Historical sheep farming in the Patagonian drylands has led to reduced grass cover, soil erosion, and shrub encroachment, compromising ecosystem function. Effective restoration requires managing shrub cover, bare soil, and patch connectivity through various strategies. This study evaluates rehabilitation interventions in a grass-steppe ecosystem, comparing grazed and ungrazed areas. Over three years, we tested the following: (a) mechanical shrub cutting with biomass redistribution, and (b) enhancing patch connectivity with Pinus spp. branch piles, alongside controls, in eighteen 5 m × 5 m plots invaded by Mulinum spinosum. Half of the plots were fenced to exclude grazing, resulting in six treatment combinations. We monitored soil properties, vegetation cover, and species composition. The treatments explained twice as much of the variation in community composition as the annual climatic variations (0.26 vs. 0.13). Livestock exclusion increased perennial grass cover more than the grazed plots did (2.14 vs. 1.42 times the initial measure). All treatments reduced the amount of bare soil except the grazed controls. Shrub cutting, especially with grazing, increased the lasting litter coverage by 5–10% and decreased the bare soil equivalently. Organic matter increased except in the non-intervened interpatches (0.95 times). The enclosures with cut shrubs trapped erodible particles, showing a 5% increase. Our study highlights that grazing destabilizes communities, while enclosures stabilize them, with interventions improving soil fertility and mitigating erosion.

In this article, controlling factors on radar interferometric coherence (IC) in a region of the Chubut River are analysed, since its variations could indicate potential sediment transfer zones. Studied control factors are vegetation cover, development of the drainage network, rainfall and winds. The results show that the major control over IC loss is given by rainfalls. A secondary control is exerted by the drainage networks development; whereas the limited changes in the vegetation cover and winds regime would not exert significant control. In addition, a permanent IC loss tendency was recognized in channelized areas whereas temporal IC variations were recognized in non-channelized areas. Finally, as different sectors of the study area under the same known conditions (meteorological phenomena, drainage network and vegetation cover) present different IC variations, the existence of at least a third control factor —likely linked to the geology of the landscape—, is deduced from this research.

In semiarid rangelands where the anthropogenic impact is currently increasing, as occurs in the rangelands of the Peninsula Valdes, the detrimental impacts of soil degradation on land resources became really dramatic. This chapter presents a review on the current knowledge of soil degradation in the Peninsula Valdes rangelands. Section 1 introduces the chapter, Sect. 2 focuses on soil degradation main processes, factors and causes, and Sect. 3 presents a review of soil degradation assessment methods and several soil degradation studies carried out since 1990 in the Peninsula Valdes region. Water and wind erosion are the degradation processes that are most strongly evidenced. Major causes of soil degradation are attributed to a combination of climatic and anthropic factors, with overgrazing being perceived to be a major factor. Four key causes associated with overgrazing in the Peninsula Valdes region rangelands are described: (1) Poor range management with respect to flock distribution and overstocking, (2) Limited access to information, (3) Top-down and largely ineffective government policy, and (4) Overdependence on grazing systems for sustained livelihoods. Assessment methods for assessing soil degradation include: expert judgment, remote sensing, productivity changes, field monitoring, pilot studies at farm level based on field criteria and expert opinion, and modeling.

Fil: Kowaljow, Esteban. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Cordoba. Instituto Multidisciplinario de Biologia Vegetal (p); Argentina

In arid and semiarid rangelands, soil erosion has been widely considered an important soil degradation process and one of the main factors responsible for declining soil fertility. In this study, we determined the sediment production and the enrichment ratios of clay, organic C, and total N by using rainfall simulations on runoff plots (0.60 x 1.67 m) in three plant communities of northeastern Patagonia: grass (GS), degraded grass with scattered shrubs (DGS), and degraded shrub steppes (DSS). Our results clearly indicate that spatial variability in soil loss rate and enrichment process exists as a result of the local differences in both plant composition and soil surface characteristics. Sediment production was significantly lower in the GS (14.2 g m(-2)) compared with the DGS and DSS (38.2 and 51.5 g m(-2), respectively). In the GS, the enrichment ratio of clay was significantly greater (3.9) and enrichment ratio of organic C was lower (3.1) than in the DGS and the DSS, though differences in enrichment ratios of total N were not significant. The high rate of soil loss and nutrients through overland-flow may limit the opportunities that promote the pathway from DGS back to GS community, favoring the dominance of shrubs. (c) 2012 Elsevier Ltd. All rights reserved.

