Urbanization has been identified as one of the issues with the greatest environmental impacts on water resources. This study aims to make an environmental diagnosis of urban water management with a systematic approach in a basin with great hydrogeological complexity. We have analyzed urban water management in the Langueyú basin, Argentina, in the period comprehended between 1940 and 2015 in which the city has had a disordered urban growth. It showed that the lack of integrated management together with urban expansion have resulted in a process of building densification and infrastructure that favors the recurrence and magnitude of exceptional hydrological events. This has been accompanied by a spatial displacement of these events and a lack of sanitary services with the same sense of urbanization. It was also demonstrated that the lack of integrated water management this not only had consequences on the Tandil city services associated with the urban hydrological cycle, but also on the quality of its surface water resources (contamination of streams in its urban section) and groundwater (elevation of nitrates levels in water from wells water supply). The absence of a systemic approach to the problem has not considered the relationships between the subsystems involved in water management. This management has been based mainly on the application of structural measures. The main non-structural measure carried out has been to expand the regulations and some neighbor's struggle movements. Other non-structural measures promoted by several actors involved in urban water management, such as authorities, should be carried out in order to raise awareness amongst the population on the importance of water resource protection, especially in areas with hydrogeological limitations.

Groundwater plays an important role in the economic development of the Chaco-Pampean Plain (Argentina), where industry, agriculture and cattle farming are the main economic activities. The 66% of the country's population lives in this area. The low slopes of this region condition the water movement and the occurrence of physical and chemical processes. The aim of this work is to update the hydrological conceptual model of the Del Azul Creek basin (Buenos Aires Province), a sub-humid and continental plain, using environmental tracers. In total, the study was based on the analysis of 201 samples (stable isotopes) and 184 samples (chemical data) including rainwater, surface water and groundwater. The temporal and spatial variation in the isotopic composition of rainfall and the hydrological physical-processes, evaporation, surface water-groundwater interaction and recharge were studied. Isotopic compositions of rainfall revealed a seasonal variation across the basin. Low δ18O rainfalls occur during the coldest seasons, while high δ18O rainfalls occur during the warmest seasons. The isotopic compositions of rainfall varied only during the cold period in the upper basin. At this time, the lowest δ18O rainfall fell in the upper basin, while in the other areas and during the warmer seasons, no differences were observed. Evaporation was a relevant process in the flatter area of the basin, mainly during the warmest seasons. Samples taken from the wetlands and from the lower section of the Del Azul Creek were strongly evaporated. In the first 30 m depth of the aquifer, groundwater reflected the isotopic composition of rainfall from the warmest seasons, thus revealing seasonal preferential recharge and a good hydraulic connection. This study provides direct evidence showing that both evaporation and the surface water-groundwater interaction are processes that play a key role in the control of the isotopic and chemical composition of water.

El presente trabajo se desarrollo en una cuenca rural del partido de Tandil, Provincia de Buenos Aires, Argentina. Su objetivo fue disenar una red ambiental de monitoreo del recurso hidrico subterraneo en la cuenca del arroyo Chapaleofu, que integre, mas alla de la mirada hidrologica clasica (hidrodinamica e hidroquimica), variables fisicoquimicas y de manejo del recurso en cada sitio de muestreo. De 104 perforaciones censadas se seleccionaron 36 aplicando en un SIG un mallado sobre la cuenca. En cada celda se selecciono una perforacion comparando las siguientes variables: accesibilidad, encamisado, mantenimiento, conductividad electrica, distancia a la perforacion mas cercana, distancia al baricentro de la celda, muestra directa del acuifero y toma de muestra y profundidad del nivel del agua en la misma perforacion. La hidroquimica y la hidrodinamica se evaluaron en una campana donde se tomaron muestras para analisis fisicoquimico y se midieron las profundidades del nivel del agua. Se relevaron variables de manejo del recurso (mantenimiento, estado, uso de suelo en el lote de la perforacion y uso de suelo en el establecimiento) y se relacionaron con la calidad del agua. Se eliminaron otras 4 perforaciones que presentaron mala calidad. Se seleccionaron 20 perforaciones en el sector de serranias, 7 en el de piedemonte y 5 en la llanura. La hidroquimica vario de bicarbonatada calcica y/o magnesica en la serrania a bicarbonatada sodica en la llanura. No se encontro relacion entre el manejo del recurso y su calidad, esto muestra la efectividad en la seleccion de sitios no contaminados.

