Mercury (Hg) contamination of aquatic ecosystems and subsequent methylmercury bioaccumulation are significant environmental problems of global extent. At regional to global scales, the primary mechanism of Hg contamination is atmospheric Hg transport. Thus, a better understanding of the long-term history of atmospheric Hg cycling and quantification of the sources is critical for assessing the regional and global impact of anthropogenic Hg emissions. Ice cores collected from the Upper Fremont Glacier (UFG), Wyoming, contain a high-resolution record of total atmospheric Hg deposition (ca. 1720-1993). Total Hg in 97 ice-core samples was determined with trace-metal clean handling methods and low-level analytical procedures to reconstruct the first and most comprehensive atmospheric Hg deposition record of its kind yet available from North America. The record indicates major atmospheric releases of both natural and anthropogenic Hg from regional and global sources. Integrated over the past 270-year ice-core history, anthropogenic inputs contributed 52%, volcanic events 6%, and background sources 42%. More significantly, during the last 100 years, anthropogenic sources contributed 70% of the total Hg input. Unlike the 2-7-fold increase observed from preindustrial times (before 1840) to the mid-1980s in sediment-core records, the UFG record indicates a 20-fold increase for the same period. The sediment-core records, however, are in agreement with the last 10 years of this ice-core record, indicating declines in atmospheric Hg deposition.
[1] The reactive transport of U(VI) in a shallow alluvial aquifer beneath a former U(VI) mill located near Naturita, CO, was simulated using a surface complexation model (SCM) to describe U(VI) adsorption. The groundwater had variable U(VI) concentrations (0.01-20 mM), variable alkalinity (2.5-18 meq/L), and a nearly constant pH equal to 7.1. U(VI) K D values decreased with increasing U(VI) and alkalinity, and these parameters were more important than sediment variability in controlling K D values. Reactive transport simulations were fit to the observed U(VI) and alkalinity by varying the concentration of U(VI) and alkalinity in recharge at the source area. Simulated K D values varied temporally and spatially because of the differential transport of U(VI) and alkalinity and the nonlinearity of U(VI) adsorption. The model also simulated the observed U(VI) tailing, which would not be expected from a constant K D model. The simulated U(VI) concentrations were sensitive to the recharge flux because of the increased flux of U(VI) to the aquifer. The geochemical behavior of U(VI) was most sensitive to the alkalinity and was relatively insensitive to pH.
Abstract. Great Salt Lake (Utah, USA) is one of the world's largest hypersaline lakes, supporting many of the western U.S.'s migratory waterbirds. This unique ecosystem is threatened, but it and other large hypersaline lakes are not well understood. The ecosystem consists of two weakly linked food webs: one phytoplankton-based, the other organic particle/benthic algae-based.Seventeen years of data on the phytoplankton-based food web are presented: abundances of nutrients (N and P), phytoplankton (Chlorophyta, Bacillariophyta, Cyanophyta), brine shrimp (Artemia franciscana), corixids (Trichocorixa verticalis), and Eared Grebes (Podiceps nigricollis). Abundances of less common species, as well as brine fly larvae (Ephydra cinerea and hians) from the organic particle/benthic algae-based food web are also presented. Abiotic parameters were monitored: lake elevation, temperature, salinity, PAR, light penetration, and DO. We use these data to test hypotheses about the phytoplankton-based food web and its weak linkage with the organic particle/benthic algae-based food web via structural equation modeling.Counter to common perceptions, the phytoplankton-based food web is not limited by high salinity, but principally through phytoplankton production, which is limited by N and grazing by brine shrimp. Annual N abundance is highly variable and depends on lake volume, complex mixing given thermo-and chemo-clines, and recycling by brine shrimp. Brine shrimp are food-limited, and predation by corixids and Eared Grebes does not depress their numbers. Eared Grebe numbers appear to be limited by brine shrimp abundance. Finally, there is little interaction of brine fly larvae with brine shrimp through competition, or with corixids or grebes through predation, indicating that the lake's two food webs are weakly connected.Results are used to examine some general concepts regarding food web structure and dynamics, as well as the lake's future given expected anthropogenic impacts.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.