As we have already discussed in section 4.3, one of the mechanisms involved in the sorption of positively charged metal species is ion-exchange. Vegetal biomaterials (constituted principally by lignin and cellulose as major constituents and by a non negligible portion of fatty acid, bearing functional groups such as alcohol, ketone and carboxylic groups that can be involved in complexation reactions with metallic cations) can be viewed as natural ion — exchange materials. These materials primarily contain weak acid and basic groups on the surface, whose ionization degree strongly depends on the pH of the solution. Several authors have performed potentiometric titrations to investigate acid-base properties on the surface of biosorbents and to determine the number of active sites for metal ion sorption.

The strong pH dependence of the sorption parameters can depend on several factors, which can be simplified as follows:

1. behaviour and speciation of metal ions;

2. dependence of the acid-base characteristics of the adsorbing material on the pH;

3. dependence of the interaction metal ion-sorbent on the pH.

As far as point 1 is concerned, we report a statement made by Baes and Mesmer, 1976, in their classical book on the hydrolysis of cations: "soluble hydrolysis products are important when cation concentrations are very low and can profoundly affect the chemical behaviour of the metals; the formulas and charges of the hydrolysis products formed in such systems can control such important aspects of chemical behaviour as:

a. sorption of the dissolved metals in mineral and soil particles;

b. tendency of metal species to coagulate colloidal particles;

c. solubility of the hydroxide (or oxide) of the metals;

d. extent to which the metals can be complexed in solution or extracted from solution by natural agents;

e. oxydizability or reducibility of the metals to another valence state."

Based on these considerations, we demonstrate the influence of pH on sorption taking as an example the behaviour of one of the most important toxic metal ion, lead, in presence of different coordinating groups. Firstly we take into account the hydrolysis of this metal ion at two different concentrations, 100 mg/L and 0.05 mg/L, i. e. at concentration in strong polluted water and at concentration equal to EU recommended value for drinking water (Fig. 2). At 100 mg L-1, the species Pb(OH)+ (pH> 6) and the polynuclear species Pb3(OH)42+ and Pb6(OH)84+(pH >7) are formed before hydroxide precipitation occurs at pH~9.5; at 50 pg L-1, Pb2+ do not form precipitates and only the mononuclear species are formed instead of the polynuclear ones observed at 100 mg L-1. Metal ion hydrolysis equilibria, as well as hydroxide precipitation, can help explain the dependence of metal ion sorption on the pH. In most cases, the observed pH dependence lies in a range in which the metal ion is completely insensitive to the acidity of the medium. In metal ion sorption, pH effects are commonly accounted for by charge variations on the sorbent surface: protonation of basic sites or dissociation of acidic groups. According to the majority of authors a negative charge favours metal ion sorption by an ionic exchange mechanism or by electrostatic interactions, i. e. the sorption is completely determined by the acid-base behaviour of the functional groups on the surface of the adsorbing material.

The real behaviour is certainly far more complex and can be rationalised in terms of metal ion coordination by surface binding groups. The presence of phenolic, carboxylic, catecholic, amino, and mercapto groups on the surface is well known. As a working hypothesis we can imagine that the different binding groups on the solid particles, dispersed in the metal ion solution, behave as different ligands. With this simplifying assumption, we can consider our system as set of solution equilibria. In this assumption we can treat our system as solution equilibria between various ligands competing for a metal ion or for various metal ions. For example, a carboxylic group near a phenolic group on the surface can be assumed to behave as a salicylate ligand, limited to form only 1:1 chelates being anchored to a solid surface.

In the example showed in Fig. 3, we took into consideration three different coordinating groups as possible ligands for lead: COOH, hard, NH2, intermediate, and SH, soft donors. Furthermore, we also considered all the possible combination of them to obtain bidentate ligands, COOH-COOH; COOH-NH2, COOH-SH, NH2-NH2, NH2-SH, and SH-SH.

pH

Fig. 2. Species distribution diagrams for Pb2+ hydrolysis at two different total concentration 100 mg/L (solid lines) and 0.05 mg/L (dashed lines).

