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Regional and global trends in population (Upper Left), crop production (Upper Right), crop area (Lower Left), and fertilizer use (Lower Right), 1961–2005.
The exchange of carbon between the atmosphere and the ecosystem is known as net ecosystem exchange (NEE) at any particular point in time (Moncrieff et al., 2000). NEP and NEE are widely used as indicators of the amount of carbon accumulated or lost (medium-term storage) by an ecosystem. However, not all these carbon remain
Green water footprint – Volume of rainwater consumed during the production process. This is particularly relevant for agricultural and forestry products (products based on crops or wood), where it refers to the total rainwater evapotranspiration (from fields and plantations) plus the water incorporated into the harvested crop or wood. Blue water footprint – Volume of surface and groundwater consumed as a result of the production of a good or service. Consumption refers to the volume of freshwater used and then evaporated or incorporated into a product . It also includes water abstracted from surface or groundwater in a catchment and returned to another catchment or the sea. It is the amount of water abstracted from groundwater or surface water that does not return to the catchment from which it was withdrawn. Grey water footprint – The grey water footprint of a product is an indicator of freshwater pollution that can be associated with the production of a product over its full supply chain. It is defined as the volume of freshwater that is required to assimilate the load of pollutants based on natural background concentrations and existing ambient water quality standards . It is calculated as the volume of water that is required to dilute pollutants to such an extent that the quality of the water remains above agreed water quality standards. Source: Hoekstra, A.Y., Chapagain, A.K., Aldaya, M.M. and Mekonnen, M.M. (2011) The water footprint assessment manual: Setting the global standard, Earthscan, London, UK. See page 187, 189, 190.
Blue water use refers to the volume of irrigation water (withdrawn from surface or ground water) that evaporates from a crop field during the growing period. The distinction between green and blue water has been introduced by Malin Falkenmark, Swedish hydrologist.
EBC ha sido aceptado como uno de los más importantes para validar los datos de eddy covariance, por lo que su aplicación resulta formar un procedimiento estándar en la aplicación de esta metodología S the rate of change of heat storage (air and biomass) between the soil surface and the level of the eddy covariance instrumentation, and Q the sum of all additional energy sources and sinks. (Wilson et al., 2002)
In temperate ecosystems, seasonal trend in CO2 exchange ( FN) follows the seasonal cycle of the sun, with qualifications. In temperate coniferous forests, seasonal patterns of FA and FR are in phase, causing FN to peak (most negative values, indicating uptake) when FA and FR do. In cold regions, temperate conifer forests lose carbon in the winter and gain it during the frostfree, growing season. And in milder regions, such as the Pacific North-west, south-western France and the south-eastern part of the United States, temperate conifer forests can be net carbon sinks year-round. In contrast, FR is delayed compared with FA in temperate deciduous and boreal coniferous forests. This lag is attributed to cold spring-time soils, which restrict FR and enable FN to be most negative then. Arid and semi-arid systems, such as Mediterranean and tropical savannas and annual grasslands, are water-limited. Consequently, the most negative rates of net carbon exchange occur during the wet winter and spring in Mediterranean-type climates and during the summer wet period for tropical savannas. Perennial grasslands, growing in temperate climates, experience summer rainfall, so their annual cycle of carbon exchange is moderated by the freeze-free period of the year, changes in leaf area index and vapour-pressure deficits. The greatest rates of carbon uptake occur for C4, C3 and mixed C3–C4 grasslands during the summer growing season. Agricultural crops achieve the highest short-termrates of carbon uptake. But, ironically, their net annual uptake is not the greatest. Spring-sown crops, such as soybeans and corn, experience a short season of effective net carbon uptake because they must grow from seed The ranking of FN, at annual time scales, is not explained well by variations in climate variables, plant functional type or photosynthetic potential (Law et al. 2002; Arain and Restrepo- Coupe 2005; van Dijk et al. 2005; Reichstein et al. 2007b). A step-wise, multiple regression analysis revealed that only 45% of the variance in annual FN, for forests across central and northern Europe, is explained by a combination of sunlight, leaf area index and air temperature (van Dijk et al. 2005). More productive ecosystems (those with greater values of FA), which occur under wetter and warmer climates, do not necessarily produce large values of FN because FR scales linearly with available light, moisture and temperature (Arain and Restrepo-Coupe 2005; van Dijk et al. 2005; Reichstein et al. 2007b). This point is illustrated with data in Fig. 5,which shows that variations in FA explain only 42% of the variation in FN. Consequently, it is better to partition FN into its components FA and FR, and relate the components to abiotic and biotic drivers, as is shown below.
El sitio de estudio se encuentra en la Región Metropolitana de Chile, 33º02'S 70º44'O 660 m.s.n.m.