In the article:Webb W., Szarek S., Lauenroth W., Linerson R.; Primary productivity and water use in native forest, grassland, and desert ecosystems, Ecology, 59(6), 1978, pp. 1239-1247, I understand that a m^3 of water enable storage of 4 kg of carbon, this is call WUE (water use efficiency); am I right? Does any others studies confirm this?
WUE was later defined as the slope of photosynthesis versus transpiration and 4 per mil is a rough figure about it in optimal condition. if we use it to apply to agriculture is better to use water quotient that is the crop yield for unit of used water. The total water isloss is apportioned as runoff, evaporation and transpiration by plants In this case evaporation should be kept as low is possible with drip irrigation, below ground pipes and so on. Literature depends on appllication but the page of Dr Gilbert at UCDavis can be a start. or GD Farquhar literature on C isotopes. http://www.plantsciences.ucdavis.edu/plantsciences_faculty/gilbert/main/water_use_efficiency.htm
Thank you, it helps a lot. My interest is to determine the benefit to irrigate arid zones in the fight against global warming.
Dear Colleague,
WUE is not directly related to carbon storage in the sense of carbon sequestration.
WUE relates to how much water is transpired by a plant in relation to how much carbon is fixed in its biomass (or yield, in its agronomic version) per unit of that transpiration. This is simple plant physiology. As you say, typical values are in the order of 1000's water transpired per biomass fixed during growth. Carbon sequestration however, refers instead to the medium or long term storage of carbon from the atmosphere into terrestrial ecosystems (above and below ground, including as SOM). And if you want to do mitigation, you will have to subtract the costs of any action involved in the course of that long term sequestration (such as, power for irrigation, etc.)
In general in nature, things do not happen for free. If you have arid areas, the long term biomass and soil carbon stored may be low, because productivity is low. In order to to increase it, you'd have to irrigate as one option. With what and how? if you use fossil-fuel powered pumps, then your long terms effects will be even worse than if you had done nothing to begin with. Additionally, you'll risk increasing the salinity of the soil as well, regardless of the source of power for irrigation.
I am not ruling this out as a potential solution, but you'll have to do the math and consider all components of the equation.
That's OK; as far figures I guess the right values are then drawn from ET and NPP and their values are about six tiems less than proposed, as recently reported from USA forest sytem:http://www.forestthreats.org/products/publications/Model_estimates_of_net_primary_productivity_evapotranspiration_and_water_use_efficiency.pdf
In same early report often it has been put the ratio of instantaneous gas fluxes, but even so there were missing slope analysis (like in wet situation there would be little exchange), canopy structure, night respiration and carbon turnover. time.
C4 plants anf irrigation in the corn belt make the most of seasonal photosynthetic sink but their turn over is very short and their carbon footprint high.
Thank you for your answers; this helps me a lot to obtain an estimation, a minimal value to expect of yield of carbon sequestration when fresh water is provided in arid areas. I'd like to expand the discussion; I know it should cost a lot but the first interest would be to use sea water in a very large scale in order to have a significant effect on the rise of sea level . Considering an average rise in sea level of 3 mm per year .This corresponds to approximately e12 m3 of saltwater. The annual production of desalinated water is 2,6∙e10 m3, and should be multiplied by 100 in order that this production have a significant effect on the rise of sea level. Is this feasible? The debate should be placed. Considering an average consuption of 6 kWh/m3, this represents about one trillion euros annually. Of course we have to consider the environement impact of every euro. The induced sequestration of carbon would be a plus.
http://agriculture.gouv.fr/video-3-minutes-understand-40-initiative-soils
Soil degradation threatens 40% of land
Thanks to plants and living organisms, soils contain two to three times more carbon than the atmosphere. Carbon-rich soil organic matter is essential: it retains the water, nitrogen and phosphorus that are indispensable to agriculture. But alternating phases of drought and intense rainfall accentuate erosive phenomena. In the long term, almost 30 million hectares of arable land could be lost every ten years.
http://www.inra.fr/en/Public/Global-warming/All-magazines/Four-parts-per-1000-carbon-storage-in-the-soil
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