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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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用现今小震推断洪洞、临汾两次历史大震的震源断层 总被引：5，自引：1，他引：5
山西临汾地区是一个历史强震多发区，1303年和1695年发生了洪洞（M＝8）和临汾（M＝73／4）两次特大地震，这两次地震所在区域至今仍在持续不断的小地震活动，具有明显的大震区地震长期活动特征，我们对临汾无线传输地震台网记录的1987－1999年期间发生的1670次中，小地震重新进行了震源定位，根据对这些地震震源位置三维空间分布特征和震源机解制的分析，认为洪洞地震的震源断层应是长80km，埋深5－26km的NNE走向，高倾角的右旋走滑型断层，而临汾地震的震源断层是长70km，埋深5－22km的NWW走向，高倾角的左旋走滑型断层。这与洪洞，临汾两次大震极震区的等震线及该地区应力场的构造环境是吻合的。 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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张家口地震台和兴隆地震台地脉动信号初步分析 总被引：1，自引：0，他引：1
选取河北省张家口和兴隆2个台站的数字化地震仪连续1年,每日02～03时的地脉动记录,计算功率谱和自相关函数。结果发现兴隆台脉动谱中有4个比较突出的峰值,分别为0．3Hz、3Hz、8Hz、15Hz,张家口台只有3个峰值0．3Hz、3Hz、15Hz。兴隆台UD向的自相关函数呈现出一种比较典型的“红噪声”形态,EW向则呈现出负相关特征,认为可能是只作用于水平向的倾斜脉动的影响。小幅度的仪器干扰信号无论从脉冲标定还是地震波形中都很难发现的,而对脉动进行谱分析则很容易分辨。兴隆台和张家口台地脉动卓越周期时间曲线,基本集中在0．3秒,比较稳定。 相似文献
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中印度洋海盆沉积岩心中稀土元素的成岩再活化作用ＪＮＰａｔａｎ等稀土元素（ＲＥＥ）是了解沉积物和沉积岩沉积环境的有效示踪剂。中印度洋海盆（ＣＩＢ）的硅质软泥稀土元素丰度通常比钙质软泥高,但是比红粘土低,并且显示出正的Ｃｅ／Ｃｅ异常。Ｔｌｉｇ和Ｓｔｅｉ... 相似文献