title: Isotopic evidence for anthropogenic impacts on aquatic food web dynamics and mercury cycling in a subtropical wetland ecosystem in the US.
abstract: Quantifying and predicting the food web consequences of anthropogenic changes is difficult using traditional methods (based on gut content analysis) because natural food webs are variable and complex. Here, stable and radioactive carbon isotopes are used, in conjunction with nitrogen isotopes and mercury (Hg) concentration data, to document the effects of land-use change on food webs and Hg bioaccumulation in the Everglades - a subtropical wetland ecosystem in the US. Isotopic signatures of largemouth bass and sunfish in reference (relatively pristine) wetlands indicate reliance on the food supply of modern primary production within the wetland. In contrast, both fish in areas impacted by agricultural runoff had radiocarbon ages as old as 540 years B.P., and larger isotopic variability than counterparts in reference wetlands, reflecting differences in the food web between impacted and reference wetlands. Consistent with this difference, particulate and dissolved organic matter in impacted areas had old radiocarbon ages (>600 years B.P.), indicating that old carbon derived from historic peat deposits in the Everglades Agricultural Area was passed along the food chain to consumers. Significant radiocarbon deficiencies in largemouth bass and sunfish, relative to mosquitofish, in impacted areas most likely indicate a reduced dependence on small fish. Furthermore, largemouth bass and sunfish from impacted areas had much lower Hg contents than those from reference wetlands. Taken together, these data suggest a shift toward lower trophic levels and a possible reduction in mercury methylation in impacted wetlands. Our study provides clear evidence that hydrological modification and land-use change in the Everglades have changed the system from one driven primarily by in-situ productivity to one that is partially dependent on allochthonous carbon input from peat soils in the agricultural area and altered the Hg biogeochemical cycle in the wetlands. The results have implications for the restoration and management of wetland ecosystems.
authors.affiliation: Department of Earth, Ocean & Atmospheric Science, Florida State University and National High Magnetic Field Laboratory, Tallahassee, FL 32306-4100, USA. Electronic address: ywang@magnet.fsu.edu.
authors.forename: Yang
authors.initials: Y
authors.lastname: Wang
authors.affiliation: South Florida Water Management District, West Palm Beach, FL 33406, USA.
authors.forename: Binhe
authors.initials: B
authors.lastname: Gu
authors.affiliation: Department of Geology and Geography, Auburn University, Auburn, AL 36839, USA.
authors.forename: Ming-Kuo
authors.initials: MK
authors.lastname: Lee
authors.affiliation: Institute of Hydrobiology/Laboratory of Eutrophication and Red Tide Prevention of Guangdong Higher Education Institutes, Jinan University, Guangzhou, Guangdong 510632, China. Electronic address: sjiang@jnu.edu.cn.
authors.forename: Shijun
authors.initials: S
authors.lastname: Jiang
authors.affiliation: Department of Earth, Ocean & Atmospheric Science, Florida State University and National High Magnetic Field Laboratory, Tallahassee, FL 32306-4100, USA.
authors.forename: Yingfeng
authors.initials: Y
authors.lastname: Xu
mesh_terms: D000818:Animals; D002247:Carbon Isotopes / Q000032:analysis; D017753:Ecosystem; D004784:Environmental Monitoring; D020387:Food Chain; D008628:Mercury / Q000032:analysis*; D009587:Nitrogen Isotopes / Q000032:analysis; D014481:United States; D014874:Water Pollutants, Chemical / Q000032:analysis*; D053833:Wetlands
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D014874:Water Pollutants, Chemical; D008628:Mercury
keywords: Bioaccumulation; Everglades; Fish; Food web; Mercury; Radiocarbon; Stable isotopes