Miguel A. Taboada

Terrestrial and Inland Water Systems

The topics assessed in this chapter were last assessed by the IPCC in 2007, principally in WGII AR4 Chapters 3 (Kundzewicz et al., 2007) and 4 (Fischlin et al., 2007), but also in WGII AR4 Sections 1.3.4 and 1.3.5 (Rosenzweig et al., 2007). The WGII AR4 SPM stated “Observational evidence from all continents and most oceans shows that many natural systems are being affected by regional climate changes, particularly temperature increases,” though they noted that documentation of observed changes in tropical regions and the Southern Hemisphere was sparse (Rosenzweig et al., 2007). Fischlin et al. (2007) found that 20 to 30% of the plant and animal species that had been assessed to that time were considered to be at increased risk of extinction if the global average temperature increase exceeds 2°C to 3°C above the preindustrial level with medium confidence, and that substantial changes in structure and functioning of terrestrial, marine, and other aquatic ecosystems are very likely under that degree of warming and associated atmospheric CO2 concentration. No time scale was associated with these findings. The carbon stocks in terrestrial ecosystems were considered to be at high risk from climate change and land use change. The report warned that the capacity of ecosystems to adapt naturally to the combined effect of climate change and other stressors is likely to be exceeded if greenhouse gas (GHG) emission continued at or above the then-current rate.

Heavy metals in soils of Argentina: Comparison between urban and agricultural soils

Abstract Trace metals, including heavy metals, can be harmful to the biota and human beings. This leads to study the accumulation of those elements in soils. In the Pampean region (Argentina) this knowledge is scarce. Our objectives were to (i) determine the trace metal concentration in soils of Buenos Aires City and agricultural areas, (ii) start to establish the soil trace metals baseline concentration, and (iii) find relationships between soil properties and those elements Topsoil samples were taken in Buenos Aires City and on farms along an arc 50 to 250 km away from the metropolis. All studied soils were Mollisols. Soil samples were analyzed for their cadmium (Cd), copper (Cu), zinc (Zn), chromium (Cr), cobalt (Co), lead (Pb), and nickel (Ni) contents by acid extraction. Soil properties were determined using standard methods. The soils of Buenos Aires City show the highest average concentrations of Cd, Cu, Pb, and Zn. The further the sampling sites were from Buenos Aires, the lower the metal concentr...

Grazing effects of the bulk density in a Natraquoll of the flooding pampa of Argentina.

The lnfiuence of grazing by cattle on soll bulk density was studied in a typic Natraquoll of the Ploodlng Pampa of Argentina for a period of 33 months, by comparing a grazed sltuatlon to an enclosure deferred from grazing for 7 years. Pioods took piace ln this period as usual. Bulk den&y (BD retention varled from 1.00 to 1.11 Mg m’ d at -33.3 kPa of water ln the ungraaed soil and ln the grued soil from 1.04 to 1.16 Mg mm3. Environmental factors were the primary agent controlling BD; only ln some periods were there sign&ant differences between treatments. Slight increases in BD occurred under graalng after the recession of the flood water, and sign&ant decreases occurred in the ungrazed soil during the large and sudden falls ln water content. In this case the effect of trampling, therefore, would con&t malnly of impeding the decrease in BD. No compaction was observed ln periods when no flood occurred or while soli remahred submerged ln water. The results indicated that the variations of buik density caused by cattle trampilng were superimposed on those produced by floods and showed an interaction between the effects of land-use and the particular environmental condltlons of the region. The Flooding Pampa is a subhumid low, very flat plain. Its 90.000 km* are mostly covered by halo-hydromorphic soils, the most conspicuous being Natraquolls (INTA 1977). The region is affected by recurrent floods caused by an excess of water: percolation, surface movement, and evaporation are less than rainfall. Soils remain saturated and ponded most years from winter to late spring, and exceptionally in autumn; they are dry in some summers. Floods and droughts sometimes follow each other. Because of several constraints, agriculture is limited and the dominant land-use in the region is the production of beef cattle on natural grasslands. Cattle remain over the field all year, including those periods when soil is very wet. Trampling in these conditions is usually considered a severe damage factor in surface structure of grassland soils (Davies 1985, Scholefield and Hall 1986). Trampling by cattle is reported by the literature as causing increases in bulk density by compaction in the soil surface (Heady 1975, Lull 1959, Van Haveren 1983, Warren et al. 1986, Willat and Pullar 1983). Nevertheless some results are in disagreement with this opinion. Laycock and Conrad (1967) found that some increases in bulk density may be ascribed to the lower water content that grazed soils usually have (Gifford and Hawkins 1978); Van Haveren (1983) showed that not ail soils may be compacted by trampling because of the high sand content of some soils; and Lagocki (1978) even found that bulk density decreased when trampling was performed on a soil with high water table. Another subject under controversy is the time required for the recovery of soil structure, as measured by the decrease of bulk density after compaction. For example, Braunack and Waiter (1985) found long periods for recovery, while Warren et al. (1986) showed that shorter terms were required. The factors causing these differences are obviously related to different soil properties, environmental conditions, and grazing intensities. They make it difficult to transfer results from one site to Authors arc wit! the Dcpartamento de Ecolo sidad de Buenos Ames, Avenida San Martin 44 f ia, Facukad de A

