Geology of the Pedwardine district,Herefordshire and Powys     

Helen E. Boynton  C. H. Holland 《Geological Journal》1997,32(3):279-292

The stratigraphy of the Pedwardine inlier of Precambrian (Longmyndian), Tremadoc, and what are now shown to be upper Llandovery rocks is described. The inlier is surrounded by Silurian rocks, including upper Llandovery (two very small areas), Wenlock, Ludlow and Přídolí (Red Downton Formation). The Ludlow rocks provide a distal record of the mass movement recorded more fully in the Wigmore Rolls area to the east. The Pedwardine area lies along the Church Stretton Fault Zone. Though ill-exposed, it shows evidence of the history of faulting, including thrusting. © 1997 John Wiley & Sons, Ltd.  相似文献   

Synthesis in Estuarine and Coastal Ecological Research: What Is It,Why Is It Important,and How Do We Teach It?     

W.?Michael?KempEmail author  Walter?R.?Boynton 《Estuaries and Coasts》2012,35(1):1-22

During the last two decades, there has been growing interest in the integration of existing ideas and data to produce new synthetic models and hypotheses leading to discovery and advancement in estuarine and coastal science. This essay offers an integrated definition of what is meant by synthesis research and discusses its importance for exploiting the rapid expansion of information availability and for addressing increasingly complex environmental problems. Approaches and methods that have been used in published synthetic coastal research are explored and a list of essential steps is developed to provide a foundation for conducting synthetic research. Five categories of methods used widely in coastal synthesis studies are identified: (1) comparative cross-system analysis, (2) analysis of time series data, (3) balance of cross-boundary fluxes, (4) system-specific simulation modeling, and (5) general systems simulation modeling. In addition, diverse examples are used to illustrate how these methods have been applied in previous studies. We discuss the urgent need for developing curricula for classroom and experiential teaching of synthesis in coastal science to undergraduate and graduate students, and we consider the societal importance of synthetic research to support coastal resource management and policy development. Finally, we briefly discuss the crucial challenges for future growth and development of synthetic approaches to estuarine and coastal research.  相似文献   

Nutrient Budgets and Management Actions in the Patuxent River Estuary,Maryland   总被引：1，自引：0，他引：1  

W. R. Boynton  J. D. Hagy  J. C. Cornwell  W. M. Kemp  S. M. Greene  M. S. Owens  J. E. Baker  R. K. Larsen 《Estuaries and Coasts》2008,31(4):623-651

Multi-year nitrogen (N) and phosphorus (P) budgets were developed for the Patuxent River estuary, a seasonally stratified and moderately eutrophic tributary of Chesapeake Bay. Major inputs (point, diffuse, septic, and direct atmospheric) were measured for 13 years during which, large reductions in P and then lesser reductions in N-loading occurred due to wastewater treatment plant improvements. Internal nutrient losses (denitrification and long-term burial of particulate N and P) were measured in tidal marshes and sub-tidal sediments throughout the estuary as were nutrient storage in the water column, sediments, and biota. Nutrient transport between the oligohaline and mesohaline zones and between the Patuxent and Chesapeake Bay was estimated using a salt and water balance model. Several major nutrient recycling terms were directly and indirectly evaluated and compared to new N and P inputs on seasonal and annual time-scales. Major findings included: (1) average terrestrial and atmospheric inputs of N and P were very close to the sum of internal losses plus export, suggesting that dominant processes are captured in these budgets; (2) both N and P export were a small fraction (13% and 28%, respectively) of inputs, about half of that expected for N based on water residence times, and almost all exported N and P were in organic forms; (3) the tidal marsh-oligohaline estuary, which by area comprised ~27% of the full estuarine system, removed about 46% and 74% of total annual upland N and P inputs, respectively; (4) recycled N and P were much larger sources of inorganic nutrients than new inputs during warm seasons and were similar in magnitude even during cold seasons; (5) there was clear evidence that major estuarine processes responded rapidly to inter-annual nutrient input variations; (6) historical nutrient input data and nutrient budget data from drought periods indicated that diffuse nutrient sources were dominant and that N loads need to be reduced by about 50% to restore water quality conditions to pre-eutrophic levels.  相似文献   