Starting from the distribution curves, obtained using the literature constants for lead complexes with different ligand bearing the above mentioned coordinating groups, some conclusions can be drawn. The soft metal Pb2+ ion prefers the soft SH group, which became completely coordinated in 4-6 pH range. No data is available in literature for a single NH2- Pb interaction. The carboxylic group forms a weak complex in the pH range corresponding to its deprotonation. The addition of a second group (COOH or SH) to the starting SH favours lead coordination, while the addition of a NH2 group has an adverse effect. Two vicinal COOH groups allow lead complexation at low pH values and act much better than a single COOH group, even if the per cent of complex formation is still much lower than that reached by SH groups. Regarding the coordinating properties related to the amino group, the complex formation, taking place at basic pH > 7, does not prevent the hydroxide formation.

2. Conclusion

The numerous studies on metal sorption by biomass are extremely spread: the investigation of the mechanism involved in metal ion sorption is performed by different techniques, methods and approaches that are related to the equipment availability in the researcher’s laboratories and to the researcher education. The use of highly sophisticated and extremely expensive techniques, as mentioned in the above sections, enables one to obtain structural information on the sorbent morphology and indirect knowledge of the implied sorption mechanisms, by comparing some physical properties of the material before and after metal sorption. Even if little importance is given to the classical chemical methods, such as potentiometry and alkaline and alkaline-earth metal ion release, these on the contrary offer several advantages, such as the easy availability in all laboratories, the fact that they are fast, cheap, and friendly-used. The main benefit of these methods is the attainment of quantitative results, which allow the evaluation of the amount and the kind of functional groups involved and the amount of exchanged metal ions.

We hope that the achievements obtained from this enormous quantity of research works can lead in the coming years to a real outlet of practical applications, even if a lack of protocol or systematic approach in this kind of studies has to be remarked. Furthermore, the reached level of knowledge acquired should allow the classification of biomass on the basis of structural coordinating groups on its surface, essential to forecast their behavior toward the different toxic metal ions. Thank to this information, it will be possible to depict the strength of interaction and the pH range more useful for metal removal.

The application of biosorption for effluent detoxification will have a strong ecological impact, joining the advantage of recycling waste biomass and of purifying contaminated waters from toxic metal ions.

The content of true protein in potato tubers was significantly differentiated by the intercrop fertilization, fertilization with straw and their interaction (table 12). The highest concentration of true protein in potato tubers was noted in potato tubers fertilized with phacelia and white clover both plowed down in the autumn, and left till spring in the form of mulch. The concentration of true protein in potato tubers fertilized with a mixture of white clover with Italian ryegrass remained at a similar level, such as on farmyard manure.

However, true protein content in potato tubers fertilized with Italian ryegrass was significantly lower than in tubers fertilized with farmyard manure. Straw fertilization also significantly differentiate true protein content in potato tubers. At the sub-block with straw concentration of true protein in potato tubers was significantly higher than on sub-block without straw. Investigated the interaction of factors we can see that the highest true protein content had potato tubers fertilized white clover, white clover with straw, and phacelia both plowed down in the autumn, and left till spring in the form of mulch in combination without straw and with straw, and the lowest potato tubers harvested from control object, without intercrop fertilization.

Plant biomass is primarily a product of photosynthesis, a process needing carbon dioxide, water as bi-products and solar radiation as the energy source and mineral nutrients as basic blocks. In majority of the instances carbon dioxide and solar radiation never limit biomass production while abiotic stresses like water deficit and soil salinity very often do. Plant response to abiotic stress is one of the most active research topics in plant biology due to its practical implications in agriculture, since abiotic stresses (mainly drought and high soil salinity) are the major cause for the reduction in crop biomass and yield worldwide, especially in the SAT.