El presente trabajo se desarrolló en una cuenca rural del partido de Tandil, Provincia de Buenos Aires, Argentina. Su objetivo fue diseñar una red ambiental de monitoreo del recurso hídrico subterráneo en la cuenca del arroyo Chapaleofú, que integre, más allá de la mirada hidrológica clásica (hidrodinámica e hidroquímica), variables fisicoquímicas y de manejo del recurso en cada sitio de muestreo. De 104 perforaciones censadas se seleccionaron 36 aplicando en un SIG un mallado sobre la cuenca. En cada celda se seleccionó una perforación comparando las siguientes variables: accesibilidad, encamisado, mantenimiento, conductividad eléctrica, distancia a la perforación más cercana, distancia al baricentro de la celda, muestra directa del acuífero y toma de muestra y profundidad del nivel del agua en la misma perforación. La hidroquímica y la hidrodinámica se evaluaron en una campaña donde se tomaron muestras para análisis fisicoquímico y se midieron las profundidades del nivel del agua. Se relevaron variables de manejo del recurso (mantenimiento, estado, uso de suelo en el lote de la perforación y uso de suelo en el establecimiento) y se relacionaron con la calidad del agua. Se eliminaron otras 4 perforaciones que presentaron mala calidad. Se seleccionaron 20 perforaciones en el sector de serranías, 7 en el de piedemonte y 5 en la llanura. La hidroquímica varió de bicarbonatada cálcica y/o magnésica en la serranía a bicarbonatada sódica en la llanura. No se encontró relación entre el manejo del recurso y su calidad, esto muestra la efectividad en la selección de sitios no contaminados.

The Chaco-Pampean Plain (Argentina) is the strongest economic region and the most inhabited in the country, comprising approximately 66% of the country's population (26,500 million) [1]. In this region, surface slopes are very low (<0.1%) and due to the current climatological features, floods and droughts alternate over time. Salinity and alkalinity of water and soil increase towards the flattest sector of the basin, as well as the contents of arsenic and fluoride, which restrict their human use. Worldwide, population growth and global warming, in addition to political decisions, are leading to abrupt land use changes. Under this premise, identifying and quantifying the hydrological processes that control water quantity and its chemical quality become an imperative task [2]. This data article provides a long-term hydrological dataset from a sector of the Chaco-Pampean Plain, the Del Azul creek basin. Hydrological data such as flow rates and piezometric levels, and physical–chemical (i.e., major and minor solutes, and trace elements) and isotopic (δ18O, δ2H; and d-excess) data from rainwater, surface (creek and wetland) and groundwater (at two depths) are available. Rainwater samples are derived from three precipitation collectors installed at different altitudes (monitoring period: 2010–2019; n = 57). Surface water samples were collected at three sampling sites located along the Del Azul Creek and six wetlands (monitoring period: 2018–2019; n = 12). Groundwater samples were collected from 17 piezometers with depths ranging between 3 and 10 m, and from 12 piezometers of 30 m depth, all located throughout the entire basin (monitoring period: 2018–2019; n = 115). Sampling campaigns were performed during the austral dry (summer) and wet (spring) seasons. This dataset provides useful information to understand a) how water moves from recharge to discharge areas, b) how water acquires salinity, and c) how particular solutes of concern, such as arsenic and fluoride, are distributed in space and time across in an extensive plain.

