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)

Producción CientíficaObservational 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 (Proyecto CGL2014-56907-R)Ministerio de Economía, Industria y Competitividad (Proyecto CGL2014-56907-R

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

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-

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-

Improving the Understanding of N Transport in a Rural Catchment Under Atlantic Climate Conditions From the Analysis of the Concentration–Discharge Relationship Derived From a High-Frequency Data Set

[Abstract] Understanding processes controlling stream nutrient dynamics over time is crucial for implementing effective management strategies to prevent water quality degradation. In this respect, the study of the nutrient concentration–discharge (C–Q) relationship during individual runoff events can be a valuable tool for extrapolating the hydrochemical processes controlling nutrient fluxes in streams. This study investigated nitrogen concentration dynamics during events by analyzing and interpreting the nitrogen C–Q relationship in a small Atlantic (NW Iberian Peninsula) rural catchment. To this end, nitrate (NO3-N) and total Kjeldahl nitrogen (TKN) concentrations were monitored at a high temporal resolution during 102 runoff events over a 6-year period. For each of the selected runoff events, C–Q response was examined visually for the presence and direction of hysteresis loops and classified into three types of responses, namely clockwise, counterclockwise, and no hysteresis. Changes in concentration (ΔC) and the hysteresis direction (ΔR) were used to quantify nitrogen ( and TKN) patterns during the runoff events. The transport mechanisms varied between compounds. The most frequent hysteretic response for was counterclockwise with enrichment. On the contrary, the main TKN dynamic was enrichment with clockwise hysteresis. Event characteristics, such as rainfall amount, peak discharge (i.e., maximum discharge of the runoff event), and event magnitude relative to the initial baseflow (i.e., the difference between the maximum discharge of the runoff event and the initial baseflow divided by initial baseflow) provided a better explanation for hysteresis direction and magnitude for TKN than antecedent conditions (antecedent precipitation and baseflow at the beginning of the event). For hysteresis, the role of hydrometeorological conditions was more complex. The hysteresis magnitude was related to the magnitude of the event relative to the initial baseflow and the time elapsed since a preceding runoff event. These findings could be used as a reference for the development of N mitigation strategy in the region.This research has been supported by the Spanish Ministry of Education and Science (grant no. REN2003-08143) and Xunta of Galicia (grant nos. PGIDIT05RAG10303PR and 10MDS103031PR)Xunta of Galicia; PGIDIT05RAG10303PRXunta of Galicia; 10MDS103031P

Assessing the Expected Impact of Climate Change on Nitrate Load in a Small Atlantic Agro-Forested Catchment

Climate change is likely to have profound impacts on quality of water resources, by altering the magnitude and timing of nutrient delivery to stream network. However, water quality responses to climate change are difficult to predict, especially for nutrient loads because of combined uncertainties in water quality and quantity projections. In this study, the potential medium (2031–2060) and long-term (2069–2098) impacts of project changes in climate variables (temperature, rainfall and CO2 concentration) on nitrate load in an Atlantic agro-forested catchment (NW Spain) were assessed using the soil and water assessment tool (SWAT) model. Climate change scenarios are based on data projected by regional models from the ENSEMBLES project and two CO2 concentration scenarios. The results showed that nitrate load will increase in the future horizons (2031–2060, 6%; 2069–2098, 7%) in relation to current values (1981–2010), possibly due to the decline in grassland biomass, as well as an increase in the rate of mineralisation linked to the increase in temperature. Consequently, lower rates of fertilisers will be needed in these areas in future horizons, which should be taken into consideration when planning management strategies in order to mitigate the impacts of potential climate change