Mapping of benthic enrichment patterns in Narragansett Bay,Rhode Island     

Raymond M. Valente  Donald C. Rhoads  Joseph D. Germano  Victor J. Cabelli 《Estuaries and Coasts》1992,15(1):1-17

A synoptic reconnaissance survey was performed over a five-day period in August 1988 to assess benthic habitat quality throughout Narragansett Bay, Rhode Island, using REMOTS^® sediment-profile photography and analysis in combination with measurements of the levels ofClostridium perfringens spores (a fecal indicator) in sediments. Three main areas of degraded benthic habitat quality related to either excessive organic enrichment or physical disturbance were identified based solely on the REMOTS^® analysis: the Providence River Reach, Greenwich Bay and its associated coves and harbors, and an area located along the southwest side of Prudence Island. Sediments at many stations in these areas exhibited shallow apparent redox-potential discontinuity (RPD) depths, high apparent oxygen demand, and low-order benthic successional stages. ElevatedClostridium perfringens spore counts in surface sediments were attributed to inputs from wastewater treatment facilities. The highest spore counts occurred at the head of the bay, where wastewater treatment discharges and associated combined sewer overflows are numerous. Using data from the REMOTS^® analysis and the sediment inventory ofC. perfringens spores, a distinction was made between organic enrichment of the bottom from sewage, versus nonsewage enrichment or physical disturbance. The combination of techniques employed in this investigation could be used to design more efficient monitoring programs to assess eutrophication effects in estuaries and determine the effectiveness of regulatory or management initiatives to reduce organic overenrichment of benthic habitats.  相似文献   

Stratification and bottom-water hypoxia in the Pamlico River estuary   总被引：1，自引：0，他引：1  

Donald W. Stanley  Scott W. Nixon 《Estuaries and Coasts》1992,15(3):270-281

Relationships among bottom-water dissolved oxygen (DO), vertical stratification, and the factors responsible for stratification-destratification in this shallow, low tidal-energy estuary were studied using a 15-yr set of biweekly measurements, along with some recent continuous-monitoring data. Hypoxia develops only when there is both vertical water-column stratification and warm water temperature (>15°C). In July, 75% of the DO readings were <5 mg 1^?1, and one-third were <1 mg 1^?1. Severe hypoxia occurs more frequently in the upper half of the estuary than near the mouth. Both the time series data and correlation analysis results indicate that stratification events and DO levels are tightly coupled with variations in freshwater discharge and wind stress. Stratification can form or disappear in a matter of hours, and episodes lasting from one to several days seem to be common. Estimated summertime respiration rates in the water and sediments are sufficient to produce hypoxia if the water is mixed only every 6–12 d. There has been no trend toward lower bottom water DO in the Pamlico River Estuary over the past 15 yr. *** DIRECT SUPPORT *** A01BY059 00002  相似文献   

Hydrogeochemical Effects of Injecting Wastes into a Limestone Aquifer Near Pensacola, Florida"     

Donald A. Goolsby 《Ground water》1971,9(1):13-19

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Geomagnetism in Marine Geology: V. Vacquier, 1972. Elsevier,Amsterdam, 1972, 200 pp., Ofl.42.50     

D. McKenzie 《Earth》1973,9(3):289-290

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Glacio-periglacial landforms within the Susquehanna Great Bend area of New York and Pennsylvania     

