The study area is located in the middle basin of the El Pescado stream, which belongs to the municipalities of La Plata and Magdalena. The objective of this work is to identify hydrogeopedological indicators and to interpret the hydromorphic gradient as a contribution to the detailed characterization and delimitation of wetlands. The hydrogeopedological interpretation was carried out at two sites by conducting transects perpendicular to the stream course. A precision topographic survey was conducted, and orthomosaics and digital elevation models were generated. Pits, auger drilling, soundings, and sampling of surface and groundwater were performed at both sites to support the geological and hydrogeopedological characterization. As a result, hydrogeopedological indicators were established and classified, proving useful in defining and categorizing a hydromorphic gradient. There is a close relationship between hydrogeopedological characteristics and the distribution and properties of the parent materials of the soils, as well as a direct relationship between geomorphology and surface and groundwater fluctuations. An integrated hydrogeopedological approach combined with the use of precision field technology and digital processing proved to be a proper tool for the detailed characterization and delimitation of wetlands.

Resumen El vínculo entre arte y naturaleza es central para construir resiliencia en el marco de la crisis climática. Dentro del Proyecto de Investigación: “Suelo vacante, riesgo hídrico y paisaje. Proceso de urbanización reciente en el sudeste del Gran La Plata y estrategias para la planificación del crecimiento urbano desde las cuencas hidrográficas” se desarrollaron distintas acciones artísticas, con el fin de visibilizar las interacciones entre naturaleza y urbanización que se dan en una nueva periferia urbana de la ciudad de La Plata (Argentina). El objetivo de este trabajo es exponer las obras desarrolladas para fomentar la experiencia persona-naturaleza, en las que la escala es la humana y la conexión con el medio es parte de ellas.

The Pampean plains in South America are well-known for their livestock and agricultural productivity. The peri-urban watershed of El Pescado Creek (Central-Eastern Argentina) has been significantly modified in the last few years due to local land-use changes. This work aims to analyze the dynamics of nutrient content associated with the surface water-groundwater relationship in this watershed and to define the trophic state of the watercourse. Sampling sites were selected for both surface water and groundwater analyses, and field surveys were carried out during the spring and summer of 2017. Handmade shallow groundwater wells were installed along the floodplain of the watercourse. Deep groundwater was analyzed in agricultural and livestock farms. In situ determinations included dissolved oxygen (DO), pH, electrical conductivity (EC), turbidity, transparency, and temperature measurements. Laboratory analyses included NO3--N, total nitrogen (TN), soluble reactive phosphorus (SRP), total phosphorus (TP), and phytobenthonic and phytoplanktonic chlorophyll-a. Results showed an increase in EC and nutrient concentration in the summer samples (both in surface water and shallow groundwater), along with higher turbidity of the surface water. Water flow was dissimilar between samplings (spring: 1.735 m3/s, summer: 0.065 m3/s), showing contrasting hydrological scenarios. Low wash-out conditions enhanced phytobenthonic algae biomass growth, turning most of the sites towards a eutrophic state in summer. Our results showed that the dynamics of nitrogen and phosphorus compounds in the watershed of El Pescado Creek depend on the hydrodynamic processes of the watershed, the different land-uses, and the chemical characteristics of these compounds. In order to develop sustainable management strategies, further understanding of nutrient concentrations effects, and the factors affecting them, must be done in this area of the Pampean region.

La cuenca del arroyo El Pescado, ubicada en el noreste bonaerense, desde principios de siglo atraviesa un proceso de cambio en el uso del suelo. El objetivo del trabajo fue realizar un diagnóstico sobre la distribución y cuantificación de elementos traza en el recurso hídrico de la cuenca, en relación con los diferentes usos del agua. Se utilizó una red de monitoreo de agua superficial y agua subterránea somera y profunda. Se determinó el contenido de elementos traza mediante un equipo ICP-MS. Las mayores concentraciones de elementos traza correspondieron al agua subterránea somera y las menores al agua subterránea profunda. En el acuífero freático el As y el Fe superaron los límites permitidos para abastecimiento de agua potable. En tanto que el V y el Zn superaron los límites para uso agropecuario en el acuífero freático y agua superficial. En las aguas superficiales el Cu, Pb y Zn excedieron los límites de protección para la vida acuática en todos los sitios, mientras que el V sólo en la cuenca media y parte de la cuenca baja.

