http://www.lakescientist.com/learn-about-lakes/lakes-climate-change/lakes-and-greenhouse-gases.html
Greenhouse Gases
By Kevin Rose | Miami University
Figure 1: Greenhouse gases, especially CO2, are increasing in the atmosphere due to human activities. Natural sources of greenhouse gases include lakes and other freshwater resources.
Gases that trap heat in the atmosphere are known as greenhouse gases. The major greenhouse gases are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O)1. At present, atmospheric CO2 is nearly 35% higher than preindustrial levels and is increasing1. Although these gases are released from natural activity, human activity is responsible for the increase of greenhouse gases in the atmosphere. According to both the European Environment Agency and the United States Environmental Protection Agency, CO2 emissions account for the largest share of total greenhouse gas emissions, equivalent to 80-85% of total emissions. Fossil fuel combustion used for transportation and electricity generation are the main source of CO2 emissions, contributing to more than 50% of total emissions.
Natural sources of greenhouse gases include lakes and other freshwaters such as rivers, streams, ponds, and wetlands as well as terrestrial landscapes such as forests and fields. Lakes are active, changing, and important regulators of (CO2), methane (CH4), and nitrous oxide (N2O).
Carbon Dioxide
Figure 2: Carbon Dioxide (CO2) is an important greenhouse gas, and most lakes act as net sources of CO2, releasing it into the atmosphere. Lakes also bury large amounts of carbon in their sediments, over three times more than the world’s oceans.
Lakes play a much greater role in global carbon cycling than their area would otherwise predict. While lakes make up less than 2% of Earth’s surface area, they bury over three times more carbon in their sediments than all of the world’s oceans combined2. This means on a per area basis lakes bury over 100 times more carbon than the oceans. Small lakes that contain large amounts of algae tend to bury the most carbon; thus, the small drainage ponds, farm ponds, and recreational lakes around the world are important sites for carbon cycling and understanding global climate change3.
Despite the fact lakes bury huge amounts of carbon, they also tend to release more carbon dioxide to the atmosphere than they absorb, making them net sources of greenhouse gases. Most of the world’s lakes are supersaturated in CO2 and consequently release some of it to the atmosphere4. In fact, lakes and other freshwaters release almost as much CO2 as all the world’s oceans. This occurs because lakes generally drain large landscapes and the carbon from forests, fields, and lawns becomes concentrated in lakes where it can be buried or released into the atmosphere. Research studies show that the CO2 released from lakes comes from organism respiration — the breathing of bacteria, algae, zooplankton, fish, and other species5.
Methane
While methane is less common than CO2, it is a highly potent greenhouse gas. It has about 20 times more warming potential than CO2. Lakes contribute about 10% of total natural methane emissions, and they produce more methane than the oceans6. Many lakes and other freshwaters produce methane during warm summer conditions or when oxygen levels underwater drop. Most methane is produced in lake sediments when oxygen is no longer present due to different communities of bacteria that grow in environments without oxygen. In some lakes, bubbles can be seen rising from sediments; these bubbles are often methane produced by bacteria in oxygen deprived sediments6. Shallow areas around the shores of warm lakes are hot spots for methane production. Overall, lakes are important sites for carbon dioxide and methane production and release.
Nitrous Oxide
Lakes and other freshwater resources are also sources of nitrous oxide (N2O) cycling, another potent greenhouse gas that is produced in warm lakes by bacteria and other microbes. Within lakes, shallow sediments contribute most to N2O emissions7, while organisms in deep open waters may consume more N2O than they release. Lake shape may be an important predictor of N2O release, as shallow lakes with expansive shorelines may release more N2O than they produce compared with round deep lakes.
Is Hydroelectric Power a “Green” Energy Source?
Lakes and reservoirs are often built or used to generate power. In fact, so much water is retained behind dams that global sea level rise has been reduced by about 0.02 inches (0.55 mm) per year over the past 50 years8. Because fossil fuels are not used to produce hydroelectric power, lakes and reservoirs are often thought of as “green” energy sources. But lakes and reservoirs release potent greenhouse gases — particularly carbon dioxide and methane — into the atmosphere. If a hydroelectric dam releases enormous volumes of greenhouse gases, is it a “green” energy source?
Figure 5: The Three Gorges Dam in China is the world’s largest producer of hydroelectric power. Lakes and reservoirs emit greenhouse gases, and studies have questioned whether hydroelectric is truly a “green” energy source.
Greenhouse gas emissions from freshwater lakes and reservoirs and their contribution to the increase of greenhouse gases in the atmosphere are at the heart of a worldwide debate concerning the electricity generating sector9. Hydropower represents about 20% of the world’s electricity generation capacity and on average emits 35 to 70 times less greenhouse gases per unit power generated than thermal power plants10. When reservoirs are first built for power generation, soils, plants, and trees are flooded. The decay of this plant and soil material can contribute to large emissions of CO2 and CH4 during the first few years after reservoir construction11. Studies show that 3-10 times more greenhouse gases are produced by newly formed reservoirs than from natural lakes of the same size in the first 2-5 years after a reservoir is constructed12.
