Historic nutrient loading and recent species invasions caused shifts in water quality and zooplankton demography in two Finger Lakes (New York, USA)     

Meghan E. Brown  Tara M. Curtin  Corey J. Gallagher  John D. Halfman 《Journal of Paleolimnology》2012,48(3):623-639

We investigated the paleolimnology of Owasco and Seneca Lakes (New York, USA) and compiled water-quality monitoring data to describe environmental change during the past two centuries. Trophic shifts were detected in the oligotrophic to mesotrophic range and were likely driven by nutrient loading and species invasion. Based on box core reconstructions, primary production increased in both lakes during the last century, which is evidenced by the amount, type and isotopic composition of material preserved in the sediment. Organic matter accumulation and its stable carbon isotopic composition, as well as carbonate abundance, began to increase during the 1960s in Owasco Lake and the 1850s in Seneca Lake. Further, the abundance of phytoplanktivorous cladocera subfossils increased beginning in the 1910s in Seneca Lake and in the 1960s in Owasco Lake. The different timing and magnitude of the trophic shifts likely resulted from contrasts in lake residence time and species assemblages between the two lakes. The increases in primary and secondary production paralleled, and are interpreted to reflect, increased allochthonous nutrient loading. However, nutrient loading was not detected in the water-quality data, perhaps because of strong uptake of phosphates by phytoplankton or due to limited data collection. Rapid changes in cladoceran subfossils and water quality were also detected during the last decade. Concurrent with the establishment of non-native Cercopagis pengoi (fishhook waterflea), phytoplanktivorous cladocera remains declined, and the mucrone length of Bosmina increased, consistent with predictions of increased invertebrate predation. Additionally, the post-1990 decline in sediment carbonate, increased Secchi depth and decreased chlorophyll a concentrations followed the establishment of filter-feeding Dreissena spp. (zebra and quagga mussels). Collectively, paleolimnological data and water-quality monitoring provided a more complete and consistent record of shifts in the productivity of Owasco and Seneca Lakes, which were useful to understand environmental changes over different time scales. Physical, geochemical and biological changes were temporally consistent among three cores collected from different locations in each lake, but differed in magnitude for several variables (e.g., grain size and cladoceran subfossils), which could reflect near-shore to offshore gradients.  相似文献   

Nature of sediment dispersal off the Sepik River, Papua New Guinea: preliminary sediment budget and implications for margin processes     

Steven A. Kuehl  Gregg J. Brunskill  Kathy Burns  David Fugate  Tara Kniskern  Linda Meneghini 《Continental Shelf Research》2004,24(19):2417-2429

A sediment budget is constructed for the slope and narrow continental shelf off the Sepik River in order to estimate the relative importance of turbid plumes versus bottom gravity transport through a near-shore submarine canyon in the dispersal of sediment across this collision margin. ²¹⁰Pb geochronology and inventories of Kasten cores are consistent with the northwestward dispersal of sediment from the river mouth via hypopycnal and possible isopycnal plumes. Sediment accumulation rates are 5 cm yr⁻¹ on the upper slope just off of the Sepik mouth, decreasing gradually to 1 cm yr⁻¹ toward the northwest, and decreasing abruptly offshore (<0.2 cm yr⁻¹ at 1200 m water depth). A sediment budget indicates that only about 7–15% of the Sepik River sediment discharge accumulates on the adjacent open shelf and slope. The remainder presumably escapes offshore via gravity flows through a submarine canyon, the head of which extends into the river mouth. The divergent sediment pathways observed off the Sepik River (i.e., surface and subsurface plumes versus sediment gravity flows through a canyon) may be common along high-yield collision margins of the Indo–Pacific archipelago, and perhaps are analogous to most margins during Late Quaternary low sea-level conditions.  相似文献   

Formation of massive galaxies at the centre of a cluster     

Tara Bhattacharyya  B. Basu 《Astrophysics and Space Science》1989,158(2):197-204

The formation of massive galaxies at the centre of a cluster is discussed here. The protogalaxies move with both rotation and random velocities through the gaseous medium pervading the cluster. Each galaxy is supposed to move through a resisting medium under the general gravitational field produced by the cluster as a whole. Also, the mass of the galaxy increases by accretion all the time as it moves through the medium. Using plausible laws for density of the medium and accretion of matter and solving equation of motion, we find that the galaxy loses angular momentum in the course of the time. The loss of angular momentum drives the galaxy towards the centre of the cluster. Thus over a sufficiently long time-scale several galaxies may merge in the central region of the cluster resulting in a single massive galaxy. The process can drive rise to several massive galaxies in the central region of the cluster.  相似文献   

Response To Stutz'S “Enhancing High School Geography”     

Christopher Salter 《The Professional geographer》1986,38(1):72-72

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WHAT CAN I DO WITH GEOGRAPHY?*     

