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Nitrogen biogeochemistry of water-agro-food systems: the example of the Seine land-to-sea continuum Full text
2021
Billen, Gilles | Garnier, Josette
As an illustration of the usefulness of the concept of water-agro-food systems, this paper describes the mechanisms behind the nitrogen cascade from agricultural soils to the coastal sea rivers through aquifers, riparian wetlands, rivers and streams and the estuary, for the case study of the Seine river watershed and its receiving coastal sea. It is stressed that the structure of the agro-food system, i.e. the way food production and trade, as well as consumption and waste management are organized, is the main determinant of the quality of ground- and surface water as well as of aquatic ecosystem functioning.
Show more [+] Less [-]Organic carbon content drives methylmercury levels in the water column and in estuarine food webs across latitudes in the Northeast United States Full text
2019
Taylor, V.F. | Buckman, K.L. | Seelen, E.A. | Mazrui, N.M. | Balcom, P.H. | Mason, R.P. | Chen, C.Y.
Estuaries are dynamic ecosystems which vary widely in loading of the contaminant methylmercury (MeHg), and in environmental factors which control MeHg exposure to the estuarine foodweb. Inputs of organic carbon and rates of primary production are important influences on MeHg loading and bioaccumulation, and are predicted to increase with changes in climate and land use pressures. To further understand these influences on MeHg levels in estuarine biota, we used a field study approach in sites across different temperature regions, and with varying organic carbon levels. In paired comparisons of sites with high vs. low organic carbon, fish had lower MeHg bioaccumulation factors (normalized to water concentrations) in high carbon sites, particularly subsites with large coastal wetlands and large variability in dissolved organic carbon levels in the water column. Across sites, MeHg level in the water column was strongly tied to dissolved organic carbon, and was the major driver of MeHg concentrations in fish and invertebrates. Higher primary productivity (chlorophyll-a) was associated with increased MeHg partitioning to suspended particulates, but not to the biota. These findings suggest that increased inputs of MeHg and loss of wetlands associated with climate change and anthropogenic land use pressure will increase MeHg concentrations in estuarine food webs.
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