The watershed of El Pescado Creek has been established as a protected landscape; however, it is currently exposed to an intense land use and coverage change process, based on the conversion of grassland areas into greenhouse horticulture and urbanized areas. The aim of this work was to analyze hydrochemical modifications in this changing scenario, to identify parameter variations associated to water balance. The monitory network included surface water and groundwater samplings during winter, spring and summer of 2017. Daily water balance was estimated throughout the annual cycle. Electrical conductivity and pH were determined together with major ions (Na+, K+, Mg2+, Ca2+, CO32−, HCO3−, Cl−, SO42− and NO3−). The analysis of water stable isotopes (δ18O and δ2H) was performed for one sampling date. Water-balance variations during short-term periods affected surface water chemistry, although no relevant influence on deep groundwater was registered. Major ions variation in the surface water of the upper watershed might be related to runoff alteration caused by recently established impervious cover and by the dynamic of groundwater inputs. Isotopic analysis of surface water shows deviation from local meteoric line, with an isotopic enrichment following a tendency associated to evaporation processes. Deep groundwater samples express a recharge process by rainfall infiltration, with little or no previous evaporation (deuterium amounts were similar to those corresponding to local rainfall). Incipient evaporation processes are registered for shallow groundwater, possibly occurring before infiltration in the non-saturated zone, or right from the phreatic, when it is near the surface.

Land-use changes in the periurban interface: Hydrologic consequences on a flatland-watershed scale

Pimelodella laticeps Eigenmann, 1917 is the most abundant siluriform in the El Pescado Stream, located in the depressed region known as pampean region (Buenos Aires, Argentina). To characterize its feeding habits in this environment, we analyzed the dietary contents on seasonal samplings from May 1991 through August 1993. To evaluate the relative contribution of the different dietary components, the index of relative importance (IRI) was used. Pimelodella laticeps preferred sectors with aquatic macrophytes, and predated mainly on organisms from the periphytic and benthic communities. The main food was cyclopoid copepods, which taxa usually have littoral or benthic habitats, and only to a lesser extent are components of the plankton community. The planktonic organisms available in the environment were analyzed by the Olmstead-Tukey-test, which diagram indicated that the dominant items were copepods, ostracods, and chironomids. Chydorid cladocerans, harpacticoid copepods, mayfly larvae, and amphipods also became dominant but less frequently. To understand the feeding strategies of P. laticeps, the fish diet was compared with the available plankton as analyzed by a nonparametric multivariate analysis (permutation-based one-way ANOSIM). Pimelodella laticeps consumed almost no phytoplankton, while the discriminating items from the latter assemblage were identified as having high values in the environment.

In the Argentine Pampa fertile soils were originally covered by grasslands, but at present are intensively cultivated. We assessed the specific composition of the fish assemblage of El Pescado stream and compared it with that recorded in 1991–1993, when land use in the watershed consisted in natural pastures. The persistence of the fish assemblage between the two studies was rather high: 0.76. Abundance, biomass and species richness were higher during drought periods. Connectivity with the huge Río de la Plata hydrographic system seems the most important contribution to the high and stable species richness of El Pescado stream.

<p>Law 232 of August 27, 2004 has a special meaning to the people residing in some of Puerto Rico's poorest communities. It was the result of the hard work, during a period of a year and a half, of leaders from some of these communities and my students, the students of the community development section of the Legal Aid Clinic of the University of Puerto Rico’s School of Law. The story of Law 232 can provide insight into what the role of a lawyer can be in the battle against poverty. To understand the story of this Puerto Rican law, one has to go back to August of 2002. During that month the University of Puerto Rico's School of Law Legal Aid Clinic inaugurated its community development section.</p>

The phreatic aquifer beneath the Pampean plain, in eastern central Argentina, constitutes a relevant source of water supply in the area. The objective of this work was to assess the significance of the cation exchange processes in the hydrochemical evolution of this aquifer, based on a study case located in the middle and upper basin of the El Pescado creek. Results indicate that Ca2+/Na+ exchange is the main process determining the evolution of groundwater from the recharge areas (Ca–HCO3) towards the local discharge areas (Na–HCO3), as well as representing a source of Na+ contribution to the water in the aquifer. This hydrochemical characteristic is central to the identification of local discharge areas within a plain environment which extends regionally. The ion exchange capacity of these discharge areas has environmental importance, due to its influence on groundwater quality and potential groundwater uses. These results may be applied to any aquifer sharing similar hydrogeological characteristics.