Effects of atrazine and linuron on photosynthesis and growth of the macrophytes, Potamogeton perfoliatus L. and Myriophyllum spicatum L. in an estuarine environment     

W. M. Kemp  W. R. Boynton  J. J. Cunningham  J. C. Stevenson  T. W. Jones  J. C. Means 《Marine environmental research》1985,16(4):255-280

Phytotoxicities of the herbicides, atrazine and linuron, were evaluated for two species of submersed vascular plants (Potamogeton perfoliatus, L. Myriophyllum spicatum, L.) which, until the late 1960s, had been abundant in Chesapeake Bay. Plants were grown in 50-liter laboratory microcosms, containing filtered estuarine water and sediments for a period of 5 weeks and then treated with atrazine or linuron at initial concentrations of 0, 5, 50, 100, 500 and 1000 gmg/liter. Plant responses were measured primarily in terms of apparent O₂ production, P₃, and above-ground biomass for 4 weeks post treatment. In general, at ≥ 50 gmg/liter there was a significant depression in P_a for both species and herbicides. However, M. spicatum appeared to be less sensitive, with a significant enhancement in P_a of this species at 5 gmg/liter, and linuron was slightly more effective than atrazine at reducing P_a for both species. Treatment effects on biomass generally paralleled those for P_a. In spite of relatively constant atrazine concentrations (84–89 % remaining at termination), both species exhibited evidence of photosynthetic recovery 2–3 weeks after treatment at concentrations ≤ 100 gmg/liter. Using an exponential dose-response model, I₅₀ (concentration for 50 % photosynthetic inhibition), ranged from 45–117 gmg/liter for all experiments. In general, in situ concentrations of atrazine and linuron in Chesapeake Bay and its tributaries appear to be sufficient to result in small reductions in P_a (2–10%, estimated from dose-response model) during a typical growing season. While such effects may be important for the survival of otherwise stressed plant populations, they suggest that these herbicides, per se, were not the cause of the general decline in abundance of these plants.  相似文献   

Long-term observations of the evolution of the southern seasonal cap of Mars: Neutron measurements by the HEND instrument onboard the 2001 <Emphasis Type="Italic">Mars Odyssey</Emphasis> spacecraft     

M. L. Litvak  I. G. Mitrofanov  A. S. Kozyrev  A. B. Sanin  V. I. Tret’yakov  W. V. Boynton  D. Hamara  S. Saunders 《Solar System Research》2007,41(5):385-394

We present the results of five-year observations of the southern seasonal cap of Mars based on neutron spectroscopy of the surface fulfilled by the Russian HEND instrument onboard the NASA 2001 Mars Odyssey spacecraft. The numerical modeling of the observational data allowed us to reconstruct the curves of the variations of the total mass of the southern seasonal cap of Mars for different years (three Martian years) and to find the year-to-year variations of the seasonal cycle.  相似文献   

Chemical evidence for the genesis of the ureilites, the achondrite Chassigny and the nakhlites   总被引：1，自引：0，他引：1  

W.V Boynton  P.M Starzyk  R.A Schmitt 《Geochimica et cosmochimica acta》1976,40(12):1439-1447

Major element and REE, Cr, Sc, V, Ni, Co, Ir, Au, Sr, Ba abundances were determined in three ureilites and the unique achondrite, Chassigny. Chondritic-normalized REE abundance patterns for the ureilites are v-shaped, similar to pallasites, indicating a possible deep-seated origin. The lithophile trace element abundances and v-shaped REE patterns of the ureilites are consistent with a two-stage formation process, the first of which is an extensive partial melting of chondrite-like matter to yield ureilite precursors in the residual solid, which is enriched in Lu relative to La. The second step consists of an admixture of small and variable amounts of material enriched in the light REE. Such contaminating material may be magmas derived from the first formed melt of partial melting of chondrite-like matter.