Plants are extremely sensitive to changes resulting from drought or salinity, and do not generally adapt quickly (Lane and Jarvis 2007). Plants also adapt very differently from one another, even from a plant living in the same area. When a group of different plant species was prompted by a variety of different stress signals, such as drought or cold, each plant responded uniquely. Hardly any of the responses were similar, even though the plants had become accustomed to exactly the same home environment (Mittler 2006). Abiotic stresses can come in many forms. The occurrence of many of these abiotic stresses is unpredictable, however, in agricultural management point of view, drought and soil salinity are relatively more predictable and common in occurrence demanding focused research. Therefore, the scope of this chapter is limited to drought and soil salinity.

Seedlings of Atriplex canescens and Salsola vermiculata were planted on degraded community rangeland during 2007. Initially, the seedlings of these species were raised in polythene bags at Arid Zone Research Centre, Quetta. Six to nine months old seedlings were transplanted on the community rangelands during late winter or early spring months. Micro-catchment water harvesting (MCWH) structures were developed on sloping lands. Contour-bunds were made by a tractor-mounted plough. Spacing between ridged was maintained at 15 m and two shrubs (Atriplex canescens and Salsola vermiculata) were planted in each micro-catchment basin with 2 m spacing. The number of shrubs in each strip ranged from 40-80. Shrub survival rate and shrub biomass was monitored. Shrub biomass production data were recorded during June 2010. Fifty shrubs from each species were randomly picked for recoding forage production. Harvested shrubs were separated into leaves and wood and oven dried for calculation of dry matter forage production. Descriptive analysis was used for calculation of average forage production of both species

One possibility for the improvement of the metabolic productivity of an organism is genetic modification. This strategy can be successful when an increase of the flux through a pathway is achieved by, e. g., the overproduction of the rate-limiting enzyme, an increase of precursors, or the modification of the regulatory properties of enzymes. In the carotenogenic yeasts, mevalonate synthesis, which is an early step in terpenoid biosynthesis, is a key point of regulation of the carotenoid biosynthetic pathway. In fact, addition of mevalonate to a culture of X. dendrourhous stimulated both astaxanthin and total carotenoid biosynthesis four times (from 0.18 to 0.76 mg/ g and from 0.27 to 1.1 mg/ g dry cells, respectively). This indicates that the conversion of HMG-CoA to mevalonate by HMG-CoA reductase is a potential bottleneck on the road to modified strains with higher astaxanthin content (Verdoes et al., 2003).

Like carotenoids, ergosterol is an isoprenoid and it is biosynthetically related to them by common prenyl lipid precursor, FPP. Astaxanthin production by P. rhodozyma strain was enhanced (1.3-fold) when sgualene synthase phenoxypropylamine-type inhibitor for sterol biosynthesis was added to the medium. The isolation and characteristic of the carotenogenic genes of yeasts facilitates the study of the effect of their overexpression on carotenoid biosynthesis. Use of recombinant DNA technology for metabolic engineering of the astaxanthin biosynthetic pathway in X. dendrourhous was described too. In several transformants containing multiple copies of the phytoene synthase-lycopene cyclase­encoding gene (crtYB), the total carotenoid content was higher (with 82%) than in the control strain. This increase was mainly due to an increase of the beta-carotene and echinenone content (with 270%), whereas the total content of astaxanthin was unaffected or even lower.

Alternatively, in recent years, several food-grade non-pigmented yeasts (Saccharomyces cerevisiae, Candida utilis) have been engineered in order to obtain strains possessing the ability to produce selected carotenoids (Verwaal et al., 2007). Identification of genes of enzymes from the astaxanthin biosynthetic pathway and their expression in a non- carotenogenic heterologous host have led to the overproduction of beta-carotene. The possibility of the use of S. cerevisiaeas a host for efficient beta-carotene production by successive transformation with carotenogenic genes (crtYB which encodes a bifunctional phytoene synthase and lycopene cyclase; crtI, phytoene desaturase; crtE, heterologous GGPP synthase; tHMGI, HMG-CoA reductase) from X. dendrorhous was studied. Like X. dendrorhous, S. cerevisiae is able to produce FPP and converts it into GGPP, the basic building block of carotenoids. S. cerevisiae, the industrially important conventional yeast, cannot produce any carotenoid, while it synthesizes ergosterol from FPP by a sterol biosynthetic pathway. Conversion of FPP into GGPP is catalyzed by GGPP synthase encoded by BTS1 gene in S. cerevisiae. Construction of a strain, producing a high level of beta-carotene (5.9 mg/g dry cells) was succesful. Oleaginous yeasts are also suitable host strains for the production of lipophilic compounds due to their high lipid storage capacity. Recently, the carotenoid-producing Yarrowia lipolytica has been generated by metabolic engineering. Acording to these results entire biosynthetic pathways can be introduced into new host cells through recombinant DNA technology and carotenoids can be produced in organisms that do not normally produce carotenoids.

