CHARACTERIZATION OF SOURCES OF ORGANIC POLLUTION TO KINGSTON HARBOUR, THE EXTENT OF THEIR INFLUENCE AND SOME REHABILITATION RECOMMENDATIONS

摘要

Sources of organic pollution to Kingston Harbour were assessed by monthly sampling at 22 rivers, gullies and discharge pipes emptying into the harbor between August 1996 and July 1997. These sources were divided into point and non-point sources and coupled with underground water and industrial flow assessed from 1992 and 1996 data. Organic pollution signatures were coliform bacteria, total suspended solids (TSS), biochemical oxygen demand (BOD), nitrite + nitrate nitrogen and phosphate phosphorous. Sewage is by far the most important contributor of organic pollution to Kingston Harbour, regardless of the signature used. The continuity and concentrations at the outfall of the Greenwich and Western sewage treatment plants render these two areas as the most significant point sources of pollution to the harbor. River flow is the second largest point source of organic pollution to the harbor; the degree of its contribution depending on rainfall since only at high flow does it make major contributions. Poor watershed management, extensive agriculture inputs from few, but large industries, large and growing residential areas and the length of the river creates problems. When the rivers are at low flow, industries and groundwater become major non-point sources of different pollutants. During periods of high water flow the gullies are small, but significant non-point sources of most pollutants. Fifty-five to 70% of the contributions of total suspended solid (TSS) is associated with sewage, while 23-30% is associated with a range of industries. Under high flow conditions, < 20% of TSS is associated with the outflow from rivers and gullies, while under low flow conditions, rivers and gullies make no meaningful contribution. Of the contributions of biochemical oxygen demand (BOD), 29-50% is associated with sewage, while 24-40% with industries. Under high flow conditions, 40% of BOD is associated with river outflow, while under low flow conditions, rivers make no meaningful contribution. Of the contributions of nitrate nitrogen, 55-65% is associated with sewage, approximately 30% is associated with ground water and < 20% associated with flow from rivers and gullies under high flow conditions. River and gully outflow under low flow conditions make no meaningful contribution. Of the contributions of phosphate phosphorous, 75-90% is associated with sewage and < 20% associated with high flow conditions from river and gully outflow. At low flow, industries and ground water make no meaningful phosphate phosphorous contribution. Having identified, quantified and ranked the sources of organic pollution to Kingston Harbour, recommendations are suggested for the improvement of the water quality. Among these are a reduction and/or cessation of sewage discharges to the harbor coupled with the use of a predictive hydrodynamic three-dimensional model and an ongoing monitoring program.