Restriction of sponges to an atoll lagoon as a result of reduced environmental quality

The lagoon at Palmyra Atoll in the central Pacific was subject to major military modifications during WWII and now the dominant fauna on the lagoon’s hard substrate are sponges, not corals. In this study, we quantified the physical and biological factors explaining the variation in sponge distribution patterns across 11 sites to determine the potential for the sponges in the lagoon at Palmyra to invade the surrounding reef systems. Significant differences in sponge assemblages were found among all but three sites. For all the models we examined the strongest environmental relationships were found for variables related to sedimentation/turbidity and food/habitat availability. Our findings suggest that the sponges in Palmyra’s lagoon are likely to be restricted to this habitat type where they are associated with conditions resulting from the earlier heavy disturbance and are unlikely to spread to the outer reef environments unless there is a dramatic decline in environmental quality.     

The Potential of Virtual Reality Technology for Analysis of Remotely Sensed Data: A Lidar Case Study

Abstract

Although the GIS community has been quick to exploit the advantages of virtual reality (VR) for display and analysis of spatial data, VR does not appear to have been exploited widely for remote sensing data analysis. A case study of high resolution lidar data acquired over a deciduous forest near Morgantown, WV was used to investigate the potential and limitations of current VR software for remote sensing analysis. The functionality within a standard remote sensing software package was found to provide a good overview of interpolated, smoothed lidar data, but was less useful for gridded data that had not been interpolated. With gridded data, it was possible to drape orthophotographs or other images over the lidar data, providing a useful method for investigating relationships between lidar and other data. Alternatively, using a commercial VR package, it was possible to view the original lidar point data, and thus visualize the multiple returns from within the canopy of each tree. The point data were preferable for identification of surfaces within the data cloud, especially the ground surface. For a fully integrated remote sensing VR package, functionality will be needed to link point and interpolated coverages, and also to enhance the interactive selection of data for further statistical analysis.     

EVALUATION OF BOTANICAL METHODS OF DATING DEBRIS FLOWS AND DEBRIS-FLOW HAZARD IN THE CANADIAN ROCKY MOUNTAINS

The vegetation on debris flow deposits is examined at seven sites in the Canadian Rocky Mountains. Plant cover, colonizing tree ages, species' presence and abundance, and new stem ages on buried willows are vegetation parameters evaluated for the purpose of dating debris flows. The results indicate that general trends of vegetation development on debris flow deposits can be used to date recent events, at least relatively. The use of several methods to corroborate estimations of deposit age is usually necessary. An optimal approach is to combine absolute and relative dating techniques in evaluating debris flow occurrence, extent, and potential hazard.     

Reconstruction of the most recent volcanic eruptions from the Valles caldera,New Mexico

Products of the latest eruptions from the Valles caldera, New Mexico, consist of the El Cajete Pyroclastic Beds and Battleship Rock Ignimbrite, a sequence of pyroclastic fall and density current deposits erupted at ~ 55 ka, capped by the later Banco Bonito Flow erupted at ~ 40 ka, and collectively named the East Fork Member of the Valles Rhyolite. The stratigraphy of the East Fork Member has been the subject of conflicting interpretations in the past; a long-running investigation of short-lived exposures over a period of many years enables us to present a more complete event stratigraphy for these eruptions than has hitherto been possible. The volume of rhyolitic magma erupted during the 55 ka event may have been more than 10 km³, and for the 40 ka event can be estimated with rather more confidence at 4 km³. During the earlier event, plinian eruptions dispersed fallout pumice over much of the Valles caldera, the southern Jemez Mountains, and the Rio Grande rift. We infer a fallout thickness of several decimeters at the site of the city of Santa Fe, and significant ash fall in eastern New Mexico. In contrast, pyroclastic density currents were channeled within the caldera moat and southwestward into the head of Cañon de San Diego, the principal drainage from the caldera. Simultaneous (or rapidly alternating) pyroclastic fallout and density current activity characterized the ~ 55 ka event, with density currents becoming more frequent as the eruption progressed through two distinct stages separated by a brief hiatus. One early pyroclastic surge razed a forest in the southern caldera moat, in a similar manner to the initial blast of the May 18, 1980 eruption of Mt. St. Helens. Ignimbrite outflow from the caldera through the drainage notch may have been restricted in runout distance due to steep, rugged topography in this vicinity promoting mixing between flows and air, and the formation of phoenix clouds. Lavas erupted during both the ~ 55 and ~ 40 ka events were largely confined to the caldera moat. Any future rhyolitic eruptions of similar magnitude in the southern or western parts of the Valles caldera will likely affect similar areas.     

