Response of saltmarsh fungi to the presence of mercury and polychlorinated biphenyls at a Superfund site

Abstract

Ascomycetous fungi are the major decomposers of standing-decaying smooth cordgrass (Spartina alterniflora), the major grass of saltmarshes of the southeastern U.S.A. In Brunswick, Georgia, smooth-cordgrass marshes have received a potentially severe chemical insult at the USEPA LCP Superfund Site [dumping of mercury and polychlorinated biphenyls (PCB)]. We have examined levels of living-fungal standing crop (as ergosterol) and fungal sexual productivity (rate of ascospore expulsion) in naturally decaying leaf blades of smooth cordgrass at the LCP site, at a nearby, moderately polluted site, and at a pristine site in Georgia. Although toxicant levels in sediments at the LCP site are very high (total Hg, to 71 μg g-1 dry sediment; methylmercury, to 190 ng g-1; PCB, to 156 μg g-1), living-fungal biomass was higher at the LCP site (about 890 μg ergosterol g-1 organic mass of decaying-leaf system, for dead blades on wholly dead shoots) than at the nearby moderately polluted site (about 630 μg g-1) or the pristine site (about 590 μg g-1). Ascospore release was also higher at LCP than at the pristine site. Only methylmercury at tens of ng g-1 sediment gave any evidence of negative impact upon levels of living-fungal crop. We speculate that urban/industrial nitrogen input was responsible for the higher biomass of fungi at the Brunswick sites, and that either the toxicants and/or the hypothesized N input were responsible for the major difference in cordgrass-fungal species composition found (replacement of Phaeosphaeria spartinicola by Phaeosphaeria halima).