Pilcomayo River Research Articles

Diversity of True Bugs from the Rio Pilcomayo National Park, Formosa Province, Argentina

The study of the Heteroptera (Hemiptera) fauna of the Rio Pilcomayo National Park, resulted in an inventory composed of: Alydidae (3 spp.), Aradidae (1 sp.), Belostomatidae (4 spp.), Berytidae (1 sp.), Blissidae (4 spp.), Colobathristidae (1 sp.), Coreidae (4 spp.), Corixidae (3 spp.), Cydnidae (12 spp.), Cymidae (1 sp.), Gelastocoridae (1 sp.), Geocoridae (1 sp.), Gerridae (1 sp.), Hebridae (1 sp.), Largidae (3 spp.), Lygaeidae (6 spp.), Miridae (14 spp.), Pachygronthidae (3 spp.), Pachynomidae (1 sp.), Pentatomidae (3 spp.), Pyrrhocoridae (1 sp.), Reduviidae (10 spp.), Rhopalidae (9 spp.), Rhyparochromidae (20 spp.), Saldidae (1 sp.), Scutelleridae (2 spp.), Tingidae (1 sp.). These findings include three new records for the Argentinean fauna: Niesthrea digna Chopra (Rhopalidae), Galgupha (Psestophleps) costomaculata McAtee and Malloch, and Dallasiellus alutaceus Froeschner (Cydnidae); and 69 new records for Formosa Province.

Twenty-eight new and significant departmental reptile records for Paraguay

Twenty-eight new distribution records are reported for twenty-seven species of Paraguayan reptiles. Ten of these species are considered threatened at the national level (6 EN, 2 VU, 2 DD). Nineteen new departmental records are documented: Phrynops hilarii (Chelidae) in Misiones department; Homonota marthae, Phyllopezus przewalskii (Phyllodactylidae), Philodryas baroni and P. psammophidea (Colubridae) in Presidente Hayes department; Teius oculatus (Teiidae), Cercosaura schreibersii (Gymnophthalmidae), Ophiodes intermedius (Diploglossidae), Amphisbaena mertensii (Amphisbaenidae), Boiruna maculata and Philodryas aestiva (Colubridae) in Caazapá department; Amphisbaena alba (Amphisbaenidae) in Caaguazú and Cordillera departments; Bothrops moojeni (Viperidae), Eunectes notaeus (Boidae), Helicops leopardinus and Hydrodynastes gigas (Colubridae) in Guairá department; Apostolepis dimidiata, Atractus paraguayensis and Mussurana bicolor (Colubridae) in Itapúa department; and Epicrates crassus (Boidae) and Phalotris nigirilatus (Colubridae) in Concepción department. Significant range extensions of threatened or poorly-known species are also documented: The known distribution of the Endangered Salvator duseni (Teiidae) is extended 128.5 km to the east within Canindeyú department; that of the Vulnerable Boa occidentalis is extended 109.2 km to the southwest within Boquerón department; that of the Vulnerable Epicrates alvarezi (Boidae) is extended 136.6 km to the west within Boquerón department and 172.4 km to the northeast into Alto Paraguay department; that of Caiman yacare (Alligatoridae) is extended 132 km west within Boquerón department to the northern reaches of the Pilcomayo River. We also document an additional specimen of the rare Philodryas agassizii (Colubridae) and confirmation of the occurrence of the disputed form Phalotris “punctatus” in Paraguay.

Frontier Constellations: A History of Land-use Regimes in Paraguay’s Pilcomayo River Basin

ABSTRACT The Paraguayan Chaco is increasingly known for the extreme rates of forest loss caused by the rapid expansion of cattle ranching and crop farming over the last few decades. Knowledge of its twentieth-century land-use history, however, remains limited. In this article, I address that gap by discussing land-use dynamics since the 1900s in the Pilcomayo River basin, a part of the Chaco that borders Argentina and Bolivia, and hosts a great diversity of actors and land uses. Using the concept of land-use regimes, I show that the area, once characterized by what can be called an Indigenous mixed-use regime, transitioned to a land-use regime dominated by livestock herding by Argentine Criollo settlers after the Chaco War (1932–35), and then again to one of large cattle ranches managed by absentee owners toward the end of the twentieth century. No land-use regime ever completely dominated the area, however, and I use this fact as a starting point to then discuss how using the concept of land regimes can help direct attention to the coexistence of regimes in space and to their relationships in a way that helps refine our understanding of land-use transitions.

