Effects of drilling muds and mud additives on the primary production of natural assemblages of marine phytoplankton

Abstract

The effects of two types of drilling mud and eight mud additives on the primary production of natural assemblages of marine phytoplankton from the Santa Barbara Channel, California, were examined. Exposure for 4 h to BaSO 4 Ca-, Cr- and Fe- lignosulfonate, Drispac (a polyanionic cellulose polymer), X-Pel-G (gilsonite), Soltex (a sulfonated asphalt) and a synthetic reference drilling mud at concentrations ranging over seven orders of magnitude did not significantly alter primary production of phytoplankton relative to untreated controls. A used drilling mud from the Santa Barbara Channel significantly enhanced primary production of phytoplankton exposed for 4 h to mud diluted by a factor of 10 1 to 10 7. Exposure for up to 120 h to low concentrations of BaSO 4, iron-lignosulfonate, paraformaldehyde and both the reference drilling mud and used Santa Barbara mud did not significantly alter primary production. Long-term exposure to Soltex and gilsonite significantly reduced primary production, but only at exposure times considerably longer than would be expected in nature. Drispac enhanced primary production by 50 % after exposure for 120 h to 1 μg liter −1. Phytoplankton composition was not altered by long-term exposure to the muds or additives. These results suggest that, where dilution is rapid, discharge of muds containing the additives studied here would not significantly alter the primary production of natural phytoplankton assemblages in the vicinity of drilling platforms.