Increases in Picocyanobacteria Abundance in Agriculturally Eutrophic Pampean Lakes Inferred from Historical Records of Secchi Depth and Chlorophyll-a

Phytoplankton size structure has profound consequences on food-web organization and energy transfer. Presently, picocyanobacteria (size < 2 µm) represent a major fraction of the autotrophic plankton of Pampean lakes. Glyphosate is known to stimulate the development of picocyanobacteria capable of degrading the herbicide. Due to the worldwide adoption of glyphosate-resistant crops, herbicide usage has increased sharply since the mid-1990s. Unfortunately, there are very few studies (none for the Pampa region) reporting picocyanobacteria abundance before 2000. The proliferation of µm sized particles should decrease Secchi disc depth (ZSD). Therefore ZSD, conditional to chlorophyll-a, may serve as an indicator of picocyanobacteria abundance. We use generalized additive models (GAMs) to analyze a “validation” dataset consisting of 82 records of ZSD, chlorophyll-a, and picocyanobacteria abundance from two Pampean lakes surveys (2009 and 2015). In support of the hypothesis, ZSD was negatively related to picocyanobacteria after accounting for the effect of chlorophyll-a. We then fitted a “historical” dataset using hierarchical GAMs to compare ZSD conditional to chlorophyll-a, before and after 2000. We estimated that ZSD levels during 2000–2021 were, on average, only about half as deep as those during 1980–1999. We conclude that the adoption of glyphosate-resistant crops has stimulated outbreaks of picocyanobacteria populations, resulting in lower water transparency.

Actividad minera y suelos contaminados en el sector de km 100 La Pampa región Madre de Dios

<p>La investigación fue realizada en Madre de Dios tomando como muestra el suelo erosionado y como testigo el suelo no erosionado. El Objetivo de la investigación fue: Determinar la humedad, textura, densidad, pH del suelo en estudio, Determinar el intercambio catiónico, contenido de carbono, contenido de materia orgánica, así como las aproximaciones de Nitrógeno, fosforo y potasio de los suelos del sector, Evaluar la incidencia en los suelos con respecto a los Componentes Físicos y químicos utilizados en la minería. Para el Procedimiento se tomó la muestra al azar cuatro puntos cercanos a una profundidad de 20 cm haciendo el cuarteo correspondiente, eso para las cinco muestras de los cuales uno es un testigo (muestra N° 05) obteniendo los siguientes Resultados: Se observó que la humedad de la muestra patrón es 27.05 % y la media de las muestras (01, 02, 03 y 04) de suelos erosionados es 12.46% esto nos hace ver que existe una variación considerable. Por lo tanto, se Concluye que: La humedad de todas sus formas sufre una alteración en las zonas alejadas de masa de agua, observamos que los suelos erosionados no pueden retener el agua que necesitaría las plantas, La textura de los suelos donde se realizó la actividad minera ha perdido considerable cantidad de limo y arcilla, La materia orgánica que de por si es poca es lamentable, la acidez de los suelos se ve incrementada ligeramente por la actividad minera.</p>

Stunting Rates in a Food-Rich Country: The Argentine Pampas from the 1850s to the 1950s

Little is known about the effects of malnutrition rates in the long-run. Applying the methodology recommended by the World Health Organization, this study estimates stunting rates for Argentine adult males from the 1850s to the 1950s. We use five large samples of army recruits, prison inmates, militiamen, and electoral records totaling 84,500 cases. These samples provide information about height in Buenos Aires province and the Pampa region, the most fertile, food-producing area of the country. As the study shows, estimated stunting rates remained stable from the 1850s to the 1880s and then declined persistently until the 1950s. The total decline was substantial: if fell from 15.3% in the 1870s to 5.6% in the 1940s, then stagnated. In this 95-year period, stunting rates went from “medium” to “low” levels in the WHO classification of malnutrition intensity. At the end of our study period (the 1950s) the Pampa’s malnutrition rate was only 3.5 to 4 percentage points above contemporary estimates for well-developed economies in Europe and North America. A significant expansion in the region’s production of grains and beef (food availability), combined with a sustained decline in infant mortality (increased health) were probably the two main underlying factors of this long-tern reduction in malnutrition. Yet, this association remains to be determined.

