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A population of Channa gachua in a small irrigation canal that supplies rice fields was studied by monthly sampling over 2 years. The population density was positively correlated with the rainfall and varied from 0.34 to 0.95 individuals m−2 . The growth parameters of the von Bertalanffy growth equation determined on monthly size–frequency data were Lx = 179 mm total length and K =0.50. Overall male to female ratio was 0.82 and there were more females than males in the middle size classes. Spawning occurred throughout the year, but all evidence indicated enhanced breeding during major rainy periods of May to July and October to December. The length at first spawning was 102 mm, which is reached in about 20 months. Fecundity, which varied between 389 and 2130, was positively correlated with gonad weight, body weight and total length. Longevity and natural mortality were estimated as 6 years and l.27 yr−1 , respectively. However, 99% of the population appeared to live for only 3 years. The mean biomass, average annual production and turnover ratio of the population were 7.35 g m−2 , 12.06 g m−2 and 1.64, respectively. 相似文献
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Measuring Success: Evaluating the Restoration of a Grassy Eucalypt Woodland on the Cumberland Plain, Sydney, Australia 总被引:10,自引:0,他引:10
Abstract We compared the floristic composition and structure of restoration areas of eucalypt woodland with untreated pasture (control) and remnant vegetation (reference) in western Sydney. The restored areas comprised over 1,000 ha of abandoned pasture, which had been treated to reduce weeds and planted with seedlings of 26 native plant species raised from seed obtained locally from remnant vegetation. Plantings were carried out 0–9 years ago. Floristic composition was measured in quadrats using frequency scores and cover abundance. As far as possible treatments and restoration ages were replicated across sites. Ordination and analyses of similarity failed to distinguish the composition of restored vegetation from that of untreated pasture, which were both significantly different from that of remnant vegetation. There was a weak compositional trend with age of restored vegetation, but this was not in the direction of increasing resemblance to remnant vegetation. There was some evidence for convergence in structural features of restored with remnant vegetation, but this was at least partly attributed to plant growth. Subject to constraints imposed by the sampling design, environmental factors, and spatial variation were discounted as explanations for the results. The results therefore suggest either failure of restoration treatments or a restoration trajectory that is too slow to detect within 10 years of establishment. Our conclusions agree with those of similar studies in other ecosystems and support: (1) the need to monitor restoration projects against ecological criteria with rigorous sampling designs and analytical methods, (2) further development of restoration methods, and (3) regulatory approaches that seek to prevent damage to ecosystems rather than those predicated on replacing losses with reconstructed ecosystems. 相似文献
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C. Marjorie Aelion J. N. Shaw R. P. Ray M. A. Widdowson H. W. Reeves 《Soil & Sediment Contamination》1996,5(3):225-241
Portable meters and simplified gas Chromatographic (GC) techniques were investigated for monitoring volatile hydrocarbon (HC), CO2, and O2, concentrations in groundwater, exhaust gases, and soil vapor during in situ remediation using soil vapor extraction (SVE) and air sparging (AS). Results of groundwater samples analyzed in‐house using a headspace technique compared well to split samples analyzed by a certified analytical laboratory (r2 = 0.94). SVE exhaust gas HC and CO2 concentrations measured using a GT201 portable HC/O2 meter and a RA‐411A meter (GasTech), respectively, were highly correlated with in‐house laboratory GC analyses (r2 = 0.91). O2 concentrations fell in a small range and meter analyses were not well correlated with laboratory analyses. Results of soil gas monitoring were not as well correlated as those for exhaust gases for HC, CO2, or O2, perhaps due to environmental conditions such as changes in relative humidity or the wider range of soil gas values. Overall, the meters were good indicators of vapor contamination, they greatly simplified estimates of total HC mass removal, and they allowed estimates of the biological contribution to contaminant removal during the remediation process. 相似文献
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北方稻田生态系统水量平衡及水分效率研究 总被引:15,自引:8,他引:7
1993~1995年研究了5种不同模式水稻田生态系统水量平衡及水分效率结果表明,不同水稻田模式其总耗水量之间有明显差异,其中节水模式和节水节肥模式较常规模式节省灌溉水达15~23%,水分生产效率增加30%以上.各模式蒸发蒸腾耗水量在同一生长季内基本相同.田间结构及调控管理对其无明显影响实测水稻生育期田间蒸发蒸腾量与计算的可能蒸发蒸腾量相差不过5%。 相似文献
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本文在青蛙胚胎诸生长期的核驰豫研究及电磁场对淡水鱼胚刺激后能促进其生长发育及机理研究的基础上,利用华东师范大学物理系研制的ACHV-2型脉冲电场刺激仪对美国青蛙的早期及神经期胚胎进行适当强度的刺激发现,它能使胚胎的孵化率提高20%以上,存活率提高30%左右,并能促进其后斯的生长发育速率达30%,研究结果进一步证明作者提出的电场作用机理的合理。 相似文献