Rio Madre De Dios Research Articles

High rates of rock organic carbon oxidation sustained as Andean sediment transits the Amazon foreland-floodplain

The oxidation of organic carbon contained within sedimentary rocks ("petrogenic" carbon, or hereafter OCpetro) emits nearly as much CO2 as is released by volcanism, thereby playing a key role in the long-term global C budget. High erosion rates in mountains have been shown to increase OCpetro oxidation. However, these settings also export unweathered material that may continue to react in downstream floodplains. The relative importance of OCpetro oxidation in mountains versus floodplains remains difficult to assess as disparate methods have been used in the different environments. Here, we investigate the sources and fluxes of rhenium (Re) in the Rio Madre de Dios to quantify OCpetro oxidation from the Andes to the Amazon floodplain using a common approach. Dissolved rhenium concentrations (n = 131) range from 0.01 to 63 pmol L-1 and vary depending on lithology and geomorphic setting. We find that >75% of the dissolved Re derives from OCpetro oxidation and that this proportion increases downstream. We estimate that in the Andes, OCpetro oxidation releases 11.2+4.5/-2.8 tC km-2 y-1 of CO2, which corresponds to ~41% of the total OCpetro denudation (sum of oxidized and solid OCpetro). A Re mass balance across the Rio Madre de Dios shows that 46% of OCpetro oxidation takes place in the Andes, 14% in the foreland-lowlands, and 40% in the Andean-fed floodplains. This doubling of OCpetro oxidation flux downstream of the Andes demonstrates that, when present, floodplains can greatly increase OCpetro oxidation and CO2 release.

A new species of Corydoras (Siluriformes: Callichthyidae) from the rio Madre de Dios basin, Peruvian Amazon, with comments on Corydoras aeneus identity

Abstract A new species of Corydoras is described from tributaries to the rio Araza, an affluent of the rio Inambari, itself a tributary to the rio Madre de Dios, rio Madeira basin in the Peruvian Amazon. The new species can be distinguished from its congeners by the following features: (I) absence of contact between the posterior process of the parieto-supraoccipital and the nuchal plate, (II) a single, large conspicuous dark brown or black blotch on anterodorsal portion of flank; blotch somewhat rounded to roughly diamond shaped, and (III) absence of dark blotches on fins. General comments on the identity of Corydoras aeneus are also provided.

Conservative transport of dissolved sulfate across the Rio Madre de Dios floodplain in Peru

AbstractMineral weathering plays a primary role in the geologic carbon cycle. Silicate weathering by carbonic acid consumes CO2 and stabilizes Earth's climate system. However, when sulfuric acid drives weathering, CO2 can be released to the atmosphere. Recent work has established that sulfuric acid weathering resulting from sulfide mineral oxidation is globally significant and particularly important in rapidly eroding environments. In contrast, if SO42− produced by sulfide oxidation is reduced during continental transit, then CO2 release may be negated. Yet, little is known about how much SO42− reduction takes place in terrestrial environments. We report oxygen and sulfur stable isotope ratios of SO42− in river waters and mass budget calculations, which together suggest that SO42− released from pyrite oxidation in the Peruvian Andes mountains is conservatively exported across ∼300 km of the Amazon floodplain. In this system, floodplain SO42− reduction does not counteract the large SO42− flux from Andean pyrite weathering or measurably affect the stable isotope composition of riverine SO42−. These findings support the hypothesis that uplift and erosion of sedimentary rocks drive release of CO2 from the rock reservoir to the atmosphere.

First record of Proechimys pattoni da Silva, 1998 (Rodentia, Echimyidae) in northwestern Bolivia

Proechimys pattoni da Silva, 1998 is one of the 3 small-bodied species of Proechimys and its geographic range is only known in western Brazil and eastern and southern Peru. However, based on morphological and molecular analyses, we report P. pattoni from the lowland forest of Bolivia (Pando: Rio Madre de Dios, near San Rosa). This is the first report of P. pattoni in Bolivia and extends its distributional range 315 km to the southeast in the Amazon biogeographic region of Bolivia, representing the southeastern most record. Furthermore, we document the karyotype (2n = 40 / FN = 56) and morphological variation in diagnostic characters.