Beyond the initial release of greenhouse gases, lakes and reservoirs also continue to release carbon dioxide and methane as they produce power. As methane and carbon dioxide enriched water passes through turbines, hydrostatic pressure drops and a large portion of the gas rapidly escapes to the atmosphere. In some regions, such as tropical reservoirs where methane production can be high, reservoirs can release more greenhouse gases than fossil fuel alternatives13.
While lakes and reservoirs used to generate hydroelectric power can release greenhouse gases, they typically release far smaller amounts than traditional fossil fuel based power plants. Hydroelectric is not a perfectly “green” energy source, but it is often much more environmentally friendly than alternative choices and can be part of an alternative energy solutions plan.
Showing posts with label GHG. Show all posts
Showing posts with label GHG. Show all posts
Sunday, January 1, 2012
Wednesday, January 12, 2011
Agriculture is responsible for one third of Antropogenic GHG emissions
Impact Investing in Sustainable Agriculture for a New Economy
According to a recent article from Scientific American, agriculture is responsible for one third of global greenhouse gas emissions from human activity. Agribusiness farming operations are notorious for nitrogen and phosphorus runoff (particularly from poultry and hog farms). In the Chesapeake Bay region, for example, one study estimated the price tag for restoring the bay at $19 billion, of which $11 billion would go toward “nutrient reduction.”
There are more than 400 such dead zones throughout the world. Additionally, heavily subsidized corn and soy feed to livestock contribute to massive deforestation in the developing world. Tufts University researchers estimate that in the United States alone, between 1997 and 2005 the industrial animal sector saved more than $35 billion as a result of federal farm subsidies that lowered the price of the feed they purchased. These statistics demonstrate both the complexity of the supply chain from feed farm to table, and illustrate the importance of sustainability in the American food production industry.
A sustainable alternative to the beef factory-farming model follows in the footsteps of conservationist pioneer Allan Savory. The recent winner of the prestigious Buckminster Fuller Prize, Savory developed the Holistic Management grazing technique during his time as a researcher and farmer in Southern Africa in the 1980s. By getting grazing cattle to stay in larger, tight herds, Savory was able to restore grassland vitality and increase grass biodiversity. Deep chewing of plant roots, paired with the repeated soil chipping of hooves, caused dormant seeds to germinate and water to penetrate below the surface. According to Shannon Horst, CEO and co-founder of the Savory Institute, ranchers can consistently double, and even quadruple livestock capacity over time. (See an article in TIMEfor more on the Savory grazing technique).
Perhaps the most interesting aspect of Savory’s work has been its appeal to both profit-driven investors and international development agencies like USAID as a tool to combat desertification in rural farming communities. Since 2005, USAID’s Office of U.S. Foreign Disaster Assistance has provided more than $1.1 million to support Savory’s African Centre for Holistic Management’s program to restore degraded land, revive water sources, mitigate the effects of global climate change, and increase crop yields. Savory and Horst have worked with range managers on ranches and community group ranches, demonstrating how to manage holistically in communal and private range lands, in partnership with USAID.
Within the past couple of years, for-profit enterprises like Grasslands, LLC are successfully implementing the Savory Holistic Management methodology. Grasslands owns and manages 14,000 acres in South Dakota, and is funded by a network of private impact investors likeArmonia, LLC and Capital Institute founder John Fullerton. The profitability of the Grasslands structure comes from ranching fees per head of cattle, and is based directly on the Savory Institute business model. By investing in companies like Grasslands, Fullterton and other impact investors are laying the foundation for new finance-based theories, tools, and metrics to serve the needs of a sustainable economic system.
In addition to increased yields of beef per acre, the Grasslands model also creates an opportunity to commoditize sequestered carbon for carbon credit trading. Steven Apfelbaum, Founder/Chairman of Applied Ecological Services, Inc., explained to TIME, ”healthy grasslands represents the ecosystem with the highest potential for carbon sequestration of any on the planet.” Ranches like those owned by Grasslands cover an estimated 30 million acres in North and South America, Australia, New Zealand, and Africa—and nearly half of the earth’s land mass. Given the shear vastness of the earth’s grasslands, holistic management and reclamation projects hold huge implications for changing the planet.
While Grasslands only just completed its first year in operation, rancher Jim Howell reports that the two South Dakota ranches are expected to double in value and in productivity over a ten-year period and to yield annual dividends on the order of 4% to 5% in the early years, increasing to 10% to 11%. In a recent Capital Institute article, Fullerton expressed his confidence that the Grasslands model can provide a profitable, scalable model for biodiversity recovery: “We have a case study here of true wealth creation in Grasslands,” he says. “We are building biodiversity, soil fertility, sequestering carbon, and generating financial returns. And if my belief of what will happen to ecosystem services plays out, we will make a lot more money with these assets than with most financial assets.”
For more on Grasslands and the Capital Institute’s sustainable investment agenda
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