Herbicides implicated as the cause of severe mangrove dieback in the Mackay region, NE Australia: consequences for marine plant habitats of the GBR World Heritage Area

Herbicides, particularly diuron, were correlated with severe and widespread dieback of the dominant mangrove, Avicennia marina (Forsk.) Vierh. var. eucalyptifolia (Val.) N.C. Duke (Avicenniaceae), its reduced canopy condition, and declines in seedling health within three neighbouring estuaries in the Mackay region of NE Australia. This unusual species-specific dieback, first observed in the early 1990s, had gotten notably worse by 2002 to affect >30 km(2) of mangroves in at least five adjacent estuaries in the region. Over the past century, agricultural production has responded well to the demands of increasing population with improvements in farm efficiency assisted by significant increases in the use of agricultural chemicals. However, with regular and episodic river flow events, these chemicals have sometimes found their way into estuarine and nearshore water and sediments where their effects on marine habitats have been largely unquantified. Investigations over the last three years in the Mackay region provide compelling evidence of diuron, and possibly other agricultural herbicides, as the most likely cause of the severe and widespread mangrove dieback. The likely consequences of such dieback included declines in coastal water quality with increased turbidity, nutrients and sediment deposition, as well as further dispersal of the toxic chemicals. The implications of such findings are immense since they describe not only the serious deterioration of protected and beneficial mangrove habitat but also the potential for significant direct and indirect effects on other highly-valued estuarine and marine habitats in the region, including seagrass beds and coral reefs of the Great Barrier Reef lagoon. This article reviews all key findings and observations to date and describes the essential correlative and causative evidence.     

Forms of bluffs degraded for different lengths of time in emmet county,Michigan, U.S.A.

Distinct differences in morphology are found among bluffs cut and abandoned by Glacial Lake Algonquin and by the Nipissing Great Lakes in Emmet County, Michigan and modern, active bluffs presently being eroded by Lake Michigan in Mason and Manistee Counties, Michigan. The Algonquin, Nipissing, and modern bluffs are all composed of a sandy, morainic material. Because the composition and mode of formation of the three sets of bluffs are similar, it is assumed that the abandoned bluffs had the same initial configuration as the modern bluff. The morphologic differences are likely a function of the different periods of time each bluff has degraded. With time, the angle of the bluff midsection decreased, the extent of the convex crest and the concave base increased, and the angle of the crest increased. This course of hillslope degradation is believed similar to that occurring elsewhere on heavily vegetated hillslopes underlain by cohesionless material and situated in temperate, humid climates. The morphologic changes may be understood in terms of an analytical model which assumes that the rate of change in elevation at a point on a hillslope profile is proportional to the profile curvature at that point.     

On modelling installation designs for soil water instrumentation,with particular reference to casagrande type piezometer systems

Appropriate installation design of soil water monitoring equipment is necessary to ensure the meaningful interpretation of the resultant data. For example, although piezometers are widely used in monitoring positive pore water pressures, the limits on the shape factor of the system in terms of the ceramic tip and filter design have not been fully studied. The filter design boundary conditions are investigated here using a finite element analysis, in which threshold ceramic tip and filter characteristics (permeability and dimensions) are identified. From the modelling results, it is possible to select the most suitable design installation.     

Satellite data analysis of ozone differences in the Northern and Southern Hemispheres

Four years of SBUV ozone data and NOAA/NMC temperature data are analyzed for the relations between the annual total ozone behaviour in the Northern and Southern Hemispheres and the transport of ozone by planetary waves. It is found that the interhemispheric differences in the annual variation of total ozone are well explained by the interhemispheric differences in the planetary waves and the resulting ozone transports. The annual variation of the ozone transports by the stationary waves is found to control the ozone behavior in both hemispheres. Both the day-to-day and the interannual variation in total ozone are found to be strongly related to the corresponding variability of the planetary waves.Contribution Number 46 of the Stratospheric General Circulation with Chemistry Project at NASA/GSFC.     