Baseline Levels of Potentially Toxic Elements in Pampas Soils

ronomia, UniverManuscript accepted 24 May 1988. 3,1417 Buenos Awes, Argentina. another. In the case of the Flooding Pampa, despite the economic importance of grazing, local literature is very scarce. Rusch and Leon (1983), for instance, attributed changes in the floristic composition of a natural grassland to soil compaction by trampling. Bulk density is a commonly used parameter of soil porosity, giving an effective indication of the compaction-regeneration processes (Bullock et al. 1985). The objective of this study was to evaluate the effects of cattle grazing upon soil bulk density in the Flooding Pampa region of Argentina. The implications for stock management are also considered. Materials and Methods Study Area Research was carried out in an area located in the middle of the Flooding Pampa near the town of Casalins (Buenos Aires Province), in which floods occur most years. In the period under study (from October 1983 to July 1986) floods submerged the soils with a few centimeters of water in winter-spring 1984 and 1985 and in autumn 1986. There were no floods in 1983. Vegetation of the area is a natural grazed grassland community characterized by Rptochaetium montevidensis, Briza subaristata, Eclipta bellidioides, and Menthapulegium (Perelman et al. 1982). It covers more than 7% of soil surface. Grasses are sparsely distributed over the soil and are stratified in the first 10 cm of plant canopy (Sala et al. 1986). The range is mainly devoted to the production of beef cattle. Dominant soil is a typic Natraquoll, General Guido series, moderately saline phases. The soil is characterized by a tough clayey and natric B2t horizon. Conversely, the 0.12 m thick Al horizon is loamy (clay %: 23.60), slightly acid (pH 6.20) with high organic carbon percentage (3.20). This horizon has a high swell-shrink capacity as its clay fraction has 30 to 50% of smectitic materials, causing bulk density to fluctuate with changes in soil water content. Taboada et al. (1988) related soil bulk density to moisture content by the function: BD = 1.20 + 0.0008 GW 0.00016 GW* r = -0.95 (1) where BD is soil bulk density and GW is gravimetric soil water percentage. Other morphological, mineralogical, and chemical properties of this soil have been published elsewhere (Lavado and Taboada 1985, Taboada and Lavado 1986, Taboada et al. 1987). Treatments The bulk density and water content of soil were measured in a grazed location and at a location excluded from grazing for 7 years prior to initiation of the study. The locations were not replicated . The grazed field was a natural grassland which had never been ploughed, but had been grazed year-round for more than a century. During the study period the mean stocking rate was 1.06 cattle ha-’ year-‘. This rate is representative of most ranges of the region. The ungrazed enclosure was a 4-ha field fenced and surrounded by the cattle range; grazing had been excluded from it since 1976. Grazing exclusion resulted in the replacement of a large number of small tussocks by a few large ones. Total biomass, mainly standing dead, increased steadily; litter accumulated. Another major effect was the disappearance of some native planophile species and most of the exotics from the enclosure (Sala et al. JOURNAL OF RANGE MANAGEMENT 41(6), November 1988 1986). Nevertheless the soil only showed significant reductions in salt content, but not in organic matter, total nitrogen, and available phosphorus contents (Lavado and Taboada 1985, 1987). Sampling and Analysis Sampling was carried out in the Al horizon. Five undisturbed soil cores (9 cm in diameter and 10 cm in depth) were taken at random from each treatment on 22 dates during the period under study. Sampling was performed carefully because of the extreme soil water content found along the time in each core. Bulk density was determined by the core method (Blake 1965) and gravimetric soil water content by the oven-dry method. Volumetric soil water content (VW) was calculated from them. The depth affected by animal hooves was evaluated by additional bulk density samples taken at the O-4,4-8, and 8-12 cm depths of the Al horizon using 6 cm diameter and 4 cm depth cores. Five samples were taken at random from each treatment in November 1984 and June 1985. In order to separate the effect of compaction by animal hooves from that caused by decreases in soil water content (Laycock and Conrad 1967), measured values of bulk density were adjusted to a fixed soil water content (Perrier et al. 1959). In this case bulk density was standardized at -33.3 kilo Pascal (kPa) of water retention (29.96% in this horizon), by means of the slopes of equation (1). This procedure was judged to be reliable because of the very high and statistically significant (a10.001) correlation coefficient found for equation (1). Soil surface strength was measured in September, November, and December 1984, using a Proctor penetrometer (Davidson 1965). In each month, 20 measurements were performed following a zig zag path over uncovered soil surfaces in each treatment. Results were statistically appraised by analysis of variances (ANOVA). When significant differences in BD were found between dates, the Tukey test was used to separate the means. Results and Discussion Volumetric water content and bulk density at -33.3 kPa in the Al horizon are shown in Figure 1. Flood periods are also included. Mean VW ranged from 17.06 to 40.79% in the ungrazed soil, and from 19.09 to 42.44% in the grazed soil. Only in the first summer of the studied period (November 1983 to January 1984) was soil dry. The rest of the time it remained with moderate to very high water contents. According to Scholefield and Hall (1986), under these conditions soil surface damage by cattle trampling is likely to occur. Mean BD ranged from 1.00 to 1.11 Mg me3 in the soil of the enclosure where cattle were removed from 1976, and from 1.04 to 1.16 Mg me3 in the soil under grazing. These values were somewhat low, but consistent (De Kimpe et al. 1982) with the high organic carbon content of the Al horizon. Different behavior was observed in BD with time in both treatments. In the ungrazed soil there were lower and significant values on 3 dates (November 1983, January and December 1985). They were reached after the soil underwent great loss of water as its VW showed a sudden fall from a previous very wet condition (it was saturated with water in 1983 and flooded both in 1984 and 1985). The sudden decreases in soil water content seemed to be associated with the parallel decreases in BD. This relationship cannot be explained

