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81.
Essien. D. Udosen 《环境科学学报(英文版)》2000,12(1):75-80
IntroductionPhysicalandchemicalpropertiesareofgreatsignificancetotheworkingofanyaquaticecosystem.Inmostcases,thechemicalproper... 相似文献
82.
A. Singh R. J. Carsky E. O. Lucas K. Dashiell 《Agriculture, ecosystems & environment》2003,100(2-3):231
Legume–cereal rotation may reduce the fertilizer requirement of the cereal crop and we hypothesize that the benefit depends on the maturity class of the soybean. Field trials were therefore conducted in 1995 in four Guinea savanna sites to monitor the effect of soybean (Glycine max (L.) Merrill) cultivation on the N balance of the soil. In trial 1, an early (TGx1485-1D) and a late (TGx1670-1F) soybean were grown to maturity along with a maize (Zea mays L.) reference plot. In trial 2, six varieties of soybean (early: TGx1485-1D, TGx1805-2E and TGx1681-3F; medium: TGx1809-12E and TGx923-2E; late: TGx1670-1F) were grown to maturity along with a reference maize plot. The total nitrogen (N) content, aboveground N2 fixed, and N remaining in the stover were higher in the medium and the late varieties than in early varieties. Also, the early varieties had higher nitrogen harvest indices (81–84%) than medium and late varieties (74–79%). From the N balance calculation, it was found that medium and late maturing soybean resulted in an addition of 4.2 kg N ha−1 to the soil, whereas the early maturing varieties resulted in depletion of the soil N reserve by 5.6 kg N ha−1 (P<0.05). On average, among the medium and late varieties, late maturing TGx923-2E resulted in an addition of 9.5 kg N ha−1 to the soil. When the stover was not returned to the field, early soybean resulted in more negative N balance than the medium and late soybean (P<0.05). Therefore, planting an early variety of soybean for one season resulted in net depletion of soil N, even when the soybean residues were returned to the soil and N2 fixed in the roots and N in the fallen leaf litter were included in the N balance calculations. Contrary to this, planting medium and late soybean for one season resulted in an addition of N to the soil. Therefore, medium and late soybean should be used as a preceding crop in legume–cereal rotation, if possible, to minimize or avoid depletion of soil N by early varieties of soybean. 相似文献
83.
MFON T. UDO 《环境科学学报(英文版)》2002,14(2):221-226
IntroductionNigerianmangroveswampshavegreatfisheriespotentialsandmuchisstillneededtopreservetheecosysteminviewofthepotentprevalenceandaggressivereplacementofthemangrove (Rhizophora)bytheexoticnipapalms (Nypa) (Moses,1 985;Wilcox ,1 985;King ,1 997) .Amongthecommonfa… 相似文献
84.
This study was carried out to determine the occurrence, prevalence and contributing factors to the incidence of goitre in
Yewa north local government area of Ogun state, southwestern Nigeria. To achieve these objectives, soil, water, and cassava
tubers were collected from four villages – Igbogila, Egua, Sawonjo and Imoto and from Lagos (about 250 m to the ocean) as
a reference location, in order to determine their iodine concentrations. The results of the analyses indicated a soil mean
iodine range of 2.1–5.8 μg g−1; a cassava mean iodine value of 2.3–3.5 μg g−1 and a drinking water mean iodine value of generally <1.0 μg L−1 in all the four villages. These values of iodine in soil and water of the four villages are considered low when compared
with the soil iodine value of 7.4 μg g−1 and water iodine value of 6.1 μg L−1 obtained from Lagos. The limestone unit of the study area remains an inhibiting factor in the bioavailability of the iodine
because of its alkalinity. Statistical analysis has shown that there was significant difference between iodine concentration
in the soils and the drinking water, and a correlation between the soil iodine and organic matter content at p < 0.05. The correlation between soil iodine and granulometric fractions occurred at p < 0.01. Potential goitrogens in the commonly consumed cassava products might also have contributed to the prevalence of goitre
in the study area. Both the females and the adults (i.e., less mobile groups) were found to be vulnerable to goitre development
in these villages. 相似文献
85.
1IntroductionNatureinitsbenevolenceproducedcomplexandinterelatedenvironmentalsystems,bothbioticandabiotic,whosefunctioningisc... 相似文献
86.
Two marine bacterial isolates from drill mud cuttings obtained from Agbara oilfield,Staphylococcus sp. andBacillus sp., were cultured aerobically in the presence of varying concentrations (0, 25, 50, and 75 μg/ml) of drilling fluids to
determine the effects of concentration of toxicants on their growth. With the exception of Clairsol, Enviromul, and Baroid
mineral oil, which had little or no effect, the exponential growth ofBacillus sp. was depressed by all other test chemicals. Additionally, all test chemicals except Clairsol had no effect on lag phase
of growth ofBacillus sp. WithStaphylococcus sp. the depressive effect on the exponential phase of growth was shown by almost all test chemicals. There was enhancement
of both growth rate and generation times ofStaphylococcus sp. and decrease of those ofBacillus sp. with increasing concentrations of drilling fluids. These results show that while some drilling fluids may be stimulatory
or depressive to bacterial growth, others may be without effect. 相似文献
87.