The structural features and O2 consumption of the epipelic biofilm in streams of the Pampean plain were explored. The study was conducted in three lowland streams subjected to different anthropic disturbances. Three sampling sites were selected in different sectors of these streams considering land use intensity (high, moderate, and low). Samples of the water and of the epipelic biofilm were taken seasonally. El Pescado stream is subjected to a low level of human impact and showed lower organic matter and nutrient contents than the Rodriguez and Don Carlos streams which are subjected to moderate and high levels of human impact. The biofilm composition of the three streams was represented by cyanophytes and diatoms but with different species composition and dominance; protozoans and nematodes were the characteristic heterotrophic groups in the three streams. The Rodriguez and Don Carlos streams showed the highest abundance of organisms. Multiple regression showed that O2 consumption, chlorophyll a and trophic index were significantly correlated with the oxygen demands. On the other hand, the Rodriguez and Don Carlos streams exhibited significant differences with the El Pescado stream in O2 consumption, trophic index, and chlorophyll a content. Our results demonstrated that the different biological descriptors responded to environmental variables that are influenced by the different land use intensities, being chlorophyll a, abundance of organisms, and O2 consumption the most sensitive variables to the changes water quality.

The Subandean ranges of northwestern Argentina are an active thin-skinned fold and thrust belt. The main detachment level in Silurian shales dips 2–3W, and all the major east-verging faults detach from it. Important intermediate detachment levels in the Devonian shales generate lift-off structures and the decoupling of the lower and upper structural levels. The Subandean thrust belt has a minimum shortening of about 60 km (36%) at about 2240 latitude. The deformation started at about 8.5–9 Ma with the uplift of the El Pescado range and the formation of an important back thrust at the Cinco Picachos range. Fault generation gets young to the east; the Pintascayo range uplift started at 7.6 Ma, while the Baja Orn range uplift began at about 6.9 Ma. These two ranges continued growing simultaneously until at least 4.7 Ma. At San Antonio range, fault movement began at approximately 4.4 Ma, and the Aguarage uplift started at about 2.7 Ma. An important stage dominated by out-of-sequence movements spans from about 4.5 Ma to present. For both proposed models of shortening, the Quaternary rates of shortening between 8 and 11 mm/yr coincide well with global positioning system results from the area. The hydrocarbon generation and migration is contemporaneous with the deformation, enhancing the possibilities of hydrocarbon entrapment in the area.

Phytoplankton, as well as physical and chemical variables of six lotic systems of Buenos Aires province, tributaries of Rio de la Plata river (Rodriguez, El Gato, El Pescado, Bunirrigo and J. Blanco streams, Samborombon river) were analysed and results were related to the degree of anthropic pollution. Surveys were carried out seasonally from May 1997 to June 1998. Sample sites were stablished at 2 or 3 stations depending on the length of the systems, from the headwaters to the mouths. Specific composition, species richness, dominance, diversity and eveness were assessed. Diatoms and clorophytes presented the highest number of species. Cyanobacteria were dominant in 60% of the samples and diatoms were subdominant in 42% of them. Samborombon river showed minimun and maximun phytoplankton densities among the six systems (50 cell.ml−1 and 188 475 cell.ml−1, respectively). Indexes values showed a non-defined pattern, increasing or decreasing in the most polluted sites. The first axis of the PCA which included the physical and chemical variables is characterized by the nutrient concentrations and it is related to the pollution of these systems, separating samples of Rodriguez and El Gato streams, which presented high positive scores, from the rest of them. The second axis is represented by variables which determine the water conductivity and separates samples from the mouths of Samborombon river and Bunirrigo stream, which presented high positive scores, from the rest of them. The species PCA indicate that its distribution is related to the first two components of the chemical data set PCA. The first axis separates species found in high-conductivity sites, such as the mouths of Samborombon and Bunirrigo systems (i.e. Cocconeis placentula, Aulacoseira granulata, Melosira varians, Actinocyclus normanii, Dictyosphaerium ehrenbergianum) from those registered in low-conductivity sites, such as J. Blanco stream (i.e. Pseudanabaena catenata, Nitzschia gracilis, Mallomonas sp.). The second axis separates α and β mesosaprobic species from polluted sites -Rodriguez and El Gato streams- (i.e. Gomphonema parvulum, Navicula cryptocephala, Nitzschia palea, N. umbonata, Oscillatoria amphibia, Lyngbya limnetica, Euglena acus) from those found in oligosaprobic non-polluted sites – J. Blanco stream – (Nitzschia gracilis, Pseudanabaena catenata, Gomphonema clavatum).

