As of July 30th, my fieldwork for the rainy season in Southern Trinidad is completed. As a reminder, I am examining two rivers, one heavily impacted by humans (the South Oropuche River), and one that is relatively undeveloped (the Moruga River). I have collected 126 river water samples to analyze for nutrients, conducted macroinvertebrate sampling in several spots in each river on two different days, and sampled for fecal bacteria (coliforms) four times in each river. In my last post, I talked a lot about nutrient and coliform testing. Sampling for macroinvertebrates was, however, probably the most difficult of all the sampling I did. There are many factors to consider with macroinvertebrate sampling, the most important being obtaining a sample that is truly representative of the macroinvertebrate community in the river. Macroinvertebrates, are organisms lacking a backbone and visible to the naked eye. As I mentioned in my fist blog post, the composition of macroinvertebrate communities serve as an indicator for overall pollution and ecological health. They occupy small, specific habitats in the bottom sediment of a river, so they do not have a uniform distribution throughout. You therefore have to cover enough ground in your sampling so as to not miss out on where these organisms happen to be hanging out. On each river, I had three sites. At each site, I collected sediment samples from each side of the river (near the banks), then as deep into the river as I could go, from both sides of the river. You collect samples by kicking sediment into a net that collects the sediment and organisms in them. After collecting sediment at the four spots and rinsing the samples in a net to retain organisms (but get rid of excess sediment), I compiled the four samples into one 16 oz container. Since I had to do this at six different sites on my two different sampling days, this was a very time consuming process!
After getting all my sediment samples, I added ethanol to kill off any decomposing bacteria and to preserve any macroinvertebrates. Because these organisms are small and there is a lot of sediment left in the collected samples (even after rinsing them through a net), I had to carefully look through each sample and individually extract all the macroinvertebrates. I spent an average of two hours sifting and observing each of the 12 samples. Between the collection and processing of these samples, macroinvertebrate samples are much more challenging than collecting and processing water samples! I really enjoyed doing it, though. These organisms are incredibly interesting and diverse.
One cool finding that matches my expectations going into this study is that I have definitely found more macroinveriebrates in the relatively undeveloped Moruga River than the heavily impacted South Oropuche River. About a total of 52 macroinvertebrates were found in the Moruga sediment samples while a total of 23 macroinvertebrates were found in the South Oropuche sediment samples. Some of the organisms I was able to identify to higher (more general) taxonomic ranks, such as mosquito larvae, bivalves and crabs, but I’m unsure of their exact species. I have posted photos of them onto iNaturalist to properly identify them to lower taxonomic levels.
Although this research project has not been yet completed, so far it has had a major impact on me. The research project itself is trying to figure out how agriculture can affect water quality and stream organisms. Seeing that human activities can affect nature and ecology, is not new to me, but new to many of the local people of Southern Trinidad that live on and use these rivers. As an environmental science major and a person of Trinidadian heritage, completing this research project is just the first step for me in my career goal of developing meaningful solutions to environmental problems that affect underserved communities of people. The fact that people I know and care about are the ones impacted by the particular environmental problems affecting rivers in Southern Trinidad makes my project of particular importance to me. The feeling of success and fulfillment I receive after completing every experiment is what motivates me to want to wake up every day and continue to do this for a living.