Lake Granby Research Paper

Lake Granby is located in the Rocky Mountains in what is known as the Middle Park. The climate can be described as subartic due to its low humidity and long winter season. The average low temperature is 21.1 degrees Fahrenheit, and the average high is 51.1 degrees Fahrenheit. Precipitation comes mainly in the form of snow, with the total amount around 14.2 inches.
The town of Granby is the nearest to Lake Granby. The lake itself is right up against the hills of the mountains, while the town sits more in the open park. Lake Granby is at an elevation of 2,543 meters, with a surface area of 2,938 hectares. The maximum depth of the lake is 61 meters, with a mean depth of 22.6 meters. The lake is between hills in the mountains, which causes the depth to be quite variable. Being the third largest body of water in Colorado, it has 64.4 kilometers of shoreline (Martinez Bergersen 1991). The Granby Dam was built in 1949 for the purpose of water storage. The project was also due in part to supply water to the Front Range through the Colorado Big Thompson Project. These projects greatly changed the surrounding landscape in the area.
Vegetation for the Lake Granby ecosystem varies between the locations. On land, aspen trees, and ponderosa pine are abundant. Other
small shrubs and grasses are present, but less obvious than the trees. In the lake, there is very sporadic vegetation, with two main species: eloda nuttalii, and pontamogeton. These two species are common in most bodies of water in the area. Aquatic vegetation has a hard time thriving in this location because of the constant fluctuation in water level (Coops et al 2003).
Lake Granby is home to numerous animals, both on land and in the water. The dominant land animals include moose, deer, elk, mountain lions, bobcats, black bears, antelope, as well as various bird species. In the water it is dominated by large fish species: Lake Trout Salvelinus namaycush, Kokanee Salmon onchorhynchus nerka, Rainbow Trout Onchorhynchus mykis. Plankton and Mysis shrimp Mysis relicta are located throughout the lake. The two different systems of land and water processes do not have much overlap, except for birds preying on fish on occasion. The fish system will be examined more closely later on.
The major processes in the lake include water use, and the multi-structured food web. Due to the Colorado-Big Thompson Project (C-BT), water is used to irrigate the Front Range, and Northeastern Colorado. This is done by transmountain water diversions that pump water through the mountains (Hiew et al 1989). Since the lake is a reservoir, it undergoes constant water level fluctuations. The need for water downstream dictates when/how much water is released. Most reservoirs only have to worry about one way that water fluctuates, but at Lake Granby water is also drawn from C-BT. This causes even more variability in the lake. As previously stated, this has a negative impact on aquatic vegetation. This also poses a threat to fish populations in the lake. Spawning grounds for multiple fish species can change on a daily basis. Another large process that is impacting the whole fisheries system is the hyperpredation of Kokanee Salmon. Hyperpredation is the increase in predation pressure following the introduction of an alternative prey (Courchamp et al 2000). The introduction of Mysis shrimp into the lake has caused the Kokanee Salmon population to come under pressure, and is in risk of crashing. If the Kokanee Salmon population were to crash, the Lake Trout population would suffer as well. This issue will be examined further. Lake Granby is part of the large Colorado River watershed. It is actually at the headwaters of the Colorado River. This watershed supplies was to over 33 million people across seven states, Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming, including Mexico. The amount of water that comes from this watershed depends greatly on the global water system. The processes inside the watershed have the potential to impact millions of people, and because of that the amount of water that comes into the system is crucial. The people that live closest to this system are those that are in the town of Granby. However, the area does take on thousands of people each year for recreation and tourist activities. The lake itself brings in many people because the want to fish the lake. Lake Granby is also home to a sailing club; so many people with sailboats also frequent the lake. This lake provides jobs for fishing guides throughout the year, as well lake managers. The lake is located just outside of Rocky Mountain National Park, which has the potential to draw people to the area as well. As previously stated, this lake provides water to the Front Range. Perhaps the most important service that this system provides is water to thousands of people. It is unique that one lake provides water for people downstream, as well as across the mountains. In years of drought, this lake has the ability to help those in need on separate sides of the state. Most people do not realize that their water is coming through the mountains, but for the most part they would not even be able to live their if it wasn’t for this system.
The great services of Lake Granby are also what cause the system the most problems.
The need for water causes the lakes water level to fluctuate throughout the year, causing numerous impacts on the fish and wildlife populations. The fish are mainly impacted because of the strain on spawning that changing water levels can cause (Coops et al 2003). However, the management of fish have caused a decrease in the Kokanee Salmon population, and thus the Lake Trout population as well. Large numbers of anglers frequent this lake because of the Kokanee Salmon and Lake Trout. This body of water was known for its impressive fishing for these two species of fish, but that is now threatened due to a decreasing salmon
population.
The drivers of this ecosystem stem from the need for water in the watershed, and surrounding area. Drought is a large driver because it dictates the water level in the lake. This year happened to be one of the best years in terms of the amount of water around the state. Lake Granby reached its fullest point in the last 20 years because the need for water out of the lake was so low that the amount being released was lower than the water coming in. However, there have been years where drought was prominent across the entire watershed (Pulwarty et al 2005). This caused the level of the lake to drop to well below its normal fluctuating lows. Another driver for the system could be climate change. It is not sure yet whether this system will receive more or less water, but it will also depend on the entire watershed. If drought becomes more prevalent, the lake could see years of extremely low levels that do not recover from year to year (Pulwart et al 2005). The opposite could also happen though, years where the level of the lake remains full and there is actually an abundance of water. Climate change could also cause the temperature of the water in the lake to change. This could have impacts on all organisms in the