In grazed semiarid ecosystems, considerable spatial variability in soil infiltration exists as a result of vegetation and soil patchiness. Despite widespread recognition that important interactions and feedbacks occur between vegetation, runoff and erosion, currently there is only limited quantitative information on the control mechanisms that lead to differences in infiltration from different vegetation types. In this paper, we determine (i) the relationship between vegetation and soil surface characteristics and (ii) the soil infiltration rate by using rainfall simulations on runoff plots (0.60 x 1.67 m) in three plant communities of northeastern Patagonia: grass (GS), degraded grass with scattered shrubs (DGS), and degraded shrub steppes (DSS). Our results clearly indicate that vegetation and soil infiltration are closely coupled. Total infiltration was significantly higher in the GS (69.6 mm) compared with the DGS and DSS (42.9 and 28.5 mm, respectively). in the GS, soil infiltration rate declined more slowly than the others communities, reaching a terminal infiltration rate significantly greater (57.7 mm) than those of DGS and DSS (25.7 and 12.9 mm, respectively). The high rate of water losses via overland-flow may limit the possibilities for grass seedling emergence and establishment and favor the persistent dominance of shrubs. (C) 2011 Elsevier Ltd. All rights reserved.

Desert pavements are prominent features of many geomorphic surfaces in arid and semiarid lands. In the semiarid soils of north-eastern Patagonia, gravel cover in the shrub interspace areas of shrub-dominated communities is generally high, and contrast with that of grass-dominated patches where gravel cover is either absent or negligible. In the present study we analyze the relationship between soil erosion and desert pavement formation, in three sites, the upper, middle and lower slope positions of a flank pediment where well-conserved soils served as reference areas. We used the gravel cover and mass, as well as the thickness of the remnant A horizon, as determined by the depth of the Bt horizon of a Xeric Calciargid, as measures of soil erosion. Surface gravel at four cardinal points in respect to mounds associated with shrub-clumps was collected and the depth to the Bt horizon was determined. The mean thickness of the A horizon in the well-conserved soils were 11.3, 10.0 and 13.5cm for the upper, middle and lower slope positions, respectively. For the same positions, the mean coarse fragment contents (>2.0mm) in the 0–10cm depth of the A horizon in the well-conserved soils were 144, 92 and 119gkg−1, and the mean surface gravel mass in the eroded patches were 5.3, 3.1 and 4.7kgm−2. Surface gravel mass and depth of the remnant A horizon gave different estimates of the magnitude of soil erosion in the flank pediment. Thus, the mean/maximum soil loss, as determined by the mean gravel mass on the soil surface for the upper, middle and lower slope positions were, 28.3/68.2, 27.0/63.8 and 31.5/56.4mm, respectively. These figures increased to a mean of 50.0, 52.5 and 82.0mm for the same positions when soil loss was determined as the difference between the thickness of the A horizon of the well-conserved soil and that of the remaining A horizon in eroded patches. The loss of the A horizon by wind and water erosion seems to initiate the change from grass steppe to a stable shrub steppe characterized, in the shrub interspaces, by well-developed desert pavements. The strong correlation between surface gravel mass and the thickness of the remaining A horizon indicates that accelerated soil erosion has played an important role in the formation of desert pavements, and that desert pavements are good indicators of the extent and intensity of the erosion process in the Punta Ninfas area.

