Nitrate and Phosphorus Transport in a Galician River (NW Iberian Peninsula): Insights From Fourteen Years of Monitoring

This article is part of the special issue Current Research on Soil Science and Related Aspects of Environmental Sciences in Galicia[Abstract] The long-term development of water quality metrics is critical to estimate the status of water resources and successful catchment management. This study looks at the temporal evolution of nitrate and phosphorus loads and concentrations in a stream draining rural catchment in Galicia (NW Iberian Peninsula) during 14 hydrological years. The concentrations of both nutrients are relatively low because of the rural nature of the research catchment and low-intensity agriculture. However, catchment nutrient reference levels were widely exceeded. The hydrology controls nutrient fluxes as flow is the main driver of nutrient transfer. For both nutrients there were no consistent trends in nutrient fluxes. The analysed nutrients, however, have been seen to behave differently. As a result, N seems to be decreasing, mainly due to decreased transit in the autumn and spring. Phosphorus, which is primarily transported as particulate matter, exhibits an increase in winter linked to a greater flow and sediment transfer.This research was carried out within the projects REN2003-08143, funded by the Spanish Ministry of Education and Science, and PGIDIT05RAG10303PR and 10MDS103031PR, financed by the Xunta of GaliciaXunta de Galicia; PGIDIT05RAG10303PRXunta de Galicia; 10MDS103031P

An Assessment of the Recent Evolution of the Streamflow in a Near-Natural System: A Case Study in the Headwaters of the Mero Basin (Galicia, Spain)

[Abstract] Observational trend analysis is fundamental for documenting changes in river flows and placing extreme events in their longer-term historical context. Observations from near-natural catchments, i.e., with little or no alteration by humans, are of great importance in detecting and attributing streamflow trends. The purpose of this study is to analyze the annual and seasonal trends of stream discharge (mean, low and high flows) in a headwater catchment in NW Spain, i.e., in the wettest corner of the Iberian Peninsula. The results showed no significant decrease in the mean annual stream discharge. However, significantly lower summer and autumn mean stream discharge and an increase in low flow period were detected, in addition to lesser autumn high flow. The rainfall pattern followed an upward trend, but was not significant. This different pattern shown by rainfall and discharge indicates that is not sufficient to explain the observed trend in stream discharge. Air temperature, most notably by enhancing evapotranspiration, may explain the altered patterns of stream discharge.Xunta de Galicia; 10MDS103031Ministerio de Economía y Competitividad; CGL2014-56907-

Aluminum Geochemical Characterization in Agricultural Soils: Sequential Chemical Extraction Combined With Mineralogical Analysis of the Fine Fraction

Paper of 6th World Multidisciplinary Earth Sciences Symposium 7-11 September 2020, Prague, Czech Republic[Abstract] Understanding both the concentration and distribution of aluminum (Al) in agricultural soils is essential to provide a benchmark on the productivity of such soils. In this study, a combination of sequential chemical extraction and mineralogical investigation of the fine fraction was used in order to evaluate Al pools in agricultural soils in Galicia (NW Spain), an Atlantic European region where the wet climate favors leaching of soil basic cations. Determination of Al (soluble/exchangeable/specifically adsorbed, bound to manganese oxides, associated with amorphous compounds, bound to oxidizable organic matter, associated with crystalline iron oxides, and residual fraction) in the topsoil samples was performed to evaluate its potential environmental availability in the study area. Aluminum contents were determined by flame atomic absorption spectrophotometry and the mineralogy of the fine fraction of these soils was studied by X-ray diffraction (XRD). The results showed that Al is mainly in the residual phase, which represents Al incorporated in the lattice minerals, and consequently the threat of toxicity to plants and the environment is reduced. The XRD results showed the presence of hydroxy-Al interlayered vermiculites and kaolinite, accompanied by small amounts of goethite, mica, and quartz.This paper is a contribution to the Project CGL2014-56907-R of the National Program of Research, Development and Innovation Oriented to the Challenges of Society, which was funded by the Spanish Ministry of Economy and Competitiveness. M. L. Rodríguez-Blanco has been awarded a postdoctoral research contract (Juan de la Cierva Programme), which was funded by the Spanish Ministry of Economy and Competitiveness

Evaluation of Cu and Zn Content in Soils and their Interaction with Some Physicochemical Soil Properties

