Wetland buffers: numerical modeling of wave dissipation by vegetation

The resiliency of coastal communities is imperative because these areas experience risk of damage from coastal storms as well as increasing population pressures and development. The severity of this hazard is compounded by sea level rise and a potential increase in storm intensities due to climate change. The ability of coastal communities to plan for, resist, and quickly and completely recover from severe coastal storm events and flooding is of critical importance. There is a growing interest in applying complementary and redundant approaches to reduce the flood risk of these vulnerable communities, such as incorporating natural and nature‐based features into the project planning process. However, accounting for the benefits of these nature‐based features in coastal design is still challenging. One of the natural features generally acknowledged to offer coastal protection benefits is wetlands. Using laboratory experiments of artificial vegetation as a foundation, the bounds of wave dissipation by vegetation are explored analytically and the effectiveness of wave dissipation by vegetation over large scales is investigated using the spectral wave model STWAVE. Wave heights modeled using a vegetation dissipation formulation are compared to those modeled with the current practice of representing vegetation using bottom friction, particularly the Manning formulation. The vegetation dissipation formulation reduced more wave energy than the Manning bottom friction formulation for submerged wetlands. Because the Manning formulation does not integrate vegetation properties, to achieve consistent results would require varying the Manning n coefficient to account for the spatial and temporal variation in form drag induced by the plants due to changes in plant density, diameter, and degree of plant submergence. Thus, a re‐evaluation of existing methods for assessing wave dissipation by vegetation is recommended for wider application of vegetation dissipation formulations in numerical models. Such models are critical for evaluating coastal resiliency of communities protected by wetland features. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.     

Trilobite tracks and other trace fossils from the Upper Cambrian of North Wales

Trace fossils are recorded from eight localities within Upper Cambrian (Ffestiniog Stage) strata in North Wales. Trilobite furrows (Cruziana), resting impressions (Rusophycus), walking and striding tracks (Diplichnites), sideways grazing tracks (Dimorphichnus) and swimming grazing marks (Monomorphichnus, gen. nov.) are described, largely on the basis of over 500 collected specimens, and are figured together with examples of other trace fossil genera including Rouaultia, Phycodes and Monocraterion. The trilobite traces are used to investigate the varied methods of locomotion of the animais. They also indicate the morphology of some of the trilobite hard and soft parts from which it is inferred that most of these traces were probably made by a population consisting of a small number of closely allied species of trilobites belonging to the Olenid family.     

Climate change adaptation in Australian mining communities: comparing mining company and local government views and activities

Effective climate change adaptation in mining communities is reliant on action by both local authorities and mining operations. This article reports the findings of two surveys conducted in late 2010, with Australian mining companies and local government authorities respectively, investigating their perceptions and activities related to climate change adaptation. The research identified the main types of weather and climate-related impacts experienced in the past and expected under future climate conditions for the two groups. There were significantly differing levels of concern about weather and climate-related impacts between the two types of organisations. Mining company respondents reported lower levels of severity of impact from both past and (expected) future weather events, as well as lower levels of belief in climate change and of adaptation activities to prepare for it. Interestingly, mining companies generally reported less concern about future impacts than those experienced in the past, suggesting discounting of risks due to climate change scepticism. The article reports on a range of factors relevant to adaptation in mining communities, including perceived barriers, collaboration and further information needs. The research findings are discussed in the context of other recent research on climate change adaptation by Australian organisations and studies of mining industry adaptation in other countries.     

