical extents given that broad-scale time series datasets become available.     

A study of optically featureless objects from the EC Survey: searching for new southern BL Lac objects

In an attempt to discover new southern BL Lac objects, 14 optically featureless objects from the Edinburgh–Cape Survey were selected. Optical polarimetry and spectroscopy, radio and IR observations were carried out in order to improve their classifications. The 14 objects were examined according to special criteria that are described. Their UBV and JHK colour–colour distributions, spectrograms, radio observations and visible-region polarimetry were utilized to conclude that the selected objects are not BL Lacs. Most of them are apparently not extragalactic objects. It is suggested that four of the 14 candidates are DC white dwarfs, one is a QSO, three are DA white dwarfs or sdB subdwarfs, one is a cataclysmic variable, one is a DAO/sdO and another is possibly a DA+dM binary (composite system with a 'primary' hot white dwarf and a 'secondary' M-type main-sequence dwarf) or a cataclysmic variable. One object is likely to be a subdwarf, while two remain unclassifiable.     

Eight new δ Scuti stars

HD 23194, a member of the Pleiades, was found to pulsate with a period of about 30 min. The literature on the star is reviewed, and it is concluded that it may be a marginal Am star in a binary system. HD 95321 is an evolved Am ( ρ Puppis) star with a 5.1-h periodicity. Mode identification of its pulsation, based on multicolour photometry, suggests that the oscillation is probably non-radial with ℓ=2. We also report on the discovery of six other new δ Scuti stars, some of which may be pulsating in gravity modes.     

Long-term waves on Cepheid pulsation period trends

The secular evolution of the pulsation period of δ Cephei, η Aquilae, and ζ Geminorum during a cumulative total of 577 years suggests wave-like departures about the smooth time trends.     

Ecology and fluvial dynamics of an Early Holocene medium‐sized European lowland river valley (Upper Scheldt,northern Belgium)

The fluvial environment of Early Holocene small‐ to middle‐sized lowland rivers in northwest Europe is mostly unstudied due to a lack of preserved and accessible deposits. A rescue excavation in the Scheldt valley in northern Belgium offered the opportunity to study a Boreal alluvial succession in detail. The results of palaeoecological and sedimentological analyses (diatoms, pollen, botanical macro‐remains, molluscs, grain size) characterize the biotic and physical environment in the middle reach of this medium‐sized river system. Although the Early Holocene in the Scheldt Basin has often been portrayed as a period of fluvial stability with marshy conditions and diffuse discharge, this study showed evidence of point bar formation by a small, low‐energy meandering river between ~9.5 and ~8.8 cal. ka BP. The point bar was at least temporarily vegetated and shows a shift from herbaceous riparian vegetation to an open willow‐dominated alluvial forest. This evidence points to a more open vegetation and a more energetic environment than traditionally described for rivers of this size and age. A link to the 9.3 ka BP cooling event is suggested and possible reasons for the scarcity of records of this type of deposits are discussed.     

Quantifying successional land cover after clearing of tropical rainforest along forest frontiers in the Congo Basin

State-of-the-art impact-modeling studies in environmental and climatological sciences require detailed future deforestation scenarios that allow forest to be replaced by a mosaic of multiple successional land-cover types, rather than the simple conversion of forest to a single land-cover type, such as bare soil or cropland. Therefore, not only the amount and location of forest removal has to be known (as is typically provided by scenarios), but also knowledge about the successional land-cover types and their relative areal proportions is needed. The main objective of this study was to identify these successional land-cover types and quantify their areal proportions in regions deforested during the past 37 years around the city of Kisangani, D.R. Congo. The fallow vegetation continuum was categorized in different stages, adapted from existing classifications. Ground-truth points describing the present-day vegetation were obtained during a field campaign and used for supervised and validated land-cover classification of these categories, using the Landsat image of 2012. Areal proportions of successional land-cover types were then derived from the resulting land-cover map. The second objective of this study was to relate these areal proportions to time since deforestation, which is expected to influence fallow landscapes. Landsat images of 1975, 1990, and 2001 were analyzed. Present-day mature tree fallow is less abundant on areas deforested during 1975–1990. The relative areal proportions were used to refine a deforestation scenario and apply it to existing data-sets of LAI and canopy height (CH). Assuming a simple conversion of forest to cropland, the deforestation scenario projected a reduction of grid-cell-averaged CH from 25.5 to 7.5 m (within deforested cells), whereas the refined scenarios that we propose show more subtle changes, with a reduced CH of 13 m. This illustrates the importance of taking successional land cover correctly into account in environmental and climatological modeling studies.     

Post-glacial regional climate variability along the East Antarctic coastal margin—Evidence from shallow marine and coastal terrestrial records

We review the post-glacial climate variability along the East Antarctic coastline using terrestrial and shallow marine geological records and compare these reconstructions with data from elsewhere. Nearly all East Antarctic records show a near-synchronous Early Holocene climate optimum (11.5–9 ka BP), coinciding with the deglaciation of currently ice-free regions and the optimum recorded in Antarctic ice and marine sediment cores. Shallow marine and coastal terrestrial climate anomalies appear to be out of phase after the Early Holocene warm period, and show complex regional patterns, but an overall trend of cooling in the terrestrial records. A Mid to Late Holocene warm period is present in many East Antarctic lake and shallow coastal marine records. Although there are some differences in the regional timing of this warm period, it typically occurs somewhere between 4.7 and 1 ka BP, which overlaps with a similar optimum found in Antarctic Peninsula terrestrial records. The differences in the timing of these sometimes abrupt warm events in different records and regions points to a number of mechanisms that we have yet to identify. Nearly all records show a neoglacial cooling from 2 ka BP onwards. There is no evidence along the East Antarctic coastline for an equivalent to the Northern Hemisphere Medieval Warm Period and there is only weak circumstantial evidence in a few places for a cool event crudely equivalent in time to the Northern Hemisphere's Little Ice Age. There is a need for well-dated, high resolution climate records in coastal East Antarctica and particularly in Terre Adélie, Dronning Maud Land and Enderby Land to fully understand the regional climate anomalies, the disparity between marine and terrestrial records, and to determine the significance of the heterogeneous temperature trends being measured in the Antarctic today.     

A re-assessment of the nearest neighbour alignment of the X-ray isophotes of galaxy clusters

Alignment is defined as the tendency of the distribution of pointing angles between the major axes of clusters and their nearest neighbours to be more concentrated towards small values for small nearest neighbour distances, whereas the distribution is expected to be uniform over all angles at larger distances. Conflicting pronouncements on the reality of this effect have been published in the astronomy literature. A re-assessment of the evidence for alignment is presented, based on three recently published X-ray data sets. We find that whereas there is evidence for alignment, it is not as convincing as previously claimed. In particular, the scale to which the effect has been claimed to extend seems to have been severely overstated.     

Observations of Hipparcos short-period red giant stars

Optical UBV(RI) _C and infrared JHK photometry is presented of a small sample of giant stars with short periods in the Hipparcos catalogue. Observations were limited, but were sufficient to rule out most of the Hipparcos periods. Radial velocity measurement were also made for a few stars, over six successive nights. Low-level variability was detected in a few stars. It is argued that in most cases the brightness variations are primarily due to temperature changes. These findings show that high-overtone pulsations in M giant stars occur, if at all, in a far more limited number of stars than proposed in the authors' previous discussion of the Hipparcos data alone.