Se analizaron los procesos de precipitación-escurrimiento en una microcuenca bajo uso agrícola (566 ha) ubicada en el área serrana/periserrana del Partido de Azul, Buenos Aires, Argentina. Se utilizó el modelo hidrológico HEC-HMS 3.2 en combinación con el software QGIS, dividiendo la cuenca en varias sub-cuencas interconectadas por un cauce interno. Para el modelo de lluvia-escorrentía se consideró el método del número de curva (CN). Se calcularon los valores de CN para el año 2012 mediante dos procedimientos: a) el método SCS-CN original y b) el método de Hawkins. Al no lograrse un ajuste adecuado entre los datos observados y los valores estimados, se utilizó finalmente un CN según calibración del modelo utilizando registros históricos propios. Los coeficientes de correlación y de eficiencia de Nash Sutcliffe fueron superiores a 0,7 para todas las crecidas. La raíz cuadrada media del error arrojó valores bajos indicando un ajuste aceptable del modelo. Luego, se realizó un análisis de sensibilidad evento a evento. A tal fin, dos de los parámetros incluidos en el modelo (número de curva y tiempo de retardo) fueron sometidos al análisis de sensibilidad. A su vez, los valores de CN estimados para el ajuste fueron analizados versus los datos de precipitación (mm), considerando todas las crecidas e incluyendo como tercer variable: a) la lluvia antecesora y b) la duración de la precipitación. El modelo predijo aceptablemente la descarga máxima, el volumen de escurrimiento y el tiempo al pico en función de los datos históricos de crecidas disponibles para el año 2012. Estos resultados ponen de relieve la importancia de contar con valores de CN calibrados in situ, e indican que bajo esas condiciones el HEC-HMS sería adecuado para modelar la respuesta hidrológica de la cuenca estudiada pudiéndose utilizar para el análisis de los datos hidro-meteorológicos disponibles y predecir futuras crecidas, lo cual resulta de importancia para el manejo y la conservación de las tierras de dicha región.

Se estudian las recargas mensuales totales, las descargas por flujo subterráneo a zonas de descarga y las pérdidas por evapotranspiración directa desde el nivel freático a partir de la variación diaria del nivel freático en una perforación somera en la zona llana de la cuenca del arroyo del Azul, ubicada en la llanura pampeana. Los niveles freáticos se registraron mediante un sensor de presión piezorresistivo. El acuífero freático analizado es el acuífero Pampeano. Los niveles freáticos variaron en el período analizado (2007-2018) entre 0.5 y 4 m de profundidad. Se ha encontrado que las descargas por evapotranspiración directa desde el nivel freático son una fracción relevante de la recarga total (42%). Las descargas por evapotranspiración directa son mayores en los meses cálidos, aunque la menor variabilidad interanual se da en los meses fríos y en los meses cálidos. La mayor variabilidad se da en otoño y primavera. En el período 2007-2018 la recarga total anual promedio fue de 252 mm, la pérdida anual promedio de la recarga a la atmósfera fue de 105mm, con una desviación estándar de 25 mm y un coeficiente de variación de 0.24. Este porcentaje importante de la recarga total que se pierde por evapotranspiración directa hace que se deban considerar con especial atención los balances de agua en el suelo para estimar la recarga al acuífero (que no consideran esta pérdida) y explica ciertas incongruencias con los modelos de flujo de aguas subterráneas que exigían una disminución de la recarga en la zona más llana para posibilitar el ajuste de los niveles freáticos.

Response time of the water table (WT) to rainfall is a relevant parameter for optimal management of water resources in plains. This study explores the response time of WT to climatological variability. WT dynamics were analyzed for a period of 10 years in 7 stations located in the Argentinean Pampean Region: Laboulaye (LAB), Arias, General Pico (GP), Azul, Dolores (DOL), Junín and Barrow. Statistical standard methods were applied on WT data series provided by the National Meteorological Service (in Spanish, SMN) and La Pampa province government. Standardized Precipitation and Evapotranspiration Index (SPEI) was applied in multiple temporal scales. Modeled SPEI data were correlated to WT and water table depth (WTD; in situ data) using the Pearson method. Results indicated that WTD response time is spatially variable in the study region when considering the rainfall and evapotranspiration balance (represented by the temporal behavior of the SPEI). These results allowed for the definition of a second-degree–function theoretical method of WTD that explains its variations for different extreme conditions. Multivariate statistical analysis was used to analyze the similarities of WTD evolution among the 5 stations for the 1986–1990 period. Highest statistical connections were found between GP and LAB, GP and DOL and between DOL and LAB stations, which indicated similarities in their dynamic and the maximum (WTD ~ 3.3 m) and mean (WTD ~ 2 m) WTD values measured during the studied period. Surface water coverage data, obtained through digital processing of satellite images of high spatial resolution, validates the relations between climatological variables and WTD showing increases (km2) during the periods in which the WTD was lowest and vice versa. The method presented in this investigation allows the use of SPEI to the prediction of WTD in zones, where it is difficult to measure it.