Condors scavenge on fish at the land–water interface in the Andean foothill of southern Bolivia

AbstractThere is very little information on Andean condors scavenging on fish. Here we report five events of condors feeding on fish carrion in the Bolivian Chaco Serrano in three consecutive years. In 2019, 2020, and 2021, condors were observed feeding on discarded fish from local fishermen, 3 km west of Villa Montes, in the ‘El Angosto’ section of the Pilcomayo River. Fishing, mainly for sábalo (Prochilodus lineatus), is the most important economic activity in that part of the Pilcomayo basin and its discards explain fish carrion availability there, while driving scavengers to feed on this resource. We believe that fish carrion abundance, the intensity of intra‐ and interspecific competition for access to carrion, and overall carrion availability hierarchically influence the fact that condors feed on fish, something we will investigate later based on the observations reported here. From a conservation perspective, the main consequence of scavengers feeding on fish from the Pilcomayo is that they could be getting heavy metal poisoning. Heavy metal poisoning is a serious threat with widely known negative effects for wildlife. Our observations should serve to promote comprehensive bio‐monitoring of the Pilcomayo basin, using approaches such as One Health, and emphasizing the importance of coexistence between humans and the rest of biodiversity, with the Andean Condor as the flagship species.

“If the Pilcomayo River is lost, the Weenhayek people will be lost” – governance of fisheries and indigenous institutional diversity in southern Bolivia

ABSTRACT Understanding institutional diversity is crucial for the recognition of rural communities and their institutional processes as fundamental to their agency and autonomy. Deficiencies hinder the adequate implementation of agricultural projects and the achievement of collective rights. Thus, this article analyses the institutional diversity of the Weenhayek people in southern Bolivia and their governance of fishing on the Pilcomayo River. Weenhayeks have a fishing identity, creating aquatic food systems and a riverine culture. We undertake document analysis (20), participant observation, and interviews (13). Our results reveal that the Weenhayek’s indigenous governance system is not homogeneous throughout their territory. The “fuzziness” of the socio-ecological boundaries shows the fragility of the formal institutional boundaries. This indicates the importance of perspectives that addresses institutions beyond formal schemes, to support sustainable food systems and food sovereignty.

On the banks of the Pilcomayo River: Wichí fishery in the age of motorcycles

In just a few years motorcycles had become an irreplaceable object for the daily life of Indigenous people in the Gran Chaco region. In spite of their pervasiveness, there are still many aspects to this current dissemination that remain to be unraveled. This paper explores the ways in which motorcycles have been incorporated into Indigenous material culture and the ways they are reshaping Indigenous perceptions and relations with the local environment. Starting from the machines and their uses is a way to not confine Indigenous people to a position as victims of modernity, but rather to recognize their proactive role in the ongoing reproduction and transformation of their cultural world. For this purpose, I take the example of the Wichí fishery to see how this cultural practice is changing as fishermen adopt motorcycles as means of transport. I investigate this practice and its transformations based on ethnographic fieldworks carried out with several communities settled on the banks of the Pilcomayo River, as well as readings of the ethnological literature which contains detailed descriptions of this practice. By tracing its past and ongoing transformations, I show how the hold and spatial organization of Wichí fishery has evolved as motorcycles spread to the whole Pilcomayo area. Their adoption redefines fishermen perceptions and relations with the surrounding environment, which is now understood from a new mechanized and motorized perspective of capitalization and exploitation. Indeed, while motorcycles allow them to integrate into the market, they further promote market penetration on Indigenous lands. At the same time, I demonstrate how motorcycles allow fishermen to overcome the inconveniences of an intractable river and new infrastructures that hinder fishing practices, as well as to bypass the attempts to privatize the riverbanks. In a way, the fishermen are more resilient to these sudden changes thanks to motorcycles.

