The relevance of rooted vascular plants as indicators of estuarine sediment quality

Toxicity assessments and numerical quality assessment guidelines for estuar ine sediments are rarely based on information for aquatic plants. The effec t of this lack of information on contaminated sediment toxicity evaluations is largely unknown. For this reason, the toxicities of whole sediments col lected from 15 sites in three urbanized Florida bayou-estuaries were determ ined for the benthic invertebrates Mysidopsis bahia and Ampelisca abdita an d the plants Scirpus robustus Pursh (saltmarsh bulrush) and Spartina altern iflora Loisel (saltmarsh cordgrass). The results of the bioassays, conducte d for 7 to 28 days, were compared for interspecific differences and to effe cts-based, sediment quality assessment guidelines. A variety of inorganic a nd organic analytes were detected in the estuarine sediments, and concentra tions of as many as 7 analytes exceeded the sediment guidelines at the 15 s ampling locations. Toxicity occurred at 2 of the 15 sampling stations based on invertebrate survival. Twelve of the 15 sediments had either a signific ant stimulatory or inhibitory effect on early seedling growth relative to a reference sediment (p < 0.05). The phytoresponse was specific to the locat ion, test species, and plant tissue. There was no consistent trend between the sensitivities of the plants and invertebrates exposed to the sediments collected from the same sites. Of the 12 sediments that significantly affec ted seedling growth, 10 were not acutely toxic to the invertebrates. Conseq uently, the plant test species provided information that would have been mi ssing if only animal test species were used. For this reason, the phytotoxi city database needs to be expanded for contaminated sediments to further ev aluate interspecific sensitivities and to provide perspective on the enviro nmental relevancy of proposed sediment quality criteria and effects-based a ssessment guidelines for which this information is usually missing. However , additional test method development and field validation are needed to sup port this effort, which includes the identification of sensitive plant test species, response parameters, and the chemical and physical sediment facto rs that influence plant growth.