Ecosystem metabolism and nutrient uptake in Peruvian headwater streams

ABSTRACTStudies of algal biomass, ecosystem metabolism, nutrient uptake, and nitrification were conducted in Peruvian headwater streams in the Amazon River basin. These are the first assessments of stream functions in this region of the tropics and they also allow a preliminary assessment of functional responses to local watershed land use. Measures were made in two tributaries of the Rio Madre de Dios. Both had low gradient and primarily soft substrata but land use at one (Q. Concepción) was 2nd‐growth forest while at the other (Q. Abejitas) it was pasture. The third stream (designated Q. Tambopata), a tributary of the Rio Tambopata, had higher gradient, primarily hard substrata, and a watershed of undisturbed forest. Algal biomass in Q. Tambopata was four to eight times greater than in the other streams. Algal primary productivity (P) in all streams was low due to shade, relatively low nutrient concentrations, and colored water at Q. Concepción, but was approximately twofold greater in the pasture stream than in the forested streams. Ecosystem respiration (R) in the pasture stream was approximately three and eight times greater than in Q. Concepción and Q. Tambopata, respectively. The ammonium uptake velocity (Vf) was nearly identical in all three streams, despite differences in land use and streambed characteristics. Nitrification Vf was relatively low in all streams, but was lowest in the pasture stream. Phosphate uptake (Vf) in the two forest streams was relatively low, while phosphate uptake in the pasture stream was among the highest of reported values, but perhaps the result of chemical precipitation as well as biological uptake. Carbohydrate (glucose and arabinose) uptake (Vf) was higher in the pasture stream than in the forest streams. Metabolism and nutrient uptake rates in the forested streams were comparable to or lower than reported values for temperate streams. Most rates of function in the pasture stream were elevated when compared to the forested streams.

Habitat and population estimates of some threatened lowland forest bird species in Tambopata, south-east Peru

Surveys of threatened lowland forest bird species and forest habitats were conducted during a 21-month census of lowland bird communities in Tambopata, Department of Madre de Dios, south-east Peru. A combination of distance sampling census methods and direct counts was used for the census in five sites located along the Rio Madre de Dios and Rio Tambopata. All five sites consisted of different forest types with significantly different habitat components. Three of these sites were classified as primary forest habitats whilst the remaining two were classified as disturbed forests. Population densities were calculated for eight of the threatened species recorded during the census. Density estimates of non-bamboo specialists were higher in primary forest habitats than in disturbed forest habitats. Density estimates of most bamboo specialists were higher in primary Old Floodplain forest with extensive bamboo understorey than in primary Middle/Upper Floodplain forest with smaller, patchy areas of bamboo understorey. Calculation of regional population estimates based on the amount of forest cover from satellite photographs shows that only two of the threatened bird species have substantial populations currently protected by the Parque Nacional Bahuaja-Sonene and Reservada Nacional de Tambopata. Selective logging operations that reduce overall tree biomass and remove a large proportion of palm tree species from primary forest habitats will have an adverse affect on local populations of four of the threatened bird species in the region.

Taxonomic revision of the South American fish genus Chalceus Cuvier (Teleostei: Ostariophysi: Characiformes) with the description of three new species

The Neotropical characid fishes of the genus Chalceus Cuvier, 1817, are reviewed. In total, five species are recognized (including three new species). Chalceus epakros sp. nov. is the most widespread geographically, occurring in many rivers of the Amazon basin, the Rio Orinoco and in the Essequibo River drainage in Guyana. Chalceus guaporensis sp. nov. is restricted to the upper Rio Madeira, Rio Guapore and Rio Madre de Dios, of Brazil, Bolivia and Peru, respectively. Chalceus spilogyros sp. nov. occurs only in the Rio Trombetas, lower Rio Tapajos and lower Rio Madeira drainages. Chalceus macrolepidotus Cuvier occurs in the Rio Negro drainage, middle and lower Rio Orinoco basin and in the rivers of the Atlantic slopes of the Guianas, and Chalceus erythrurus Cope in the Rio Amazonas and Rio Solimoes to Rio Ucayali drainage in Peru. Chalceus ararapeera Cuvier & Valenciennes and Creagrutus pellegrini Puyo are considered synonyms of C. macrolepidotus, and Pellegrinina heterolepis Fowler is placed into the synonymy of C. erythrurus. Characters pertaining to the monophyly of Chalceus are discussed and a key to species is presented. © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society, 2004, 140, 103−135.

Temporal Fluctuations in Abundances of Anuran Amphibians in a Seasonal Amazonian Rainforest

Temporal Fluctuations in Abundances of Anuran Amphibians in a Seasonal Amazonian Rainforest

A New Species of Myxidium (Myxozoa: Myxidiidae) from the Gall Bladders of Anuran Amphibians from Peru

Myxidium typhonius, a myxosporidian protozoan, is described from the gall bladders of 13 species of anuran amphibians in Peru, Departamento de Madre de Dios, Provincia Tambopata, Cusco Amaz6nico, Rio Madre de Dios, ca. 15 km E Puerto Maldonado. The ellipsoidal spores of the parasite are distinguished from those of other myxidia infecting anurans on the basis of overall size, nature of the sutural line, number of longitudinal ridges, number and features of transverse ridges, polar capsule size, coils in polar filament, and identical left and right sides. Each spore of M. typhonius has a longitudinal suture extending pole to pole, 2 longitudinal ridges, and 9 or 10 transverse ridges. Two nuclei are located between the 2 polar capsules and each polar filament has 4 or 5 turns (coils). Average measurements (and ranges) in microns of 325 spores from the frontal view are: spore length 10.9 (9.8-12.2); spore width 7.2 (5.7-8.9); polar capsule length 3.8 (3.3-4.9); polar capsule width 3.6 (3.3-5.0). Myxidium typhonius appears to be a common parasite of the gall bladder of anurans from Cusco Amazonico, Peru, with an average prevalence of 85.5%.

