Topographic, lithospheric and lithologic controls on the transient landscape evolution after the opening of internally-drained basins. Modelling the North Iberian Neogene drainage.

The opening of internally-drained (endorheic) sedimentary basins often leads to a major drainage change, re-excavation of the basin sedimentary infill, and transient landscape. The timing of such basin openings can be dated only in exceptional cases in which the youngest sedimentary infill remains preserved. For this reason, the processes and timing involved in their transient landscape evolution are poorly known. We explore the role of erodibility, basin geometry and flexural isostasy during the capture of internally-drained basins by means of numerical modelling techniques constrained by recent terrace cosmogenic dating and geomorphological analysis, addressing the issue as to why the Duero and Ebro rivers, draining two Cenozoic sedimentary basins in N Iberia with similar geographical dimensions and drainage histories, have undergone a markedly different erosion evolution leading to distinctly different present morphology. To evaluate how these intrinsic parameters affect the transient landscape evolution, we design a synthetic scenario inspired by those basins. The results show that, once a basin becomes externally drained, its drainage integration and erosion rates are strongly dependent on 1) the basin elevation above the base level; 2) the width of the topographic barrier, 3) its erodibility; and 4) the rigidity of the lithosphere. The results show that transient landscape evolution can last for tens of millions of years even in absence of tectonic activity and changes in base level or climate. Basins isolated by wide and resistant barriers such as the Duero Basin may undergo a multi-million-year time lag between drainage opening and basin-wide incision. In the case of the Duero Basin, this delay may explain the paradoxical time lag between the last lacustrine sedimentation dated at 9.6 Ma and the onset of widespread basin incision variously estimated at 3.5 to 1 Ma.

Unravelling the origin of placer gold: A case study on the largest Roman gold mining sector of NW Spain (Jamuz, León)

<p>NW Iberia hosts a substantial number of mineral resources. Among them, gold (Au) acquired particular relevance since Antiquity, representing one of the largest Roman Au mining provinces in Europe. While primary deposits associated with orogenic Au have been widely studied in the past years, the Plio-Quaternary <em>Raña </em>Au-bearing placer deposits of the western Duero Basin have received little attention. Besides, the different morphology of Au particles suggests complex processes that may have been responsible for the secondary formation of colloidal particles and Au growth grains from complex geochemical soil interactions and biological activity. In this context, exploring the mechanism by means these secondary deposits developed may contribute to understanding the source of Au (extrinsic or intrinsic factors that rule in within <em>Raña </em>deposits) and the formation of potential mineral exploration sectors. This paper outlines the geochemical analysis of a Cenozoic <em>Raña</em>-like deposit in the Jamuz valley (León), where the source of Au and the main characteristics are established. The correlation matrix showed notable relationships between Au, Fe, Na, K, Ca, Pb and As, among the most important. High values in Fe and As provides direct evidence of Au precipitation. Likewise, a non-linear correlation was found between Au-Na, and Au-Ca, suggesting a direct link to soil formation processes. Finally, the presence of apparent differences in grain roundness and the particles' characteristics ranging from monomineral angular Au to polymineral rounded-shaped particles points towards a complex process affecting the <em>Raña </em>deposits. The ubiquitous rubefaction and top-bottom leaching activity produced during rainwater percolation aided by the extreme drainage affecting this conglomeratic formation have often been argued to be responsible for the transformation of mineral phases in soils. The presence of secondary silicification processes and pH drop due to biological reactions (i.e., presence of P) may have been a triggering mechanism for digestion and reprecipitation of Au colloids in these sediments. Our results have outstanding implications on the mechanisms that may determine the Au enrichment of certain levels within the <em>Raña </em>deposits of the western Duero Basin.</p><p>This work was funded by the wine company “Fuentes del Silencio”.</p>

Simple Height and Volume Equations for on-the-Fly Estimation of Productivity in Hybrid Poplar (Populus × euroamericana) Plantations in the Duero Basin (Northwestern Spain)