Christopher L. Salter 《The Professional geographer》1983,35(3):266-273

As professional geographers we ask the above question in terms of problem solving, but undergraduate students ask it in regards to employment. To determine what exactly our recent majors have done, we prepared a questionnaire on careers, salary, and the utility of the major. Responses indicate they held a wide variety of employment opportunities and annual salaries from under $8,000 to well above $20,000 in 1981. Particularly useful courses include cartography, quantitative techniques and field course work. Special interest was shown in our new Internship Program.  相似文献   

Estimation of growth stages of wheat from spectral data     

Tara Sharma  R. R. Navalgund 《Journal of the Indian Society of Remote Sensing》1989,17(2):1-6

Growth stages of wheat subjected to different fertillizer treatments and sown on different dates have been estimated using spectral data. Greenness profiles were generated for different wheat plots. The profile parameters have been used to calculate growth stages at various times in the growing season. The model proposed by Badhwar (1981) has been used for this purpose. Results show that the model is capable of predicting growth stages accurately. There is a high correlation (r=0.97) between the observed and the predicted growth stages of wheat grown under various treatments.  相似文献   

Achieving development and mitigation objectives through a decarbonization development pathway in South Africa     

Katye E. Altieri  Hilton Trollip  Tara Caetano  Alison Hughes  Bruno Merven  Harald Winkler 《Climate Policy》2016,16(4):S78-S91

Achieving the international 2 °C limit climate policy requires stringent reductions in GHG emissions by mid-century, with some countries simultaneously facing development-related challenges. South Africa is a middle-income developing country with high rates of unemployment and high levels of poverty, as well as an emissions-intensive economy. South Africa takes into account an assessment of what a fair contribution to reducing global emissions might be, and is committed to a ‘peak, plateau and decline' emissions trajectory with absolute emissions specified for 2025 and 2030, while noting the need to address development imperatives. This work utilizes an economy-wide computable general equilibrium model (e-SAGE) linked to an energy-system optimization model (TIMES) to explore improving development metrics within a 14 GtCO₂e cumulative energy sector carbon constraint through to 2050 for South Africa. The electricity sector decarbonizes by retiring coal-fired power plants or replacing with concentrated solar power, solar photovoltaics and wind generation. Industry and tertiary-sector growth remains strong throughout the time period, with reduced energy intensity via fuel-switching and efficiency improvements. From 2010 to 2050, the model results in the unemployment rate decreasing from 25% to 12%, and the percentage of people living below the poverty line decreasing from 49% to 18%. Total energy GHG emissions were reduced by 39% and per capita emissions decreased by 62%.

Policy relevance

Lower poverty and inequality are goals that cannot be subordinated to lower GHG emissions. Policy documents in South Africa outline objectives such as reducing poverty and inequality with a key focus on education and employment. In its climate policy and Intended Nationally Determined Contribution (INDC), South Africa is committed to a peak, plateau and decline GHG emissions trajectory. As in many developing countries, these policy goals require major transformations in the energy system while simultaneously increasing affordable access to safe and convenient energy services for those living in energy poverty. The modelled scenario in this work focuses on employment and poverty reduction under a carbon constraint, a novel combination with results that can provide information for a holistic climate and development policy framework. This study has focused on the long term, which is important in generating clear policy signals for the necessary large-scale investments.  相似文献   

On the formation of superdense gaseous cores in the nuclei of disk galaxies — I     

B. Basu  Tara Bhattacharyya 《Astrophysics and Space Science》1980,70(2):263-279

A model for the formation of superdense gaseous cores by accretion in the nuclei of disk galaxies has been proposed. Equations for radial flow of gas into the nucleus in the presence of aweak galactic magnetic field have been solved, and time scales for the accretion of an exploding mass in the nucleus (10⁹ M ) have been obtained under several different situations in the absence of any rotation. The time scales are found to lie in the range between a few times 10⁷ yr and 10⁸ yr. Such time scales have been proposed by some authors for repeated explosions in the nuclei of galaxies; they have also proposed that spiral arms in disk galaxies are repeatedly formed and destroyed over such time scales. It is shown that the presence of rotational velocities in the infalling gas practically destroys the efficiency of the accretion process unless such velocities are dissipated by frictional forces within the system. Viscosity of gas is the most obvious dissipative agent. The problem of accretion of a rotating viscous gas will be discussed in a subsequent paper.  相似文献   

Excursion to Hertingfordbury,Bayford, and Brickenden Green: Saturday,May 19th, 1900     

A.E. Salter  A.K. Coomara Swamy 《Proceedings of the Geologists' Association. Geologists' Association》1900,16(8):447-448

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Excursion to Sheppey: Saturday,July 16th, 1898     

W. Whitaker  T.V. Holmes  W.H. Shrubsole  A.E. Salter 《Proceedings of the Geologists' Association. Geologists' Association》1898,15(10):459-462

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