The effect of salinity on the microbial mineralization of two polycyclic aromatic hydrocarbons in estuarine sediments

Abstract

Sediments from the lower Hudson River estuary and two other coastal environments were examined experimentally for their ability to mineralize (convert to CO 2) the polycyclic aromatic hydrocarbons (PAHs) naphthalene and anthracene over a range of salinities. Routine assays employed 1:1 (vol fresh sed:vol water) sediment slurrys in order to overcome natural variability in mineralization rates among replicates. Mineralization rates were stimulated by about 2·5 fold, compared to unslurried controls, while the coefficient of variation fell from 13% to 3·5%. Rates of naphthalene mineralization in surface sediments from along the mainstem of the Hudson River (salinities from 2 to 27%) ranged from 0·011 to 1·5 nmol cm −3 day −1 (pool turnover [T n] from 60 to 2040 days) with no discernible trends along the estuarine gradient. For two stations examined experimentally (mile point 5, salinity 23%; mile point 26, salinity 5%), microbial assemblages appeared acclimated to broad salinity variations as alter rates of mineralization compared to controls. Sediments from two upstream marshes of the Hudson (mile points 36 and 45) showed rates of naphthalene mineralization from 0·007 to 0·15 nmol cm −3 day −1 (T n from 14 to 368 days), while sediments from a third marsh in freshwater (mile point 76) had high rates (66 nmol cm −3 day −1; T n 40 days). For the two upstream marsh stations which rarely experienced salt intrusion, there was a substantial decrease in mineralization of naphthalene and anthracene with increasing salinity. Consistently high rates of naphthalene mineralization (780 to 1600 nmol cm −3 day −1; T n 5 to 6 days) were observed in petroleum contaminated sediments from Port Jefferson Harbor (PJH) on the north shore of Long Island. PJH has a relatively constant salinity regime (about 27%) and imposed decreases in salinity effected decreases in rates of naphthalene and anthracene mineralization. Lowest rates of naphthalene mineralization (0·003 to 0·004 nmol cm −3 day −1; T n from 714 days to 833 days) were found in sediments from two stations in the relatively pristine Carmans River estuary on the south shore of Long Island. The ability of increases or decreases in salinity to affect the rate of model PAH mineralization appeared to be dependent on the natural variation in the salinity regime from which a sample was obtained. Data from all the environments studied indicated a strong positive correlation between PAH concentration and the rates of mineralization of naphthalene. Rates of PAH mineralization in all environments examined appear to be primarily controlled by the extent of pollutant loading and not by natural variations in the salinity regime.