1.3 Agricultural advantages

1.3.1 Salt tolerance

Sorghum is characterized as moderately tolerant to salinity (Almodares and Sharif, 2005; Almodares and Sharif, 2007). Salinity reduces sorghum growth and biomass production. Salinity greatly reduced sorghum growth and this effect was more pronounced at 250 mM than at 125 mM NaCI (Ibrahim, 2004). However it was reported that sorghum growth was significantly reduced at all salinity levels from 50 to 150 mM (El-Sayed et al., 1994). Imposition of salt stress resulted in decreases in the percentage of seeds germinated (Almodares et al., 2007), although the strongest decline in germination occurred at the highest salt concentration (Table 2). Nevertheless, the development of high-yielding salinity tolerant sorghums is the best option to increase the productivity in soils (Igartua et al. 1994). Similarly, Gill et al. (2003) observed a great reduction in germination rate due to salt stress, in sorghum seeds at 37 °C in NaCl (-1.86MPa).

Relative percent germination(%)in osmotic potential (Mpa)created by NaCl

According to Prado et al. (2000), the decrease in germination may be ascribed to an apparent osmotic ‘dormancy’ developed under saline stress conditions, which may represent an adaptive strategy to prevent germination under stressful environment. Germination time delayed with the increase in saline stress and root growth was more sensitive to salt stress than was germination (Gill et al., 2003). It seems that grain weight is related to salt tolerance in sweet sorghum. It showed that higher total seedling dry weight was obtained with larger seed size in 18 sweet sorghum cultivars under salt stress (Table 3 and Fig. 1). The presence of large genotypic variation for tolerance to salinity is reported in sorghum (Maiti et al, 1994). Sorghum seems to offer a good potential for selection, as intraspecific variation for germination under saline conditions (Table 2) or in the presence of other osmotic agents that has already been reported. Selection of salt tolerant cultivars is one of the most effective methods to increase the productivity of salinity in soils (Ali et al., 2004). By using these salt tolerant plants in breeding they produced progranuned an improved plant having higher chlorophyll concentration, more leaf area, early and better yield potential etc. The advancement of salinity tolerance during the early stages of sorghum growth been successfully accomplished through selection.

Genotypes possessing salt tolerance characteristics will help in boosting up plants production in salt-affected soils (Ali et al., 2004). Azhar and McNeilly (1988) found that, for salinity tolerance of young sorghum seedlings, both additive and dominant effects were involved, the latter being of greater importance. Attempts have been made to evaluate salt tolerance at the germination and emergence stages in sorghum (Igartua et al., 1994). In fact, the variation in whole-plant biomass responses to salinity was considered to provide the best means of initial selection of salinity tolerant genotypes (Krishnamurthy et al, 2007). The presence of large genotypic variation for tolerance to salinity reported in sorghum (Krislmamurthy et al., 2007). There are large genotypic variations for tolerance to salinity in sorghum (Table 4). The other possible solution could be either using physical or biological practice (Gupta and Minhas, 1993). Sudhir and Murthy (2004) reviewed both multiple inhibitory effects of salt stress on photosynthesis and possible salt stress tolerance mechanisms in plants. Salinity reduced relative growth rates and increased soluble carbohydrates, especially in the leaves of salt sensitive genotype (Lacerda et al., 2005). In addition salt-stressed sorghum plants additionally accumulate organic solutes, like proline, glycinabetaine, sugars, etc. (Lacerda et al., 2001). The total soluble sugar increased in sorghum sap with increasing salinity level (Ibrahim, 2004; Almodares et al., 2008a). Sucrose content of plant parts is an indicator of salt tolerance (Juan et al., 2005). The imposition of strong water or salt stresses in sorghum has been demonstrated to be accompanied to an increase in the sugar levels of embryos, which may help in osmoregulation under stress conditions (Gill et al., 2003). The fructose level is always higher than glucose and sucrose levels in response to various salinity treatments (Gill et al., 2001; Almodares et al., 2008a).