The cattle-ranching economy in the Bolivian Chaco during the 1800s

The Bolivian Chaco on the margins of Pilcomayo River was a contested area during the 1800s. Tobas and other Indigenous Peoples boldly resisted the state’s occupation of their territories, keeping the frontier unstable for decades. I argue that Bolivian settlers gradually occupied the pastures along the river using violence, encouraged by state policies, and supported by army officers stationed in forts. Local merchants, Franciscan missionaries, and Avá-Guaraní neófitos played important roles in this process. I sought to better understand the viewpoints of state administrators and settlers. The views of Toba people remained opaque, beyond their actions to protect their lands from the ranchers’ encroachment. My approach combined ethnographic and historical methods to shed light on the expansion of the cattle-ranching economy from a perspective inspired in settler colonial studies.

First record of Camarochilus confusus (Heteroptera: Pachynomidae) from Argentina, the second pachynomid and first Pachynominae registered for the country

Fieldwork in two protected areas from northeastern Argentina (P.N. El Impenetrable in Chaco Province, and the P.N. Rio Pilcomayo in Formosa Province) exploring the Heteroptea fauna, resulted in the discovery of a Camarochilus confusus Harris 1930 male that was collected by sweeping the vegetation. The species belongs to the subfamily Pachynominae, representing the first record of the group in the country. Aphelonotus simplus Uhler 1894 (Aphelonotinae), was also collected using light traps, confirming its occurrence in the Chaco ecoregions in Argentina.

Functional fluvial landforms of the Pantanal: Hydrologic trends and responses to climate changes

Large-scale fluvial landforms emerge from iterative processes that sculpt Earth's surface. Tectonics, climate variability and erosion are major recurrent processes reshaping fluvial landforms ending up in self-affine patterns. In the case of the Pantanal, the largest wetland in South America, its depositional tract can be subdivided as fluvial megafans, interfans and the main trunk system. Here we provide an outlook of their origins by means of self-affine landforms and on the feedback of climate changes over landform functionalities. Climate variability modulates the magnitude of interannual fluvial discharge and sediment load from highlands to plains, affects groundwater recharge, as well as the subsidence and generation of accommodation in the depositional tract through river avulsion. Scenarios are envisaged by analyzing long-term summer rainfall intensity and the number of dry days in autumn/winter over the Upper Paraguay River Basin, and annual flood peaks measured at fluvial gauge stations in the Paraguay River at Ladário (Brazil) and Asunción (Paraguay). The frequency distributions of the annual flood peaks are found unimodal for Asunción and bimodal for Ladário, which suggests an unknown water supply at Asunción, likely from Pilcomayo River and Pantanal's groundwater. The latter might play a delayed role on Pantanal's hydrologic functioning at 20–40 years timescales. Besides the Paraguay River flood peaks, summer rainfall intensity and the number of dry days in autumn/winter are quasi-periodic at interannual and decadal scales. Cross-correlations analyses indicate a long-range memory between river floods and rainfall intensity, and 15–20 years lag between river floods and the number of dry days in drought seasons. Trends analysis suggests that summer rainfall intensity and the number of dry days in autumn/winter have been consistently increasing by about 0.6 mm/day/decade and 1 day/decade, respectively. Therefore, magnifications of fluvial discharge and sediment load at wet seasons and water deficits at drought seasons are anticipated. Such a scenario indicates extreme dry cycles over all self-affine functional landforms, particularly on abandoned lobes relying exclusively on rainwater, whereas extremes of rainfall intensity at rivers headwaters may amplify the risks of large-scale avulsions at active lobes of the fluvial megafans. In contrast, active lobes of megafans, interfans and the main trunk river system emerge as hotpots for wildlife refuge and ecosystem services.

Adaptation of river channels to a wetter or drier climate: Insights from the Lower Pilcomayo River, South America

Climate change has a direct influence on both hydrology and floodplain vegetation of water courses, which are key players in river morphodynamics. The river system response to climate change is complex and the effects of non-linear interactions between alterations in water, sediment and vegetation remain incompletely understood. Which of these components becomes dominant in shaping the river channel when climate becomes drier or wetter? To answer this question, we investigate the cross-sectional response of sand-bed rivers to climate change focusing on channel width and depth, which respond directly to changes in boundary stresses. Thanks to the exceptional availability of long time-series of daily discharge and cross-sectional profiles, the Pilcomayo River is an ideal living lab for this investigation. We constructed a two-dimensional model of the river using the open-source state-of-the-art, structured Delft3D code. The highly dynamic behaviour and quick morphological adaptation of the Pilcomayo allowed reducing the period of time covered by the simulations because the river cross-section adapts its morphology to a new value of the water discharge within hours or days, which is crucial for modelling investigations. Calibration and validation were successfully performed by comparison with historical data. We considered several scenarios representing current, dryer and wetter climates. The results show that a dryer climate reduces the river channel depth and enlarges the width. A wetter climate increases the channel depth but produces negligible widening. Vegetation, sparser with a drier climate and denser with a wetter climate, is found to control the channel width. This analysis is unique and shows which alterations can be expected in alluvial sand-bed rivers with natural vegetated banks due to climate change.

