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An investigation into the causes of massive destruction of the vegetation around Tsekelewu Oil Field in the Niger Delta was carried out. The 200 km2 area suffering varying degrees of damage was mapped and the damage quantified by photo interpretation of black and white aerial photographs. Soil, surface and ground water samples were taken from the various zones for chemical analyses which included the determination of pH, electrical conductivity and soluble salt analysis.The results showed that salt accumulation decreased from the sea inland-wards, with some upsurge in the saline-fresh water transitional zone where the greatest damage occurred. The electrical conductivity of the ground water varied from 45 dS m−1 in the area of greatest damage to less than 4 dS m−1 in the fresh water zone where there was no apparent damage. The salt-tolerant species along the coast were not affected, but in the transitional saline-fresh water zone in which the electrical conductivity of ground water was greater than 30 dS m−1, all the vegetation including the relatively salt-tolerant white mangrove (Avicennia africana) were killed. This destruction is attributed to high salinity caused by salt water incursion from the sea.

S U M M A R YAcetylene reduction by Beijerinckia indica in shaken liquid cultures increased with increase of pC2H, up to 0.74 atm. Acetylene reduction was linear for at least 40 min. The oxygen partial pressure also affected activity with most acetylene reduction at a PO, of 0.15 atm for liquid cultures grown in air. I N T R O D U C T I O NThe reduction of acetylene to ethylene (Dilworth, 1966; Schollhorn & Burris, 1966 (1970) have reported that the oxygen sensitivity of the Azotobacteriaceae can lead to a false assessment of nitrogenase activity by the acetylene reduction test. We report here that different partial pressures of acetylene and oxygen greatly affect the level of acetylene reduction by Beijerinckia, a nitrogen-fixing bacterium found in some acidic tropical soils. METHODSBeijerinckia was obtained from the American Type Collection as Azotobacter indicum 9037. Cultures for subsequent inoculation were grown in 500 ml conical flasks, containing IOO ml of medium, at 30 "C on a reciprocating shaker (150 strokesimin). The medium contained : KH2P04, I -0 ; sucrose, 20.0 ; MgS04. 7H20, 0.5 ; Na,MoO,, 0.02 ; ferric citrate, 0.09; in g/1 distilled H,O, pH 5-5. The sugar and phosphate were autoclaved separately and added just before inoculating the flasks.Nitrogenase activity was measured by the acetylene reduction technique : 5 mi serum bottles equipped with gas-tight rubber stoppers were evacuated, flushed (using a vacuum line) several times with high purity argon and refilled with the desired partial pressure of oxygen and acetylene and then with argon to I atm, the calculated volume of the gases being injected directly into the bottles with a plastic disposable syringe. Three replicate vials were used for each treatment as well as a blank without added culture, to determine the level of ethylene contamination in the added acetylene. A, O2 and C2H, were obtained as high purity cylinder gases (Matheson Co., U.S.A.) and were used without further purification. A I ml sample of Beijerinckia culture (or of water for blanks) was usually injected to initiate the reaction. The reaction was usually terminated by injecting 5 N-H,SO, into the reaction mixture.The bottles were incubated in a 30 "C water bath with reciprocal shaking (152 strokes/ min). The ethylene produced was measured with a Varian aerograph model 6ooD gas