Null Creation Of Air-filled Structural Pores By Soil Cracking And Shrinkage In Silty Loamy Soils

The soils of the Pampas are thought to be generally non-contaminated but there is growing evidence of trace element accumulation at some specific sites. The goal of this study was to measure the current levels of the main Potentially Toxic Elements (PTE) in the top horizon and in specific soil profiles so that we would establish the baseline concentrations of these elements. Eighty-eight top soils and three soil profiles were sampled. The samples were acid digested. Arsenic, boron, barium, cadmium, cobalt, chromium, copper, lead, manganese, mercury, molybdenum, nickel, silver, selenium and zinc were determined with inductively coupled argon plasma emission spectrometry (ICPES). All of the values found are within the normal range for uncontaminated soils as reported from several continents. Elements with high environmental risk potential are lower than the admissible range of the European Union and some of them are orders of magnitude lower than those of the United States Environmental Protection Agency (US-EPA) 501 levels. Potentially Toxic Elements contents increased with depth or showed a maximum concentration at the B2 horizon. This is related to the parent material and the pedogenetic processes but not to recent contamination. Soil profiles showed higher concentrations of PTE in clayey horizons. However, these relationships did not appear in top soil samples in any soil Great Group studied. The shown data establishes a baseline for PTE concentrations for Pampas soils.

