Linking the Abundance of Estuarine Fish and Crustaceans in Nearshore Waters to Shoreline Hardening and Land Cover

Human alteration of land cover (e.g., urban and agricultural land use) and shoreline hardening (e.g., bulkheading and rip rap revetment) are intensifying due to increasing human populations and sea level rise. Fishes and crustaceans that are ecologically and economically valuable to coastal systems may be affected by these changes, but direct links between these stressors and faunal populations have been elusive at large spatial scales. We examined nearshore abundance patterns of 15 common taxa across gradients of urban and agricultural land cover as well as wetland and hardened shoreline in tributary subestuaries of the Chesapeake Bay and Delaware Coastal Bays. We used a comprehensive landscape-scale study design that included 587 sites in 39 subestuaries. Our analyses indicate shoreline hardening has predominantly negative effects on estuarine fauna in water directly adjacent to the hardened shoreline and at the larger system-scale as cumulative hardened shoreline increased in the subestuary. In contrast, abundances of 12 of 15 species increased with the proportion of shoreline comprised of wetlands. Abundances of several species were also significantly related to watershed cropland cover, submerged aquatic vegetation, and total nitrogen, suggesting land-use-mediated effects on prey and refuge habitat. Specifically, abundances of four bottom-oriented species were negatively related to cropland cover, which is correlated with elevated nitrogen and reduced submerged and wetland vegetation in the receiving subestuary. These empirical relationships raise important considerations for conservation and management strategies in coastal environments.     

Using <Superscript>36</Superscript>Cl exposure dating to date mass movement and assess land stability on the Nicholas Range,Tasmania

Detailed mapping of dolerite slope deposits overlying sedimentary Triassic rocks on the northern slopes of the Nicholas Range in northeastern Tasmania has revealed an extensive mass movement complex. Landforms north of the summit plateau of the Nicholas Range include the following: (1) a cliff of dolerite columns with associated scree slopes at its base; (2) a topple landscape consisting of several topples that have fallen in a north-easterly direction; (3) a “ripple” landscape consisting of a series of long boulder ridges aligned approximately east-west. Exposure dates were obtained for three large boulders (collapsed dolerite columns) from a ridge within the ripple landscape. The two youngest dates gave a mean age of 52.1 ± 1.9 ka using ³⁶Cl. This is the estimated age for collapse of the dated columns from the cliff face c. 750 m to the south. Boulder ages and landscape morphology indicate that the ripple landscape developed by physical and chemical degradation and concurrent northern displacement of topples over a slip plane formed at the contact between dolerite colluvium and underlying Triassic sedimentary rocks. There is no evidence of movement today, other than localised debris flows associated with knickpoints in streams, and it is deduced that movement on the slip plane occurred under a cooler climate than that prevailing today, possibly under the influence of melting of winter snow during the last glacial cycle. As there is no evidence of significant recent mass movement and forests in the area are likely to have experienced many stand-destroying forest fires in the Holocene, forest harvest is not considered to pose a risk to landscape stability.     

Hydrogeologic modeling of the genesis of carbonate-hosted lead-zinc ores

 Carbonate-hosted lead–zinc ore deposits in the Mississippi Valley region of North America and in the central midlands region of Ireland provide good examples where ancient groundwater migration controlled ore formation deep within sedimentary basins. Hydrogeologic and geochemical theories for ore genesis are explored in this paper with mathematical models that allow for complex permeability fields in two or three dimensions, hydrothermal flows in fault systems, and coupled effects of geochemical reactions. The hydrogeologic framework of carbonate-hosted ores is analyzed with the aim of developing a quantitative understanding of the necessary and sufficient processes required to form large ore deposits. Numerical simulations of basin-scale hydrodynamics and of deposit-scale reactive flow are presented to demonstrate the processes controlling low-temperature Pb–Zn ore genesis in two world-class ore districts, in southeast Missouri, USA, and central Ireland. The numerical models presented here provide a theoretical basis for the following observations: (1) topography-driven brine migration was the most effective mechanism for forming the large ore districts of the Mississippi Valley, such as the Viburnum Trend of southeast Missouri, during the uplift of the Appalachian–Ouachita mountain belt in late Paleozoic time; (2) three-dimensional flow fields were created by a dolomite facies of the Viburnum Trend, which acted as a giant lens for focusing metal and heat in southeast Missouri to produce the largest known concentration of lead in the Earth's crust; (3) ore-mineralization patterns were controlled locally by basement relief, permeability structure, and sandstone pinchouts, because of their effects on cooling and fluid-flow rates along the Viburnum Trend; (4) both density-driven and topography-driven fluid flow were important for ore genesis in the Irish midlands, where brines moved northward away from the Variscan orogen, leaked into the Hercynian basement, and discharged along normal faults up into the sedimentary cover; and (5) mixed convection within northeast–southwest fault planes elevated heat flow and flow rates that fed ore deposition by fluid mixing, in some cases near the Carboniferous seafloor in Ireland. Received, February 1998 · Revised, July 1998 · Accepted, September 1998     

