By Ezeilo, Ebelechukwu Fabian
In this research work, the effect of environmental pollution on the dissolved oxygen resources of a receiving stream, Amadi creek, was investigated .Amadi creek, located in Port- Harcourt metropolis is a unique creek that is of high economic importance to the residents of Rumuobiakani, Mini-Ewa, Oginigba, Woji and Okujagu communities as it hosts the activities of the majority of the companies around the Trans- Amadi Industrial area and also provides water for fishing and water transportation The study was carried out to evaluate the water quality changes resulting from increasing human and industrial activities in and around the creek. For this purpose the physic o -chemical characteristics of the water in the creek at different seasons were measured and the results compared against W.H.O standards. Statistical methods were used at some point to calculate the mean, variance and the standard deviations in all stations and the results were then presented using computer based excel spreadsheet. The results show that the creek has relatively low concentrations of heavy metals ranging from (0.26-0.30mg\l), (0.00-0.01mg\l), (0.01-0.02mg\l), and (0.85-1.17mg\l for chromium, copper, aluminum and iron respectively. Mean values of other physic o- chemical parameters like temperature, salinity, suspended solids, pH, DO, BOD, range from (22.1-29.5oC), (0.1-2.7mg\l), (7.0-59.5mg\l), (6.3-8.4), (2.3-5.11mg\)],(0.8-5.7mg\l) respectively. Dissolved oxygen water quality standards for creeks and rivers require the maintenance of DO level of 5mg\l or more at any time. However, practical analysis of the water samples for dry and wet seasons showed that the conditions in the creek fall below this standard. .Measured DO concentrations were found to be as low as 2.3mg\l. Hence this research attempted to solve this problem of DO depletion by optimizing the locations of waste discharge locations into the creek. The DO deficit equations are solved by the methods of simple calculus (classical optimization), which simplifies the mathematical solution of the model equations by avoiding difficult to evaluate integrals. Two scenarios were identified and used to investigate the effect of BOD on the DO level in the stream, using mathematical simulation techniques. Simulation results of the two scenarios suggest that the dissolved oxygen deficit is dependent on the distance between waste discharge points .Hence to ensure minimum impact on water quality, waste discharge locations should be placed at the optimal locations of 10015m and 6992m upstream and downstream waste discharge points respectively, at an optimum DO deficit of 4.14 mg/l for the first scenario, and at 41233m, 40995m, 33605m upstream and downstream waste discharge points respectively for the second scenario at an optimum DO deficit of 4.57mg/l. This means that if a new waste input ( e.g., a new sewage treatment plant) is proposed for a stream or river, both its BOD input and the proposed location with respect to the other inputs are important in order to determine the effects of pollution on the stream DO level. Comparing the Dt values predicted by the new models with Ugbebor, the new models are in good agreement with the values of observed Dt with a standard error of 1.05%. It is recommended that Industrial establishments planning to site their treatment facilities along rivers or streams should be compelled to discharge their waste stream in compliance with the optimal locations (with respect to any existing plant) ,and the existing effluent standards, so as to avoid undue dissolved oxygen (DO ) depletion .