Browsing by Subject "Heavy metals"

Now showing 1 - 3 of 3
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    A long-term temporal analysis of heavy metal concentrations in seabird feathers with implications for overgeneralized trophic dynamics
    (2019-04-26) Johnson, Elizabeth
    Anthropogenic deposition and natural cycling of heavy metal can impact ecosystem function: They can accumulate in marine sediment layers and remain there for long periods of time. As these metals accumulate and move through the ecosystem to higher trophic level organisms, these metals have known toxic effects including decreased reproductive success and compromised immune systems. Seabird feather levels may be representative of broader ecosystem signals and heavy metal cycling. This study combines heavy metal concentration data from seabird feathers and builds on the results of previous studies looking at trophic declines across time. The aim is to emphasize the importance of tracking trophic levels of top predators, looking at heavy metal concentrations from the 1880s to 2016, as well as carbon and nitrogen stable isotopes to determine if changing trophic levels will alter estimated trends and environmental heavy metal concentrations. We present temporal trends in seabird tissue concentration, and examine the complex field of trophic transfer, proposing a protocol for interpreting environmental concentrations. Our results show that trophic declines do not drastically impact directional trends, but that extrapolating to other trophic levels creates a large margin of uncertainty. We observe declines in heavy metals that correspond with relevant legislation, and suggest further studies into lesser known metals to strengthen environmental monitoring methods.
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    Accumulation and Distribution of Trace Elements and Radionuclides in Agricultural Soils Impacted from Long-term Phosphate Fertilizer Application
    (2023-04-20) Hu, Jun
    Excessive application of phosphate fertilizers can result in the accumulation of both phosphorus (P) and trace metals (U, Cd) in agricultural soils, which could end up in crops and cause chronic harms to the environment. Here we investigate the quality of soils in a long-term trial corn/soybean field at the Tidewater Research Station, North Carolina, where both surface soils (top 20 cm) and subsurface soils (up to 150 cm) were collected from five plots with different application rates of P-fertilizer since 1966. We analyzed a broad range of major nutrients and trace elements with focus on metals and metalloids including Cd, U, V, Cr, As, and Sr, which are notably enriched in the used P-fertilizer relative to local background soil. The study aims to investigate the trace elements accumulation, distribution, and mobilization in the soils. The results show that the impact of long-term P-fertilizer application was mostly manifested in the top layers of the soils compared to deeper soils, with the exception of As showing accumulation in the deeper soils. Among the five plots, bulk soils applied with higher rates of P-fertilizers had higher concentrations of P and trace elements than soils without using P-fertilizers. The concentration of Cd was significantly correlated with that of P (r = 0.97, p = 0.005) in the bulk surface soils, indicative of its direct contribution from P-fertilizer and accumulation in the soil. In contrast, other trace elements exhibited weaker or little correlations with P in the bulk surface soils. The potential bioavailability of elements in soils was assessed via the Mehlich III extraction method, showing that the higher application rate of P-fertilizer, the higher percent of bioavailability was found for Cd (up to 65% of the bulk soil) and P (up to 56%), whereas the other trace elements had much lower bioavailable fractions (0.4 – 12%). Strong correlations (r > 0.9, p < 0.05) were observed between the bioavailable concentrations of P and that of Cd, U, Cr, V, As, Sr in the surface soils. This indicates that the bioavailable form of trace elements is more sensitive in reflecting the impacts from P- fertilizer on surface soils. Four-step sequential leaching tests (i.e., F1: exchangeable, F2: reducible, F3: oxidizable, and F4: residual) conducted for the surface soils indicated differential mobilization of trace elements under different P-fertilizers application rates. Greater portions of Cd were found in the mobile fractions (F1 – F3) of soils with higher P-fertilizer input, while Sr was dominantly present in the residual fraction (F4: 95 – 97%), and redox-sensitive elements were higher in the reducible (As, V) and oxidizable (U, Cr) fractions than Sr, reflecting their redox-dependent mobilization potential. Overall, our systematic data analysis shows the effect of long-term P-fertilizer application on the accumulation of trace elements in soils. Further studies should evaluate the uptake of trace elements by crops and their mobilization to the underlying groundwater resources.
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    Alterations of Endophytic Microbial Community Function in Spartina alterniflora as a Result of Crude Oil Exposure
    (2021) Addis, Samantha

    The 2010 Deepwater Horizon disaster remains one of the largest oil spills in history. This event caused significant damage to coastal ecosystems, the full extent of which has yet to be fully determined. Crude oil contains both toxic substances that are detrimental to microbes and compounds that may be used as food and energy resources by some microbial species. As a result, oil spills have the potential to cause significant shifts in microbial communities. In this study, we assessed the impact of oil contamination on the function of endophytic microbial communities associated with saltmarsh cordgrass (Spartina alterniflora). Soil samples were collected from two locations in coastal Louisiana, USA: one severely affected by contamination from the Deepwater Horizon oil spill and one relatively unaffected location. Spartina alterniflora seedlings were grown in both soil samples under greenhouse conditions, and GeoChip 5.0 was used to evaluate the endophytic microbial metatranscriptome shifts in response to host oil exposure. Microbial functional shifts were detected in functional categories related to metal homeostasis, organic remediation, and phosphorus utilization. These findings show that host oil exposure elicits multiple changes in metabolic response from their endophytic microbial communities, producing effects that may have the potential to impact host plant fitness.