| Isotope ratios of carbon (13C/12C) and nitrogen (15N/14N), on a parts per thousand (‰) basis relative to a standard, were used to trace carbon flows (δ 13C) and trophic positions of organisms (δ15N). Values of δ13C and δ15N were obtained for sediments, suspended particulate matter (SPM), plants, and animals found in the Miramichi River Estuary (New Brunswick, Canada) and used to show the relationship between food web structure and patterns of mercury biomagnification.; On a δ13C and δ15N basis, three different sources of energy were identified: terrestrial carbon, in situ estuarine primary production, and marine phytoplankton. Isotopically depleted δ13C and δ15N values verified terrestrial carbon was a major source of energy to estuarine sediments and SPM.; A cluster analysis of mean δ13C and δ 15N values for 47 abiotic and biotic groups in this study helped to structure the community of plants and animals. Eight distinct clusters were formed: (1) estuarine sediment, and estuarine and freshwater SPM; (2) estuarine and marine primary producers; (3) freshwater fish and submerged terrestrial leaf litter, and estuarine oysters; (4) estuarine filter-feeding invertebrates; (5) estuarine deposit-feeding invertebrates; (6) estuarine planktivorous and benthivorous fish, some benthic invertebrates, and two filter-feeding marine fish; (7) estuarine carnivorous and two benthivorous fish; and (8) double crested cormorant eggs (whites and yolks). The results of this analysis show that for this coastal ecosystem, no distinction can be made in δ13C and δ15N values between estuarine and marine primary producers and filter-feeding fish, whereas freshwater fish and submerged terrestrial leaf litter were characterised by their isotopically light δ13C values.; Based on measurements of δ13C and δ 15N differences between a predator and its prey, an average δ 13C- and δ15N-trophic enrichment factor (TEF) of 1.87 ± 0.16‰ and 2.94 ± 0.14‰, respectively, were calculated for the Miramichi River Estuary food web. Consistent with observations in other aquatic studies, a total of 4.7 δ15N-defined trophic levels were identified for the Miramichi River Estuary food web. (Abstract shortened by UMI.)... |