Cuchlaine A.M. King  Donald R. Coates 《Quaternary Research》1973,3(4):600-620

Previous attention has been called to the morphology of the glaciated Appalachian Plateau, including periglacial phenomena (Coates, 1970; Conners, 1969). This paper deals with an unusually well-developed hierarchy of small landforms in the Great Bend area of the Susquehanna River. Essential properties of these features include: (1) concentration in N-S valleys, (2) till composition, (3) concavo-convex form, sometimes ending in a hill on the valley floor, (4) alternation with steep, truncated bedrock spurs, (5) a col in the interfluve at their head. These characteristics could be explained by the following sequence of events. A prior fluvial landscape was eroded with tributary streams forming lateral valleys that head in cols along the divides. The main stream flowed south between interlocking spurs. Ice then widened the valley, leaving truncated spurs and a straightened stream. Deposition of locally derived till filled tributary valleys, similar to till shadows (Coates, 1966). In periglacial conditions, while nivation was widening the tributary valley heads, solifluction in the unstable till was forming the concavo-convexities that alternate with the truncated bedrock spurs. The hierarchy of forms range from minor convexities to small hills on the main valley floor. Thus, the features are primarily of periglacial origin, but owe their development and position to prior subaerial and glacial events. The cycle may have occurred during more than a single glacial episode. The recession of bedrock spurs and the valley floor convexity of the till features have caused a reversal in stream sinuosity of the main valley.  相似文献   

The occurrence frequency of white-light flares     

Donald F. Neidig  Edward W. Cliver 《Solar physics》1983,88(1-2):275-280

We derive an occurrence frequency for white-light flares (WLF) of 15.5 ± 4.5 yr^?1 during a 2.6 year period following the maximum of solar cycle 21. This compares with a frequency 5–6 yr^?1 derived by McIntosh and Donnelly (1972) during solar cycle 20. We find that the higher frequency of the more recently observed WLFs is due to the availability of patrol data at shorter wavelengths (λ ? 4000 Å), where the contrast of the flare emission is increased; the improved contrast has allowed less energetic (and hence more frequently occurring) events to be classified as WLFs. We find that sufficient conditions for the occurrence of a WLF are: active region magnetic class = delta; sunspot penumbra class = K, with spot group area ≥ 500 millionths of the solar hemisphere; 1–8 Å X-ray burst class ≥ X2.  相似文献   

Generalized Ray Theory for a Layered Sphere   总被引：1，自引：0，他引：1  

Freeman Gilbert  Donald V. Helmberger 《Geophysical Journal International》1972,27(1):57-80

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K/S two-point-boundary-value problems     

Donald J. Jezewski 《Celestial Mechanics and Dynamical Astronomy》1976,14(1):105-111

A method for developing the missing general K/S (Kustaanheimo/Stiefel) boundary conditions is presented, with use of the formalism of optimal control theory. As an illustrative example, the method is applied to the K/S Lambert problem to derive the missing terminal condition. The necessary equations are developed for a solution to this problem with the generalized eccentric anomaly,E, as the independent variable. This formulation, requiring the solution of only one nonlinear, well-behaved equation in one unknown,E, results in considerable simplification of the problem.Presented also at the AAS/AIAA Astrodynamics Specialist Conference, Nassau, Bahamas, July 1975 (AAS Paper No. 75-032).  相似文献   

On a recent theory of the origin of the X-ray backgroun-dfurther arguments: Comments on the preceding note     

John E. Mack  Donald E. Robbins 《Astrophysics and Space Science》1973,20(1):45-46

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Spectral development of a solar X-ray burst observed on OSO-7     

D. L. McKenzie  D. W. Datlowe  L. E. Peterson 《Solar physics》1973,28(1):175-185

The UCSD solar X-ray instrument on the OSO-7 satellite observes X-ray bursts in the 2–300 keV range with 10.24 s time resolution. Spectra obtained from the proportional counter and scintillation counter are analyzed for the event of November 16, 1971, at 0519 UT in terms of thermal (exponential spectrum) and non-thermal (power law) components. The energy content of the approximately 20 × 10⁶K thermal plasma increased with the 60 s duration hard X-ray burst which entirely preceded the 5 keV soft X-ray maximum. If the hard X-rays arise by thick target bremsstrahlung, the nonthermal electrons above 10 keV have sufficient energy to heat the thermally emitting plasma. In the thin target case the collisional energy transfer from non-thermal electrons suffices if the power law electron spectrum is extrapolated below 10 keV, or if the ambient plasma density exceeds 4 × 10¹⁰ cm^–3.Formerly at UCSD.  相似文献