IB Group Four Conclusions
On March 21, 1998, a hot sunny Saturday in Rio de Janeiro, we, the International Baccalaureate Sciences student of the American School of Rio de Janeiro, studied the beach of Grumari from nine in the morning until three thirty in the afternoon. The project was divided into three parts; physics, biology, and chemistry. After gathering data, we spent the week analyzing it, and these are our conclusions:
Cross-section of the Beach:
(not drawn to scale)
The sublittoral zone -
Seawater is composed of sodium chloride (NaCl), Epsom salt (MgSO4), plaster of Paris (CaSO4), bicarbonate, and potassium chloride. It was found that the surface of the water had a greater concentration of magnesium and calcium than underwater. The reason for this is the decomposition of the shells washed to shore by the sea, and not the Epsom salt and plaster of Paris, which are found throughout the sea. The density (1.007g/mL), salinity (5%, when the normal salinity is 3.5%), heavy current, and the magnesium and calcium, are the factors that give the deeper portion of the area a visibility of only four meters in depth. The surface has a temperature of twenty-six degrees Celsius, whereas the under part has one of twenty-five. Knowing that colder water holds more oxygen, it can be reasoned that the underwater holds more life than the surface, especially because the strong waves which were found to have a mean frequency of 0.121 Hertz, and an amplitude of 0.725 meters (which are also reasons for causing the visibility to become smaller, not allowing the sediments to settle on such a turbulent area). Over twenty varieties of small fishes were found in the deeper area of the sublittoral zone (found by asking fishermen). However, the visibility can be an influencing factor in altering the species of fish found at the beach. These fishes, we later discovered, could grow much more, making us deduce that they were young, meaning that fishes must lay their eggs somewhere around the beach area. Three types of algae were found in the water (sea lettuce, brown kelp, and green estuary plant), which we could only deduce had been washed by the sea from the rocky coastline, and from the river whose estuary was at the beach. It was also found that deep-water samples tested three days later became more acidic. This most surely means that there were microscopic (bacteria and planktons) organisms in the water that had died and were beginning to decompose. We were also able to gather a variety of different planktons and view them through the microscope. These have been drawn for later identification and analysis. In a further analysis of the water, it was found that it contained a low quantity of excremental matter, which means that this beach is already being influenced by men.
The intertidal zone -
Because of the beaches profile (the beach slopes down to the water but before getting there, it slopes up then down, straight to the water, causing a small barrier between the water and the rest of the beach), a high amount of shells are deposited in the depression found in the intertidal zone. It can be seen that at high tide waters go over the mound, leaving the shells there, and either evaporating or getting absorbed by the sand. A huge population of a Brazilian burrowing sandbug (tatu�) was found at the shore. Other smaller burrowing sand-insects were found throughout the dryer area of the beach. These insects had for basic defense, the ability to camouflage with the sand and their burrowing characteristic. Fine sand is found throughout the beach (proven by having a mean slope of around three degrees, which by the book indicates its a fine sand beach), causing other life forms (especially plants) to not be able to survive in or on it. The salinity (caused by sea water particles brought by air or by waves) of the beach is also another factor that causes plants to distance themselves from the ocean.
The splash zone -
This zone can best be described as a transitional zone which separates the primary dunes from the intertidal and sublittoral. Sand-crabs and small insects (except tatu�) were found in this area, that are part of the intertidal. Lizards and other small vegetation organisms were found here too, that are part of the primary dunes. This area is the driest area on the beach, where sand particles are looser, not giving the life species from the neighboring zones, the best living environment.
The primary dunes zone -
In this area, it was found from soil samples, that it has a more clayish property, providing a better environment for the plants. This clayish characteristic must be due to the decomposition of organic substances from the edges of neighboring zones found further from the sea, which slowly spread closer to the sea. The area could be called a tropical salt marsh, since there is a river there, and the vegetation is mainly made of grasses and shrubs such as the Ipomoea pes-caprea and the Cenchrus tribuloides. The vegetation has the name of halophytes (halo=salt, phytes=plants), which evolved from glycophytes (found further inland, not having the adaptive evolutionary characteristic of dealing with the toxic sodium found in seawater), further proving that the vegetation came from the inland to the coast. Lizards, insects of larger proportions (including flying insects), and to crab species were found in this zone, showing how it has a better environment for organisms of a bit larger scale.
This report does not have all the information that could have been gathered to more fully explain the area ( such as how deep in the water did the study go, and all the studies that could have been made about the atmosphere). We were also unable to study a different beach, which would have given us an enormous amount of comparable data, from which we could develop more complex interpretations. There was some research done on the books, to learn about the main characteristics that should be found and annotated. We were also unable to study the entire sublittoral zone (which extends two hundred meters deep into the ocean) due to lack of tools and ability. More research could have been done in the physics part, such as the study of heat and light in the water (finding out which went deeper), in the chemistry part, studying the soil for chemical pollutants, pH, etc., and in the biology part, studying the bacteria present in the different zones. But we did not have enough technology or time to do everything. There must also be some unknown inaccuracies, since we were not able to compare the data to other ones that had already been done.
This project took a lot of hard work and a lot of our time, but it was also entertaining. This was also the first time when all the three sciences in our school join to make a massive project from which everybody gets a greater scope of knowledge from the experiment, understanding better the applications of the sciences (and how they interact). It was also a project where we learn about the environment where we live (since there are beaches all over Rio)
Back to Index Page