Soil volumetric changes in natric soils caused by air entrapment following seasonal ponding and water table rises

Information about abiotic regeneration of air-filled porosity in silty soils is scarce. It could be a key mechanism to explain their low physical resilience. In the present work, we aim at evaluating whether changes in intrinsic soil properties (e.g., soil organic carbon, clay content, and clay mineralogy) caused by degradation affected soil volume response to wetting-drying cycles. Volume and size distribution of cracks and clod shrinkage curves were determined in silty loamy soils (Typic Argiudoll) of Argentina under nearby conventionally tilled (CT), eroded CT, and Pasture management. Crack volume increased from 1000 cm3 in CT and Pasture soils to 6000 cm3 in the more clayey and swelling eroded CT soil. Crack size distribution was similar in all studied soils with large cracks (first and second size order) prevailing over small ones (fourth and fifth size order). Clod shrinkage curves had no S-shape, thus showing the lack of structural shrinkage in all studied soil management regimens. Air content in structural pores was as low as 0.03 to 0.10 cm3 g−1 at the air entry point. This little air entry during drying agreed with the lack of small cracks and can be related to the prevalence of plasma (i.e., silt and clay) over sand. Results showed that key intrinsic properties did not drive soil volume changes in the studied silty loamy soils. They change their volume during drying, but the creation of air-filled structural pores is little or null.ABBREVIATIONS: ACr: area of the crack calculated from its width and length; AE: air entry; Airp: air content of the plasma; Airstr (AE): air content of structural porosity at the air entry transition point; Airstr (SAT): air content of structural porosity at saturation; CT: conventionally tilled; Cter: eroded conventionally tilled; DCr: depth of the crack; Id: density of cracks; KBs: slope of the basic shrinkage; KR: slope of the residual shrinkage; KStr: slope of the structural shrinkage; LCr: length of the crack; ML: macroporosity limit; MS: aximum swelling; PD: particle density; S: surface of the pot; SC: swelling capacity of the soil from saturation to the shrinkage limit transition point; ShC: shrinkage curve of the soil; SL: shrinkage limit; Subang Bk: subangular blocks; V: bulk specific volume; VAE: specific volume at the air entry transition point; VCr: specific volume of the crack calculated from its area and depth; VML: specific volume at the macropore limit transition point; VMS: specific volume at the maximum swelling transition point; VP(AE): plasma porosity at the air entry transition point; Vp(ML): plasma porosity at the macropore limit transition point; Vp(MS): plasma porosity at the maximum swelling transition point; Vp(SL): plasma porosity at the shrinkage limit transition point; VSL: specific volume at the shrinkage limit transition point; Vstr(AE): structural porosity at the air entry transition point; Vstr(ML): structural porosity at the macropore limit transition point; Vstr(MS): structural porosity at the maximum swelling transition point; Vstr(SL): structural porosity at the shrinkage limit transition point; W: gravimetric water content; WAE: gravimetric water content at the air entry transition point; WCr: width of the crack; W/D cycles: soil wetting and drying cycles; WML: gravimetric water content at the macropore limit transition point; WMS: gravimetric water content at the maximum swelling transition point; Wp: water content in the plasma porosity; W range (SAT-SL): gravimetric water content range from saturation to the shrinkage limit transition point; WSL: gravimetric water content at the shrinkage limit transition point; WStr: water content in the structural porosity; &phgr;ML: bulk density at the macropore limit transition point; &phgr;MS: bulk density at the maximum swelling transition point; &phgr;SAT: bulk density at saturation; &phgr;SL: bulk density at the shrinkage limit transition point.

Assessment of topsoil properties in integrated crop–livestock and continuous cropping systems under zero tillage

Soil volumetric changes have been seldom studied in seasonally ponded soils subjected to periodic water table rises. In the Flooding Pampa of Argentina the topsoils develop significant swelling and shrinkage, despite their low percentages of total and expansible clay. We tested the hypothesis that: (a) the swelling of a Natraquoll and a Natraqualf of this region is caused by the wide change in water contents during ponding–drying cycles; and (b) soil swelling is accentuated by the effect of air entrapment ahead of the advance of soil wetting fronts. The relationship between the reciprocal of bulk density (i.e. soil specific volume), ν, and water content, θ, was determined in the laboratory (clod shrinkage curves) and in the field (repeated core sampling). Soil clods behaved in accordance to their inherent soil properties, with zero and residual shrinkage (slope n=δν/δθ<1) in both top horizons, and normal shrinkage (slope n=δν/δθ≈1) throughout the water content range of Bt horizons. Unlike the clods, in the field the slope, n, was as high as 1.47–1.48 in top horizons, and 1.93–1.98 in both Bt horizons, showing the occurrence of abnormal soil swelling processes. Taking into account the narrow volumetric water content range found in the field (i.e. 0.25 v/v in both Bt horizons), this rejects our first proposed hypothesis. Soil air became trapped ahead of the advance of two field wetting fronts: (a) water table rises from depth and (b) surface ponded water. As a result, pore air volume increased during soil wetting, and was as high as 0.24–0.34 v/v, and 0.35 v/v at the maximum swelling limit of top and Bt horizons, respectively. Results show that air entrapment caused the swelling or “inflation” of soils, which agrees with our second hypothesis. However, the influence of air entrapment was more pronounced than a simple accentuation of swelling in Bt horizons. Air entrapment caused the whole soil to a depth of about 0.4 m to expand.