Bubble nucleation in rhyolite and dacite melts: temperature dependence of surface tension

Surface tension (σ) profoundly influences the ability of gas bubbles to nucleate in silicate melts. To determine how temperature impacts σ, experiments were carried out in which high-silica rhyolite melts with 5 wt% dissolved water were decompressed at temperatures that ranged from 775 to 1,085°C. Decompressions were also carried out using dacite melts with 4.3 wt% dissolved water at 1,150°C. Water bubbles nucleated in rhyolite only when decompressions exceeded 95 MPa at all temperatures. Bubbles nucleated in number densities that increased as decompression increased and at hotter temperatures at a given amount of decompression. After correcting decompression amounts for temperature differences, values for σ were estimated from nucleation rates and found to vary between 0.081 and 0.093 N m⁻¹. Surface tension decreases as temperature increases from 775 to 875°C, but then increases as temperature increases to 1,085°C. Those values overlap previous results, but only when melt viscosity is less than 10⁴ Pa s. For low-viscosity rhyolite, there is a strong correlation of σ with temperature, in which σ increases by 6.9 × 10⁻⁵ N m⁻¹ C⁻¹. That variation is robust for 5–9 wt% dissolved water, as long as melt viscosity is ≤10⁴ Pa s. More viscous rhyolite deviates from that correlation probably because nucleation is retarded in stiffer melts. Bubbles nucleated in dacite when decompressions exceeded 87 MPa, and occured in one or more events as decompression increased. Surface tension is estimated to be 0.083 (±0.001) N m⁻¹ and when adjusted for temperature agrees well with previous results for colder and wetter dacite melts. At a given water content, dacite melts have lower surface tensions than rhyolite melts, when corrected to a fixed temperature.     

Application of the littoral cell concept to managing a protected atoll: Palmyra Atoll National Wildlife Refuge

The recognition of littoral sediment cells has proven valuable to coastal zone management in many areas of the world because it emphasises that sediment transport and deposition relate to physical processes rather than to administrative boundaries and that sedimentary units are self-contained. To date, cells identified for shoreline management planning are often extensive, extending for tens to hundreds of km. We suggest that the concept is also applicable to the management of atoll coastlines which, although spatially very small overall, consist of isolated segments with efficient intervening sediment sinks. As an example, Palmyra Atoll, a protected wildlife refuge in the northern Line Islands, is undergoing natural major changes resulting from sediment-related processes. Defining sediment cells as integral parts of management units here will aid decision-making necessary for the protection of specific areas, potentially giving savings in research effort and remedial costs and minimising disruption to other sensitive areas of the reserve. Similar benefits would apply to the management of the coastlines of other atolls.     

Land cover effects on soil infiltration capacity measured using plot scale rainfall simulation in steep tropical lowlands of Central Panama

Understanding land use/land cover (LULC) effects on tropical soil infiltration is crucial for maximizing watershed scale hydro-ecosystem services and informing land managers. This paper reports results from a multiyear investigation of LULC effects on soil bulk infiltration in steep, humid tropical, and lowland catchments. A rainfall simulator applied water at measured rates on 2 × 6 m plots producing infiltration through structured, granulated, and macroporous Ferralsols in Panama's central lowlands. Time-lapse electrical resistivity tomography (ERT) helped to visualize infiltration depth and bulk velocity. A space-for-time substitution methodology allowed a land-use history investigation by considering the following: (a) a continuously heavy-grazed cattle pasture, (b) a rotationally grazed traditional cattle pasture, (c) a 4-year-old (y.o.) silvopastoral system with nonnative improved pasture grasses and managed intensive rotational grazing, (d) a 7 y.o. teak (Tectona grandis) plantation, (e) an approximately 10 y.o. secondary succession forest, (f) a 12 y.o. coffee plantation (Coffea canephora), (g) an approximately 30 y.o. secondary succession forest, and (h) a >100 y.o. secondary succession forest. Within a land cover, unique plot sites totalled two at (a), (c), (d), (e), and (g); three at (b); and one at (f) and (h). Our observations confirmed measured infiltration scale dependency by comparing our 12 m² plot-scale measurements against 8.9 cm diameter core-scale measurements collected by others from nearby sites. Preferential flow pathways (PFPs) significantly increased soil infiltration capacity, particularly in forests greater than or equal to 10 y.o. Time-lapse ERT observations revealed shallower rapid bulk infiltration and increased rapid lateral subsurface flow in pasture land covers when compared with forest land covers and highlighted how much subsurface flow pathways can vary within the Ferralsol soil class. Results suggest that LULC effects on PFPs are the dominant mechanism by which LULC affects throughfall partitioning, runoff generation, and flow pathways.     