[Abstract] The content of metals in soils depends on the combined effect of several factors, which include the properties of the metals themselves and their concentrations in the soil, environmental conditions and soil components. Topsoil samples from different plots of a rural area, which combines reforestation (forests soils) with agriculture (pasture and cultivation soils) and livestock in the Galicia region, NW Spain, were analyzed for total Cu and Zn, pH, organic matter content, and particle size distribution. The geological substrate of the study area is mainly biotitic schist. The aims of this study were to investigate the total Cu and Zn concentrations in the topsoil samples, and to examine the relationship of these metals with the mentioned physicochemical properties using a correlation analysis. Soils were characterized by conventional analytical methods. Total Cu and Zn contents were determined by atomic absorption spectrophotometry after wet digestion with a hot mixture of nitro-perchloric-hydrofluoric acids. The results showed that the soils have on average moderately acid pH, considerable organic fraction and clay loam texture. The total Cu and Zn concentrations were low (mean about 25 mg kg-1 and 78 mg kg-1 respectively), which reveals that these topsoils are not contaminated. The statistical analysis showed positive correlations between the sum of the clay and silt contents, and the total Cu and Zn concentrations. There are no significant correlations between total Cu and Zn, and organic matter content.Xunta de Galicia; 10MDS103031Ministerio de Economía y Competitividad; CGL2014-56907-

Potential Impact of Climate Change on Suspended Sediment Yield in NW Spain: A Case Study on the Corbeira Catchment

[Abstract] Soil losses and the subsequent sediment delivery constitute significant environmental threats. Climate change is likely to have an impact on the availability of water and therefore on sediment yield in catchments. In this context, quantifying the sediment response to an increased atmospheric CO2 concentration and climate change is of utmost importance to the proper management of rural catchments. However, quantitative assessment of climate change impact remains a complex task. In this study, the potential medium (2031–2060) and long-term (2069–2098) impacts of projected changes of temperature, rainfall and CO2 concentration on sediment yield in a small rural catchment located in NW Spain were evaluated using the Soil and Water Assessment Tool (SWAT) model. Climate change scenarios were created using future climate data projected by regional climate models from the ENSEMBLES project and two CO2 concentration scenarios (550 and 660 ppm). The results showed that climate change would have a noticeable impact on suspended sediment if the forecast temperature, rainfall and CO2 concentration changes included in this study were met. Overall, suspended sediment is expected to decrease (2031–2060: −11%, 2069–2098: −8%) compared to the baseline period (1981–2010), mainly due to decreased streamflow. However, an increase in sediment transport in winter is predicted, possibly associated with increased erosion in cultivated areas (11%–17%), suggesting that, at this time of the year, the effect of soil detachment prevails over sediment transport capacity. Consequently, management practices aimed at reducing soil erosion in cultivated areas should be carried out, because these are the main source of sediment in the study area.Galicia. Consellería de Economía e Industria; 10MDS103031Ministerio de Economía y Competitividad; CGL2014-56907-

Recent Evolution of Water Resources in the Headwater of the Mero Basin (Galicia, NW Spain)

[Abstract] The trends analysis of hydroclimatic variables (rainfall, temperature, streamflow) in headwater catchments provides basic scientific criteria necessary for water resource planning and management. However, relatively few studies have been carried out in these relatively near-natural systems, i.e. with little or no alteration by humans. In this context, the overall aim of the present study is to characterize the recent trend of stream discharge in a headwater catchment of the Mero Basin (NW Spain). The results showed no significant decrease in annual stream discharge. However, a significant decrease in summer and autumn stream discharge and an increase in the duration and severity of low flow was detected. In this study, a parallelism between hydrological processes and rainfall was not appreciated. So, the trends observed for streamflow are probably related to upward trend in temperature, by enhancing evapotranspiration.[Resumen] El estudio de la evolución y tendencia de variables hidro-climáticas en cuencas de cabecera proporciona criterios científicos de base necesarios para la planificación y gestión sostenible de los recursos hídricos. Sin embargo, se han realizado pocos estudios en naturales sistemas, es decir cuencas donde la actividad humana no repercute notablemente en el funcionamiento hidrológico natural. En este contexto, el objetivo del presente estudio es caracterizar la tendencia reciente del caudal en una cuenca de cabecera del Mero (noroeste de España). Los resultados no permiten confirmar la existencia de una tendencia regresiva del caudal a escala anual. Sin embargo, se detecta una disminución significativa en el caudal en verano y otoño, así como un incremento en la duración y severidad de los caudales bajos. En este estudio no se aprecia un paralelismo entre los procesos hidrológicos y las precipitaciones, por lo que el descenso del caudal y el incremento de las frecuencias de días con baja descarga podría estar relacionado con el incremento térmico observado, al intensificar procesos como la evapotranspiración