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Experimenting with organic matter

Investigating the fate of terrestrial organic matter in the near-shore ocean.
April 6, 2015

The near-shore coastal ocean is an exciting place. In addition to the dynamic macroscopic beauty of the intertidal zone, there is a whole other level of excitement occurring on a microscopic level. When freshwater rivers and streams enter the salty marine environment, a variety of important processes can occur that influence carbon and nutrient cycling, productivity, and food webs. Rivers and streams carry tiny particles of organic matter that serve as a favourable meal to microbial communities. The leftovers from these meals for microbes (or even the microbes themselves!) then become important food for bigger critters in the water. So what does this river-buffet look like to a microbe? How much of this terrestrial organic matter do microbes end up consuming? And what are the consequences of this microbial feeding frenzy – the process of biodegradation? Meanwhile, while microbes munch, the shining sun breaks up organic matter that meets the ocean. Ultraviolet light can have a strong influence on the breakdown of molecular compounds, and might make river-food more or less enticing to hungry microbes. We call this process - the solar breakdown of organic matter - photodegradation. So do microbes like their meals cooked? Or do they prefer uncooked, raw fare?

These are questions that we (Dr. Allison Oliver and Dr. Colleen Kellogg, Hakai Institute Post-Doctoral Scholars) set out to investigate with our recent experiment, which we affectionately called DORMAT (Degradation of Organic MATter). Using Kwakshua Channel as our natural laboratory, we devised a series of treatments to look at how these processes play out within the marine environment in different seasons. We discovered there is a bit of an art to deploying delicate plastic bags filled with water into the powerful ocean and then expecting to return to that same location at some later date and find them happy and afloat. Combining a bit of hardware store supply tinkering and some minor chainsaw work, we devised a setup that allowed us to successfully deploy bags of river water, combined with different treatments of microbial communities. This was a challenging enough endeavour during the month of August, 2014, when skies were blue and seas were calm. A repeat of this experiment, in March 2015, found our bags pummelled for days with high seas, gale force winds, and torrential rain. It was not a pleasant time to be an experiment deployed at sea. Yet despite these adverse conditions, a week later our bags were legion.

The results from our experiments are currently being processed and analyzed. We will gain important information about changes in the microbial community as they consume terrestrial organic matter (using powerful nucleic acid - DNA and RNA - sequencing methods), as well as an understanding of how the organic matter itself changes. To see these changes in the river-food, we are using techniques that allow us to visualize a generalized molecular “fingerprint” of this tasty organic matter. We can even tell what “ingredients” of this food the microbes, and the sun, consume and ultimately how they change composition of the river-food over time! Better understanding of these processes will help us to make estimates about the importance of terrestrial organic matter to the productivity and structure of marine communities of the BC Coast, and ultimately the role of this region in the context of global biogeochemical cycles. Stay tuned!  - Allison and Colleen


Lead Researchers
Allison Oliver, Hakai Postdoctoral Fellow
Colleen Kellogg, Hakai Postdoctoral Fellow