780 research outputs found

    Analysis of Jovian decamteric data: Study of radio emission mechanisms

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    This research effort involved careful examination of Jovian radio emission data below 40 MHz, with emphasis on the informative observations of the Planetary Radio Astronomy experiment (PRA) on the Voyager 1 and 2 spacecraft. The work is divided into three sections, decametric arcs, decametric V bursts, and hectometric modulated spectral activity (MSA)

    Evaluating Restored Tidal Freshwater Wetlands

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    Tidal freshwater wetlands are recognized as highly productive coastal wetlands that support diverse assemblages of plants and animals and complex biogeochemical cycles (in this book, see Chapter 18 by Whigham et al. and Chapter 19 by Megonigal and Neubauer). Many tidal freshwater wetlands and their associated ecosystem services have been damaged or destroyed by urbanization, agriculture, and other human activities (Baldwin, 2004; Barendregt et al., 2006). Increasing recognition of the value of remaining wetlands and environmental regulations requiring wetland mitigation (i.e., enhancement, creation, or restoration of wetlands to compensate for wetland losses; Kentula, 2000) has driven the restoration of all types of wetlands, including tidal freshwater wetlands. These restoration projects have been increasingly studied by restoration ecologists, with the overarching goal of improving restoration approaches. In this chapter, we first review characteristics of restored tidal freshwater wetlands in North America and Eurasia, where most studies have been done, including their distribution, general construction methods, and motivating factors for restoration (Section 2). Then we present criteria for evaluating tidal freshwater wetland restoration projects (Section 3). Next we describe a case study of restored tidal freshwater wetlands in the Anacostia River watershed in Washington, DC, USA (Section 4). Finally, we provide conclusions and recommendations to increase the successful restoration of tidal freshwater wetlands (Section 5)

    Bioaccumulation and Biomagnification of Mercury and Methylmercury in Four Sympatric Coastal Sharks in a Protected Subtropical Lagoon

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    Mercury bioaccumulation is frequently observed in marine ecosystems, often with stronger effects at higher trophic levels. We compared total mercury (THg) and methylmercury (MeHg) from muscle with length, comparative isotopic niche, and diet (via δ13C and δ15N) among four sympatric coastal sharks in Florida Bay (USA): blacknose, blacktip, bull, and lemon. Mercury in blacknose and blacktip sharks increased significantly with size, whereas bull and lemon sharks had a high variance in mercury relative to size. Both δ13C and δ15N were consistent with general resource use and trophic position relationships across all species. A significant relationship was observed between δ13C and mercury in blacktip sharks, suggesting an ontogenetic shift isotopic niche, possibly a dietary change. Multiple regression showed that δ13C and δ15N were the strongest factors regarding mercury bioaccumulation in individuals across all species. Additional research is recommended to resolve the mechanisms that determine mercury biomagnification in individual shark species
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