Using a macroalgal 5~(15)N bioassay to detect cruise ship waste water effluent inputs

摘要

Green macroalgae bioassays were used to determine if the 6~(15)N signature of cruise ship waste water effluent (CSWWE) could be detected in a small harbor. Opportunistic green macroalgae {Ulva spp.) were collected, cultured under nutrient depleted conditions and characterized with regard to N content and 515N. Samples of algae were used in controlled incubations to evaluate the direction of isotope shift from exposure to CSWWE. Algae samples exposed to CSWWE exhibited an increase of l-2.5%o in 8~(15)N values indicating that the CSWWE had an enriched isotope signature. In contrast, algae samples exposed to field conditions exhibited a significant decrease in the observed 8~(15)N indicating that a light N source was used. Isotopically light, riverine nitrogen derived from N_2-fixing trees in the watershed may be a N source utilized by algae. These experiments indicate that the 5~(15)N CSWWE signature was not detectable under the CSWWE loading conditions of this experiment.