Los modelos matemáticos son herramientas útiles para la predicción de las pérdidas de suelo por erosión hídrica. El desarrollo reciente del modelo WEPP y su utilización para evaluar los riesgos de erosión en pastizales naturales ha significado un avance interesante en el campo de la erosión y la conservación de suelos de estos ecosistemas. En este trabajo examinamos la eficiencia del modelo WEPP para predecir los procesos hidrológicos y de erosión del suelo en los pastizales naturales semiáridos del noreste de la provincia de Chubut. Se identificaron tres comunidades de plantas ubicadas a lo largo de un gradiente de degradación del suelo: estepa herbácea con arbustos aislados (EH), estepa herbáceo-arbustiva (EHA) y estepa arbustiva degradada (EA). En cada una de estas comunidades se aplicó una lluvia simulada (100 mm h-1 durante 30 min) sobre parcelas de 1 m² (0,6 x 1,67 m) y se colectó el escurrimiento y los sedimentos totales. A partir de los datos de la condición superficial de cada parcela se estimó el escurrimiento y la producción de sedimentos mediante el modelo WEPP. En este trabajo se observó una baja eficiencia del modelo WEPP para predecir el escurrimiento (Eficiencia, E = 0,14) y la erosión del suelo (E = -0,93). La predicción del escurrimiento y pérdida de suelo del modelo WEPP mostró mayor sensibilidad a cambios en los parámetros de lluvia y pendiente del terreno y una sensibilidad moderada a cambios en la cobertura, textura, erodabilidad del suelo y conductividad hidráulica efectiva. El escurrimiento y la producción de sedimentos estimados por WEPP fueron significativamente diferentes en las distintas comunidades de plantas (p < 0,05). La diferencia entre los valores medios estimados y observados varió en las distintas comunidades. Así, el escurrimiento medio estimado fue un 55,5% más elevado en la EH y la producción de sedimentos fue un 69,6; 62,7 y 17,5% más baja en la EH, EHA y EA, respecto a los valores observados. El uso del modelo WEPP en los ecosistemas de pastizales naturales constituye una importante herramienta para estimar la erosión. Sin embargo, estos resultados sugieren que es necesario calibrar el modelo para las condiciones locales e incorporar una estratificación de los pastizales de acuerdo a las diferentes unidades de suelo y vegetación.Mathematical models are useful tools to predict soil loss by water erosion. The recent development of the WEPP model and its use in assessing the risks of erosion in rangelands has led to significant advances in the field of erosion and soil conservation of these ecosystems. In this work we examine the efficiency of the WEPP model in predicting the hydrological processes and soil erosion in semiarid rangelands of the northeast Chubut Province. Three plant communities along a soil degradation gradient were identified: grass with scattered shrubs (EH), grass-shrubs (EHA), and degraded shrub steppes (EA). In each of these communities simulated rainfall (100 mm h-1 for 30 min) was applied on 1 m² (0.6 x 1.67 m) plots and total runoff and sediment production were collected. Using the soil surface condition data from each plot, runoff and sediment production were estimated by means of the WEPP model. We found a low efficiency of the WEPP model to predict runoff (Efficiency, E = 0.14) and soil erosion (E = -0.93). The WEPP-estimated runoff and soil losses showed high sensitivity to changes in rainfall and slope parameters and moderate sensitivity to changes in soil cover, texture, soil erodability and effective hydraulic conductivity. The runoff and sediment production estimated by the WEPP model were significantly different among plant communities (p < 0.05). The difference between the estimated and observed mean values varied in the different plant communities: runoff according to the WEPP model was 55.5% greater in the EH and sediment production was 69.6, 62.7 and 17.5% lower, respectively, in the EH, EHA, and EA than the observed values. These results suggest that it is necessary to calibrate the model for local conditions and to incorporate rangeland stratification according to the different soil-vegetation units.

In this work we describe the impact of a gas-pipeline installation and the replacing of the material removed in part of the clear-cutting, on some physical and chemical properties of the soils and vegetation in three ecological sites of Northeastern Chubut. In these sites we identified four different areas: area 1, clear-cut strip, where the traffic of heavy machinery was intense; area 2, clear-cut strip, with soil and vegetation replaced; and other two areas in the undisturbed adjacent steppe: mounds associated to shrubs and mound interspaces. The highest bulk densities were recorded in area 1 and in the mound interspaces (1.43 Mg m -3 ). The penetrometer resistance was significantly higher in the areas 1 and 2, recording values higher than 1 MPa. The infiltration rate was much higher in the mound (261 mm h -1 ) than in the other areas. The infiltration rate of area 2 (85 mm h -1 ) was higher than that of area 1 (35 mm h -1 ) and the mound interspaces (50 mm h -1 ). Total nitrogen and organic carbon content in soils of the areas 1 and 2 were similar to those of the mound interspaces and significantly lower than those of the mound, except in the area 2 of one ecological site. Clear-cut and topsoil removal, and the subsequent traffic of heavy machinery caused by underground gas-pipeline installation produced a strong impact on the physical properties of these soils. The main limitation in the highly disturbed soils was the decrease in the infiltration rate, mainly due to high compaction and low porosity. This may in part explain the slow vegetation cover recovery in the area 1. The replacement of the stripped sediment and vegetation on the disturbed strip did not improve the recovery of the vegetation cover. It was mainly due to the low quality of the sediments extracted from the pipeline ditch.

