1,720,983 research outputs found
Methylmercury contamination and diet of nestling red-winged blackbirds
No full textRed-winged Blackbirds (Agelaius phoeniceus) feed their nestlings both methylmercury (MeHg)-contaminated emergent aquatic insects and terrestrial insects containing low concentrations of MeHg. There have been no studies of the relationship between MeHg contamination of nestling Red-winged Blackbirds and their diet. The objectives of this study were to monitor MeHg concentrations in nestling Red-winged Blackbird blood, estimate proportion of aquatic and terrestrial prey in diet, and quantify percentage of aquatic and terrestrial habitats around nests. Methylmercury concentrations in nestling blood were low, and ratios of MeHg and nitrogen stable isotopes indicate terrestrial insects composed a higher proportion of nestling diets. Nestling Red-winged Blackbirds may have been fed primarily terrestrial insects because there was more terrestrial foraging habitat than aquatic around nests. Red-winged blackbird nestlings may not be at risk of MeHg contamination when terrestrial organisms dominate their diet, however, proportion of terrestrial and aquatic habitats around nests may influence MeHg contamination risk
Effect of body size on mercury concentrations in shoreline spiders
No full textRecently, shoreline spiders have been proposed as biosentinels of mercury (Hg) contamination in the environment. Shoreline spiders become contaminated with Hg by feeding on Hg-contaminated emergent aquatic insects. Although body size is known to affect Hg bioaccumulation in other organisms (e.g. fish), few studies have tested the effect of body size on Hg concentrations in shoreline spiders. In this study, we determined the effect of body size on Hg concentrations in 6 taxa of shoreline spiders (Araneidae, Tetragnatha spp., Salticidae, Pardosa spp., Rabidosa spp. and Schizocosa spp.) from 14 human-made ponds at the LBJNG, Texas. Average concentrations of total-Hg (THg) were significantly different between spider taxa. We found that concentrations of THg in spiders increased significantly with body size (measured by tibia + patella length of the first leg) for Araneidae, Tetragnatha spp., Salticidae and Pardosa spp. This study indicates that Hg accumulation in shoreline spiders differs between spider taxa and within taxa by spider size
Spatial patterns of mercury risk to piscivorous wading birds of the south central United States
No full textMercury (Hg) is a toxic heavy metal that can pose a risk to birds. Piscivorous birds are exposed to Hg by consuming Hg-contaminated fish. Although there is data on concentrations of Hg in fish, the data on concentrations of Hg in birds is limited. I used a published relationship between concentrations of Hg in the blood of piscivorous birds and concentrations of Hg in prey fish to estimate concentrations of Hg in the blood of four species of piscivorous wading birds in the south central United States. Estimated concentrations of Hg in birds increased with the size of prey fish and increased with conifer-adjusted Hg deposition. This study shows that wading bird species that consume small prey fish are at little risk from exposure to Hg in while those that consume large prey fish are at moderate risk from Hg exposure in ecoregions with high conifer-adjusted Hg deposition
Mercury contamination of eight taxa of shoreline spiders and possible risk to arachnivorous songbirds
No full textMercury (Hg), a hazardous contaminant, can be transferred from aquatic to terrestrial environments by emerging aquatic insects. Spiders living along water shorelines may consume emerging aquatic insects and become contaminated with Hg. Mercury-contaminated spiders may pose a risk to arachnivorous songbirds. The objectives of this study were to determine 1) Hg concentrations in seven families of shoreline spiders, 2) if each family was connected to the aquatic food web via the consumption of emergent insects and 3) determine the risk contaminated spiders pose to arachnivorous songbirds. Methylmercury (MeHg) concentrations and stable isotopes of nitrogen (δ15N) revealed all spider taxa in the present study were contaminated with Hg and connected to the aquatic food chain. Calculated songbird wildlife values revealed six of the seven families of shoreline spiders contained MeHg concentrations high enough to pose a serious risk to arachnivorous songbirds that forage for spiders along water shorelines
An evaluation of mark-recapture and electrofishing CPUE-based models as techniques to estimate densities of largemouth bass in ponds
No full textEffects of bluegill on experimental mesocosm communities in the presence and absence of a fish assemblage
No full textSpatial patterns of mercury contamination of fish in the south central United States
No full textMercury (Hg) is a toxic metal that is found in aquatic food webs and is hazardous to humans. An emerging conceptual model predicts areas with the potential to contain food webs with elevated concentrations of Hg receive high amounts of Hg and sulfate deposition, have high coverage of forests and wetlands and low coverage of agriculture. The objective of this study was to test this conceptual model using concentrations of Hg in fish in the south central United States. Coverage by evergreen forests explained 73 percent of the variance of average mercury concentrations in the 14 ecoregions. Over 70% of the water bodies in ecoregions with evergreen forest coverage of 20% or greater have Hg concentrations in largemouth bass above the EPA criterion level of 300 ng/g. Evergreen forests in states in the southern ecoregions may constitute a significant hazard to human health through increased exposure to Hg from fish
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