Field estimate of paleoseismic slip on a normal fault using the Schmidt hammer and terrestrial LiDAR: Methods and application to the Hebgen fault (Montana,USA)

The weathering characteristics of bedrock fault scarps provide relative age constraints that can be used to determine fault displacements. Here, we report Schmidt hammer rebound values (R‐values) for a limestone fault scarp that was last exposed in the 1959 Mw 7.3 Hebgen Lake, Montana earthquake. Results show that some R‐value indices, related to the difference between minimum and maximum R‐values in repeated impacts at a point, increase upward along the scarp, which we propose is due to progressive exposure of the scarp in earthquakes. An objective method is developed for fitting slip histories to the Schmidt hammer data and produces the best model fit (using the Bayesian Information Criterion) of three earthquakes with single event displacements of ≥ 1.20 m, 3.75 m, and c. 4.80 m. The same fitting method is also applied to new terrestrial LiDAR data of the scarp, though the LiDAR results may be more influenced by macro‐scale structure of the outcrop than by differential weathering. We suggest the use of this fitting procedure to define single event displacements on other bedrock fault scarps using other dating techniques. Our preliminary findings demonstrate that the Schmidt hammer, combined with other methods, may provide useful constraints on single event displacements on exposed bedrock fault scarps. Copyright © 2018 John Wiley & Sons, Ltd.     

Plate tectonics in relation to mantle temperatures and metamorphic properties

When plate tectonics emerged and how it has evolved over Earth history are two of the most fundamental challenges in Earth Sciences. These questions are tackled using a holistic approach to analyze tectonic styles in the history of Earth, giving rise to the interpretation of two styles of plate tectonics since the Archean. In these interpretations, there are different styles of deformation and metamorphism between early times dominated by warm subduction, and later times preferring cold subduction.The two styles of plate tectonics are recorded by different properties of regional metamorphism at convergent plate boundaries,which are linked to the differences in mantle temperature between the Archean and Phanerozoic. A transition to modern plate tectonics is recorded by the signature of blueschist facies metamorphism developed in the Neoproterozoic. This is consistent with geological evidence for the operation of ancient plate tectonics since the early Archean. The temporal cooling of the mantle explains the geochemical trends of mantle-derived melts, the likely change from numerous small plates to fewer but larger plates,changes in thickness and preservation of oceanic crust and lithosphere in accretionary and collisional orogens, and led to the oxygenation of the surface environment providing the environments needed to foster life.     

Topographic variation in soil erosion and accumulation determined with meteoric 10Be

Understanding natural soil redistribution processes is essential for measuring the anthropogenic impact on landscapes. Although meteoric beryllium-10 (¹⁰Be) has been used to determine erosion processes within the Pleistocene and Holocene, fewer studies have used the isotope to investigate the transport and accumulation of the resulting sediment. Here we use meteoric ¹⁰Be in hilltop and valley site soil profiles to determine sediment erosion and deposition processes in the Christina River Basin (Pennsylvania, USA). The data indicate natural erosion rates of 14 to 21 mm 10⁻³ yr and soil ages of 26 000 to 57 000 years in hilltop sites. Furthermore, valley sites indicate an alteration in sediment supply due to climate change (from the Pleistocene to the Holocene) within the last 60 000 years and sediment deposition of at least 0.5–2 m during the Wisconsinan glaciation. The change in soil erosion rate was most likely induced by changes in geomorphic processes; probably solifluction and slope wash during the cold period, when ice advanced into the mid latitudes of North America. This study shows the value of using meteoric ¹⁰Be to determine sediment accumulation within the Quaternary and quantifies major soil redistribution occurred under natural conditions in this region. © 2018 John Wiley & Sons, Ltd.     

