Effects of Petroleum Releases on Bacterial Numbers and Microheterotrophic Activity in the Water and Sediment of an Arctic Marine Ecosystem

Abstract

The effects of a petroleum slick and chemically dispersed petroleum on bacterial numbers and microheterotrophic activity (uptake,of glutamic acid by heterotrophic microorganisms) were monitored in the watecro lumn and sediments of selected bays at Cape Hatt, Northwest Territories. Observations were made between 1980 and 1983 as a component study of the Baffin Island Oil Spill (BIOS) Project. These data were augmented by measurements of chlorophyll a , particulate and dissolved organic carbon and inorganic nutrients in the water column, while total organic carbon (TOC) was measured in the sediments in some years. Petroleum was released on two occasions in 198 1.I n the firstr elease, nondispersed petroleum moved across the surface of test Bay 11 and adhered to the intertidal sediments at low tide. No significant effects were seen in chemical or microbiological variables measured in 1981 or 1982. During thes econd release in 198 1 , dispersed petroleum was carried by the current through the water otef st Bays 9 and 10 and into the channel beyond. Measurements of V, (maximum velocity) of glutamic acid uptake in waters amples taken in these bays during the release showed a transient decrease in V , , compared with control Bay 7. Bacterial numbers were unaffected, as were variables measured in the sediment of test Bays 9 and 10 during and after the release. I n virro experiments with water samples demonstrated that a combination of petroleum and dispersant or dispersant alone reduced the V, of glutamic acid uptake to a greater extent than petroleum alone. A bay-year analysis of variance between 1981 and 1982 demonstrated that TOC and bacterial numbers increased in the sediments of test Bay 9 over 1981, while the , V of glutamic acid uptake remained constant. In control Bay 7 and test Bay1 1 , all variables decreased over 198 1 except TOC in Bay 1 1 . In 1983, trends in the sediments of Bay 9 were similar to those of Bay 7. In test Bay 1 1 , petroleum beached on the intertidal zone in 1981 was observed entering subtidal sediments between 1981 and 1983 and forming a decreasing gradation of petroleum concentrations from nearshore to offshore areas. TOC increased between 1982 and 1983. Microheterotrophic activity remained constant in Bay 11, although it decreased in Bays 9 and 7. Bacterial numbers increased in Bay 1 1 but decreased in Bays 9 and 7. It was concluded that the changes in Bay 9 in 1982 and in Bay 11 in 1983 were a consequence of perturbations by petroleum. Effects on the benthic macrofauna and flora increased the levels of detritus, and hence TOC, in the sediments. This caused changes in bacterial numbers and microheterotrophic activity.