Updated: Jul 20
By Md. Abid Azad Sakib
Greenhouse Gas refers to the list of gasses that absorb infrared radiation from the sun. The three main greenhouse gasses (GHGs) in the atmosphere include Carbon dioxide (CO2), methane (CH4 ) and nitrous oxide (N2O). The constant increase in atmospheric concentrations of these GHGs is closely linked to global climate change (Yang et al., 2014).
GHG emission occurs from a number of sources. Among them is the emission of GHG from water bodies as a newly discovered area but the contribution is not small. This sector was discovered nearly two decades ago and the idea has led to the evidence that water bodies around the world are significant GHG contributors to the earth's atmosphere.
Before this, the concept of hydroelectricity was considered green energy but then scientists observed that spillways even increase the natural rate of emission of GHG at a higher rate. So, now as a new field, this section needs lots of research and fieldwork to understand the behavior of emissions around the world due to the natural and artificial factorial differences.
According to the natural belts where reservoirs are located, the global reservoirs could be divided into tropical reservoirs (e.g., reservoirs in Brazil, French Guiana, and Laos) and temperate reservoirs (e.g., reservoirs in Canada, Switzerland, and China).
The geographic locations of reservoirs have an impact on the organic matter storage and water temperature, and influence CO2 and CH4 emissions subsequently. In comparison to latitudes, CO2 emissions from reservoirs are also affected by water depths, wind speeds, pH values, precipitation, chlorophyll-a levels, and dissolved organic carbon in the water body, although CH4 emissions from reservoirs are affected by water depths, water level fluctuations, water temperatures, and wind speeds (Yang et al., 2014).
When the profound water moves through the turbines and spillways, the dissolved gas (especially CH4) in the hypolimnion before the dams are released into the atmosphere becomes an enormous source of CH4 due to the abrupt shift in temperature and pressure called "degassing".
Greenhouse Gas and reservoirs
There are four pathways for reservoir GHG emissions, i.e. diffusive emissions, ebullition emissions, turbine and spillway emissions degassing, and downstream emissions. CO2 is the largest amount of gas that is emitted from a water reservoir then comes CH4 and at the last NO2. CH4 has 24 times greater Global Warming Potential (GWP) than carbon dioxide (CO2) per molecule over a 100-year time horizon and 298 times GWP of nitrous oxide (N2O) than CO2 (Deemer et al., 2016).
GHG emissions from reservoirs differ from natural water bodies, such as lakes and rivers, as the reservoir's impoundment has led to large areas of terrestrial and natural aquatic ecosystems being flooded (Yang et al., 2014).
Greenhouse Gas emissions from lakes
In lakes, CH4 is delivered, expended, and traded with the air in an unexpected way in comparison to CO2. CH4 is delivered in anaerobic situations (for the most part in dregs), while CO2 in lakes starts from breath all through the water segment and silt, the inflow of presently got broke down inorganic carbon from encompassing watersheds, and photo-oxidation of dissolved organic carbon (DOC).
CO2 is additionally framed in lakes by oxygen-consuming oxidation of CH4, a procedure that can devour a huge division of CH4 delivered in lakes. The proportion of CO2 outflowing versus carbon sequestration in northern lakes was observed to be constrained by nitrate focuses on lake water. In the meantime, CO2 is devoured by photosynthesis and other autotrophic or compound procedures that rely upon pH and additionally the accessibility of light.
Greenhouse Gas and climate change
The inputs of Carbon and Nitrogen from the land to the water source are mainly responsible for the emission of greenhouse gasses. These gasses finally reach the atmosphere and create an impact on climate change. Streams are reactors for debasement and metabolic procedures among watery C and N, making them dynamic territories of GHGs with the environment (Qu et al., 2017). For instance, after going into the amphibian framework from the land and atmosphere, some portion of the natural carbon will experience debasement and result in GHGs outflows.
Simultaneously, denitrification and nitrification in the amphibian framework will likewise modify the nitrogen pools and transmit N2O gas, which has an Earth-wide temperature boost potential roughly multiple times that of CO2, to the environment. It was evaluated that CO2 emanations from worldwide streams are at 1.8 × 106 Gg C d-1, while the size of inland water CH4 and N2O avoidance were assessed at 0.2 Gg C d-1 and 32.2 Gg N d-1, separately (Qu et al., 2017).
Measuring all the possible emission rates of the GHGs is significant for a sustainable future because all those GHGs have an active interruption in the Earth’s energy budget. Atmosphere forecasts require a full and hearty record of common and anthropogenic greenhouse gas (GHG) emissions, particularly for CO2, CH4, and N2O, which together represented 94% of the anthropogenic worldwide radiative constraining by well-blended GHGs in 2011 in respect to 1750 (Borges et al., 2015).
GHG emission from water reservoirs has come into the concern for contributing a deal of greenhouse gas into the atmosphere and for its impact on climate change. CO2 and CH4 are two main GHG gasses and their emission pathways that affect most have been identified. The contribution of GHG gas to a small water reservoir or a particular region has been estimated but on the global scale, this measurement still needs a lot of work. An appropriate amount of reservoir or the area determination is quite impossible but through the correct process, we will be able to estimate the GHG emission on the global scale.
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Md. Abid Azad Sakib is a Youth Empowerment in Climate Action Platform (YECAP) Fellow.