Our manuscript analyses the surface runoff variability, and its controlling factors in a small basin with gentle slopes, at the headwaters of a flat catchment, to improve the knowledge of the hydrology of plain areas under agriculture. We study runoff, rainfall and antecedent conditions in the argentine Pampas region. We use correlations, regressions and quantitative and qualitative descriptive information of the system: erosion signs, ground cover by crops, groundwater depth data and temporal changes in the drainage network, to discuss and understand the complexity of the runoff process by frameworks to study (dis)connectivity. The analysis of 56 events evidenced a nonlinear rainfall–runoff relationship. In contrast with other works, we identified clear upper limit events, under which hydrological responses emerge, as a result of combinations of antecedent wetness, rainfall erosivity, ground cover and preferential drainage paths. We separated the nonlinear rainfall–runoff response in three linear relationships according to differences in antecedent wetness conditions. We found differences in runoff responses under wet and dry antecedent conditions, but complex responses under medium antecedent conditions. The analyses of the inputs, the structural and the functional elements of the (dis)connectivity frameworks, were key in the understanding of the temporal changes of runoff, and its complex responses. Temporal coincidences of connectivity components and their feedbacks appear to be strongly associated with the runoff dynamics. High‐magnitude hydrological responses occur with complete coincidences, while partial coincidences between the components reduce connectivity and low magnitude and/or heterogeneous responses prevail. Thus, these analyses suggest that runoff is controlled by (dis)connectivity in this basin with gentle slopes. Our work contributes to the understanding of the process of surface runoff in the context of humid flatlands under agricultural land use, by the identification of the complex combinations of factors which regulate/control the (dis)connectivity that helps to interpret the nonlinearities of runoff.

Recharge in arid zones has been studied thoroughly due to the scarcity of groundwater that is available for extraction. However, the issue of depressed groundwater levels in sub-humid areas is mainly reflected by the contribution of the base flow to a watercourse; this contribution constitutes a very important alteration of the ecological conditions of a watercourse, including its substrate and surroundings. Continuous groundwater records from 2007 to 2014 for six wells located within the Del Azul Creek basin were analyzed. The recharge was calculated using the water table fluctuation method. The relationship between the groundwater level in each well and the base flow through a section of the creek was analyzed on a monthly basis to obtain a quadratic equation. The ecological flow of the stream was also determined, using the 7-day minimum flow method. Due that the base flow variations can strongly affect the ecological quality of this type of basin, with vertical flows more important than horizontal flows, the results are a contribution for water resource management practices in the areas of influence of surface water bodies. Groundwater mean monthly levels in wells located in the lower area of the basin, showed high adjustment coefficients for the quadratic equations that relate these levels to the base flow. These equations are good tools for decision makers regarding land use planning. Because our interest is low-flows, an equation that relates mean monthly base flow versus groundwater levels during the summer months are adjusted.

In areas with very mild relief, water drains in a disordered way due to the lack of a developed drainage network, as it occurs in extremely flat sedimentary regions like the Argentine Pampas. The study analysed the flood spatial arrangements in 2014 by calculating landscape metrics and relating them to soil water balance. The study area is located at Del Azul creek lower basin (Pampa Ecoregion, Argentina). Daily soil water balances were obtained, and seven landscape metrics were calculated in 15 windows in five LandSat images, all along 2014, to explore the relationship between hydrological scenarios and spatial pattern summarized with principal component analysis. Water excess concentrated in winter (June and August); deficits were in late spring and summer (January and November), whereas the beginning of autumn (March) was an intermediate situation. Principal component 1 (44.7%) reflected area and shape metrics and correlated positively with water table level; principal component 2 (32.3%) summarized aggregation ones and was negatively associated with accumulated water excesses or deficits in previous 30 days and useful reserve. Both exhibited possible threshold‐driven behaviour. Internal heterogeneity between NW and SE zones within the study area coincided with the existence of ancient alluvial fans. The results highlight the peculiarities of the flood spatial patterns in regions with very mild relief, where landforms usually determine water flows.