Comparative analysis of climate and topography in Chaco and Oriental, Paraguay

The article reports the issues corresponding to the climate variability and possibility of droughts in spatially distinct regions of Paraguay, the Chaco and the Oriental (Paraná Basin). Based on the GMT scripting approach and high-resolution datasets from the TerraClimate and GEBCO, the study examined the extent of the annual climate and environmental variables over Paraguay in 2020: extreme temperatures, wind speed, precipitation, soil moisture, evapotranspiration, Palmer's Drought Severity Index (PDSI), vapour pressure deficit (VPD) and the topography of the country. The environmental and climate parameters demonstrated spatial variability in the Dry Chaco with notable differences in Gran Chaco and Chaco Boreal, wetlands of Pantanal, and tropical rainforests in east of the Paraguay. Besides climate analysis, technical snippets from the GMT scripts regarding the mapping techniques and data processing were explained and commented. Research results show that actual evapotranspiration reaches maximal values in the Paraná Basin (180 mm/yr), and has peaks along the Pilcomayo river (140-150 mm/yr) which well coincides with the soil moisture; the PDSI values are maximal in Chaco Boreal and Gran Chaco; the temperatures are the highest in the N and NW regions of Paraguay; the highest VPD (over 2.0) corresponds to the Chaco Boreal.

Grammatical replication: First-person non-singular verbal indexes in Eastern Toba, Western Toba (Guaicuruan) and Tapiete (Tupi-Guaraní)

In this paper we suggest that linguistic features can show traces of the frequency and intensity of social interactions between indigenous peoples. We focus on peoples of the alluvial fan of the Pilcomayo River (South American Chaco), and analyze first-person non-singular verbal encoding in their languages. The corpus is composed of (a) data obtained during fieldwork, (b) descriptive grammars, and (c) published reports by missionaries, army officers, and European travelers. Combining environmental and ethnohistorical information, we propose that the first-person non-singular subject verbal indexes split visible in Eastern Toba of the Lower Pilcomayo River, Western Toba from the Upper-Middle Pilcomayo River (Guaicuruan), and Tapiete of the Upper Pilcomayo River area (Tupi-Guaraní) could be an outcome of language-internal resources used by the speakers of these languages to replicate the Matacoan (Maká, Nivaclé, and Wichí) external model.

Los tobas de Bolivia: resiliencia y adaptación en el Chaco Boreal

Nuestro estudio está centrado en los tobas de Bolivia. Describimos un modelo estacional de uso del ambiente empleado por cazadores-recolectores de las sabanas semiáridas del chaco boreal en el cual grupos demográficamente pequeños pescaban en los ríos y cursos de agua temporarios y plantaban en humedales, desplazándose durante otros períodos del ciclo anual entre campamentos de caza y recolección en los campos y lagunas interiores. Este modelo de apropiación de recursos, si bien adaptado y flexibilizado, mantuvo una probada resiliencia entre cazadores-recolectores históricos. Debido a la relativa escasez de información etnográfica sobre los tobas bolivianos, cuando resulta apropiado utilizamos datos etnográficos equivalentes obtenidos entre sus parientes, los tobas del Oeste de Formosa, Argentina. Presentamos estimados sobre la cantidad de población toba en el siglo XIX y otros elementos que permitirían modelizar: (a) los lugares de campamento y la movilidad estacional, (b) el tamaño de los pequeños grupos familiares, (c) los campamentos, y (d) las relaciones intergrupales. Considerando la poca información disponible en este momento sobre los cazadores-recolectores prehistóricos que habitaban el abanico del Alto Pilcomayo, las descripciones etnográficas que presentamos aquí podrían contribuir al análisis de los modos de vida en la prehistoria reciente de la región.