Determination of Te,As, Bi,Sb and Se (TABS) in Geological Reference Materials and GeoPT Proficiency Test Materials by Hydride Generation‐Atomic Fluorescence Spectrometry (HG‐AFS)

The study of Te, As, Bi, Sb and Se (TABS) has increased over the past years due to their use in the development of low‐carbon energy technologies. However, there is a scarcity of mass fraction values of TABS in geological reference materials. This underlines the difficulty in undertaking routine determinations of these elements. The mass fractions of TABS were determined in geological reference materials using hydride generation‐atomic fluorescence spectrometry (HG‐AFS), calibrated with standard solutions. Comparisons with literature values were used to validate the method. Samples from the GeoPT proficiency test were also analysed. For most elements, there are no assigned or even provisional values for many of the GeoPT and reference materials because of the wide range of results reported. For mass fractions above the quantification limit of the method, our results are in good agreement with the median of GeoPT results. Thus, we propose GeoPT median values as informational values for these elements. In contrast, at mass fractions < 0.5 µg g^?1 median values of Se from GeoPT are systematically higher than our results. Our Se results are in agreement with the reference materials down to 0.02 µg g^?1, which suggest that many of the results for Se reported in GeoPT testing are too high.     

Spatial Association of Mineral Occurrences and Curvilinear Geological Features

Qualitative and quantitative knowledge about the spatial association between mineral occurrences and geological features are important in mineral potential mapping. Two existing methods for quantifying spatial association between mineral occurrences and curvilinear geological features are applied to the Baguio district of the Philippines. An experimental method is described and applied to the study area as well. The results of the three methods are highly similar, which demonstrates the effectiveness of the experimental method presented here for quantifying spatial association between mineral occurrences and curvilinear geological features. It is shown that gold occurrence in the Baguio district are strongly spatially associated with northeasterly trending faults/fractures rather than with northwesterly trending faults/fractures. It is also shown that the spatial association between the gold occurrence and older batholithic intrusives is stronger than the spatial association between gold occurrence and younger porphyry intrusives. These spatial geoinformation characteristics can be used as evidential data layers in GIS-based mineral potential mapping.     

The Effects of Salinity on Nitrogen Losses from an Oligohaline Estuarine Sediment

Benthic respiration, sediment–water nutrient fluxes, denitrification and dissimilatory nitrate reduction to ammonium (DNRA) were measured in the upper section of the Parker River Estuary from 1993 to 2006. This site experiences large changes in salinity over both short and long time scales. Sediment respiration ranged from 6 to 52 mmol m⁻² day⁻¹ and was largely controlled by temperature. Nutrient fluxes were dominated by ammonium fluxes, which ranged from a small uptake of −0.3 to an efflux of over 8.2 mmol N m⁻² day⁻¹. Ammonium fluxes were most highly correlated with salinity and laboratory experiments demonstrated that ammonium fluxes increased when salinity increased. The seasonal pattern of DNRA closely followed salinity. DNRA rates were extremely low in March, less than 0.1 mmol m⁻² day⁻¹, but increased to 2.0 mmol m⁻² day⁻¹ in August. In contrast, denitrification rates were inversely related to salinity, ranging from 1 mmol m⁻² day⁻¹ during the spring and fall to less than 0.2 mmol m⁻² day⁻¹ in late summer. Salinity appears to exert a major control on the nitrogen cycle at this site, and partially decouples sediment ammonium fluxes from organic matter decomposition.     

Spatiotemporal development of physical,chemical, and biological characteristics of stormwater plumes in Santa Monica Bay,California (USA)

This study characterized stormwater plume development and associated phytoplankton dynamics in a coastal marine ecosystem through shipboard monitoring. We focused on plumes within Santa Monica Bay, California (USA), a coastal system that is subject to rapid pulses of untreated runoff from the urbanized watershed of Los Angeles during the winter rainy season. The physical, chemical, and biological signatures of stormwater plumes were tracked over time after each of 4 precipitation events ranging in magnitude from 1.5 cm to 9 cm. Low salinity surface plumes persisted in Santa Monica Bay for at least 2 to 5 days over spatial scales of up to 15 km. This is consistent with a 6-day residence time for surface water plume parcels, which was estimated from a drifter trajectory in the bay. Shipboard sampling and salinity measurements in the surf zone showed that plumes often persisted even longer nearshore. Plume waters were generally characterized by higher concentrations of dissolved nitrogen, colored dissolved organic matter, and higher light attenuation than non-plume waters. The magnitude of the effect of stormwater runoff on phytoplankton dynamics was dependent on the size of each storm and subsequent residence time of runoff within the bay. Rain events led to increases in primary productivity, phytoplankton biomass, and specifically, increases in diatom biomass, as measured by concentrations of biogenic silica.     

