The Impact of Agriculture on Water Quality in Southern Trinidad

I am spending my summer conducting field work in Southern Trinidad to find out the impact of agriculture on water quality. This area and these river systems are very important to me personally, because my family is from Trinidad and they interact with these rivers quite a bit. The rivers here are not only the recipient of a lot of agricultural runoff (which can contain animal waste and fertilizers, among other contaminants), but of great cultural and economic importance to Trinidadians. People practicing the Hindu faith use the river for religious ceremonies, and a big part of the economy here is tourism, which means that the beaches and marine wildlife need to be clean and healthy.

Due to the importance of both agriculture and water quality to the human population living there, southern Trinidad is considered an appropriate model to study human-induced water pollution and its effects on ecosystem and human health. For this reason, I am spending this summer examining how agricultural runoff contributes to microbial and nutrient (nitrogen, phosphorus) pollution.  I will also be sampling and characterizing macroinvertebrate communities in the next few weeks.  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. I will elaborate on this more in my next blog post.

Right now, 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. For the past few weeks, I have been conducting water sampling, both during rain events and between storms. I have chosen to collect water samples in two different river systems in Southern Trinidad. One is heavily developed by agriculture (the South Oropouche river) and the other has low levels of human land use (the Moruga River). By comparing levels of fecal contamination and nutrients in the two rivers, I hope to make some conclusions about the impact that agriculture is having, and how future agricultural development might influence the ecology of river systems here. Before starting my field work, I walked along each river to find sampling sites.  I found three sites on each river, determining them by accessibility.

Once samples are collected, they need to be tested for fecal contamination and for nutrients (nitrogen, ammonium, and phosphorus). Fecal contamination is found by testing for the presence of bacteria (called coliform bacteria) that are typically found only in the gut of warm-blooded animals. There are many types of coliform bacteria and not all are harmful, but they do indicate that animal waste is making its way into a river. Coliform bacteria produce acid and gas from lactose, and you can take advantage of this to perform a simple test on water to see if they are there. I add 1 mL of the river water sample into a test tube with lactose and a color solution that is sensitive to pH (i.e., acidity) – kind of like litmus paper. I then agitate the solution for about 30 seconds, then leave it for 72 hours at room temperature to let the bacteria do their thing. If the broth does not change color, fecal coliforms were not present in high enough numbers to change the acidity of the water. If it turned yellow, that means that fecal coliforms consumed the lactose, lowering the pH of the water and causing the color solution to change. Interestingly enough, fecal coliforms have been indicated in all the water samples I tested, including the samples from the Moruga River (i.e., the “pristine” river in my study). Although I am not sure of the extent of contamination (only that the samples are contaminated with some level of fecal waste), it was surprising to find that both rivers have this contamination, and that contamination was found even when it wasn’t raining.

My nutrient analysis of river samples will require the use of analytical machines, so unlike the coliform testing, I can’t perform these analyses at the house I am staying at. Nutrient concentrations can change very quickly in water if algae and bacteria are present, so I have to freeze my samples right after collecting them, and keep them stored in the freezer until they can be analyzed. Luckily, I have been in touch with a Professor at the University of Trinidad and Tobago, where I will run a portion of my samples to measure concentrations of nitrate and phosphate, to get some experience with the analysis. When I get back to NYC, I will test all samples for nutrient concentrations (nitrate, phosphate, ammonium).


Doing my field work has been an amazing experience, and has confirmed to me the importance of the small study I am doing. Before I came to Trinidad for the summer, I tried to find other water quality studies of the rivers here, and didn’t find any. It also seemed like most residents on the island, even though they use the rivers quite a bit, are largely unaware of the presence or repercussions of river pollution there. These findings have been reflected in my experiences in the field. While collecting samples from the South Oropouche, some of the local people noticed I was collecting water samples near their homes and asked what I was doing and where I was from. I explained to them what my research was on, and they were shocked to find out what was happening in the river system they use daily. They were glad to find out that someone was conducting water quality tests on the river system they rely on for food and water. Hearing this made me happy because I felt that my research can potentially help better people’s everyday lives.