Environmental Anomaly? Well, not exactly...

This week I was able to get back into the field with trusty research team member, Owen. He and I braved 43 degree Fahrenheit (that's 6 degrees Celsius) winds to collect the final sediment samples for the first chapter of my PhD dissertation. Because there were only two of us, Owen pulled double-duty, collecting the environmental data and helping me get sediment samples on board and into their proper containers. We also set sail with a different captain, which meant someone new got to see the glorious mess that is my field work. Darren, our captain, was really interested in what I was doing and why I was doing the specific tasks in the field, and it meant I had the chance to talk about my work rather than chit chatting to fill the time. 

While collecting the environmental data, Owen noticed a few 'anomalies' in some of the oxygen saturation levels, in that some of the levels were above 100%. While one of the readings was an anomaly (it was a device error and we had to redo the measurement), the rest of the readings that were above 100% oxygen saturation were normal. You might ask yourself, "How can seawater oxygen levels above 100% be normal?" Great question! Oxygen saturation is representative of the balance between photosynthesis and aerobic (oxygen-using) respiration; if photosynthesis is occurring in greater amounts than aerobic respiration, oxygen saturation levels will be greater than 100%, and vice-versa. Again, how is this possible? The chemical reactions that underlie photosynthesis and respiration give us the answer.

Photosynthesis and aerobic respiration are coupled reactions; the products of photosynthesis are the same materials used in aerobic respiration (shown here). Therefore, if one of the reactions is occurring more than the other, the end products will be more abundant in the water column. Therefore, when photosynthesis is occurring more than aerobic respiration, oxygen is more abundant in the water column, which means that the oxygen saturation is above 100%. Alternatively, in areas where aerobic respiration is the dominant metabolic pathway, oxygen saturation levels are below 100% and carbon dioxide is abundant.

If metabolic pathways, like aerobic respiration, are lowering the availability of oxygen in the water column, then not all organisms in a given area may not have access to their nutrients of choice. Many organisms in the ocean can use multiple nutrients to keep themselves alive, and while oxygen is always the nutrient of choice, animals and bacteria can use alternatives, including nitrogen (nitrate), sulfur (sulfate), and many more, to carry out their daily tasks. Since oxygen is preferred by all organisms, scientists use the presence of oxygen in the water column as an indicator of environmental health; environments are considered healthy where oxygen levels are relatively high, and unhealthy where oxygen levels are low. In the Gulf of Mexico, and other waterbodies close to land, coastal pollution can release nutrients (think food sources) in the water column that get used up by organisms very quickly, and drastically deplete oxygen levels. These pollution events are reported by the news as algal blooms or eutrophication--large growths of marine algae caused by increased nitrogen levels in the water--and can be quite detrimental to marine ecosystems. The algae use up surface level oxygen and deplete oxygen through the water column, which can cause widespread oxygen stress in fishes and other marine creatures, and even widespread mortality events.

While my work does not focus on eutrophication, nor do I survey in areas of low oxygen (hypoxia nor anoxia), some of my sites receive increased nutrient pollution and therefore have lowER oxygen levels than other parts of St. Andrews Bay. These areas may be host to less animals than areas of high oxygen saturation, and as part of my research I will be investigating differences in nematode communities that may be related to these differences in oxygen availability. Although I won't get to investigating the relationships between nematodes and the environmental quality of St. Andrews Bay until this summer, I thought this week's blog and the 'anomalies' in the oxygen saturation measurements would be a great starting point to talk about how differences in environmental quality might affect animals and plants in a given area. Tune in next week for more information about the nematodes and microplastics in St. Andrews Bay, Florida.   

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