EFFECT OF COVER CROP USE ON A CONTINUOUS SOYBEAN SEQUENCE IN THE PAMPEAN SEMIARID REGION

The objectives were to quantify its effect on the yield of the successor summer crop, to evaluate the dynamics of the decomposition of rye residues from a fertilized and unfertilized cover crop (CC), and to evaluate the cumulative effect of 5 years of rye CC in a rotation with a high incidence of soybean on the soil organic matter contents. The study was carried out on a petrocalcic Paleustoll, located in the Southern Plain of the Semiarid Pampa Region. The experiment was part of a long-term trial where in 2010 two treatments for soybean management were installed, continuous soybean without CC and soybeans in rotation with CC. In 2018 an experimental design was established where plots were arranged in completely randomized blocks and 4 management treatments for soybean cultivation were established: continuous soybean without CC, soybean in rotation with CC without fertilization, fertilized with 60 kg N .ha-1, and with 120 kg N.ha-1. Nitrogen fertilization in the CC improved the capture rate of both carbon, nitrogen and phosphorus. The results showed that 40% carbon, 60% nitrogen, and 61% phosphorus contained in above-ground biomass were lost from the CC from drying to soybean harvest. The highest soybean yields were recorded in the rotation with fertilized CC, due to a positive effect between the higher soil water content in the early stages of cultivation due to a greater amount of residues, and also by the contribution of different nutrients during the soybean crop-cycle. The long-term trial showed that after 5 years of cover crops in the soybean rotation there was no effect on the organic matter contents.

COVER CROPS AS PREDECESSOR OF PUMPKIN CROP IN THE SEMIARID PAMPA REGION

The objective was determine the effect of cover crops on the water use efficiency and total yield of the pumpkin crop. The study was carried out on a soil called petrocalcic Paleustoll, located in the south of the rugged plain of the semi­arid Pampa region. In the same lot for three consecutive seasons, Rye (C) and rye + vetch (CV) were sown and fallow was established without cover cultivation. In this way, 6 management treatments for pumpkin cultivation were established: T1: without CC predecessor, with tillage prior to pumpkin planting, and without weed control during the pumpkin cycle. T 2: without predecessor CC with tillage prior to planting the pumpkin, with weed control (tillage and herbicide), during the pumpkin cycle. C H: Rye ancestor used as CC, with growth arrest by herbicide. C R: Rye ancestor used as CC, with growth arrest by rolling. CV H: Rye + Vetch ancestor used as CC, with growth arrest by herbicide. CV R: Rye + Vetch ancestor used as CC, with growth arrest by rolling. The results showed that on average in the 3 seasons C was higher than C V, in 22, 19 and 6% with respect to the total biomass, for the first, second and third seasons, respectively. Cover crops had higher fallow efficiency with respect to treatments without prior CC (T1 and T2). The highest pumpkin yields were over the CC, these being the ones with the lowest UC and the highest EUAt

THE CHIRONOMIDS (DIPTERA: CHIRONOMIDAE) OF SHALLOW LAKES OF THE HUMID PAMPA REGION, ARGENTINA: AN APPROACH TO PALEOPRODUCTIVITY RECONSTRUCTION

ABSTRACT The Humid Pampa, center-east of Argentina, is the most important socio-economical area of the country. Several shallow lakes have been the focus of many studies due to the significant changes in their trophic status related to human activities and to global warming recorded since the beginning of the twentieth century. Although chironomids have been used extensively in paleoclimatic and paleoenvironmental research, they are rarely used for paleoenvironmental reconstructions of the Pampean shallow lakes. The aim of this paper is to contribute to the knowledge of the chironmids' community composition and distribution in the Pampa region, and to relate their distribution to selected climatic and limnological variables. The ultimate goal is to retrieve new ecological information for future paleoenvironmental and paleoclimate reconstructions by using chironomid-based inference models. In this study, chironomids head capsules were collected from surface sediments from 17 shallow lakes of the Humid Pampa. Our analyses indicate that the chironomid assemblages reflect the decreasing NE-SW rainfall gradient of the region as well as the land use intensity, which in turn affects the aquatic ecosystems, in terms of lake productivity. Some chironomids are associated with brackish conditions (e.g., Chironomus, Ablabesmyia, Tanytarsini D2). Additionally the occurrence of assemblages of detritivore taxa such as Goeldochironomus, Chironomus, Polypedilum, and Dicrotendipes reflect the natural eutrophic state of Pampean shallow lakes, whereas assemblages mostly dominated by Coelotanypus, Procladius, and Chironomus are indicative of hypertrophic conditions, which are usually the result of human activity. This is the first study of chironomids from surface sediments from the central temperate plains of Argentina, and our records extend the ecological information of the Diptera in temperate areas. Although more studies are necessary to fully understand the main factors determining the chironomid fauna distribution in the Pampa region, we conclude that chironomids are potentially good proxies for paleoproductivity and salinity reconstructions of Pampean shallow lakes.