This study deals with the changes induced by grazing on soil erosion processes in vegetated dune fields of Peninsula Valdes, in the Patagonia region of Argentina. We performed a spatial analysis to assess erosion features' patterns. Blowouts, used as main indicators of aeolian erosion processes, as well as dune crests, which are susceptible to erosion, were mapped on aerial photographs and images from Landsat 7 Enhanced Thematic Mapper Plus, in eight paddocks under two grazing conditions: lightly (0.4 sheep center dot ha(-1)) and heavily grazed (0.8 sheep - ha(-1)). From the mapped locations of water points, crests, and blowouts we calculated a spatial statistic (O-ring statistic), which gives the expected intensity of blowouts within the area covered by crests as function of distance away from water points. Additionally, to explore if the density of crests around water points influences the density of blowouts, we estimated the intensity of dune crests in the neighborhood of water points and compared the densities of blowouts among water points with low, medium, and high densities of crests. For the heavy grazing treatment we found highly significant (P < 0.05) aggregation of blowouts around water points with peak densities threefold higher than expected at random occurring between 90 and 210 in. However, the aggregation was only weakly significant for the light grazing treatment and occurred only at distances of about 30 in away from the water point. We found that the impact of grazing on soil stability A contrasted among sites with different sensitivity to accelerated erosion. In sites with a high density of dune crests close to water points, wind erosion becomes more intense and the density of blowouts increases. A more sustainable management of these rangelands depends primarily on the conservation of the soils. Therefore, the location of water points in sites not susceptible to accelerated soil erosion would represent a better management strategy of the dune fields of Peninsula Valdes.

In many rangeland ecosystems, the role of fire on vegetation dynamics has been the object of detailed studies. In Argentina, and especially in Patagonia, the knowledge of how fire changes vegetation is scarce. In 3 areas affected by wildfires on different dates (in 1988, 1994, and 1998), we determined the structure of the vegetation (plant cover, density, and biomass) and compared it with that of nearby unburned areas. Based upon these data, we present a qualitative state-and-transition model of this rangeland. For the sites burned in 1988 and 1994, aerial biomass, density, and cover of perennial grasses were significantly greater (P < 0.05) for burned than for unburned areas. For the site burned in 1998, although there were no significant differences in perennial grass biomass and cover, density was significantly greater compared to the unburned area. Total shrub cover was significantly lower (P < 0.05) in burned than in the unburned areas, attaining 49.7%, 15.0%, and 5.5% of that of the unburned areas for the sites burned in 1988, 1994, and 1998, respectively. Similar to cover, density for most shrubby species was significantly greater in the unburned than in the burned areas for the 3 sites. Grazing and fires of different intensities, combined with variable rainfall, makes the prediction of postfire vegetation changes difficult. However, it can be generalized that fire changed the vegetation from shrub-dominated steppes, a persistent state in northeastern Patagonia, into a grass-dominated transient state. This change has persisted for more than 10 years after a fire event. From the perspective of sheep raising, the significant postfire increase in perennial grass biomass represents a substantial improvement in the condition of these rangelands. However, repeated fires would be necessary to control the sprouting shrubs and maintain the grass-dominated state.

In semiarid rangelands, continuous grazing may decrease vegetation cover, accelerating soil erosion and eventually causing a transition to an alternative, degraded state. State-and-transition models invoke process-based explanations of alternative states, but there are few examples that use empirical data on key factors and processes. We used rainfall simulation to determine 1) the relationships between soil surface characteristics and interrill erosion in 3 spatially related plant communities: stable grass with scattered shrubs (GS), degraded grass with scattered shrubs (DGS), and degraded shrub steppes (DSS), and 2) the site conservation threshold (SCT) of this rangeland. We also analyzed the effect of past erosion on soil and vegetation characteristics. In the GS, sediment production and sediment concentration were significantly lower (P<0.05) than in the DGS and the DSS.The main soil protection factors in the GS and in the DGS were perennial grass and litter cover, while in the DSS, gravel cover became the main soil protection factor. The SCT, the point at which the rate of soil erosion increases markedly, corresponded to a plant-and-litter cover close to 90% and occurred within the DGS. Although this plant community may reverse back to the conserved GS, long-term accelerated erosion may result in enough soil loss to trigger irreversible changes and prompt the transition to the DSS. The threshold underlying this transition would be reached when the A horizon is severely reduced by erosion. Under these conditions, the soil hydrological properties are affected irreversibly, preventing perennial grass establishment. While the GS represents a resource conserving plant community, desirable for both forage production and soilprotection, the DSS represents a dysfunctional state with a minimum forage value. The DGS represents an unstable and transitional community that, without management intervention to halt soil erosion, will likely change into the DSS.