Channel‐planform evolution in four rivers of Olympic National Park,Washington, USA: the roles of physical drivers and trophic cascades

Identifying the relative contributions of physical and ecological processes to channel evolution remains a substantial challenge in fluvial geomorphology. We use a 74‐year aerial photographic record of the Hoh, Queets, Quinault, and Elwha Rivers, Olympic National Park, Washington, USA, to investigate whether physical or trophic‐cascade‐driven ecological factors – excessive elk impacts after wolves were extirpated a century ago – are the dominant drivers of channel planform in these gravel‐bed rivers. We find that channel width and braiding show strong relationships with recent flood history. All four rivers widened significantly after having been relatively narrow in the 1970s, consistent with increased flood activity since then. Channel planform also reflects sediment‐supply changes, evident from landslide response on the Elwha River. We surmise that the Hoh River, which shows a multi‐decadal trend toward greater braiding, is adjusting to increased sediment supply associated with rapid glacial retreat. These rivers demonstrate transmission of climatic signals through relatively short sediment‐routing systems that lack substantial buffering by sediment storage. Legacy effects of anthropogenic modification likely also affect the Quinault River planform. We infer no correspondence between channel evolution and elk abundance, suggesting that trophic‐cascade effects in this setting are subsidiary to physical controls on channel morphology. Our findings differ from previous interpretations of Olympic National Park fluvial dynamics and contrast with the classic example of Yellowstone National Park, where legacy effects of elk overuse are apparent in channel morphology; we attribute these differences to hydrologic regime and large‐wood availability. Published 2016. This article is a U.S. Government work and is in the public domain in the USA     

The interplay between extrinsic and intrinsic controls in determining floodplain wetland characteristics in the South African drylands

Controls on the characteristics of floodplain wetlands in drylands are diverse and may include extrinsic factors such as tectonic activity, lithology and climate, and intrinsic thresholds of channel change. Correct analysis of the interplay between these controls is important for assessing possible channel–floodplain responses to changing environmental conditions. Using analysis of aerial imagery, geological maps and field data, this paper investigates floodplain wetland characteristics in the Tshwane and Pienaars catchments, northern South Africa, and combines the findings with previous research to develop a new conceptual model highlighting the influence of variations in aridity on flow, sediment transport, and channel–floodplain morphology. The Tshwane–Pienaars floodplain wetlands have formed in response to a complex interplay between climatic, lithological, and intrinsic controls. In this semi‐arid setting, net aggradation (alluvium >7 m thick) in the wetlands is promoted by marked downstream declines in discharge and stream power that are related to transmission losses and declining downstream gradients. Consideration of the Tshwane–Pienaars wetlands in their broader catchment and regional context highlights the key influence of climate, and demonstrates how floodplain wetland characteristics vary along a subhumid to semi‐arid climatic gradient. Increasing aridity tends to be associated with a reduction in the ability of rivers to maintain through‐going channels and an increase in the propensity for channel breakdown and floodout formation. Understanding the interplay between climate, hydrology and geomorphology may help to anticipate and manage pathways of floodplain wetland development under future drier, more variable climates, both in South African and other drylands. Copyright © 2016 John Wiley & Sons, Ltd.     

Discriminating sources of PCB contamination in fish on the coastal shelf off San Diego, California (USA)

Management of coastal ecosystems necessitates the evaluation of pollutant loading based on adequate source discrimination. Monitoring of sediments and fish on the shelf off San Diego has shown that some areas on the shelf are contaminated with polychlorinated biphenyls (PCBs). Here, we present an analysis of PCB contamination in fish on the shelf off San Diego designed to discriminate possible sources. The analysis was complicated by the variability of species available for analysis across the shelf, variable affinities of PCBs among species, and non-detects in the data. We utilized survival regression analysis to account for these complications. We also examined spatial patterns of PCBs in bay and offshore sediments and reviewed more than 20 years of influent and effluent data for local wastewater treatment facilities. We conclude that most PCB contamination in shelf sediments and fish is due to the ongoing practice of dumping contaminated sediments dredged from San Diego Bay.