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Feeding of benthic foraminifera on diatoms and sewage-derived organic matter: an experimental application of lipid biomarker techniques 总被引：1，自引：0，他引：1
Foraminiferal ecology at sewage outfalls has been investigated in numerous field studies over the last 30 years. Foraminifera have been frequently used as biomonitors of sewage pollution since they are both abundant and ubiquitous. Sewage outfalls have been demonstrated to have both positive and negative effects on adjacent foraminiferal populations, but it has never been shown conclusively why sewage affects foraminifera in these ways. Such information on the impact mechanisms of sewage pollution is essential if foraminifera are to be used as sewage pollution biomonitors, and also to understand the ecology of these important protists. One possible cause of a positive effect is the direct consumption of sewage-derived particulate organic matter (POM) by the foraminifera themselves. However this hypothesis has never been tested experimentally. Here, lipid (fatty acid and sterol) biomarker techniques were applied to study the ingestion of two potential food items by the foraminiferan Haynesina germanica in the laboratory. An experiment was conducted to confirm that the laboratory conditions were conducive to the survival and feeding of the foraminifera. In this experiment, foraminifera were provided with the pennate diatom Phaeodactylum tricornutum, which was considered to be a suitable food source. After 2 weeks, a four-fold increase in the levels of the diatom fatty acid biomarker, 20:5(n-3), in the foraminifera suggested that they had fed actively on the diatoms and survived under the experimental conditions. These experimental conditions were used in the main experiment, where foraminifera were fed the POM from sewage. Lipid biomarker analysis indicated that H. germanica did not consume secondary treated sewage-derived POM. Neither fatty acid profiles in the sewage nor coprostanol, the diagnostic human faecal sterol, were detected in foraminifera after exposure to the potential sewage food source. However, foraminifera may have consumed bacteria associated with the sewage in the experiment. The findings are discussed in terms of current EU legislation on sewage treatment that has affected the composition of sewage discharges, and therefore possibly reduced the nutritive value of sewage to the marine benthos. 相似文献
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地震迁移有两种类型,一种是沿构造带迁移,另一种是短时间、长距离、直线式的震中迁移,其迁移路线能跨越不同的构造单元。这后一种迁移类型,其迁移方向与构造压力方向呈45°夹角。按照立交模式的观点,它反映了下岩石圈中剪切蠕滑断层的运动。本文利用上述观点和地震迁移资料对与中国大陆相邻板块运动方向进行了确定,得到太平洋板块、印度板块和欧亚板块分别向西、向北和向南南西方向运动。研究结果还表明,我国最近一次大震高潮期和低潮期板块运动方向是稳定的。此外,本文还讨论了由地球自转引起的纬向和经向地震迁移。 相似文献
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NGC 4945 is one of the brightest Seyfert galaxies on the sky at 100 keV, but is completely absorbed below 10 keV; its absorption column is probably the largest that still allows a direct view of the nucleus at hard X-ray energies. Our observations of it with the Rossi X-Ray Timing Explorer (RXTE) satellite confirm the large absorption, which for a simple phenomenological fit using an absorber with solar abundances implies a column of 4.5+0.4-0.4x1024 cm(-2). Using a more realistic scenario (requiring Monte Carlo modeling of the scattering), we infer the optical depth to Thomson scattering of approximately 2.4. If such a scattering medium were to subtend a large solid angle from the nucleus, it should smear out any intrinsic hard X-ray variability on timescales shorter than the light-travel time through it. The rapid (with a timescale of approximately 1 day) hard X-ray variability of NGC 4945 discovered by us with RXTE implies that the bulk of the extreme absorption in this object does not originate in a parsec-size, geometrically thick molecular torus. Instead, the optically thick material on parsec scales must be rather geometrically thin, subtending a half-angle less than 10 degrees, and it is likely to be the same disk