10.1021/es902361j.s001
David B. Senn
David B.
Senn
Edward J. Chesney
Edward J.
Chesney
Joel D. Blum
Joel D.
Blum
Michael S. Bank
Michael S.
Bank
Amund Maage
Amund
Maage
James P. Shine
James P.
Shine
Stable Isotope (N, C, Hg) Study of Methylmercury Sources and Trophic Transfer in the Northern Gulf of Mexico
American Chemical Society
2010
baseline δ15 N signatures
food webs
Δ201
influence MeHg accumulation
MeHg sources
GOM
oceanic MeHg sources
MR
oceanic species
2010-03-01 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Stable_Isotope_N_C_Hg_Study_of_Methylmercury_Sources_and_Trophic_Transfer_in_the_Northern_Gulf_of_Mexico/2788570
We combined N, C, and Hg stable isotope measurements to identify the most important factors that influence MeHg accumulation in fish from the northern Gulf of Mexico (nGOM), and to determine if coastal species residing in the Mississippi River (MR) plume and migratory oceanic species derive their MeHg from the same, or different, sources. In six coastal species and two oceanic species (blackfin and yellowfin tuna), trophic position as measured by δ<sup>15</sup>N explained most of the variance in log[MeHg] (<i>r</i><sup>2</sup> ∼ 0.8), but coastal species and tuna fell along distinct, nearly parallel lines with significantly different intercepts. The tuna also had significantly higher δ<sup>202</sup>Hg (0.2−0.5‰) and Δ<sup>201</sup>Hg (∼1.5‰) than the coastal fish (δ<sup>202</sup>Hg = 0 to −1.0‰; Δ<sup>201</sup>Hg ∼0.4‰). The observations can be best explained by largely disconnected food webs rooted in different baseline δ<sup>15</sup>N signatures (MR-plume vs oceanic) and isotopically distinct MeHg sources, with oceanic MeHg having undergone substantial photodegradation (∼50%) before entering the base of the food web. Given the MR’s large, productive footprint in the nGOM and the potential for exporting prey and MeHg to the adjacent oligotrophic GOM, the disconnected food webs and different MeHg sources are consistent with recent evidence in other systems of important oceanic MeHg sources.