Hybrid poplar plantations are becoming increasingly important as a source of income for farmers in the Duero Basin (northwestern Spain), as rural depopulations and aging prevent farmers from planting other labor-intensive crops. However, forest owners, usually elderly and without formal forestry backgrounds, lack simple tools to estimate the size and volume of their plantations by themselves. Therefore, farmers are usually forced to rely on the estimates made by the timber companies that are buying their trees. With the objective of providing a simple but empowering tool for these forest owners, simple equations based only on the diameter to estimate individual tree height and volume were developed for the region. To do so, growth in height, diameter, and volume were measured for 10 years (2009–2019) in 404 trees planted in three poplar plantations in Leon province (northern Spain). An average growth per tree of 1.66 cm year−1 in diameter, 1.52 m year−1 in height, and 0.03 m3 year−1 in volume was estimated, which translated into annual volume growth of 13.02 m3 ha−1 year−1. However, annual volume growth was different among plots due to their fertility, with two plots reaching maximum growth around 13 years of tree age and another at 15 years, encompassing the typical productivity range in plantations in this region. Such data allowed developing simple lineal, polynomic, and power equations to estimate height and volume explaining 76% to 97% of the observed variability. Such equations can be easily implemented in any cellphone with a calculator, allowing forest owners to accurately estimate their timber existences by using only a regular measuring tape to measure tree diameter.

Geophysical Prospecting for Geothermal Resources in the South of the Duero Basin (Spain)

The geothermal resources in Spain have been a source of deep research in recent years and are, in general, well-defined. However, there are some areas where the records from the National Institute for Geology and Mining show thermal activity from different sources despite no geothermal resources being registered there. This is the case of the area in the south of the Duero basin where this research was carried out. Seizing the opportunity of a deep borehole being drilled in the location, some geophysical resources were used to gather information about the geothermal properties of the area. The employed geophysical methods were time-domain electromagnetics (TDEM) and borehole logging; the first provided information about the depth of the bedrock and the general geological structure, whereas the second one gave more detail on the geological composition of the different layers and a temperature record across the whole sounding. The results allowed us to establish the geothermal gradient of the area and to discern the depth of the bedrock. Using the first 200 m of the borehole logging, the thermal conductivity of the ground for shallow geothermal systems was estimated.

Estimation of evapotranspiration by the Food and Agricultural Organization of the United Nations (FAO) Penman–Monteith temperature (PMT) and Hargreaves–Samani (HS) models under temporal and spatial criteria – a case study in Duero basin (Spain)

The evapotranspiration-based scheduling method is the most common method for irrigation programming in agriculture. There is no doubt that the estimation of the reference evapotranspiration (ETo) is a key factor in irrigated agriculture. However, the high cost and maintenance of agrometeorological stations and high number of sensors required to estimate it make it non-plausible, especially in rural areas. For this reason, the estimation of ETo using air temperature, in places where wind speed, solar radiation and air humidity data are not readily available, is particularly attractive. A daily data record of 49 stations distributed over Duero basin (Spain), for the period 2000–2018, was used for estimation of ETo based on seven models against Penman–Monteith (PM) FAO 56 (FAO – Food and Agricultural Organization of the United Nations) from a temporal (annual or seasonal) and spatial perspective. Two Hargreaves–Samani (HS) models, with and without calibration, and five Penman–Monteith temperature (PMT) models were used in this study. The results show that the models' performance changes considerably, depending on whether the scale is annual or seasonal. The performance of the seven models was acceptable from an annual perspective (R2>0.91, NSE > 0.88, MAE < 0.52 and RMSE < 0.69 mm d−1; NSE – Nash–Sutcliffe model efficiency; MAE – mean absolute error; RMSE – root-mean-square error). For winter, no model showed good performance. In the rest of the seasons, the models with the best performance were the following three models: PMTCUH (Penman–Monteith temperature with calibration of Hargreaves empirical coefficient – kRS, average monthly value of wind speed, and average monthly value of maximum and minimum relative humidity), HSC (Hargreaves–Samani with calibration of kRS) and PMTOUH (Penman–Monteith temperature without calibration of kRS, average monthly value of wind speed and average monthly value of maximum and minimum relative humidity). The HSC model presents a calibration of the Hargreaves empirical coefficient (kRS). In the PMTCUH model, kRS was calibrated and average monthly values were used for wind speed and maximum and minimum relative humidity. Finally, the PMTOUH model is like the PMTCUH model except that kRS was not calibrated. These results are very useful for adopting appropriate measures for efficient water management, especially in the intensive agriculture in semi-arid zones, under the limitation of agrometeorological data.