Grain susceptibility to the effects of microboring: implications for the preservation of skeletal carbonates   总被引：2，自引：0，他引：2  

Christopher T. Perry 《Sedimentology》1998,45(1):39-51

The boring activity of microendolithic organisms such as cyanobacteria, chlorophytes, rhodophytes and fungi, represents a major destructive process affecting sediment preservation within reef environments. This study demonstrates the presence of two distinct assemblages of microborers within sediments collected from the fringing reefs of north Jamaica, correlating to the upper (<18 m depth) and lower (>18 m depth) photic zones. The upper photic zone assemblage is dominated by cyanobacteria and chlorophytes, whilst rhodophytes and fungi become more abundant with increasing water depth. Most significant from a grain preservation perspective is the variable nature of grain infestation observed between different reef sites and different carbonate grain types. The highest degree of grain infestation occurs within shallow, low-energy back-reef environments and the most susceptible grains (at all sites) are corals, molluscs and foraminifera. Coralline algae, Halimeda and echinoid fragments are rarely heavily infested. High rates of infestation at back-reef sites result in rapid diminution of the most susceptible grains, especially coral, which are either underrepresented, or contribute only to the finer sediment fractions, in the subsurface. Fore-reef grain assemblages undergo relatively little alteration. Microboring therefore has potential to bias the fossil record by removing the most susceptible skeletal grains. The impact of microboring upon back-reef grain assemblages must be considered when attempting to model depositional processes within both modern and ancient reef environments.  相似文献   

Marine ecosystem variability and human community responses: The example of Ghana,West Africa     

R. Ian Perry  U. Rashid Sumaila 《Marine Policy》2007

This study describes variability in the marine ecosystem of Ghana, West Africa, on several temporal and spatial scales and discusses how the human communities using this ecosystem respond to this variability to cope socially and economically. Ghanaian marine waters are part of an upwelling system with strong seasonal and inter-annual variability. Much of this variability is forced at large spatial scales in the tropical Atlantic and by El Niño—Southern Oscillation events in the Pacific Ocean, which influence inter-annual variability of sea surface temperature and pelagic fish landings off Ghana. At decadal scales, Ghanaian marine waters experienced cool sea temperatures and low fishery landings during the 1960s, rapid warming and increases in fishery landings during the late 1970s and 1980s, and variable temperatures and fishery landings during the 1990s. In the late 1990s, pelagic and demersal fish populations appeared to be declining, partly due to over-fishing, although the per capita supply (domestic production plus net imports) of fish was kept high by increased imports. Artisanal fishers and fishing communities in Ghana have devised strategies to deal with variability on seasonal and inter-annual scales. These livelihood strategies include: (i) exploiting marine and terrestrial natural resources more intensively, initially at local scales but expanding to regional scales; (ii) ensuring multiple and diversified income sources; (iii) investing in social relationships and communities for support; and (iv) undertaking seasonal or permanent migrations. In addition, the national government imports fish to deal with shortages. However, these strategies may be less adapted to variability at decadal scales, and may not be sustainable when viewed at the larger scales of environmental change.  相似文献   

Public Awareness of and Visitation to National Parks by Racial/Ethnic Minorities     

Xiao Xiao  Robert Manning  Elizabeth Perry  William Valliere 《社会与自然资源》2018,31(8):908-924

National parks are an important manifestation of the United States’ democratic ideal and attract more than 300 million visits annually. However, racial/ethnic minorities are substantially underrepresented among visitors, and this has led to three hypotheses—marginality, subculture, and discrimination—designed to help explain this pattern of visitation. Moreover, research suggests that the awareness of and visitation to national parks may relate to several variables, including race/ethnicity, socio-economic characteristics, and childhood visitation history. To investigate these issues, an online general population survey of New York City residents was conducted. Study findings suggest that (1) racial/ethnic minorities are underrepresented at some types of parks but not others, (2) Hispanics and Blacks generally have lower rates of awareness about national parks than Whites, and (3) awareness and childhood visitation history significantly affect visitation to national parks. These findings suggest potential approaches to enable and encourage diverse racial/ethnic groups to engage with national parks.  相似文献   

Amenability of nitrilotriacetic acid to biodegradation in a marine simulation     

P.W.W Kirk  J.N Lester  R Perry 《Marine pollution bulletin》1983,14(3):88-93

The behaviour of the detergent builder nitrilotriacetic acid (NTA) has been studied in the presence of a marine bacterial population potentially associated with a sewage discharge to coastal waters. Additions of 500 μg l^?1 NTA were made over a period of 80 days and 7500 μg l^?1 NTA over 40 days in both aerobic and anoxic environments. It was concluded that NTA was not degraded at either concentration under aerobic or anoxic conditions, despite the presence of a significant bacterial population under aerobic conditions. Possible effects of NTA recalcitrance and its accumulation in coastal marine waters are discussed.  相似文献   

Modeling of Trace Organics Biotransformation in the Subsurface   总被引：1，自引：0，他引：1  

Edward J. Bouwer  Perry L. McCarty 《Ground water》1984,22(4):433-440

Biofilm processes are potentially important for transformations of organic micropollutants in ground water. Some theoretical hypotheses and empirical observations suggest that a concentration threshold exists for some compounds below which the concentration cannot be reduced by bacterial action. However, in the presence of one compound at a relatively high concentration, termed the primary substrate, another compound present at trace concentrations, termed the secondary substrate, can be biotransformed as well. These concepts were evaluated through laboratory column studies with several halogenated organic compounds of importance in ground water. A biofilm model can successfully describe utilization of trace substrates, and application to modeling the subsurface is discussed. A simplified batch model with first-order kinetics may be adequate for describing subsurface microbial processes when low active organism and pollutant concentrations exist over a large scale.  相似文献   