The understanding of the hydrology of plain basins may be improved by the combined analysis of rainfall–run‐off records and remote sensed surface moisture data. Our work evaluates the surface moisture area (SMA) produced during rainfall–run‐off events in a plain watershed of the Argentine Pampas Region, and studies which hydrological variables are related to the generated SMA. The study area is located in the upper and middle basins of the Del Azul stream, characterized by the presence of small gently hilly areas surrounded by flat landscapes. Data from 9 rainfall–run‐off events were analysed. MODIS surface reflectance data were processed to calculate SMA subsequent to the peak discharge (post‐SMA), and previous to the rainfall events (prev‐SMA), to consider the antecedent wetness. Rainfall–run‐off data included total precipitation depth (P), maximum intensity of rainfall over 6 hr (I6max), surface run‐off registered between the beginning of the event and the day previous to the analysed MODIS scene (R), peak flow (Qp), and flood intensity (IF). In contrast with other works, post‐SMA showed a negative relationship with the R. Three groups of cases were identified: (a) Events of low I6max, high prev‐SMA, and low R were associated with slow and weakly channelized flow over plain areas, leading to saturated overland flow (SOF), with large SMA; (b) events of high I6max, low prev‐SMA, and medium to high R were rapidly transported along the gentle slopes of the basin, related to Hortonian overland flow (HOF) and low post‐SMA; and (c) events of medium to high I6max and prev‐SMA with medium R were related to heterogeneous input‐antecedent‐run‐off conditions combined: Local spatial conditions may have produced HOF or SOF, leading to an averaged response with medium SMA. The interactions between the geomorphology of the basin, the characteristics of the events, and the antecedent conditions may explain the obtained results. This analysis is relevant for the general knowledge of the hydrology of large plains, whose functioning studies are still in their early stages.

Fil: Weinzettel, Pablo. Universidad Nacional del Centro de la Provincia de Buenos Aires. Rectorado. Instituto de Hidrologia de Llanuras - Sede Azul. Provincia de Buenos Aires. Gobernacion. Comision de Investigaciones Cientificas. Instituto de Hidrologia de Llanuras - Sede Azul; Argentina

From a hydrological point of view, the characteristic of the water behaviour in catchments so depressed as the Azul creek basin (centre of Buenos Aires province, Argentina) is water accumulation above the land surface. Thus, water on the ground does not have a single runoff direction, but moves in a disorderly, indefinite and unpredictable way. Considering that periodic floods are a typical disturbance of the region, the objective of this study is to analyse, under field conditions, the transformative effect of prolonged flooding on floristic composition, taking into account the different vegetation patches and their relative position over the relief, the chemical characteristics and the groundwater fluctuation, and some edaphic properties in each site.Vegetation samplings were performed during three consecutive springs, when the grassland was on different hydrological conditions due to very different rainfall precedent histories. A digital terrain model of the study area was built and a flow accumulation map was created from it. Pits were dug to describe edaphic variables and shallow wells were drilled for monitoring the groundwater characteristics. Flooding, in relation with surface and groundwater dynamics and soil characteristics, is the factor that determines and promotes the differentiation among sites that are relatively close, contiguous and even topographically in almost identical positions. So, some patches of vegetation get their differentiation through the limiting conditions of their soils, while others receive greater influence from the hydrodynamics to which they are subject. Thus, in this study it becomes evident how certain stands are floristically homogenised or differentiated over time according to their flooding conditions and, hence, according to the area from which they receive surface and groundwater flow. Also, results corroborate the way the water regime determines the structure and heterogeneity of plant communities in such environments.

The contents of arsenic (As), fluoride (F) and other trace elements (B, Cd, Cr, Cu, Fe, Mn, Ni, Pb, V, Zn, Ba, Si and Sr) have been determined in groundwater samples from the Langueyú creek basin, in the Argentina Pampean plain. This research aims to establish the baseline concentration and geographical distribution of trace elements in this basin. This aim has particular interest to public health in the city of Tandil where groundwater is the principal source of water for human supply. The baseline concentrations of elements in the Langueyú creek basin are in good agreement with published data from other locations of the Pampean aquifer. The arsenic limit of 10mg/l, established as provisional limit by the World Health Organization (WHO), was exceeded in 78% of the sampled wells, with As concentration increasing in the direction of groundwater flow. Concentrations of B, Cd, Cu, Cr, Fe, Mn, Ni, Pb and Zn regulated by the Argentinian Food Code (CAA) do not exceed the maximum limit for drinking water, although concentrations of Ni, Zn or Pb peaked up at some wells, probably due to pipeline corrosion. The strong correlation observed between As, F, V, Cr and B has been related to their anionic character at the groundwater natural alkaline pH that is likely associated with similar mobilization (adsorption/desorption) processes. Worst consequences for human health have arisen in areas with the highest arsenic concentration in drinking water. The conclusions of this study contribute to understand the provenance and mobilization processes of some trace elements in groundwater. It enables the decision making regarding the public health priorities and the technological treatments of water resources in urban and rural areas.

