A screening model analysis of mercury sources, fate and bioaccumulation in the Gulf of Mexico

Mercury levels of yellowfin tuna (Thunnus albacares) are associated with capture location

“…As with previous studies we also detected relatively high levels of methylmercury in the fish caught from the GOM and NWAO, suggesting anthropogenic sources of mercury contamination in these fish. Indeed, this might be consistent with mercury contamination via the Atlantic Ocean Loop Current and/or mercury originating in the Mississippi River and being drained into the GOM (Buck et al, 2015; Harris et al, 2012a, 2012b).…”

Flux of Total Mercury and Methylmercury to the Northern Gulf of Mexico from U.S. Estuaries

“…Our data show that regardless of the efficiency of Hg retention within estuaries and the magnitude relative to other sources, rivers export substantial quantities of ∑MeHg and ∑Hg T to the nGOM. The fluxes determined in this study can be put into context by comparison to those predicted in a screening model of Hg in the GOM . After scaling of our ∑MeHg F sea to the area of the adjacent coastal ocean applied in the screening model (9.3 × 10 10 m 2 ), the loading is 1.3 nmol m –2 y –1 .…”

Nutrient supply and mercury dynamics in marine ecosystems: A conceptual model

“…One additional factor contributing to this difference is the tight coupling between the water column and sediments in some coastal waters, and the lack of any benthic influence on an oligotrophic open-ocean environment. Note that the benthic influence is also likely small for offshore areas of coastal ecosystems such as the Gulf of Mexico and the Gulf of Maine (Harris et al, this issue; Sunderland et al, this issue). Differences in MeHg inputs/availability can be normalized by calculating a bioaccumulation factor (BAF; L kg −1 ) for phytoplankton, which is the wet-weight concentration of MeHg in phytoplankton divided by that in filtered water.…”

“…Moreover, the response of primary production to a change in loading of the limiting nutrient is complex and variable across coastal waters due to factors such as tidal exchange, hydraulic residence time, photic depth and the importance of suspension feeders (Cloern, 2001). Depending on the watershed area and associated watershed sources, depth, area, bathymetry and exchange with the open ocean, substantial sources of ionic Hg and MeHg to coastal ecosystems could include atmospheric deposition, riverine inputs, coastal sediments and/or the open ocean (Balcom et al, 2010, 2008; Hammerschmidt and Fitzgerald, 2004; Harris et al, this issue; Sunderland et al, this issue, 2009). For example if ionic Hg and MeHg inputs are largely derived from riverine sources, then the impacts of nutrients on Hg dynamics might be manifested largely through enhanced deposition (removal) from the water column to sediments, biodilution associated with increased primary, secondary and tertiary production or decreases in photodecomposition (e.g., Bay of Fundy, New York Harbor).…”

“…There are multiple approaches to test ecosystem-level hypotheses (Carpenter, 1998), including time-series measurements at one or more sites (temporal patterns); ecosystem-level experiments (Harris et al, 2007); gradient studies (i.e., spatial patterns; Chen et al, 2009; Hammerschmidt and Fitzgerald, 2004; Hollweg et al, 2009); and ecosystem models (Harris et al, this issue; Hudson et al, 1994; Kim et al, 2008). Each has advantages and disadvantages, and research efforts are strengthened by the use of multiple approaches.…”