Dark matter subhaloes in numerical simulations

We use cosmological Λ cold dark matter (CDM) numerical simulations to model the evolution of the substructure population in 16 dark matter haloes with resolutions of up to seven million particles within the virial radius. The combined substructure circular velocity distribution function (VDF) for hosts of 10¹¹ to  10¹⁴ M_⊙  at redshifts from zero to two or higher has a self-similar shape, is independent of host halo mass and redshift, and follows the relation  d n /d v = (1/8)( v _cmax/ v _cmax,host)⁻⁴  . Halo to halo variance in the VDF is a factor of roughly 2 to 4. At high redshifts, we find preliminary evidence for fewer large substructure haloes (subhaloes). Specific angular momenta are significantly lower for subhaloes nearer the host halo centre where tidal stripping is more effective. The radial distribution of subhaloes is marginally consistent with the mass profile for   r ≳ 0.3 r _vir  , where the possibility of artificial numerical disruption of subhaloes can be most reliably excluded by our convergence study, although a subhalo distribution that is shallower than the mass profile is favoured. Subhalo masses but not circular velocities decrease towards the host centre. Subhalo velocity dispersions hint at a positive velocity bias at small radii. There is a weak bias towards more circular orbits at lower redshift, especially at small radii. We additionally model a cluster in several power-law cosmologies of   P ∝ kⁿ   , and demonstrate that a steeper spectral index, n , results in significantly less substructure.     

Episodic intraplate deformation of stable continental margins: evidence from Late Neogene and Quaternary marine terraces,Cape Liptrap,Southeastern Australia

The Waratah Fault is a northeast trending, high angle, reverse fault in the Late Paleozoic Lachlan Fold Belt at Cape Liptrap on the Southeastern Australian Coast. It is susceptible to reactivation in the modern intraplate stress field in Southeast Australia and exhibits Late Pliocene to Late Pleistocene reactivation. Radiocarbon, optically stimulated luminescence (OSL), and cosmogenic radionuclide (CRN) dating of marine terraces on Cape Liptrap are used to constrain rates of displacement across the reactivated Waratah Fault. Six marine terraces, numbered Qt₆–Tt₁ (youngest to oldest), are well developed at Cape Liptrap with altitudes ranging from ～1.5 m to ～170 m amsl, respectively. On the lowest terrace, Qt₆, barnacles in wave-cut notches ～1.5 m amsl, yielded a radiocarbon age of 6090–5880 Cal BP, and reflect the local mid-Holocene sea level highstand. Qt₅ yielded four OSL ages from scattered locations around the cape ranging from ～80 ka to ～130 ka. It formed during the Last Interglacial sea level highstand (MIS 5e) at ～125 ka. Inner edge elevations (approximate paleo high tide line) for Qt₅ occur at distinctly different elevations on opposite sides of the Waratah Fault. Offsets of the inner edges across the fault range from 1.3 m to 5.1 m with displacement rates ranging from 0.01 mm/a to 0.04 mm/a. The most extensive terrace, Tt₄, yielded four Early Pleistocene cosmogenic radionuclide (CRN) ages: two apparent burial ages of 0.858 Ma ± 0.16 Ma and 1.25 Ma ± 0.265 Ma, and two apparent exposure ages of 1.071 Ma ± 0.071 Ma (¹⁰Be) and 0.798 Ma ± 0.066 Ma (²⁶Al). Allowing for muonic production effects from insufficient burial depths, the depth corrected CRN burial ages are 1.8 Ma ± 0.56 Ma and 2.52 Ma ± 0.88 Ma, or Late Pliocene. A Late Pliocene age is our preferred age. Offsets of Tt₄ across the Waratah Fault range from a minimum of ～20 m for terrace surface treads to a maximum of ～70 m for terrace bedrock straths. Calculated displacement rates for Tt₄ range from 0.01 mm/a to 0.04 mm/a (using a Late Pliocene age, ～2 Ma), identical to the rates calculated for the Last Interglacial terrace, Qt₅. This indicates that deformation at Cape Liptrap has been ongoing at similar time-averaged rates at least since the Late Pliocene. The upper terraces in the sequence, Tt₃ (～110 m amsl), Tt₂ (～140 m) and Tt₁ (～180 m) are undated, but most likely correlate to sea level highstands in the Neogene. Terraces Tt1–Tt4 show an increasing northward tilt with age.The Waratah Fault forms a prominent structural boundary in the Lachlan Fold Belt discernible from airborne magnetic and bouger gravity anomalies. Seismicity and deformation are episodic. Episodic movement on the Waratah Fault may be coincident with sea level highstands since the Late Pliocene, possibly from increased loading and elevated pore pressure within the fault zone. This suggests that intervals between major seismic events could be on the order of 100 ka.