Multiple calcrete profiles in the Tabernas Basin,southeast Spain: their origins and geomorphic implications

The paper describes a sequence of Pliocene(? ) to Quaternary age calcretes developed within alluvial fan and fluvial gravels in the Tabernas Basin, Almería Province, southeast Spain. Calcrete profiles are described from sites adjacent to major tributaries of the Rambla de Tabernas. Six distinct calcrete units are identified within the basin. These have variable distributions but have developed in an identifiable evolutionary sequence. Two pairs of calcrete units are widely present across the basin preserving two former land surfaces. Each of the former land surfaces has been planated and subsequently buried by alluvial fan or fluvial gravels. A massive calcrete unit is present at the base of each gravel sequence, immediately in contact with the underlying bedrock, with a less well developed calcrete unit situated at the top of the gravel sequence. The lowest two calcrete units within the basin are more spatially restricted and are confined to the floors and flanks of incised drainage lines. The geochemistry, macro- and micromorphological properties and geomorphological positions of the calcrete units are outlined and, on the basis of this information, their mode of origin identified. Two main modes of calcrete genesis appear to be present: massive calcretes situated in direct contact with bedrock are suggested to have formed by groundwater processes, whilst calcretes situated at the top of gravel sequences are likely to have developed by pedogenic processes. Calcrete genesis is subsequently considered in the context of the reconstruction of the early phases of landscape development, and is suggested to have been controlled by phases of uplift and stability within the Tabernas Basin. © 1998 John Wiley & Sons, Ltd.     

Geological interpretation of Landsat TM imagery and aeromagnetic survey data, northern Precordillera region, Argentina

Este estudio de caso muestra una metodología para obtener el máximo valor geocientífico de datos aeromagnéticos regionales (espaciamiento entre líneas: 1000 m), a través de su integración con imágenes satelitarias de alta resolución. En este estudio, la interpretación litoestratigráfica de las imágenes Landsat TM a escala regional (1:100,000) ha sido llevada a cabo como precursor de la interpretación geofísica, proveyendo el marco geológico-estructural de base para el análisis de las imágenes geofísicas. Este marco geológico-estructural derivado de las imágenes Landsat muestra las posiciones y vergencias correctas de las estructuras mayores; en este marco, las ubicaciones de las anomalías aeromagnéticas mayores de origen somero relacionadas con rocas extrusivas y subvolcánicas intermedias/máficas, como así también de las estructuras que controlan estos eventos magmáticos de importancia económica, pueden ser correctamente interpretadas.Los resultados del estudio indican la existencia de un centro volcánico/subvolcánico no reconocido previamente, de edad post-pérmica y pre-miocena, probablemente asociado con fallamiento regional transcurrente sinistral desarrollado a lo largo de una sutura acrecional norte-sur reactivada y a una estructura preexistente del basamento precámbrico/paleozoico. El subsecuente evento de corrimientos de tipo ‘piel gruesa’ y vergencia oeste al que está asociado el ascenso del bloque precámbrico de la Sierra de Valle Fértil, desarrolló un distintivo juego de fallas transcurrentes de orientación NO–SE en el área del centro volcánico. Estas estructuras de orientación NO–SE cortan y rotan a estructuras miocenas tardías correspondientes a la tectónica de tipo ‘piel fina’ de la faja plegada y corrida de la Precordillera. Las rocas intrusivas asociadas con el centro volcánico de edad oligocena inferida, forman anomalías dipolares parcialmente remanentes fácilmente reconocibles, están asociadas con alteración y mineralización de oro (minas Cerro Guachi, El Pescado, Gral. Belgrano) y están ubicadas a lo largo de fallas ‘en cola de caballo’ sinistrales de orientación NO–SE. Este evento tectónico-magmático relacionado con la deformación transcurrente es considerado como oligoceno y puede estar relacionado con la convergencia oblicua oligocena y la mineralización de pórfiros de esta misma edad en Chile.     

Tracing the Seepage of Subsurface Sinkhole Vent Waters into Lake Huron Using Radium and Stable Isotopes of Oxygen and Hydrogen

Exchange of water between groundwater and surface water could alter water quality of the surface waters and thereby impact its ecosystem. Discharges of anoxic groundwater, with high concentrations of sulfate and chloride and low concentrations of nitrate and oxygen, from three sinkhole vents (El Cajon, Middle Island and Isolated) in Lake Huron have been recently documented. In this investigation, we collected and analyzed a suite of water samples from these three sinkhole vents and lake water samples from Lake Huron for Ra, radon-222, stable isotopes of oxygen and hydrogen, and other ancillary parameters. These measurements are among the first of their kind in this unique environment. The activities of Ra are found to be one to two orders of magnitude higher than that of the lake water. Isotopic signatures of some of the bottom lake water samples indicate evidences for micro-seeps at distances farther from these three vents. A plot of δD versus δ¹⁸O indicates that there are deviations from the Global Meteoric Line that can be attributed to mixing of different water masses and/or due to some subsurface chemical reactions. Using the Ra isotopic ratios, we estimated the transit times of the vent waters from the bottom to the top of the vent (i.e., sediment–water interface) to be 4–37 days. More systematic studies on the distribution of the radioactive and stable isotope studies are needed to evaluate the prevalence of micro-seeps in Lake Huron and other Great Lakes system.