Worldwide, and for a long time, poplars have been used for, inter alia, pulpwood and timber production. Currently, short rotation plantations intended for biomass production are being established. In Sweden poplars have been planted in experiments or plots for practical survey for the last 20 years. Poplar plantations covering small areas of 0.5-2 ha on former farmland can produce 80-100 tonnes ha-1 of wood in ten years (Mean annual increment (MAI): 8-10 tonnes ha-1 years-1). If rotations are longer than 10 years, some of the material harvested will be suitable for use as pulpwood. Nowadays short rotation plantations aiming biomass production has been established. In Sweden poplars have been planted in experiments or plots for practical survey the last 20 years. After harvesting, regeneration of older trees by suckers or sprouts is limited. Certain clones and species produce no or only a few sprouts or suckers. This may be because poplars must be young when they are cut for

on pulpwood and timber production, with bioenergy derived from tops and branches. After harvesting the trees, the stumps produce 50,000-100,000 suckers ha-1. During the subsequent 5-10 year period the sucker biomass will amount to 50-100 tonnes ha-1. However biomass production during a 10-year-old rotation was found to amount to 47, 51 and 87-124 tonnes ha-1 respectively for the aspen stands.

1.3 Differential response of cereals and legumes to drought and salinity stress

Abiotic stresses (mainly drought and high soil salinity) are the major cause for the reduction in crop biomass and yield worldwide, especially in the SAT. Generally, Cereals are relatively better equipped to tolerate those stresses than the legumes, partly due to the carbon pathway differences between these two crop groups. Data collected using destructive measurements showed that under terminal drought the reduction of shoot biomass production in legumes can reach 50% especially in groundnut. In cereals, shoot biomass reduction is hardly above 40%.

Depending on the level of stress, both legumes and cereals may suffer from yield losses to a larger extent than shoot biomass reduction, however, in some cases, a better partitioning can help in a better yield. For example, reduction of chickpea seed yield due to terminal drought was recorded to be 26 to 61 % and the shoot biomass at maturity to be 31 to 63 % during three years of study using a large number of germplasm accessions. Whereas, the haulm yield of groundnut was reduced to 24 and 23% while the pod yield by 47 and 37% in the two years of field experimentation.

At a salinity level where the legumes would be completely dead, cereals like pearl millet and sorghum can thrive and be productive. However under salinity the larger adverse effect is on the reproductive growth than on the vegetative growth. Salinity affects plant growth and also equally the partitioning leading to a greater loss in seed yield. Reproductive biology is known to be more affected leading to greater yield damage. The partitioning to the root system plays a key role in tolerance to both drought and salinity.

1.4 Monitoring crop growth and productivity using remote sensing and GIS is key

The traditional approach of estimating the effect of a given abiotic stress on crop growth and productivity is becoming obsolete because of various reasons related to precision and up­scaling. Remote sensing data provide a complete and spatially dense observation of crop growth. This complements the information on daily weather parameters that influence crop growth. RS-crop simulation model linkage is a convenient vehicle to capture our understanding of crop management and weather with GIS providing a framework to process the diverse geographically linked data. Currently RS data can regularly provide information on regional crop distribution, crop phenology and leaf area index. This can be coupled to crop simulation models in a number of ways. CSM-RS linkage has a number of applications in regional crop forecasting, agro-ecological zonation, crop suitability and yield gap analysis and in precision agriculture.