Structural stability changes in a grazed grassland natraquoll of the Flooding Pampa (Argentina)

A regional study was conducted in the northern Pampas of Argentina in order to compare soil quality at proximal cropland sites that are managed under either continuous cropping (CC) (n = 11) or integrated crop–livestock (ICL) (n = 11) systems under zero tillage. In the ICL system, samples were taken in the middle of the agricultural period. Although soil total and resistant organic carbon (TOC, ROC) were significantly higher in silt loam soils than in loam/sandy loam soils, variations in carbon concentration were not associated with differences in soil management. Soil relative compaction was the only property that was significantly (P < 0.05) affected by the soil type × management interaction. Soil relative compaction values were significantly lower with ICL in loam/sandy loam soils, but there were no significant differences in silt loam soils. Structural instability index showed little change from CC to ICL sites, indicating that there was no soil structural damage. Soil penetration resistance was significantly higher in ICL soils within the first 0.075 m of soil depth, slightly exceeding the critical threshold (2000 kPa). However, firmer topsoil under ICL was not due to shallow compaction, as evidenced by no increase in soil bulk density.

ROOT ABUNDANCE OF MAIZE IN CONVENTIONALLY- TILLED AND ZERO-TILLED SOILS OF ARGENTINA (1)

Several factors affecting soil structural stability interact in the natural grasslands of the Flooding Pampa (Argentina). This seasonal and flat wetland (usually ponded in winter-spring and dry in summer) has swelling soils, which are affected by seasonal increases in sodium, and continuous grazing by cattle. Our study aimed to determine the period of structural deterioration, the magnitude of deterioration, and the time for recovery in a widely distributed soil of the region. The mean weight diameter of wet-sieved aggregates (MWD) was determined in grazed and ungrazed (exclosure) plots. Aggregate MWD was often lower in the soil under grazing (from 4.4 to 5.1 mm) than in that of the exclosed area (from 4.7 to 5.4 mm). This reduction in aggregate size was attributable to the mechanical shearing action of trampling. Soil water content accounted for 74% of the variation in aggregate MWD under grazing. At low soil water contents, the structure of the grazed soil became less stable. Grazing effects on soil structural stability are significant only in periods when the soil dries. Stocking rates must be regulated at those dry periods.

The deterioration of tall wheatgrass pastures on saline sodic soils

SUMMARY Maize root growth is negatively affected by compacted layers in the surface (e.g. agricultural traffic) and subsoil layers (e.g. claypans). Both kinds of soil mechanical impedances often coexist in maize fields, but the combined effects on root growth have seldom been studied. Soil physical properties and maize root abundance were determined in three different soils of the Rolling Pampa of Argentina, in conventionally-tilled (CT) and zero-tilled (ZT) fields cultivated with maize. In the soil with a light Bt horizon (loamy Typic Argiudoll, Chivilcoy site), induced plough pans were detected in CT plots at a depth of 0–0.12 m through significant increases in bulk density (1.15 to 1.27 Mg m -3 ) and cone (tip angle of 60 o) penetrometer resistance (7.18 to 9.37 MPa in summer from ZT to CT, respectively). This caused a reduction in maize root abundance of 40– 80 % in CT compared to ZT plots below the induced pans. Two of the studied soils had hard-structured Bt horizons (clay pans), but in only one of them (silty clay loam Abruptic Argiudoll, Villa Lia site) the expected penetrometer resistance increases (up to 9 MPa) were observed with depth. In the other clay pan soil (silty clay loam Vertic Argiudoll, Perez Millan site), penetrometer resistance did not increase with depth but reached 14.5 MPa at 0.075 and 0.2 m depth in CT and ZT plots, respectively. However, maize root abundance was stratified in the first 0.2 m at the Villa Lia and Perez Millan sites. There, the hard Bt horizons did not represent an absolute but a relative mechanical impedance to maize roots, by the observed root clumping through desiccation cracks.