If it isn t Broken, Don t Mess with It Figure 1 The Guri dam, located in the Guayana region of Venezuela

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If it isn t Broken, Don t Mess with It Across the world, developing countries continue to expand. Their economies, populations, and infrastructure continue to grow.

1 If it isn t Broken, Don t Mess with It Across the world, developing countries continue to expand. Their economies, populations, and infrastructure continue to grow. Along with that growth comes an increased need for resources and energy. Often times, rivers play a huge role in the development and support of a society. Developing practical forms of management on the rivers of these regions is essential to the success and growth of the area. While there are certainly benefits of developing rivers and their basins, some management techniques can have adverse effects on key aspects of the basin. This is certainly the case throughout northern South America. In South America, one of the biggest influences on the Northern part of the continent is the Orinoco River. The Orinoco River Basin stretches 366,000 square miles and encompasses roughly four fifths of Venezuela and one fourth of Colombia. As a result of its sheer size, management of the rivers throughout the Orinoco River Basin has great effects on the region. One very common management technique applied to the Orinoco River and its tributaries is the practice of river diversion. This is where the path of a river is diverted to another route in order to accomplish some objective. In the case of the Orinoco Basin, this is often done to clear lands of flooding in order to raise cattle. This practice has also been used to develop land for the growing of crops like sugarcane, cotton and rice. Another form of management related to the altering of water flow throughout the Orinoco basin is the implementation of dams. When it comes to the effects of dams on the Orinoco River, its tributaries, and the Orinoco River Basin, one dam and its day-to-day operations have lasting effects on both the natural landscapes, and urban populations throughout the Orinoco River Basin. Perhaps the biggest contributor to the development of the Orinoco River Basin is the Guri dam. The Guri dam, located in Venezuela about one hundred kilometers upstream from where the Caroni River meets the Orinoco River, operates as a hydroelectric power plant. Development of the dam began in 1963 with the eventual goal of reducing Venezuela s fossil fuel consumption. Today, the plan is accomplishing just that, saving the country roughly 300,000 barrels of oil a day. The plant produces 12,900 GW/h annually to the country of Venezuela. This equates to right around 70% of the country s electricity consumption. Along with supplying the area with a reliable energy, the dam allows the floods of the region to be somewhat controlled. There is no doubt that the implementation and development of the Guri dam has had some positive effects on the region. The dam provided the area with a reliable energy source, aided in the development of agricultural land, and helped control floods in the area. However, despite all its success, the dam (along with others in the region) has caused some pretty alarming concerns to arise. Many of these concerns are related to the ecology of the Orinoco River Basin and should certainly be addressed when considering future management techniques applied to the dams of the region. Figure 1 The Guri dam, located in the Guayana region of Venezuela The Venezuelan Ministerio del Ambiente y de los Recursos Naturales Renovables and the US National Science Foundation conducted an extended study (15 years) of the Orinoco River that looked at aspects such as annual patterns in biogeochemistry, population dynamics, and relationships between the river and its floodplain. They found that since the river remains essentially natural compared to most other large rivers, the annual repetition of the physical and chemical aspects allowed for the survival of the Orinoco s vast ecosystem which accounts for over half of Venezuela s biodiversity. It is important to maintain these patterns to ensure that the ecology of the

2 Orinoco and its floodplain remains stable. The Orinoco River, being fairly rapid moving and having a riverbed mainly composed of sand, has many of its aquatic organisms using the river for migration and instead using the floodplain for food and survival. The river has some tributaries draining the Andes and others from the east which drain from a Precambrian shield. This contrast in suspended loads of sediment and organic matter creates an environment where a diverse group of organisms can live. One of these organisms is the Orinoco Crocodile. This critically endangered species lives in the middle to lower areas of the Orinoco River. During the wet season when flooding occurs (April- December), this species can be found in the Llanos savannah, but withdrawal into burrows in the floodplain during the dry season (January-February). During the dry season is when the crocodiles breed. Eggs are laid in holes along the bank and usually hatch 70 days later during the beginning of the wet season when water levels rise once more. In short, the livelihood of this organism relies heavily on the annual hydrology of the river; however, after the construction of the dam, water levels have been falling drastically. This resulted in a critical disruption to the hydrograph by shortening the annual flooding of the floodplain. This reduction in water not only impacts the survival of fish and other aquatic vertebrates that the Orinoco Crocodile feeds on, but more so, the dam can disrupt the breeding behaviors of the crocodiles, possibly resulting in their extinction. In the north of the Orinoco delta, the Orinoco wetlands hold a vast number of different species and consists of flooded grasslands, mangroves, swamp forests and llanos (treeless grassy plains). The alluvial floodplain created by the Orinoco also produces a landscape of habitats of varying succession. Having a dam disrupting the natural shifting of these channels by manipulating water flow results in fewer connected channels and isolated habitats. The Orinoco s floodplain is made up of 2300 basins and regulated by the annual wet and dry seasons. During the wet season, the river is connected to the floodplain and while most land is flooded forest, 21% is an area with half open water and half macrophyte mats (aquatic plant). Macrophyte mats not only provide invertebrates with food and protection from predators, but also help to clarify the water; Steady moving water through the mats catches sediment and plankton from the water column and thus prevents algae blooms. Algae blooms, when uncontrolled, can deplete the oxygen levels in the water, which kill other life. As the water flows into the floodplain, it carries with it nutrients and sediment that promote aquatic plant grown and support the local ecosystem. As the dry season approaches, the water slowly recedes from the forests and into nearby lakes, which are maintained until the next flood season. It is only during this time of low flow when phytoplankton can appear due to the re-suspension of sediment into the water column. This constant transfer of oxygen and other nutrients between the river and the surrounding floodplain creates a rich ecosystem for Venezuela s diverse species. The macrophyte mats provide great habitat for local aquatic organisms while help clarifying the water, and the later growth of algae provides some energy to that same ecosystem. With the construction of the Guri dam, the lower water flow will disrupt this equilibrium between the river and its floodplain. The growth of the macrophyte mats will be hindered and algae blooms will be more prone to grow. Overall, the development of the Orinoco River and its basin plays a huge role in both the natural and urban environments throughout northern South America. The installment of the Guri has had some of the greatest impacts on the region. The dam has allowed for the expansion of the region both industrially and agriculturally. These benefits do not come free of cost however. The dam has been linked to disruptions throughout the Orinoco floodplain. Implementing management techniques on the Guri dam, and the Orinoco River Basin in general, is

3 essential to successful expansion of the 1 area. 1 Alex Ransom, Lauren Rudloff

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AP Environmental Science

AP Environmental Science Types of aquatic life zones MARINE Estuaries coral reefs mangrove swamps neritic zone pelagic zone FRESHWATER lakes and ponds streams and rivers wetlands Distribution of aquatic