Iron just never ceases to amaze...

By Matt Quinan:

Terrestrially derived iron minerals may safeguard marine ecosystems from eutrophication and sulfidization, but the full extent of their ecosystem benefits has not been established.  Iron redox cycling can generate hydrocarbon-degrading hydroxyl radicals, with reactions probably occuring more frequently in sediments with elevated iron content such as those in the RiOMars (River-dominate Ocean Margins). To determine if iron in marine sediment affects the degradation of hydrocarbons, we augmented sediments with iron and Deepwater Horizon crude oil to simulate conditions similar to those of a post-spill seafloor environment. Significant differences in the redox environment and oil degradation result as a function of sediment composition. These results could have significant implications for environmental policy decision making.

In order to determine if redox conditions do indeed affect hydrocarbon degradation rates and pathways, artificial sediment cores were created with variable compositions of play-sand, iron-coated sand, Indian River Lagoon (IRL) mud, and clay. The cores were separated into three oil treatments: Control, Oil 1, and Oil 2. Five replicates of each core were assembled to provide five sacrificial timepoints. They were then incubated in natural IRL water using a flow through system constructed for this experiment in the Harbor Branch Sediment Incubation Laboratory.

A black layer consistent with FeS minerals and concentrated in microbes formed in the cores almost immediately after incubation started.  But, the concentration of crude oil and iron in the cores seems to control the extent of the black layer.  It is possible that the presence of iron slows the slows the establishment of sulfur chemistry in the core.





 
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Oil extraction and analysis (GC/MS) after 2 months of incubation, has shown that an increase in the sedimentary iron concentration leads to an increase in the n-alkane degradation rate.  Also, the shorter chain alkanes that are not present in the source crude oil have appeared in cores with higher oil concentrations after incubating.  It is possible that the longer chain alkanes are being transformed into shorter chain alkanes when iron is present in the sediment. 

The next phase of this project will include the incubation natural sediment from the northern Gulf of Mexico amended with crude oil. The culmination of this project will be the construction of a model capable of estimating the length of time required for natural river systems to degrade hydrocarbons under different discharge scenarios that affect mineral delivery.

Whale Parts

By Matt Quinan:

Anthropogenic activities have significantly altered the chemistry of the world’s oceans.  Heavy metals from manufacturing are constantly transported to the oceans via rivers and streams and bring with them the potential to harm much of the life off our coasts.  One group that is particularly at risk is cetaceans.  As these large mammals consume prey laden with heavy metals, the contaminants build up in their tissue leading to potentially serious health problems.  One thing that is not well understood is the partitioning of different heavy metals throughout their bodies.  300 whale tissue samples collected from strandings in Georgia, North Carolina, and Florida are currently being processed and will soon be sent out for heavy metal analysis.  Concentrations of different heavy metals in liver, kidney, muscle, blubber, and skin samples will be compared to determine where different heavy metals tend to collect within the mammals.  This information, measured against known heavy metal concentrations in prey tissue from different areas may be able to offer us a glimpse into the lifestyles of these elusive animals. For example, if a whale is stranded on the beach in the southeastern U.S., can we develop a model that will help us determine where it spent its life based on its heavy metal fingerprint? In other words, if we know the geographic distribution of mercury, cadmium, lead etc. in the environment (e.g. in the whale's prey), can we inversely determine the geographic life history of a whale assuming that the cumulative uptake as a function of time spent in different areas will manifest a specific heavy metal fingerprint in its tissues? We are working with Dr. Annie Page-Karjian, Dr. Adam Schaefer, and Dr. Mingshun Jiang at Harbor Branch to tackle this problem, with a grant from the Harbor Branch Foundation.

 

Matt gets down and dirty subsampling frozen stranded whale tissue that will be sent off for basic heavy metals analysis by ICP-MS.