of material that is responsible for the water maser emission observed in NGC 4945. Local number counts of Seyfert 1 and Seyfert 2 galaxies show a large population of heavily obscured active galactic nuclei (AGNs) which are proposed to make up the cosmic X-ray background (CXRB). However, for this to be the case, the absorption geometry in the context of axially symmetric unification schemes must have the obscuring material subtending a large scale height-contrary to our inferences about NGC 4945-implying that NGC 4945 is not a prototype of obscured AGNs postulated to make up the CXRB. The small solid angle of the absorber, together with the black hole mass (of approximately 1.4x106 M( middle dot in circle)) from megamaser measurements, allows a robust determination of the nuclear luminosity, which in turn implies that the source radiates at approximately 10% of the Eddington limit. 相似文献
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The water quality in Biscayne Bay has been significantly affected by past and continuing coastal and watershed development. The nutrient concentrations in the Bay have been dramatically changed by the conversion of natural creeks and sheet flow freshwater inputs to rapid and episodic canal inputs from the large and rapidly expanding Miami metropolitan area. This study is an evaluation of nutrient loadings to Biscayne Bay for 1994-2002 from canal, atmospheric, and groundwater sources. Dissolved inorganic nitrogen (DIN, as nitrate, nitrite, and ammonium) and total phosphorus (TP) loadings by the canals were influenced by their geographic locations relative to discharge amount, watershed land use, stormwater runoff, and proximity to landfills. Annual budgets showed that canals contributed the bulk of N loading to the bay as 1687.2 metric ton N yr(-1) (88% total load). Direct atmospheric DIN load for Biscayne Bay was only 231.7 ton N yr(-1), based on surface area. Of the canal DIN load, nitrate+nitrite (NO(x)(-)) loading (1294.5 ton N yr(-1)) made up a much greater proportion than that of ammonium (NH(4)(+), 392.6 ton N yr(-1)). In the urbanized north and central Bay, canal DIN load was evenly split between NO(x)(-) and NH(4)(+). However, in the south, 95% of the DIN load was in the form of NO(x)(-), reflecting the more agricultural land use. Contrary to N, canals contributed the only 66% of P load to the bay (27.5 ton P yr(-1)). Atmospheric TP load was 14 ton Pyr(-1). In the north, canal P load dominated the budget while in the south, atmospheric load was almost double canal load. Groundwater inputs, estimated only for the south Bay, represented an important source of N and P in this zone. Groundwater input of N (141 ton N yr(-1)) was about equal to atmospheric load, while P load (5.9 ton P yr(-1)) was about equal to canal load. 相似文献
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Salt marshes are important ecological areas and play a significant role in coastal flood defence schemes. In many areas of the UK they are adjacent to agricultural areas utilised for the growth of cereal crops, for which mecoprop is used as a selective herbicide in the control of broad-leaf weeds. This study measured concentrations of mecoprop in soils, drainage ditch waters and sediments and salt marsh sediments over a period of 138 days following spring application. Soil concentrations of up to 1827 microg/g were recorded after application, which demonstrated a half life for mecoprop of from 9 to 12 days, with first order kinetics. However, a major rainfall event 9 days after application resulted in significant transport of herbicide to the salt marsh via subsurface field drains, drainage ditches and discharge sluice. Mecoprop concentrations of up to 386 microg/l observed in water samples were above UK guidelines. 相似文献
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报告了利用泡沫橡胶模拟浅部软弱层对走滑破裂引起的强地面运动影响的结果。走滑地震引起强地面运动的计算机模拟,有时与对断层浅部滑动特性的某些任意假设有关（如：断层面上部２ｋｍ处的滑动固定为０）。断层滑动反演研究表明,走滑断层浅部的高频辐射通常低于断层深部。在多数情况下,（１）断层区上部几公里的断层可能较弱,不能维持地震高动能释放期间所需求的高水平的剪应力;（２）断层滑动可能具有不同的本构关系,例如,滑 相似文献