Fisheries of two tropical lagoons in Ghana, West Africa     

H. R. Dankwa  J. M. Shenker  & J. Lin  P. K. Ofori-Danson  Y. Ntiamoa-Baidu 《Fisheries Management and Ecology》2004,11(6):379-386

Abstract  The fisheries of two coastal lagoons, Keta and Songor, were studied as part of Ghana Coastal Wetlands Management Project (GCWMP) aimed at sustainable exploitation of wetland resources. Fish samples were obtained with seine nets and cast net as well as from local fishermen. Water quality parameters (pH, dissolved oxygen, temperature and turbidity) were similar in the two lagoons, except for salinity, which was significantly different ( P  < 0.001). Despite their close geographical proximity, the two lagoons supported different fish assemblages with the blackchin tilapia, Sarotherodon melanotheron Rüppell, and the redchin tilapia, Tilapia guineensis (Bleeker), being the most important commercial fishes in both lagoons. The number of individuals for each species in Songor Lagoon were far more abundant, with densities several orders of magnitude higher than in Keta Lagoon. However, both species were significantly larger ( P  < 0.01) in the latter [15–121 and 25–157 mm standard length (SL)] than in the former lagoon (30–102 and 15–95 mm SL) for S. melanotheron and T. guineensis respectively. Over-fishing, use of small-size mesh nets, limited mixing of marine and fresh water were some of the factors limiting fish production in both lagoons.  相似文献   

Recognised veterinary practice     

Sparkes A  Wray J  Leece E  de Risio L  Murphy S  Furneaux R  Sansom J  Coatesworth J 《The Veterinary record》2007,161(24):826; discussion 826-826; discussion 827

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Beyond MIRAB: Do aid and remittances crowd out export growth in Pacific microeconomies?     

Jon Fraenkel 《Asia Pacific viewpoint》2006,47(1):15-30

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宇宙核素地学研究的理论基础与应用模型   总被引：1，自引：0，他引：1  

李英奎  Jon Harbor  刘耕年  周力平  崔之久 《水土保持研究》2005,12(4):139-145

宇宙核素是宇宙射线与地表物质相互作用的产物，具有蜕变、中子捕获和介子反应三种形成机制。宇宙核素产生率随深度的变化而变化，同时还受纬度、高度和时间等因素的影响，其浓度变化与表面的暴露时间和侵蚀速率密切有关。宇宙核素的应用模型主要基于单一核素和核素对，单一核素方法只能解决一个未知因素，但核素浓度-深度分布曲线可用于复杂问题的解决。核素对方法可以解决具有多种未知因素的复杂状况，实际应用中主要基于核素比值变化曲线的分析。另外，基于核素对还可以解决埋藏年龄等问题。  相似文献   

Genetic tracking of the brown bear in northern Pakistan and implications for conservation     

Eva Bellemain  Muhammad Ali Nawaz  Alice Valentini  Jon E. Swenson  Pierre Taberlet 《Biological conservation》2007,134(4):537-547

Asian bears face major threats due to the impact of human activities as well as a critical lack of knowledge about their status, distribution and needs for survival. Once abundant in northern Pakistan, the Himalayan brown bear (Ursus arctos isabellinus) has been exterminated in most of its former distribution range. It presently occurs sparsely, in small populations, the Deosai National Park supporting the largest isolate. This decline might imply a reduction in genetic diversity, compromising the survival of the population. Using a combination of fecal DNA analysis and field data, our study aimed at assessing the size and genetic status of the Deosai population and give guidelines for its conservation and management. Using fecal genetic analysis, we estimated the population to be 40-50 bears, which compares well with the field census of 38 bears. The northern Pakistani brown bear population may have undergone an approximate 200-300-fold decrease during the last thousand years, probably due to glaciations and the influence of growing human population. However, in spite of the presence of a bottleneck genetic signature, the Deosai population has a moderate level of genetic diversity and is not at immediate risk of inbreeding depression. Gene flow might exist with adjacent populations. We recommend careful monitoring of this population in the future both with field observations and genetic analyses, including sampling of adjacent populations to assess incoming gene flow. The connectivity with adjacent populations in Pakistan and India will be of prime importance for the long-term survival of Deosai bears.  相似文献   

Empirical predictions of plant material C and N mineralization patterns from near infrared spectroscopy, stepwise chemical digestion and C/N ratios     

Sander Bruun  Bo Stenberg  Jon Gudmundsson  Lars S. Jensen  Jesper Luxhøi  Anders Pedersen 《Soil biology & biochemistry》2005,37(12):2283-2296