This research focuses on the effect of debris-flow on thevarious hydrogeochemical processes occurring at Cross-River as aresult of disposal of industrial and household wastes as well as sewage into the river. It also focuses on development anddetermination of the saline nature of the rivers dry land.The study is carried out by a survey at different depths of theriver for water and soil samples analysis.The results show that concentrations of cations and anionsreasonably high and uniform except for nitrates which is quitehigh due to agricultural activities occurring in the study areas.Also Mg and SO4 ions are high due to reactions within thecolluvium include ion exchange of calcium for sodium in basalclays; dissolution of sodium chloride from dust – derived saltparticles in the clay-rich colluvium reactions.The Electrical conductive shows that Cross-River containsdissolved solids. Soil analysis indicates the presence of K, Ca,Mg, and Cl. pH values were also deducted from soil samples (6.30–6.45). 相似文献
88.
Innocent Chidi Nnorom 《毒物与环境化学》2016,98(2):149-166
Major and trace elements were determined in nzu (calabash clay) from Abia State, Nigeria, by atomic absorption spectrophotometry. Mean calcium content was 1900 ± 100 mg/kg dry weight, followed by Na 1400 ± 96, Fe 1500 ± 480, K 260 ± 150, and Mg 100 ± 48 mg/kg. The mean concentration of Zn was 35 ± 5, Cu 16 ± 2.0, Mn 17 ± 5.0, Cr 10 ± 1.0, Ni 9.0 ± 2.0, Cd 4.3 ± 1.7, Co 3.9 ± 1.1, and Pb 3.0 ± 0.8 mg/kg. The contents of Ba and V were <0.4 mg/kg. The mean Pb content was higher than the WHO safe limit (0.4 mg/kg) and EU (1 mg/kg) limit for food. Estimates of daily intake of Cd, Cr, Fe, and Ni upon consuming 30–80g of nzu were above the recommended daily intake values. The Ba, Ca, Co, K, Mg, Na, and Zn contents should not exceed the recommended daily intake while Cd, Ni, and Pb would pose health risks, especially in pregnancy. The total target hazard quotient indicated potential health risks to consumers. 相似文献
89.
Disturbance of the Macroinvertebrate communities of bank-root biotope of a river in southern Nigeria
J.O. Olomukoro 《毒物与环境化学》2013,95(2):305-314
The impact of disturbance on the macroinvertebrate community was investigated in the biotope of a river catchment area. A total of 56 and 18 taxa were recorded at Stations 1 and 2, accounting for 71 and 29% individual organisms, respectively. Twelve taxa were common at both stations. Baetidae (Ephemeroptera) constituted the predominant group with the 46% density at the upstream biotope of Station 1, whereas, family Hydrobidae (Mollusca) dominated numerically the downstream Station 2. Data revealed that months of sampling at stations significantly influenced the occurrence and abundance of the major groups. Three distinct patterns of seasonal affiliation among the benthos were observed. Monthly variation in species diversity occurred. The macroinvertebrate community was affected by disturbances at the downstream bank-root biotope, limiting the occurrence of life forms to a few adaptable groups. 相似文献
90.
Chukwujindu M.A. Iwegbue 《毒物与环境化学》2013,95(7):1341-1358
Sequential chemical extraction of metals (Cu, Ni, Mn, Fe, Pb, Cr, and Zn) from core sediments of the Orogodo River was carried out with a view of providing information on the phase distribution of these metals with respect to depths and seasons. The results indicate that copper was speciated into organic matter/sulfide, Fe–Mn oxides, and residual forms at 0–5?cm depth while at deeper sections copper was predominantly in the residual form. Nickel was speciated mainly into Fe–Mn oxides and residual forms. The average of lead in various particulate phases of the sediment are 0–100% for residual; 0–8% for carbonate; 0–16.2% for exchangeable; 0–10% for organic matter/sulfide form and 22–56% for Fe–Mn oxides bound metals. Manganese was speciated into exchangeable (10–36%) and Fe–Mn oxides bound (10–48%) at the surface layers of 0–20?cm depths and predominantly in the residual form in deeper sections implying partitioning into trioctahydral clay and/or well-defined crystalline oxides. Iron was predominantly in the Fe–Mn oxides and residual fractions, less than 8% in the organic fraction, and 24.4–37.3% in the exchangeable and carbonates fractions at the surface. The percentage contributions of iron in the exchangeable and carbonate fractions decreased to 3.2% at 55–60?cm depth. The amount of chromium in the exchangeable fraction ranged from 0% to 7% for exchangeable; 0–26.5% for organic matter/sulfide bound; 3.8–17.9% for Fe–Mn oxides; and 46.8–100% for residual fraction. The mobility factors of the metals indicated that these metals were relatively mobile at top sections as compared with deeper sections. The overall picture of metal mobility and availability indicates potential contamination risk by Fe, Zn, Mn, and Pb in the Orogodo River sediment system. 相似文献