A wide urban area in the Northeast of Buenos Aires Province (Argentina) is exposed to anthropogenic influence, mainly due to industrial and urban activity. In this area two streams were chosen, Del Gato and El Pescado streams. They have similar characteristics, although the first one runs through the built-up area and the other one through a rural area; consequently, Del Gato stream has a higher input of pollutants (fluvial effluents, fly ashes, solid wastes, etc.) than El Pescado stream. Magnetic measurements and geochemical studies were carried out on five sediment cores taken out from both streams with the aim of establishing a link between concentration of ferrimagnetic materials and contents of heavy metals. In order to investigate concentration of magnetic carriers and its intrinsic features (present magnetic minerals and grain size distribution) several magnetic parameters were measured and relations between them were analyzed. The magnetic characteristics for both sites indicate the presence of magnetically soft minerals in both streams, predominantly in Del Gato stream and with the additional presence of relatively hard minerals in El Pescado stream. Besides, a higher concentration of secondary ferrimagnetic minerals was found in Del Gato stream than in El Pescado stream. Chemical studies show (in some cases) a high concentration of some heavy metals (lead, copper, zinc, nickel and iron) on the upper 22 cm. Magnetic parameters, especially anhysteric remanent magnetization and contents of some heavy metals, showed a very good correlation.

Geological interpretation of Landsat TM imagery and aeromagnetic survey data, northern Precordillera region, Argentina

The fluvial system within the southwestern coastal sector of the Río de la Plata interacts with a very large and efficient mixing basin known as the Río de la Plata estuary. The region is a densely populated and productive sector of Argentina and is characterised by a temperate humid climate. The streams Carnaval, Martín, Del Gato and El Pescado of the study area drain two main geomorphologic units: a higher inner zone and the low lands of the coastal plain. In particular, the Del Gato stream receives heavily polluted discharges from agricultural, urban and industrial point and non-point sources of pollution, while the other streams collect a lower and variable discharge input. As a part of an initial assessment of the role of fluvial bottom sediments in the fate of metals through the stream ecosystems, the spatial distribution of trace and major elements related to particles in the accumulation areas was examined. Concentration of Cr, Ni, Cu, Zn, Cd, Hg, Pb, Fe and Mn, grain size, mineralogy (clay-X ray diffraction) and organic matter content were analysed in the four streams considering both geomorphologic units at different depositional time. Untreated and iron-normalised trace metal concentrations in the most polluted streams show higher levels in the upper layers of most contaminated sectors and accumulation areas associated to topographic low lands. The coastal plain sector behaves as a regional sink between the upstream area and the estuary.

Water quality assessment of six pampean lotic systems through the study of physichal and chemical variables. Physical and chemical composition of six lotic systems of Buenos Aires province (Rodríguez, El Gato, El Pescado, Buñirrigo and J. Blanco streams, Samborombón river) was determined seasonally in order to evaluate the water quality of them. Sample sites were stablished in 2 or 3 stations from the headwaters to the mouths (E1 to E3). The systems presented low values of transparency; minimum values corresponded to El Pescado stream (E1) and Samborombón river (E3). Maximum suspended solids concentrations were registered in Rodríguez stream (E1) and in Samborombón river (E3). Rodríguez and El Gato streams were seriously impacted by anthropogenic activities, mostly downstream E2 where industrial efluents are discharged. These streams registered the highest nutrient concentrations in these sites. The lowest value of dissolved oxygen was registered in El Gato stream (E2). J. Blanco system, which is situated in a natural reservation, presented the lowest values of nutrients; minimun values were registered in E1. Nutrient’s concentrations in El Pescado stream were usually higher in E3. Buñirrigo stream is impacted in its lower basin by the discharge of efluents of several industries which caused the increase of nutrients, conductivity and the decrease of dissolved oxygen downstream E3. Samborombón river registered an increased of nutrients and conductivity downstream E2 due to the industrial and extensive agricultural activities developed in this area. Suspended solids concentrations were higher in E3 because of the effect of a coagulation process due to the presence of tides and salinity gradients.

El Pescado (literally ‘the fish’) is a lowland stream in the pampean plain, entering the Rio de La Plata at 35°55¢S,57°45¢W, 70 km SW of the city of Buenos Aires. The stream develops as a potamon with variable flood frequency along its 36 km length. The water is slightly soft, with relatively high conductivity and dominance of HCO–3 , Na + and Cl – ions. Three fish families, Characidae (29%), Pimelodidae (14.6%) and Loricariidae (12.8%) are most abundant among 55 species. Differences in species composition among four stations with different environmental traits were observed. Flooding slightly affected the fish fauna. In open-water and rocky-bottom stations, both species number and number of individuals were correlated with conductivity, an indication of the decrease of fish density with floods. Species richness was well over worldwide means. Diversity values, higher than in small tropical streams in Venezuela and southern Brazil, ranged from 0.32 to 2.59, being higher during autumn and spring. The stream has a high persistence, with the composition of the fish community maintained or recovering as soon as flooding ends. One Synbranchus marmoratus specimen was found among rocks, the first record of this behaviour for the species.