Cercomacra manu, a New Species of Antbird from Southwestern Amazonia

Cercomacra manu, a New Species of Antbird from Southwestern Amazonia

Variation, distribution, and life history ofEdalorhina perezi(Amphibia, Anura, Leptodactylidae)

The leptodactylid frog genus Edalorhina contains two species ‐ E. nasuta, known from two localities in centra! Peru, and E. perezi that is widespread in the upper Amazon Basin. The latter species varies geographically in dorsal skin texture and ventral color pattern. The most distinctive ventral pattern occurs in specimens from the southeastern part of the range in the drainages of the Rio Punis and Rio Madre de Dios. Limited data on advertisement calls suggests that the calls are essentially the same in different parts of the range. Edalorhina perezi is diurnal and inhabits leaf litter on the forest floor in lowland tropical rainforest. Eggs are deposited in a foam nest at the edge of shallow, temporary pools, and the aquatic tadpoles are generalized. The life history data support the placement of the genus in the subfamily Leptodactylinae

Petrology of fluvial sands from the Amazonian foreland basin, Peru and Bolivia

Modal sand compositions in nine rivers draining the proximal part of the Amazonian retroarc foreland basin in Peru and Bolivia provide support for the Recycled Orogen provenance model of Dickinson and Suczek. Average compositions of 52 sand samples from the Rio Madre de Dios and its tributaries are: %QFL = 74, 5, 21; %QmFLt = 60, 5, 35; %QpLvmLsm = 44, 10, 46; %LmLvLs = 69, 18, 13; and %QmPK = 91, 4, 5. These compositions accurately reflect the predominance of sedimentary and metasedimentary rocks in the Cordillera Oriental of the Andean orogen, the ultimate source terrane for the sands of the modern foreland basin. Rivers of the Madre de Dios basin can be classified in one of three ways: (1) rivers that head in the Subandean fold-thrust belt; (2) rivers that are actively incising a subtle intraforeland uplift overlain by Quaternary and upper Tertiary foreland-basin fill; and (3) trunk rivers that collect both type 1 and type 2 rivers. The rivers that drain the fold-thrust belt carry sands that are slightly more lithic than those carried by rivers that drain the intraforeland uplift. The intraforeland-derived sands are relatively enriched in volcanic rock fragments (%LmLvLs = 70, 22, 8), whereas sands derived from the fold-thrust belt are relatively enriched in sedimentary rock fragments (%LmLvLs = 66, 9, 24). The overriding control on sand composition is the relative area of bedrock type exposed in the fold-thrust belt. Sands reworked from Tertiary and Quaternary foreland-basin fill are relatively enriched in quartz, possibly owing to intense weathering of sediments in the soil profile. The preservation of predictable and systematic mixing patterns in sand compositions from different rivers suggests that sandstone petrologic data may be augmented by paleocurrent, isopach, and textural data to facilitate detailed reconstruction of drainage patterns in ancient, nonmarine foreland basins.

A New Peruvian Styloceras (Buxaceae): Discovery of a Phytogeographical Missing Link

A New Peruvian Styloceras (Buxaceae): Discovery of a Phytogeographical Missing Link

Geological Reconnaissance in Southeastern Peru

This paper gives the results of a reconnaissance made by the writer across the Cordillera de Vilcanota and the Cordillera de Carabaya, both forming the Cordillera Oriental, and as far as Maldonado on the Madre de Dios River in southeastern Peru. As it is the first time that this part of Peru has been geologically investigated, it was possible to obtain interesting data on the geology, stratigraphy, and structure of this little-known part of the Andes. The Cordillera de Carabaya is a rugged, snow-clad range. The elevation of the lowest pass, Abra de Hualla-Hualla, is 4,820 meters above sea-level. Toward the east the range drops in a short distance to an elevation of about 600 meters at Rio Nusiniscato. A complete traverse could be made across the Cordillera Oriental between Urcos and the valley of Rio Madre de Dios. The regional geology is largely represented by older, pre-Cambrian, metamorphic schists and quartzites, which are overlain by Ordovician slates. Upper Paleozoic brown-red shales and sandstones occur west of the section, at Urcos. At its eastern half, east of Quincemil, vast Tertiary plains extend. A remarkable feature of the section is the Araza gneiss underlying the Marcapata metamorphic rocks. The Araza gneiss appears o be early pre-Cambrian, probably Archean, in age. From the writer's knowledge of the South American Andes, it would seem that this is the first recognized occurrence of gneiss on the eastern slope of the Andes, since none is known to have been described from Colombia, Ecuador, northern Peru, or Bolivia. Structurally, this part of the Cordillera Oriental appears to be block-faulted. The faulting is normal; there is no evidence of large-scale thrusting.