In future the RS-CSM linkage will be broadened due to improvements in sensor capabilities (spatial resolution, hyper-spectral data) as well as retrieval of additional crop parameters like chlorophyll, leaf N and canopy water status. Thermal remote sensing can provide canopy temperatures and microwave data, the soil moisture. The improved characterization of crop and its growing environment would provide additional ways to modulate crop simulation towards capturing the spatial and temporal dimensions of crop growth variability.

Plants of experimental field plots were harvested at physiological maturity (growth stage 90 DC) by a harvester thresher HEGE 140 (Hans-Ulrich Hege GmbH & Co, Germany). After the harvest, the grains were cleaned on the sieves by flow of air and then yield and thousand — grain weight were determined. Analytical samples were made according to methodology ISO 13690:1999 by quartering of cleaned grain. A common (average) analytical sample of four trial plots grain was prepared.

Sampling from the experimental pots was performed three weeks after the application of brassinosteroids in plant growth stages referred to a decimal code for the growth stages of cereals. The first sampling was performed in the plant growth phase 47-49 DC (visible awns), the second sampling in the growth stage 73-75 DC (30-50 % of final grain size). Grain and straw samples were taken in the growth phase Z90-92 (full ripeness). Green plants were taken from experimental pots cleaned up with distilled water and subsequently freeze-dried.

Vertical cross sections at latitudes 15° S, 25° S and 35° S, across the smoke plume contribute to depict the distribution of the meridional transport of PM2.5 (in pgmUs-1) (Figure 10) and water vapour mixing ratio (in gmkg-V1) (Figure 11). The cross-sections clearly illustrate the role of the SALLJ as a transport mechanism. In general, the meridional transport of PM2.5 is limited to the layer between the surface and 4000 m and the higher values are near the emission sources. In the case of the water vapour the vertical extent is greater, reaching 8000m.

At 15° S (Figure 10a), on 23 August, the meridional flux of PM2.5 was mainly southward and on the layer between 1000 and 4000m, with the maximum located between 1500 and 2000m with values between -60 and -180 pgmrV1. The transport was on a narrow region east of the Andes range, centred at 65° W. During the following day, the level of maximum meridional transport was closer to the surface and the longitudinal extent increased. The values were similar than those on the previous day. On 25 August, two relative maxima were present, one close to the surface at 65° W and the other one between 1500 and 3500m above the ground at 62.5° W, ranging from -60 to -300 pgmUs-1. During the following day, the conditions were almost similar, but the maximum close to the surface weakened. During 27 August, the southward transport east of the Andes was comparable, ranging from -180 to -240 pgm-2s-1 and a secondary maximum west of the mountain range near 3000m was present. On 28 and 29August, the southward transport was mainly in the layer between the surface and 3000m, with a longitudinal extent from 72.5° W to 55° W. The maximum values varied from -240 to -360 pgm"2s_1. A narrow elevated maximum occurred, at upper levels and 40° W. On 30 August, the southerlies reached this latitude, and a northward transport occurred near the surface from 65° W to 50° W with values between 80 and 120 pgm-2sA The southward transport persisted at upper levels close to the Andes, but gradually vanished according to the cold front movement. During 31 August, the northward flux near the surface prevailed, ranging from 80 to 140 pgm-2sA

At 25° S (Figure 10b), on 23 August, the meridional flux showed a maximum of -120 pgm-2s_1 centred at 60° W. The next day the maximum flux occurred westward, at 62.5° W and ranged from -120 to -240 pgm-2sA During 25 August, the location was similar and the values increased, varying from -180 to -360 pgm-2s-h On the following two days, one region of maximum transport was located close to the Andes from surface up to 3500 m, with values that ranged from -300 to -660 pgm-2s_1 and the second one, was near the surface centred at 57.5° W, varied from -60 to -180 pgm-2s_1 and spanned ten degrees east of 65° W.