In contrast to the ureilites, Chassigny has a chondritic-normalized REE pattern which decreases smoothly from La(1.8 × ) to Lu(0.4 × ) and is parallel to and ˜0.25 × the REE pattern in the nakhlitic achondrites. The composition of the magma from which Chassigny crystallized was highly enriched in the light REE; e.g. chondritic normalized La/Lu ˜ 7. The similarity in the fractionated REE patterns (no Eu anomalies) for the olivine-pyroxene Chassigny and for the nakhlites suggests a genetic relationship.

Siderophile trace element relationships in ureilites can be interpreted by three components: (1) ultramafic silicates enriched in Co relative to Ni, (2) an indigenous metal phase remaining after the partial melting event, and (3) a component of the carbon-rich vein material added after the partial melting.  相似文献   

A comparative analysis of eutrophication patterns in a temperate coastal lagoon     

W. R. Boynton  L. Murray  J. D. Hagy  C. Stokes  W. M. Kemp 《Estuaries and Coasts》1996,19(2):408-421

The coastal bays and lagoons of Maryland extend the full length of the state's Atlantic coast and compose a substantial ecosystem at the land-sea margin that is characterized by shallow depth, a well-mixed water column, slow exchange with the coastal ocean, and minimal freshwater input from the land. For at least 25 years, various types of measurements have been made intermittently in these systems, but almost no effort has been made to determine if water quality or habitat conditions have changed over the years or if distinctive spatial gradients in these features have developed in response to changing land uses. The purpose of this work was to examine this fragmented database and determine if such patterns have emerged and how they may be related to land uses. Turbidity, dissolved inorganic phosphate, algal biomass, and primary production rates in most areas of the coastal bays followed a regular seasonal pattern, which was well correlated with water temperature. Nitrate concentrations were low (<5 μM), and only modestly higher in tributary creeks (<20 μM). Additionally, there was little indication of the spring bloom typical of river-dominated systems. There does appear to be a strong spatial gradient in water quality conditions (more eutrophic in the upper bays, especially in tributary creeks). Comparisons of water quality data collected between 1970 and 1991 indicate little temporal change in most areas and some small improvements in a few areas, probably related to decreases in point-source discharges. Seagrass communities were once extensive in these systems but at present are restricted to the eastern portion of the lower bays where water clarity is sufficient to support plant survival. Even in these areas, seagrass densities have recently decreased. Examination of diel dissolved oxygen data collected in the summer indicates progressively larger diel excursions from lower to upper bays and from open bays to tributary subsystems; however, hypoxic conditions (<2 mg 1^?1) were rarely observed in any location. Nitrogen input data (point, surface runoff, groundwater and atmospheric deposition to surface waters) were assembled for seven regions of the coastal bay system; annual loading rates ranged from 2.4 g N m^?2 yr^?1 to 39.7 g N m^?2 yr^?1. Compared with a sampling of loading rates to other coastal systems, those to the upper and lower bays were low while those to tributaries were moderate to high. Regression analysis indicated significant relationships between annual nitrogen loading rates and average annual total nitrogen and chlorophyll a concentrations in the water column. Similar analyses also indicated significant relationships between chlorophyll a and the magnitude of diel dissolved oxygen changes in the water column. It is concluded that these simple models, which could be improved with a well-designed monitoring program, could be used as quantitative management tools to relate habitat conditions to nutrient loading rates.  相似文献   

Inputs,transformations, and transport of nitrogen and phosphorus in Chesapeake Bay and selected tributaries   总被引：1，自引：0，他引：1  