Contributions of phytoplankton and nitrifying bacteria to ammonium and nitrite dynamics in coastal waters     

B.B. Ward  M.C. Talbot  M.J. Perry 《Continental Shelf Research》1984,3(4):383-398

Ammonium and nitrite dynamics in coastal waters off Washington were examined using stable nitrogen isotope methods. Assimilation rates of ammonium into particulate nitrogen exhibited maxima (up to 500 nmol l⁻¹d⁻¹ at shallow depths and were negligible below the photic zone. Rates of ammonium oxidation by nitrifying bacteria showed surface minima and increased with depth (up to 35 nmol l⁻¹ d⁻¹). Both processes showed evidence of control by light intensity: light stimulated assimilation and inhibited oxidation. Ammonium turnover was dominated by phytoplankton assimilation at shallow depths and at inshore stations, while the relative contribution of bacterial oxidation of ammonium to turnover increased with increasing depth and increasing distance from shore. Nitrite turnover due to ammonium oxidation approached 60% per day in the primary nitrite maximum at the outer stations.  相似文献   

Experimental studies in natural groundwater recharge dynamics: Assessment of recent advances in instrumentation     

Marios Sophocleous  Charles A. Perry   《Journal of Hydrology》1984,70(1-4):369-382

To quantify and model the natural groundwater-recharge process, two sites in south-central Kansas, U.S.A., were instrumented with various modern sensors and data microloggers. The atmospheric-boundary layer and the unsaturated and saturated soil zones were monitored as a unified regime. Data from the various sensors were collected using microloggers in combination with magnetic-cassette tape, graphical and digital recorders, analog paper-tape recorders, and direct observations to evaluate and automate data collection and processing.

Atmospheric sensors included an anemometer, a tipping-bucket raingage, an air-temperature thermistor, a relative-humidity probe, a net radiometer, and a barometric-pressure transducer. Sensors in the unsaturated zone consisted of soil-temperature thermocouples, tensiometers coupled with pressure transducers and dial gages, gypsum blocks, and a neutron moisture probe operated by an observer. The saturated-zone sensors consisted of a water-level pressure transducer, a conventional float gage connected to a variable potentiometer, soil thermocouples, and a number of multiple-depth piezometers.

Evaluation of the operation of these sensors and recorders indicated that certain types of equipment such as pressure transducers are very sensitive to environmental conditions. Extraordinary steps had to be taken to protect some of the equipment, whereas other equipment seemed to be reliable under all conditions. Based on such experiences, a number of suggestions aimed at improving such investigations are outlined.  相似文献   

The Mid-Atlantic Ridge at 33°N: the Hayes Fracture Zone     

R.H. Feden  H.S. Fleming  R.K. Perry  J.D. Phillips 《Earth and Planetary Science Letters》1975,26(3):292-298

A geophysical study was conducted over the Mid-Atlantic Ridge between 32–39°N and 30–40°W. A particularly deep fracture was observed which offset the ridge crest 110 km in the vicinity of 33°N. A pole of relative motion between the North American and African plates was deduced from this fracture zone as being at 63.1°N, 17°W.  相似文献   

Mg,Ca and $\text{O}{}^{18}\text{O}{}^{16}$ exchange in the sediment-pore water system,hole 149, DSDP     

Edward A. Perry  J.M. Gieskes  J.R. Lawrence 《Geochimica et cosmochimica acta》1976,40(4):413-423

The diagenesis and geochemical evolution of deep-sea sediments are controlled by the interaction between sediments and their associated pore waters. With increasing depth, the pore water of Hole 149 (DSDP) exhibits a strong depletion in Mg and a corresponding enrichment in Ca, while the alkalinity remains relatively constant. Dissolved SiO₂ is nearly constant in the upper 100 m of sediment, but is highly enriched in the deepest pore waters. The pore waters exhibit a depletion in K with increasing depth, and $\text{O}{}^{18}\text{O}{}^{16}$ pore water ratios also decrease.The sediment section has three zones of sedimentary regimes with increasing depth in the drill hole: an upper 100 m section of detrital clays, a middle section enriched in calc-akalic volcanics which have undergone submarine weathering to a smectite phase, and a lower section of siliceous ooze which still has a diagenetic smectite phase. The quartz-feldspar ratios and $\text{O}{}^{18}\text{O}{}^{16}$ composition of the silicate phases are in agreement with these interpretations.The submarine weathering of volcanics to a smectite can account for the observed pore water gradients. Volcanics release Ca and Mg to the pore waters causing the alkalinity values to increase. Smectite is formed, depletes the pore waters in Mg and O¹⁸ and causes the alkalinity to decrease. The net reaction allows for the observed relationship between pore water Ca and Mg gradients with little net change in alkalinity. Given the abundance of volcanics in many deep-sea sediments, especially in lower sections which often form near ridge crests, the submarine formation of smectite may be an additional oceanic Mg sink which has not yet been fully considered.  相似文献   

Asiatic clam (Corbicula manilensis) and other foods used by waterfowl in the James River,Virginia     

Matthew C. Perry  Francis M. Uhler 《Estuaries and Coasts》1981,4(3):229-233

Corbicula manilensis was found in the gizzards of 24 ducks of 5 species taken from the James River, Virginia, between 1973 and 1976. Percent average volume in these species ranged from trace to 6%. This is the first known occurrence of this exotic clam in the food of duck in Chesapeake Bay. A total of 135 other food items was identified from the 116 gizzards of 9 species that were examined. Food that predominated includedCyperus spp.,Leersia oryzoides, Polygonum spp., andZea mays. The great diversity of food consumed in this fresh tidal section of the James River indicates the high value of these wetlands to waterfowl. *** DIRECT SUPPORT *** A01BY015 00008  相似文献