Use of remote sensing in agriculture

The remote sensing studies of (a) cultivated peanut areas in Southeastern Virginia; (b) studies at the Virginia Truck and Ornamentals Research Station near Painter, Virginia, the Eastern Virginia Research Station near Warsaw, Virginia, the Tidewater Research and Continuing Education Center near Suffolk, Virginia, and the Southern Piedmont Research and Continuing Education Center Blackstone, Virginia; and (c) land use classification studies at Virginia Beach, Virginia are presented. The practical feasibility of using false color infrared imagery to detect and determine the areal extent of peanut disease infestation of Cylindrocladium black rot and Sclerotinia blight is demonstrated. These diseases pose a severe hazard to this major agricultural food commodity. The value of remote sensing technology in terrain analyses and land use classification of diverse land areas is also investigated. Continued refinement of spectral signatures of major agronomic crops and documentation of pertinent environmental variables have provided a data base for the generation of an agricultural-environmental prediction model

Use of remote sensing in agriculture

Remote sensing studies in Virginia and Chesapeake Bay areas to investigate soil and plant conditions via remote sensing technology are reported ant the results given. Remote sensing techniques and interactions are also discussed. Specific studies on the effects of soil moisture and organic matter on energy reflection of extensively occurring Sassafras soils are discussed. Greenhouse and field studies investigating the effects of chlorophyll content of Irish potatoes on infrared reflection are presented. Selected ground truth and environmental monitoring data are shown in summary form. Practical demonstrations of remote sensing technology in agriculture are depicted and future use areas are delineated

Review and appraisal - Cost-benefit analyses of earth resources survey satellite systems

Review and assessment of documents concerning cost and benefits of ERS satellites, and value of these studies in directing R and D activitie

Gravitational wave asteroseismology with fast rotating neutron stars

We investigate damping and growth times of the f-mode for rapidly rotating stars and a variety of different polytropic equations of state in the Cowling approximation. We discuss the differences in the eigenfunctions of co- and counterrotating modes and compute the damping times of the f-mode for several EoS and all rotation rates up to the Kepler-limit. This is the first study of the damping/growth time of this type of oscillations for fast rotating neutron stars in a general relativistic framework. We use these frequencies and damping/growth times to create robust empirical formulae which can be used for gravitational wave asteroseismology. The estimation of the damping/growth time is based on the quadrupole formula and our results agree very well with Newtonian ones in the appropriate limit.Comment: 15 pages, 8 figures, version accepted for publication in PhysRev

An assessment of scup (Stenotomus chrysops) and black sea bass (Centropristas striata) discards in the directed otter trawl fisheries in the Mid-Atlantic Bight

This study was undertaken to re-assess the level of scup (Stenotomus chrysops) discards by weight and to evaluate the effect of various codend mesh sizes on the level of scup discards in the winter-trawl scup fishery. Scup discards were high in directed scup tows regardless of codend mesh — typically one to five times the weight of landings. The weight of scup discards in the present study did not differ significantly from that recorded in scup-targeted tows in the NMFS observer database. Most discards were required as such by the 22.86 cm TL (total length) fish-size limit for catches. Mesh sizes ≤12.7 cm, including the current legal mesh size (11.43 cm) did not adequately filter out scup smaller than 22.86 cm. The median length of scup discards was about 19.83 cm TL. Lowering the legal size for scup from 22.86 to 19.83 cm TL would greatly reduce discard mortality. Scup discards were a small fraction (0.4%) of black sea bass (Centropristis striata) landings in blacksea-bass−targeted tows. The black sea bass fishery is currently regulated under the small-mesh fishery gearrestricted area plan in which fishing is prohibited in some areas to reduce scup mortality. Our study found no evidence to support the efficacy of this management approach. The expectations that discarding would increase disproportionately as the trip limit (limit [in kilograms] on catch for a species) was reached towards the end of the trip and that discards would increase when the trip limit was reduced from 4536 kg to 454 kg at the end of the directed fishing season were not supported. Trip limits did not significantly affect discard mortality

Pseudopeptidic ligands: exploring the self-assembly of isopthaloylbisglycine (H2IBG) and divalent metal ions

No description supplie

Modeling Oyster Populations. IV. Rates of Mortality, Population Crashes, and Management

A time-dependent energy-flow model was used to examine how mortality affects oyster populations over the latitudinal gradient from Galveston Bay, Texas, to Chesapeake Bay, Virginia. Simulations using different mortality rates showed that mortality is required for market-site oysters to be a component of the population\u27s size-frequency distribution; otherwise a population of stunted individuals results. As mortality extends into the juvenile sizes, the population\u27s size frequency shifts toward the larger sizes. In many cases adults increase despite a decrease in overall population abundance. Simulations, in which the timing of mortality varied, showed that oyster populations are more susceptible to population declines when mortality is restricted to the summer months. Much higher rates of winter mortality can be sustained. Comparison of simulations of Galveston Bay and Chesapeake Bay showed that oyster populations are more susceptible to intense population declines at higher latitudes. The association of population declines with disease agents causing summer mortality and the increased frequency of long-term declines at high latitudes result from the basic physiology of the oyster and its population dynamics cycle. Accordingly, management decisions on size limits, seasons and densities triggering early closure must differ across the latitudinal gradient and in populations experiencing different degrees of summer and winter mortality relative to their recruitment rate. More flexible size limits might be an important management tool. When fishing is the primary cause of mortality, populations should be managed more conservatively in the summer. The latitudinal gradient in resistance to mortality requires more conservative management at higher latitudes and different management philosophies from those used in the Gulf of Mexico

