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Microbiology of the Mississippi River (by Dr. Cameron Thrash)

Microorganisms, or microbes, are any organism that is too small to see without the aid of a microscope. Typically, these organisms are single-celled, although they can occur in groups or filaments. They generally have smaller amounts of genetic material than plants and animals (like humans). However, in spite of their diminutive sizes, these organisms occur in vast numbers throughout the various ecosystems on Earth. Estimates for the total number of microbes on the planet usually number around 1×1030 (humans, by comparison, number around 7×109). With numbers like these, it’s not surprising that microorganisms have significant effects on the way the major elements of our planet are cycled. For example, microorganisms in the ocean account for roughly half of the total photosynthesis occurring on Earth, with land plants completing the other half. Similarly, microorganisms are involved in a myriad of additional metabolisms that are important to the global carbon cycle and other cycles of important nutrients like nitrogen.

Because of the importance of microorganisms, we are trying to understand their role in particular cycles of concern in the Mississippi River, such as the degradation of pollutants and interactions with carbon and nitrogen compounds. The samples being taken by the rowers will be shipped to Dr. Thrash’s laboratory at Louisiana State University for processing. These samples will tell us about the microorganisms present in the water of the Mississippi River, and how these organisms change as the river goes by major cities and tributaries. Some of our hypotheses include:

  1. Microbial communities will be different upstream and downstream of major cities.
  2. Microbial communities will be altered by the influx of water from major tributaries.
  3. Microbial taxa capable of various nitrogen metabolisms will correlate with nitrogen loading along the river.
  4. Total microbial richness (a measure of diversity) will increase with the volume of flow in the river.

Watch Dr. Thrashes webinar about the preliminary results here: http://cwf-fcf.org/en/discover-wildlife/resources/webinars/school/members/microbial-community-changes.html

Along with microbial samples, the team will also be taking measurements of water chemistry to help us correlate the organisms that we find in the river with the types of compounds with which they may be interacting. Here’s how they’ll collect the water samples:

More Science…

The crew will be doing some secondary sampling as well. We’ll be …

Practicing water clarity testing using a secchi disc
  1. … using a “Secchi Disc” to check for water clarity, turbidity, and estimating the photic zone for plankton (What the heck is the ‘photic zone’?!?).
  2. … measuring water pH and Temperature (otherwise known as, seeing what kind of environment is present for bacterial growth, and checking if it’s too cold for a swim).
  3. … measuring Dissolved Oxygen (what’s available for bacteria and all the other oxygen consumers in the water).
  4. … measuring Phosphate and Nitrate (what nutrients are available in the water for plankton, etc).


Dissolved Oxygen monitoring – match the colors!


You don’t have to spend the high-tech dollars to research your environment. Sometimes all it takes is standard, inexpensive equipment like this, used to measure dissolved oxygen in your backyard creek.



Check out this video to see a data visualization of one of the real world results of all that microbial interaction at the mouth of the Mississippi River:

Data Table – collected during AMR 2014