Petroleum hydrocarbon concentrations in a salmonid stream contaminated by oil field discharge water and effects on macrobenthos

Abstract

The concentration of total hydrocarbons in the water effluent from an oil field was 5.6 mg/L and resulted in concentrations of 46 to 85μg/L in the receiving stream. Total hydrocarbons were 55,000 times more concentrated in the sediment than in the water, ranging from 979 (778) to 2,515 (1,263) mg/kg. Saturated hydrocarbons contributed most to the total hydrocarbon concentration in both water and sediment. Naphthalenes were found in stream water, but not in sediment. Cadmium, chromium, copper, lead, and zinc were detected in water and sediment. Zinc was elevated in the sediment, probably because an organic zinc complex was used by the oil company during processing to enhance oil-water separation. Species diversity of macrobenthos was reduced below the discharge, as evidenced by the almost complete elimination of Plecoptera and Trichoptera. Shannon-Weaver diversity index values ranged from 3.4 at the upstream control station to 1.2 to 1.7 below the oil field effluent. The representation of Diptera increased from 10% of the total insects at the least polluted station to 46% at the station containing the most dissolved hydrocarbons. On the basis of our findings, discharge of oil into fresh water should be closely regulated to prevent the development of concentrations in water and sediment of the receiving stream that would alter the structure of macrobenthos communities and thereby threaten the fishery resources.