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201.
Otte ML Haarsma MS Broekman RA Rozema J 《Environmental pollution (Barking, Essex : 1987)》1993,82(1):13-22
The aim of the research reported here was to investigate the relation between heavy metal concentrations in salt marsh plants, extractability of the metals from soil and some soil characteristics. In April 1987, Spartina anglica and Aster tripolium plants and soil were collected from four salt marshes along the Dutch coast. The redox potential of the soil between the roots of the plants and at bare sites was measured. Soil samples were oven-dried and analyzed for chloride concentration, pH, fraction of soil particles smaller than 63 microm (f < 63 microm), loss on ignition (LOI) and ammonium acetate and hydrochloric acid extractable Cd, Cu and Zn concentrations. The roots and shoots of the plants were analyzed for Cd, Cu and Zn. Because drying of the soil prior to chemical analysis might have changed the chemical speciation of the metals, and therefore the outcome of the ammonium acetate extraction, a second survey was performed in October 1990. In this survey A. tripolium plants and soil were collected from two salt marshes. Fresh and matched oven-dried soil samples were analyzed for water, ammonium acetate and diethylene triaminepentaacetic acid (DTPA) extractable Cd, Cu and Zn concentrations. The soil samples were also analyzed for f < 63 microm, LOI and total (HNO(3)/HCl digestion) metal concentrations. Soil metal concentrations were correlated with LOI. Drying prior to analysis of the soil had a significant effect on the extractability of the metals with water, ammonium acetate or DTPA. Plant metal concentrations significantly correlated only with some extractable metal concentrations determined in dried soil samples. However, these correlations were not consistently better than with total metal concentrations in the soil. It was concluded that extractions of metals from soil with water, ammonium acetate or DTPA are not better predictors for metal concentrations in salt marsh plants than total metal concentrations, and that a major part of the variation in metal concentrations in the plants cannot be explained by variation in soil composition. 相似文献
202.
López Gappa J Tablado A Magaldi NH 《Environmental pollution (Barking, Essex : 1987)》1993,82(2):157-165
Seasonal changes in structure of a rocky intertidal community affected by sewage pollution at Quequén (Argentina) were studied over a period of 2 years. Most species showed a decrease in cover values in the polluted area. On the other hand, a small proportion of organisms favoured by organic enrichment predominated around the outfall during the period of study. Community structure was not significantly altered by frosts or windstorms. Desiccation is identified as the main physical stress. A combination of late spring high temperatures with extreme midday low-tides caused by northerly winds was responsible for heavy losses in dominant algae. Major seasonal changes in community structure were primarily due to variations in area covered by the chlorophyte Ulva lactuca, and crusts of blue-green algae and diatoms in the vicinity of the outfall. Highest diversity values were attained during either late winter or spring, due to increased abundances of several seasonal algae. Abundance of the dominant organism, the bivalve Brachidontes rodriguezi, remained stable, showing only slight, non-seasonal, changes. Since the absence of B. rodriguezi is an indication of heavy pollution, temporal stability of this species suggests that the intensity of sewage discharges did not vary over the period of study. 相似文献
203.
Summary We tested the proposition that among humans (1) differences in lactational duration result in differences in costs of reproduction even under rich nutritional conditions; and (2) elimination of factors postulated to favor male-biased parental care will be reflected in elimination or reversal of sex-biased care. To do so, we examined the relationship between lactational duration and fertility among Hutterites, a communal-living human population in which the levels of nutritional resources and fertility are high, breast-feeding is the norm, contraceptive use is limited and the collective social and economic system results in low resource variance among individuals. We demonstrate that even under good nutritional conditions, duration of nursing was a significant predictor of the length of time to next pregnancy and that nursing continued to suppress fertility after the resumption of menses. Moreover, we find that daughters were nursed longer than sons, leading to a longer interval to next pregnancy. We examine this uncommon, but not unique, finding of female-biased human parental care in the light of Hutterite social structure, and we explore the consistency of this finding with the most applicable models of parental investment.
Correspondence to: S.W. Margulis 相似文献
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本文主要研究模糊控制技术在柴油发动机隔振系统中的应用,将模糊控制技术引入柴油发动机隔振主动控制系统,针对柴油发动机隔振模拟实验台架的振动特点,建立了控制系统数学模型,进行了柴油发动机隔振模拟实验台架垂直方向的仿真研究。 相似文献
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浙江城镇空间扩展与经济发展的遥感研究 总被引:1,自引:0,他引:1
近年来。浙江省经济飞速发展。城镇规模迅速扩大。但有关全省城镇建成区扩展面积的具体数量和扩展速度的客观数据还很缺乏。利用多时相的Landsat卫星遥感图像数据。采用目视解译与计算机自动分类方法,对1998~2001年浙江省城镇时空扩展进行了调查。调查结果显示,1998年和2001年浙江省县级以上城市建成区面积分别为977.85km^2和1499.06km^。3年内全省县级以上城市建成区面积扩展了521.21km^2,年增长速率达15.31%。在此基础上,根据区域社会经济统计数据,对城镇经济发展与城市空间扩展的相关性进行了分析。 相似文献
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如何发挥我国传统农业的优势,挖掘有机食品市场的巨大潜力,已引起有关方面的高度重视。本文在对铁岭市农业发展现状进行阐述的基础上,分析了铁岭市发展有机食品的优势,提出了发展铁岭市有机食品的若干建议。 相似文献