Trends in wrack composition and biomass, and its relationship with the anthropogenic impact were studied along a coastal area in Nuevo Gulf (south Patagonia) in front of Puerto Madryn city. Beach-cast macroalgae composition was sampled from 1992 to 1999 in the Puerto Madryn beaches and in several other nearby beaches in 1993, 1996 and 1998. Historical information was based on local knowledge and observations reported by marine biologists who worked in the area. The botanical composition of the beach-cast macroalgae in Puerto Madryn indicates a succession in the dominance from Codium spp. to Ulva spp. during the 1990s and from Ulva to Undaria pinnatifida since 1998, accompanied by a significant decrease in biomass of Gracilaria gracilis and Macrocystis pyrifera . The increase of the opportunist species such as Ulva may be supported by the continuous delivery of waste waters into the Nuevo Gulf while the dominance of U. pinnatifida may be associated with port activities. During the sampling period the highest wrack biomass values were recorded in spring and summer. The beach-cast seaweed biomass harvested by the municipality of Puerto Madryn during beach cleaning operation, ranged between 2500 and 12000 t year −1 ( 200 and 960 t dry weight). Wrack harvesting produces an environmental impact by removing sand from the beach and affecting coastal communities. Composting of wrack is proposed as one of the environmental alternatives to land disposal.

Soil erosion is the primary cause of irreversible loss of soil productivity on most rangelands. In northeastern Patagonia, the increase in soil erosion has been closely associated with the increase in shrub cover in the grass or shrub-grass steppes. We used rainfall simulation to compare infiltration and sediment production from patches of grass, shrub-grass, and shrub steppes of the Punta Ninfas range site. Bare soil and gravel covers were higher and litter cover was lower in the shrub steppe than in the shrub-grass and the grass steppes. In the shrub inter-spaces of the shrub steppe, bulk density was greater and macroporosity and soil organic matter were lower (P less than or equal to 0.05) than in the mounds beneath shrubs and in the grass and shrub-grass areas. Infiltration rate was 60 to 65% lower in the shrub steppe than in the grass and shrub-grass steppes, respectively. On the contrary, total sediment production and concentration were higher (P less than or equal to 0.05) in the shrub steppe as compared to the grass and the shrub-grass areas. Gravel cover was the variable that best predicted infiltration and sediment production. The organic matter content of the sediment, mostly litter, in the shrub and the shrub-grass steppes were similar and greater (P less than or equal to 0.05) than in the grass steppe. Runoff litter removal may represent one of the processes that drive the transition from shrub-grass to shrub steppes. High rates of sediment removal, mainly litter, from the shrub interspaces of the shrub steppe may limit the natural recovery of the soil physical and hydrological properties. These degraded patches fail to capture incident rainfall and restrict the possibilities for the recovery of perennial grasses favoring the dominance of shrubs.

Surface-applied biosolids can affect the physical properties of the topsoil and promote the rehabilitation of degraded soils. In this study, the effects of time after biosolids application (1-3, 6, 12, and 18 months) and biosolids application rate (0, 7, 18, 34, and 90 Mg ha-1) were assessed on selected physical soil properties, from shrubland (Ustic Calciargid) and grassland (Vertic Paleargid) soils. The bulk density (BD) of the 0- to 2.5-cm soil depth was significantly (P

Surface-applied biosolids, the option most often used on range-lands, can increase the concentration of macronutrients and trace elements in the runoff water and can potentially produce eutrophication or contamination of surface waters. In this study, the effects of postapplication age of biosolids (18, 12, 6, and 0.5 mo) and rate of application (0, 7, 18, 34, and 90 Mg ha(-1)) on the quality of runoff water from shrubland and grassland soils were assessed. Between July and October 1996 simulated rainfall was applied to 0.50-m2 plots for 30 min at a rate of 160 mm h(-1). All of the runoff water was collected. The concentration of NH4+ -N, NO3- -N, PO4(3-)-P, total dissolved phosphorus (TDP), Cu, and Mn in the runoff water increased with rate of biosolids application and decreased with time of postapplication on the two soils. The highest PO4(3-)-P and NH4+ -N concentrations, 4.96 and 97 mg L(-1), respectively, were recorded in the grassland soil treated with 90 Mg ha(-1) of biosolids 0.5 mo postapplication. For the same soil, rate, and postapplication age of biosolids, Cu exceeded the upper limit (0.50 mg L(-1) in drinking water for livestock. Ammonium N and PO4(3-)-P should be the main compounds considered when surface-applying biosolids. Ammonium N at concentrations found in all biosolids-treated plots may affect the quality of livestock drinking water by causing taste and smell problems. Orthophosphate can contribute to eutrophication if the runoff from biosolids-treated areas enter surface waters.