W. R. Boynton  J. H. Garber  R. Summers  W. M. Kemp 《Estuaries and Coasts》1995,18(1):285-314

In this paper we assemble and analyze quantitative annual input-export budgets for total nitrogen (TN) and total phosphorus (TP) for Chesapeake Bay and three of its tributary estuaries (Potomac, Patuxent, and Choptank rivers). The budgets include estimates of TN and TP sources (point, diffuse, and atmospheric), internal losses (burial in sediments, fisheries yields, and denitrification), storages in the water column and sediments, internal cycling rates (zooplankton excretion and net sediment-water flux), and net downstream exchange. Annual terrestrial and atmospheric inputs (average of 1985 and 1986 data) of TN and TP ranged from 4.3 g TN m^?2 yr^?1 to 29.3 g TN m^?2 yr^?1 and 0.32 g TP m^?2 yr^?1 to 2.42 g TP m^?2 yr^?1, respectively. These rates of TN and TP input represent 6-fold to 8-fold and 13-fold to 24-fold increases in loads to these systems since the precolonial period. A recent 11-yr record for the Susquehanna River indicates that annual loads of TN and TP have varied by about 2-fold and 4-fold, respectively. TN inputs increased and TP inputs decreased during the 11-yr period. The relative importance of nutrient sources varied among these estuaries: point sources of nutrients delivered about half the annual TN and TP load to the Patuxent and nearly 60% of TP inputs to the Choptank; diffuse sources contributed 60–70% of the TN and TP inputs to the mainstream Chesapeake and Potomac River. The direct deposition of atmospheric wet-fall to the surface waters of these estuaries represented 12% or less of annual TN and TP loads except in the Choptank River (37% of TN and 20% of TP). We found direct, although damped, relationships between annual rates of nutrient input, water-column and sediment nutrient stocks, and nutrient losses via burial in sediments and denitrification. Our budgets indicate that the annual mass balance of TN and TP is maintained by a net landward exchange of TP and, with one exception (Choptank River), a net seaward transport of TN. The budgets for all systems revealed that inorganic nutrients entering these estuaries from terrestrial and atmospheric sources are rapidly converted to particulate and organic forms. Discrepancies between our budgets and others in the literature were resolved by the inclusion of sediments derived from shoreline erosion. The greatest potential for errors in our budgets can be attributed to the absence of or uncertainties in estimates of atmospheric dry-fall, contributions of nutrients via groundwater, and the sedimentation rates used to calculate nutrient burial rates.  相似文献   

X‐ray fluorescence measurements of the surface elemental composition of asteroid 433 Eros     

Larry R. Nittler  Richard D. Starr  Lucy Lim  Timothy J. Mccoy  Thomas H. Burbine  Robert C. Reedy  Jacob I. Trombka  Paul Gorenstein  Steven W. Squyres  William V. Boynton  Timothy P. Mcclanahan  Jesse S. Bhangoo  Pamela E. Clark  Mary Ellen Murphy  Rosemary Killen 《Meteoritics & planetary science》2001,36(12):1673-1695

Abstract— We report major element ratios determined for the S‐class asteroid 433 Eros using remote‐sensing x‐ray fluorescence spectroscopy with the near‐Earth asteroid rendezvous Shoemaker x‐ray spectrometer (XRS). Data analysis techniques and systematic errors are described in detail. Data acquired during five solar flares and during two extended “quiet Sun” periods are presented; these results sample a representative portion of the asteroid's surface. Although systematic uncertainties are potentially large, the most internally consistent and plausible interpretation of the data is that Eros has primitive Mg/Si, Al/Si, Ca/Si and Fe/Si ratios, closely similar to H or R chondrites. Global differentiation of the asteroid is ruled out. The S/Si ratio is much lower than that of chondrites, probably reflecting impact‐induced volatilization and/or photo‐ or ion‐induced sputtering of sulfur at the surface of the asteroid. An alternative explanation for the low S/Si ratio is that it reflects a limited degree of melting with loss of an FeS‐rich partial melt. Size‐sorting processes could lead to segregation of Fe‐Ni metal from silicates within the regolith of Eros; this could indicate that the Fe/Si ratios determined by the x‐ray spectrometer are not representative of the bulk Eros composition.  相似文献   

A seismic refraction investigation of crustal structure beneath the Lesser Antilles island arc   总被引：2，自引：0，他引：2  

C. H. Boynton  G. K. Westbrook  M. H. P. Bott  R. E. Long 《Geophysical Journal International》1979,58(2):371-393

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