Effects of substrate salinity on early seedling survival and growth of Scirpus robustus Pursh and Spartina alterniflora Loisel.

Rooted aquatic plants are being used increasingly to test the toxicity of sediments. However, effects of naturally occurring substrate constituents on most potential test species are not well understood even though their effects could affect the test results. The objective of this study was to determine the effect of substrate salinity (NaCl) on early seedling survival and growth of the emergent macrophytes, Scirpus robustus Pursh and Spartina alterniflora Loisel. Results of four 21- and 28-day toxicity tests, conducted in an artificial sediment, indicated interspecific differences in NaCl sensitivity when based on changes in shoot, root and whole plant dry-weight biomass. Concentrations of 7.8 g NaCl/l and 19.2 g NaCl/l first reduced early seedling biomass of S. robustus and S. alterniflora (P<0.05), respectively, when compared to plants grown in sediment containing no measurable salinity. Seedling survival was not affected at average concentrations of 17.5 g NaCl/l or less for S. robustus and 22.3 g NaCl/l or less for S. alterniflora. The results indicate that substrate salinity is an important consideration in the selection of test species for laboratory phytotoxicity tests conducted with estuarine sediments, particularly if determination of chronic toxicity attributable to anthropogenic contamination is the primary objective.