Phosphorus export dynamics and hydrobiogeochemical controls across gradients of scale,topography and human impact

Concentration‐discharge (c‐Q) plots are routinely used as an integrated signal of watershed response to infer solute sources and travel pathways. However, the interpretation of c‐Q data can be difficult unless these data are fitted using statistical models. Such models are frequently applied for geogenic solutes, but it is unclear to what extent they might aid in the investigation of nutrient export patterns, particularly for total dissolved phosphorus (TDP) which is a critical driver of downstream eutrophication problems. The goal of the present study was therefore to statistically model c‐Q relations (where c is TDP concentrations) in a set of contrasting watersheds in the Northern Great Plains—ranging in size from 0.2 to 1000+ km²—to assess the controls of landscape properties on TDP transport dynamics. Six statistical models were fitted to c‐Q data, notably (a) one linear model, (b) one model assuming that c‐Q relations are driven by the mixing of end‐member waters from different landscape locations (i.e., hydrograph separation), (c) one model relying on a biogeochemical stationarity hypothesis (i.e., power law), (d) one model hypothesizing that c‐Q relations change as a function of the solute subsurface contact time (i.e., hyperbolic model), and (e) two models assuming that solute fluxes are mostly dependent on reaction rates (i.e., chemical models). Model performance ranged from mediocre (R² < 0.2) to very good (R² > 0.9), but the hydrograph separation model seemed most universal. No watershed was found to exhibit chemostatic behaviour, but many showed signs of dilution or enrichment behaviour. A tendency toward a multi‐model fit and better model performance was observed for watersheds with moderate slope and higher effective drainage area. The relatively poor model performance obtained outside these conditions illustrates the likely importance of controls on TDP concentrations in the region that are independent of flow dynamics.     

Geochemistry of mafic dykes in the Antarctic Peninsula continental-margin batholith: a record of arc evolution

Mafic dykes of the Antarctic Peninsula continental-margin arc are compositionally diverse, comprising calc-alkaline (dominant), shoshonite, tholeiite, and OIB-like varieties. Their compositions give information about different mafic magma sources tapped during arc evolution. The compositional groups represent partial melts of at least five distinct mantle sources: a low-ɛNd subduction-modified, garnet-bearing, lithospheric mantle (older calc-alkaline); a high-ɛNd subduction-modified, garnet-bearing, lithospheric mantle (shoshonites); a high-ɛNd subduction-modified, spinel-bearing, asthenospheric mantle (younger calc-alkaline); E-MORB-like spinel-bearing asthenosphere depleted by a previous melting event (tholeiites); and within-plate non-subduction modified, garnet- and spinel-bearing, asthenosphere (OIB-like). Slab-derived fluids, subducted sediment, and arc crust also contributed to the magmas. Consideration of previous work in the light of our new compositional and geochronological data enables presentation of a summary of arc evolution. For most of the Cretaceous and Tertiary, the tectonic regime of the Antarctic Peninsula arc was transtensional, and calc-alkaline magmas intruded. An oceanic spreading centre collided with the trench during the Late Cretaceous and induced tectonic changes which caused tapping of different magma sources. A pulse of shoshonitic, tholeiitic, and OIB-like mafic magmatism resulted. Three ridge-trench collisions are now recognized during the history of the arc, in Mid–Late Jurassic, Late Cretaceous, and Early–Mid Tertiary times. Received: 13 January 1997 / Accepted: 5 December 1997