Macroinvertebrates of Eichhornia crassipes (Pontederiaceae) roots in the alluvial floodplain of large tropical rivers (Argentina)

Introduction: Eichhornia crassipes is a dominant aquatic plant of neotropical-river floodplains and is invasive in warm waters of different continents. Plants provide food and habitat for fish, especially Prochilodus lineatus and Gymnotus omarorum, which are relevant to subsistence fishing by local indigenous communities. Objective: In this study we describe the main traits of E. crassipes floating meadows, and analyze the abundance and composition of macroinvertebrate assemblages associated with their roots in two floodplain wetlands of the Paraná River (within the Ramsar site Wetlands Chaco) and of the Pilcomayo River (within the Pilcomayo River National Park). Methods: During spring and summer, the macroinvertebrates were collected in monospecific stands of E. crassipes with a net of 962 cm2 area and 500 µm mesh size. Leaf density, the biomass of leaves and roots, the length of leaves and roots, and the water quality were measured simultaneously. Results: Temperature, oxygen concentration, and nutrient content were significantly higher and electrical conductivity was lower in the Pilcomayo than in the Paraná floodplain. E. crassipes growing in the Pilcomayo floodplain had longer leaves and less root biomass than those found in the Paraná floodplain. The number of macroinvertebrates per 1 000 g root dry weight and per m2 was significantly different between both floodplains, but the taxon richness was similar. Non Metric Multidimensional Scaling analysis differentiated the abundance of 14 selected taxa between both floodplains, and showed a high correlation between the environmental variables and macroinvertebrate abundance. The most abundant taxonomic groups in the Paraná River floodplain were oligochaetes (Naididae), ostracods mainly Cytheridella ilosvayi and larvae of non-biting midges (Chironomidae). Two families, Hydrobiidae (Heleobia parchappii) and Chironomidae accounted for 49.3 % of the total abundance in the Pilcomayo floodplain. The prawns Macrobrachium jelskii and M. amazonicum, frequent in the Pilcomayo floodplain, were not found in the Paraná floodplain. Conclusions: The different environmental conditions in both floodplains affect the abundance, composition, and the dominance of macroinvertebrate assemblages; however, the total taxa richness was similar. The area occupied by E. crassipes in the floodplains of these rivers provides the habitat that contributes most to overall biotic diversity, which must be considered in management strategies.

Gastrointestinal nematodes of freshwater fish from Pilcomayo River, Argentina, including description of a new species of Procamallanus (Spirocamallanus).

Helminthological examination of viscera of six freshwater fish species, collected from Misión la Paz, Pilcomayo River, Province of Salta, Argentina, revealed the presence of five species of parasitic nematodes belonging to the Camallanidae, Cystidicolidae, Cucullanidae and Anisakidae The material also contained one unknown species, Procamallanus (Spirocamallanus) tomsici sp. nov. collected from Pimelodus albicans, Pygocentrus nattereri and Hoplias misionera. This species is distinguished from its congeners all over de world by possessing six pores distinctly surrounding the mouth aperture, a buccal capsule with 3-4 spiral thickenings complete, females possessing a lateral cuticular ornamentation along the body, and two pairs of preanal and three pairs of postanal papillae in males. The findings represent new hosts and geographical records.

Water quality impacts of in-stream mine tailings on a headwater tributary of the Rio Pilcomayo, Potosí, Bolivia

