Final Blog Post: Human Induced Agricultural Pollution: The Impact of Agriculture on Water Quality in Southern Trinidad


Two main nutrients in crop fertilizer which promotes plant growth are nitrate and ammonium. Once agricultural sites are fertilized, more nitrogen and ammonium are applied to fields than are removed by the crops (Smil, 1999). This excessive level of nutrients in water cause algal blooms, which harms aquatic life. Nitrogen degrades ecosystems by making water more acidic, even killing some aquatic plants while promoting the growth of other kinds of plants (Weldeslassie, 2018). Excess amounts of nutrients in bodies of water will contribute to the excessive plant growth. This process is known as eutrophication, which can lead to hypoxia (Bennet, 2017). The effects of eutrophication can be massive.
Benthic macroinvertebrate communities serve a specific niche in aquatic environments. They feed on dead organism material which will later help recycle nutrients back into the system (Jun et al., 2018). An increase in nutrient levels in aquatic environments can affect benthic macroinvertebrate communities, displacing their ecological niches which will eventually affect water quality.

South Oropuche and Moruga River Water Sampling:
From June to November, it is the “rainy season” in Trinidad, which is the time of year when most of Trinidad’s average yearly rainfall occurs. Large amounts of rainfall during the rainy season potentially will flush a hoard of pollution into nearby river systems. Water sampling has been conducted during both rain events and between storms. The South Oropuche river is heavily developed by agriculture and the Moruga river has low levels of human land use. By comparing levels of fecal contamination and nutrients in the two rivers, enough data is generated to draw conclusions about the impact that agriculture is having, and how future agricultural development might influence the ecology of river systems.
Water sampling was intentionally conducted during the rainy season (June – July 2018). This was done to find out the levels of nutrients, specifically nitrate and ammonium. During rain events, nutrients from agricultural sites would runoff to nearby water bodies. It is expected that nutrient levels of nitrate and ammonium would be greater during this time, but with flooding it is probable these nutrient levels would be low. Therefore when the water samples are ran, river discharge calculations along with standard error calculations would be taken into consideration when drawing conclusions.

Two Season Benthic-Macroinvertebrate Sampling in Both River Systems:
Benthic macroinvertebrate sampling has been conducted in both the South Oropuche and Moruga rivers during the rainy and dry seasons. These macroinvertebrate communities consist of organisms such as worms, shellfish, and insects (e.g. dragonflies and mosquitoes) that spend their larval phase in water. The composition of these communities is an indicator for overall pollution and ecological health (Deborde, 2016). It is expected that there is a more diverse macroinvertebrate community in the Moruga River than the South Oropuche River. There were major differences in each season of macroinvertebrate sampling in both river systems.

Rainy Season Macroinvertebrate Sampling (June – July 2018): During the rainy season, a total of 33 macroinvertebrates have been identified from the South Oropuche, while a total of 123 macroinvertebrates have been identified from the Moruga. One single Polychaete was found in the Moruga. Historically, Polychaetes have survived mass extinctions. They are indeed native to both river systems, but none were found in the South Oropuche.

Dry Season Macroinvertebrate Sampling (January 2019): During the dry season, a total of 40 macroinvertebrates have been identified from the South Oropuche, while a total of 91 macroinvertebrates have been identified from the Moruga.
Overall, more organisms were found in the Moruga river than the South Oropuche river.

Fecal Coliform Testing:
Interestingly enough, fecal coliforms have been indicated in all the river water samples tested, including the samples from the Moruga River (i.e., the “pristine” river in the study). After all fecal coliform tests turned out to be positive, distilled water was used to test the fecal coliform test broth. After turning out to be positive, the fecal coliform results will not be taken into consideration while generating conclusions.

Future Progress:
To better this scientific study, more river water sampling and macroinvertebrate sampling can be conducted on a larger scale along with replication. Specifically, instead of three sampling sites on each river, it can be extended to 10 sites, further apart. A larger sample size tends to produce more reliable results. Replication every few years of both tests can also help produce more reliable results.

Although this research project if still being finalized, 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.

Author: Danny Deo

Danny Deo Pace University NYC, Dyson College of Arts and Sciences Department of Environmental Studies and Science

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