The world’s reservoirs according to Washington State University (WSU)researchers produce 1 gigaton of carbon emissions or 1.3% of all anthropogenic sources of global warming gases. That 1.3% is greater than Canada’s entire contribution to global greenhouse emissions.
The study appears in the journal BioScience. It looks at the biomass contained in reservoirs and the resulting emissions, largely methane (CH4) a gas 34 times more potent than carbon dioxide (CO2).
Bridget Deemer, WSU research associate, remarks that reservoirs are responsible for 25% more CH4 than what was previously thought. Some have been created to control river flow to minimize flooding. Others are built to produce hydroelectric power which has always been described as a green renewable energy source.
The study, however, suggests that hydroelectric dams although renewable power generators, may not be green at all. And this just adds to the reputation that some artificial reservoirs have been getting of late. Many are being removed to allow for the restoration of river ecosystems leading to improved fish, animal and plant populations.
Artificial reservoirs, unlike lakes, create widespread destruction of vegetation at the onset. As water backs up behind dams existing flora is drowned and begins to decay. In addition rivers deposit upstream debris into the reservoirs further adding to submarine biomass. Decomposition leads to leaking of emissions of CO2, CH4 and nitrous oxide (N2O). All three are potent contributors to global warming. In reservoirs fed by runoff from farms where there is excess application of fertilizers containing phosphorus , algae blooms further contribute more greenhouse gas emissions.
Deemer states, “there’s….a growing sense in the literature that methane bubbles are a really important component of the total emissions from lake and reservoir ecosystems.”
In fact, collected data from the Washington State University in Seattle, suggests that greenhouse gas emissions from composites are up to 330% higher than timber harvested from redwood forests for use in decking and other construction. Currently U.S. statistics show that the plastic wood market, around for the last 20 years accounts for 10% of the total market for decking materials and is expected to grow to 32% by 2016.
What are the implications of replacing wood with plastic wood? In an article appearing in the June 5th issue of Nature, the author, Jeff Tollefson, describes how New York’s Coney Island pier is being reconstructed not with wood but recycled plastic wood over steel-reinforced concrete. So what was once a boardwalk made from wooden boards will no longer exist. Instead composite plastic wood will be underfoot.
Plastic wood is most commonly made from high-density polyethylene, polypropylene or polystyrene often recovered from waste. The plastic is combined with wood waste which can be collected from a variety of sources including sawmills and construction sites. The collected wood shavings and splinters are ground into a fine powder and mixed with the plastic. Some plastic wood manufacturers don’t even use wood. Instead they substitute agricultural fibers and in some cases combine them with fiberglass to create a lumber substitute. The market for these products includes automotive parts, pallets, playground equipment, picnic tables and benches, chairs, and substitutes for timber in landscaping, decking, docks and railroad ties.
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