During 27 August, there is also a transport towards the south between 3000 and 4000m west of the Andes. The next day, the transport had similar longitudinal and vertical span and values from -360 to -600 pgm-2s_1. By 29 August the southward flux was -180 to -600 pgm-2s_1 between 62.5° and 50° W and the northward transport was centred at 60° W, ranging from 60 to 260 pgm-2s-h During 30 August the northward flux occurred between 63° and 50° W and values from 20 to 60 pgm-2s_1 and towards the south in upper levels at 47° W ranging from — 180 to -80 pgm"2s_1. The last day of the studied period had very light northward transport smaller and equal than 20 pgm-2s-1, and southward flux in upper levels from 45° to 40° W with a maximum of -60 pgm-2s-h

Figure 10c illustrates the PM2.5 meridional flux at 35° S. The southward flux started on 24 August, the plume was near the surface between 60° and 50° W, with values from -60 to -120 ^gm-2s-1.

Fig. 10b. Vertical cross-sections at 25° S of PM2.5 meridional transport (pgm’2s-1) against the height above the surface. Terrain height profile is included.

During the next day, two maxima appeared, one located near the surface and the other one centred at 2000m and values ranging from -60 to -120 pgm-2s-1. During 26 August, the upper
level maximum, centred at 2500m and east of 60° W strengthened, the values ranged from — 60 to -360 pgm-2s-1. On 27 August the southward transport was widespread and ranged from -60 to -420 pgm-2s-1. On the following day, the smoke transport extended up to 5000m, remaining towards the south and east of 60° W and the maximum values ranged from -60 to -360 pgm-2s-h Close to the mountains a northward transport occurred near the surface, with values between 20 and 100 pgm-2s_1. By 29 August the plume was over the Atlantic Ocean and the northward transport was west of 55° W, ranging from 40 to 60 pgm"2s_1. During the next two days the flux gradually disappeared at this latitude due to the fast movement of the cold front.

rv meridional flux — 15 S 25AUG2002 rv meridional flux — 15 S 2BAUG2002

Fig. 11a. Vertical cross-sections at 15° S of water vapour mixing ratio meridional transport (g m kg-1 s-1) against the height above the surface. Terrain height profile is included.

Figure 11 shows the vertical cross sections at similar latitudes, but illustrates in this case, the water vapour meridional transport. At 15° S (Figure 11a) on 23 August there was a prevalence of the southward transport of water vapour, spanning from 72.5° W to 47° W, from the surface up to 3000m, and the maximum flux centred at 1500m with a mean daily value of -60 gmkg-1s_1. The northward transport took place over the oceans near the surface. The next day the pattern was similar and the value of the meridional flux increased. On the following three days the longitudinal extent of the zone with southward flux was narrower and the values -80 and -60 gmkg-V1 respectively. West of the Andes, at upper levels the water vapour southward flux also occurred. The northward transport over the oceans was still present. On 28 and 29 August the longitudinal extent increased as well as the value of the maximum flux, the difference is the location near the surface. The northward water vapour transport increased over the Pacific Ocean. During 30 August, the incursion of the cold front caused a northward flux near the surface between 65° and 50° W. The flux from the north was restricted next to the Andes centred at 1000m. The following day the pattern was nearly similar, with a decrease in the southward transport.

At 25° S (Figure 11b) from 23 to 28 August, there was a southward flux at all longitudes east of the Andes from the surface up to middle levels in the troposphere.

rv meridional flux — 25 S 25AUG2002 rv meridional flux — 25 S 26AUG2002

Fig. 11c. Vertical cross-sections at 35° S of water vapour mixing ratio meridional transport (g m kg-1 s-1) against the height above the surface. Terrain height profile is included.

The values ranged from -140 to -260 gmkg^s-1. West of the mountain range, the southward flux also occurred on 26 and 27 August reaching a daily maximum of -80 gmkg-1s-1. From 29 to 31 August the progression of the cold front caused a northward flow that varied between 20 and 120 gmkg-1s-1 with a longitudinal range that moved to the east.

Figure 11c depicts the water vapour meridional transport at 35° S. The southward water vapour transport was present from 23 to 27 August from the surface up to 8000m and 75° W and 35° W, the maximum values varied from -100 to -260 gmkg-1s-1. The opposite transport directions associated with the surface cold front is sharply marked in the cross-sections on 28 and 29 August, and the maximum values are located near the surface. The next days showed the contrast in the air masses water vapour as well.