Dada la complejidad de la evaluación integral de los recursos hídricos es necesario que los estudios hidrogeológicos a nivel de cuenca se enriquezcan con el análisis regional, por ejemplo a través de la comparación entre cuencas de una región. Se planteó como objetivo del trabajo elaborar una propuesta para el estudio comparativo del recurso hídrico subterráneo y analizarla a través del ejemplo de caso de las cuencas de los arroyos Langueyú y Del Azul. Los aspectos definidos para la comparación fueron: litología, hidrodinámica, hidroquímica e influencia antrópica. Se consideraron mediciones de niveles freáticos y análisis fisicoquímicos en redes de monitoreo del agua subterránea; se analizaron los impactos potenciales al sistema según las características del medio físico y las actividades antrópicas. De acuerdo a los resultados, en ambas cuencas la disponibilidad de agua subterránea está dada por dos ambientes hidrogeológicos (fisurado y poroso); el modelo conceptual hidrodinámico e hidroquímico es similar. En tanto, existen diferencias respecto a las dimensiones de los servicios sanitarios en los centros urbanos (consumo y efluentes domiciliarios) y las principales cargas contaminantes potenciales. Se concluyó que a nivel regional es importante profundizar el estudio en el uso y la gestión del recurso, ya que las diferencias relevantes se presentaron en este aspecto, no en sus características naturales. El trabajo permitió tanto sistematizar la información con que cuenta el grupo de trabajo, como probar que la comparación es un camino metodológico posible para trabajar posteriormente con otras cuencas del faldeo de las Sierras de Tandilia en la elaboración de propuestas de gestión conjuntas.

The objective of this work is to compare the chemical composition and the spatial and temporal variabilities of groundwater in two basins, the Langueyú and Del Azul creeks basins, located in the Pampean plain, Buenos Aires province (Argentina). The Pampean plain is the most productive region in Argentina, agriculture and livestock being the main economic activities. Groundwater is the principal water resource in the region, with a strong and growing demand for human supply and for agriculture and industrial activities. Several sampling campaigns were carried out on shallow wells of the two studied basins along a period of 3 years (2010–2013) to identify seasonal variations. Electrical conductivity, pH, bicarbonate, chloride, sulphate, nitrate, calcium, magnesium, sodium and potassium were determined following standard methods. For hydrochemical interpretation, descriptive statistical analyses, matrix augmentation principal component analysis, MA-PCA, and multidimensional principal component analysis, N-PCA (Parafac and Tucker3 models), were applied to the hydrochemical datasets from both basins. Three main hydrochemical processes have been identified in both basins: saline enrichment in the groundwater flow direction caused by dissolution of carbonates; exchange of calcium and magnesium by sodium in the same direction, and located areas of nitrate pollution. The paper shows that N-PCA is a good tool to deepen in the understanding of the hydrochemical features of groundwater from two neighbour basins, simplifying the analysis of large amounts of data, as well as establishing relations between the compared basins. Therefore the work is considered an interesting contribution to the study of groundwater resources with a regional scope. This knowledge is essential in basins with high socio-economic interests it causes a direct impact on resources management.

In the Argentine Pampas region, there is little information about sediment concentration in agricultural catchments. The aims of this work are: (1) to analyse fluctuations in sediment concentration and discharge, as a first attempt to characterize hysteresis patterns; and (2) to study sediment concentration controlling factors and to assess the importance of these factors using principal component analysis and a multiple regression model. Twenty-five events registered during 4years in a 560ha gauged basin of Argentina were studied. Analysis of data suggested a positive clockwise pattern. The multiple regression model was performed with three factors obtained by principal component analysis: runoff, precipitation and antecedent conditions. The model explained 83% of the variability of sediment concentration. The runoff factor contributed to modelled sediment concentration with the highest magnitude, followed by precipitation and antecedent condition factors. Although the watershed is under conservation tillage, rill erosion seems to be the main source of sediment concentration.