Rio Tarapaya, a major tributary of the upper Rio Pilcomayo and a crucial water resource in the arid Southeastern Bolivian highlands, has been impacted by in-stream mine tailings and acid rock drainage over the past five centuries, from historic and ongoing mining at Cerro Rico de Potosí. Identification of the effects of in-stream mine tailings on the waters of Rio Tarapaya is essential to better understand the dynamics of these complex systems and propose successful management strategies. A study was performed on river waters and sediments at six sites in a reach of Rio Tarapaya, beginning at the city limits of Potosí and ending just after the confluence with Rio Cayara, a relatively unimpaired river 7.3 km downstream. Concentrations of dissolved metals (such as Fe, Al, Mn, and As) in the Ca–Mg–HCO3–SO4 dominated stream were generally orders of magnitude greater than Bolivian receiving water body criteria and United Nations Food and Agriculture Organization irrigation and livestock drinking water guidelines. Variability of Ca and Mg in water and sediment was controlled by dissolution of gypsum, dolomite and calcite, which was supported by Spearman correlation coefficients. The primary ionic products of in-stream sulfide mineral weathering (SO42−, Fe, Al, Mn, Zn and As), are the dominant ions of stream water and sediment leachate. Results are consistent with PHREEQC modeling of minerals such as gibbsite, melanterite, goethite, calcite and dolomite. In general, the reactivity of bed material increased and stream water quality decreased with increasing distance from Potosí. Metals and metalloids are spiraling downstream via seasonally driven particle transport, sulfide weathering, and salt dissolution coupled with biotic interactions. The reactivity of the millions of tonnes of in-stream tailings in Rio Tarapaya and persistence of contemporary illicit tailings discharges indicates that the upper Rio Pilcomayo will remain severely degraded for the foreseeable future unless substantial remediation is undertaken.

Transient scour and fill. The case of the Pilcomayo River

Transient scour and fill refers to the general scour and fill in a riverbed due to flood passage. It was given much attention in times of Leopold and Maddock (1953) and Colby (1964) from records of outstanding case studies. Field data from a station in a contracted, long reach of the large sand-bed Pilcomayo River –1192 newly typed in forms– are presented, with sediment concentration in the database up to 60 kg/m3, mostly wash load. Water surface rises and falls during a flood event, whereas streambed evolves in reverse (it renders the analogy to an accordion). Streambed scouring accounts for 36% of the change in flow area during floods and data reveal scouring up to 4 m from the streambed elevation when flood starts. Velocity data display large hysteresis loops inexplicable by unsteady flow only. Once streambed starts to fall, river bed scour is self-sustaining. Water depth gradient appears to be a crucial variable in a novel equation for transient scour and fill derived from Exner equation. It turns out that flow non-uniformity is relevant to explain transient scour and fill in contrast to flow unsteadiness, which is not. Quasi-steady gradually varied flow equation solved along the contracted reach is the base for a model that captures well the recorded bed evolution. The model explains most of the transient scour and fill by the downstream expansion, but the non-uniform flow and the bed material suspended load also play a role. The model fails on the days of highest sediment concentrations.

The Bolivian Toba (Guaicuruan) Expansion in Northern Gran Chaco, 1550–1850

Abstract The Bolivian Tobas in northern Gran Chaco were mobile hunter-gatherers organized in bands. They called themselves qomleʔk, and spoke a distinctive variation of Guaicuruan language. For three hundred years, coalitions of Toba braves successfully rejected Jesuit missionaries, alternatively fought and aligned with neighboring groups, and resisted the advance of colonial settlers. However, little is known about the remote past of these resilient peoples, who became mounted foragers in the early 1600s. A careful review of historical, ethnographic, and linguistic records on Tobas around the Upper Pilcomayo River produced a considerable amount of information, pointing to the long-term continuity of their presence in the region. The materials were less informative on cultural and social changes in their society through time. This study presents new insights on Toba bands trekking territories on the Manso Plains,

Extended Engelund–Hansen type sediment transport relation for mixtures based on the sand-silt-bed Lower Yellow River, China

ABSTRACTWhile the grain-sorting morphodynamics of gravel- and sand-bed rivers has been intensively studied, sand-silt bed rivers such as the Lower Yellow River (LYR), China and the Pilcomayo River, Paraguay/Argentina have received much less attention. As a first step, we use a database from the LYR in the 1980s to develop a grain size specific extended Engelund–Hansen total bed material load relation. We then use this relation in two morphodynamic calculations. First, we “spin-up” the calculation from an arbitrary bed slope over 600 years to reproduce the downstream fining observed before the closing of Xiaolangdi Dam in 2000. We then cut off the sediment supply, and reproduce the observed pattern of bed coarsening as the bed armours in response to degradation. We argue that our model is likely not site-specific, but applies to other sand-silt bed rivers, basic data for which is as yet lacking.

A systems thinking approach for eliciting mental models from visual boundary objects in hydropolitical contexts: a case study from the Pilcomayo River Basin

A systems thinking approach for eliciting mental models from visual boundary objects in hydropolitical contexts: a case study from the Pilcomayo River Basin