What Can Sediment Tell Us?

Why do we study sediments? Sediments have long been studied because of their ability to retain information about environmental conditions and about the organisms that lived in a geographic area during specific times. Oceanic sediments are not different in that regard. However, sand and mud face more turnover and physical forces than terrestrial sediments do. Oceanic sediments do retain the ability to inform scientists about the environmental quality of an area and allow us to extrapolate habitat suitability based on the environmental parameters found in sediment samples. For example, the sediment that I took on my recent trip to Panama City, Florida (shown left), has distinct color patterns from very dark grey--almost black--at the top of the sediment column moving down to lighter grey tones at the bottom. Dark muds are areas of low or no oxygen in the ocean. Some organisms can thrive in areas of low oxygen but low oxygen concentrations can also be representative of high levels of pollution, which may cause declines in species abundance and biomass. This specific sediment core came from one of the stations polluted by the wastewater treatment plant, where oxygen saturation levels of the water were approximately 40%. This sediment, therefore, will likely contain only resilient species of nematodes that can withstand low oxygen concentrations, as the anoxic sediment zone of this core is within the top 5 cm, the zone in which most nematodes live. Although I don't have pictures of cores from the reference sites, I did not observe any stratification in the reference sediment cores, and the oxygen saturation levels were in the mid 80s to 90%, suggesting different environmental conditions which may facilitate different nematode communities.

Another important aspect of sediments, in both terrestrial and aquatic environments, is that they are often sinks for environmental pollutants. One of the reasons that I am interested in sampling sediments for microplastics pollution rather than conducting water column sampling, is that pollution that starts in the water column will end up in the sand and mud through independent sinking activity, hydrodynamic forces such as wave activity, or due to colonization of particles by organisms that increase the density of the particle. Unfortunately, unlike determining oxygen stratification in sediments, determining microplastic concentrations isn't a visual task. Over the next few weeks to months I will begin the process of extracting the plastics from the sediments, cleaning them, and analyzing the particles to determine what the microplastics are made of--what polymer they consist of--and to learn how many microplastics there are in these sediments. I can't wait to show you everything that sediments can tell us about the health of an environment. 

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