Prediction of carbon (C) and nitrogen (N) mineralization patterns of plant litter is desirable for both agronomic and environmental reasons. Near infrared reflectance (NIR) spectroscopy has recently been introduced in decomposition studies to characterize biochemical composition. The purpose of the current study was to use empirical techniques to predict C and N mineralization patterns of a wide range of plant materials incubated under controlled temperature and moisture conditions. We hypothesized that the richness of information in the NIR spectra would considerably improve predictions compared to traditional stepwise chemical digestion (SCD) or C/N ratios. Initially, we fitted a number of empirical functions to the observed C and N mineralization patterns. The best functions fitted with R²=0.990 and 0.949 to C and N, respectively. The fractions of C and N mineralized at different points in time were then either predicted directly with regression functions or indirectly by prediction of the parameters of the empirical functions fitted to incubation data. In both cases, partial least squares (PLS) regressions were used and predictions were validated by cross-validations. We found that the NIR spectra (best R²=0.925) were able to predict C mineralization patterns marginally better than the SCD fractions (best R²=0.911), but considerably better than the C/N ratios (best R²=0.851). In contrast, N mineralization was better predicted by SCD fractions (best R²=0.533) than the C/N ratio (best R²=0.497), which was better than NIR predictions (best R²=0.446). Although the predictions with the NIR spectra were only slightly better for C and worse for N mineralization compared to SCD fractions, NIR spectroscopy still holds advantages, as it is a much less laborious and cheaper analytical method. Furthermore, exploration of the applications of NIR spectroscopy in decomposition studies has only just begun, and offers new ways to gain insights into the decomposition process.  相似文献   

Agricultural Sediment Reduction by Giant Cane and Forest Riparian Buffers     

Jon E. Schoonover  Karl W. J. Williard  James J. Zaczek  Jean C. Mangun  Andrew D. Carver 《Water, air, and soil pollution》2006,169(1-4):303-315

The sediment filtering capabilities of giant cane (Arundinaria gigantea (Walt.) Chapm.) and forest riparian buffers were compared in a southern Illinois, USA non tile drained agricultural watershed. Giant cane, a bamboo species, serves as important wildlife habitat throughout its native range in the southeastern and lower midwestern United States. Overland flow samples were collected at the field edge and at 3.3 m, 6.6 m, and 10.0 m within the riparian buffers during 19 precipitation events over a 1-year period. On an annual basis, significant sediment reductions occurred by 3.3 m and 6.6 m in the cane and forest buffers, respectively. The giant cane buffer reduced incoming sediment mass by 94% within the first 3.3 m, while the forest buffer reduced sediment by 86% over 6.6 m. Within 10.0 m of the field edge, the cane and forest buffers reduced sediment mass by 100% and 76%, respectively. On a seasonal basis, the cane buffer outperformed the forest buffer. During each of the four seasons, the cane buffer reduced sediment masses within 3.3 m of the field edge, while the forest buffer showed initial reductions occurring at 6.6 m during the summer, fall, and winter. No detectable reductions occurred during the spring in the forested buffer. Reductions in sediment concentrations were less evident compared to mass basis, indicating that infiltration may be a more important sediment reduction mechanism than particle settling. Both the forest and giant cane buffers had relatively high measured soil infiltration rates. Study results indicate that giant cane is an appropriate species to include in riparian buffer restoration designs for sediment control.  相似文献   

Epidemiology. New estimates scale back scope of HIV/AIDS epidemic     

Cohen J 《Science (New York, N.Y.)》2007,318(5855):1360-1361

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Infectious diseases. Global fund pulls Myanmar grants     

Cohen J 《Science (New York, N.Y.)》2005,309(5739):1312

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Year-to-Year and Maturity Variation in Rainfed Soybean Yield by Planting Dates     

YANG Jin-zhong  Mark Alley  Jon Roygard 《中国农业科学(英文版)》2004,3(3)

The interactions on rainfed soybean yield among planting date,maturity,and year-to-year climate change were studied using CROPGRO-soybeanmodel.Simulations were based on 19 planting dates,maturity groupsⅢ,Ⅳ and V,30 years recorded weather data from Corbin,Suffolk,West Point in Virginia,USA.Yield was similar on early plantings and went down with late plantings.Both grand and year-to-year variation of soybean yield declined linearly with planting date.Year-to-year climate variation was dominant yield variation source in rainfed soybean production.Interaction occurred between planting date and maturity.Optimal planting dates for different sites lied within 130th-170th day of a year.Irrigation is recommended for profitable crops,especially in Corbin and West Point.  相似文献