Environmental Effects on the Growth and Development of Eastern Oyster, Crassostrea virginica (Gmelin, 1791), Larvae: A Modeling Study

The effects of temperature, food concentration, salinity and turbidity on the growth and development of Crassostrea virginica larvae were investigated with a time-dependent mathematical model. Formulations used in the model for larval growth are based upon laboratory data. Simulations were done using temperature conditions characteristic of Laguna Madre, Galveston Bay, Apalachicola Bay, North Inlet and Chesapeake Bay. These simulations show that the duration of the planktonic larval phase, which is determined by larval growth rate, decreases at lower latitudes in response to warmer water temperatures. Also, oysters in the more southern locations have a longer spawning season during which the oyster population can produce more larvae. Simulations were done for Galveston Bay and Chesapeake Bay using idealized time series of food supply that included higher concentrations in the spring, summer or fall. Additional simulations considered the effects of increased food supply in both spring and fall seasons. The results show that shifting the period of enhanced food supply from March-April to April-May, when temperatures are warmer, reduces the minimum larval planktonic period from 44 to 34 days. Shifting the fall bloom from August-September to September-October, however, does not appreciably change the minimum larval planktonic period. The final set of simulations considered the effect of low salinity events and turbidity on the planktonic period of the larvae of Crassostrea virginica. By imposing a simulated low salinity (5 ppt) event of one month duration in August, the larval planktonic time is increased by about 39% over normal August salinities. Turbidity concentrations less than 0.1 g l-1 result in slightly decreased planktonic times. These model results show clearly the importance of ambient environmental conditions in determining the planktonic time of larvae of Crassostrea virginica, and hence their ultimate recruitment to the adult oyster population

Ecosystem effects of shell aggregations and cycling in coastal waters: an example of Chesapeake Bay oyster reefs

Disease, overharvesting, and pollution have impaired the role of bivalves on coastal ecosystems, some to the point of functional extinction. An underappreciated function of many bivalves in these systems is shell formation. The ecological significance of bivalve shell has been recognized; geochemical effects are now more clearly being understood. A positive feedback exists between shell aggregations and healthy bivalve populations in temperate estuaries, thus linking population dynamics to shell budgets and alkalinity cycling. On oysterreefs a balanced shell budget requires healthy long-lived bivalves to maximize shell input permortality event thereby countering shell loss. Active and dense populations of filter-feeding bivalves couple production of organic-rich waste with precipitation of calcium carbonate minerals, creating conditions favorable for alkalinity regeneration. Although the dynamics of these processes are not well described, the balance between shell burial and metabolic acid production seems the key to the extent of alkalinity production vs. carbon burial as shell. We present an estimated alkalinity budget that highlights the significant role oyster reefs once played in the Chesapeake Bay inorganic-carbon cycle. Sustainable coastal and estuarine bivalve populations require a comprehensive understanding of shell budgets and feedbacks among population dynamics, agents of shell destruction, and anthropogenic impacts on coastal carbonate chemistry

Modeling Diseased Oyster Populations. II. Triggering Mechanisms for Perkinsus marinus Epizootics

Densities of Crassostrea virginica remain high enough to support substantial fisheries throughout the Gulf of Mexico despite high mortality rates produced by the endoparasite Perkinsus marinus. The infrequency of epizootics in these populations suggests that controls exist on the disease intensification process. The progression of epizootics in oyster populations, the factors that trigger epizootics, and the factors that terminate epizootics once started were investigated with a coupled oyster population—P. marinus model. The time development of a simulated epizootic was triggered by environmental conditions that occurred and disappeared as much as t8 months prior to the onset of mortality in the oyster population. Initiation of epizootic conditions was detected as an increase in infection intensities in the submarket-size adult and juvenile portions of the oyster population. Infection intensity of the market-size adults is maintained at a relatively stable level by the death of heavily infected individuals and the slow rate of P. marinus division at high infection intensities. Once started, most of the simulated epizootics resulted in population extinction in 2 to 4 years. Stopping an epizootic required reducing the infection intensity in the submarket-size adults and juveniles. The infection intensity of market-size adults does not need to be reduced to stop an epizootic nor must it be raised to start one. The simulated oyster populations show that a reduction in ingestion rate (by reduced food supply or increased turbidity) can trigger an epizootic, especially if the reduction occurs during the summer. lncreasing food supply or decreasing turbidity in the following year does not necessarily prevent the occurrence of an epizootic. Rather, the onset or the event is simply delayed. Additional simulations show that the relative combination of variations in salinity and temperature is important in determining the occurrence of an epizootic. A dry (high-salinity) summer followed by a warm winter produces conditions that favor the development of an epizootic. Conversely, a warm dry year followed by a cool wet year fails to produce an epizootic. Simulations that consider variations in the biological characteristics of oyster populations, such as changes in recruitment rate or disease resistance, show that these are important in regulating the occurrence of an epizootic as well as in terminating the event. In particular, increased recruitment rate dilutes the infected population sufficiently to terminate an epizootic. One primary conclusion that can be obtained from these simulations is that epizootics of P. marinus in oyster populations are difficult to generate simply with changes in either temperature or salinity. Rather, the epizootics are triggered by some other factor, such as reduced food supply or reduced recruitment rate, that occurs prior to or coincident with high salinity or temperature conditions