Ana Navas

Spatial distribution of heavy metals and arsenic in soils of Aragón (northeast Spain): controlling factors and environmental implications

Abstract Legal regulation of heavy metal contents is an important issue in many European countries, where laws still do not exist establishing the heavy metal levels permitted in soils. As a first step to determine the reference levels of heavy metals, it is necessary to know their contents in soils under natural conditions. To achieve this goal in the Autonomous Community of Aragon, a total of 133 sites have been sampled. A balanced allotment of the sampling sites, according to soil spatial distribution in the region, has been carried out by selecting 9 soil types that represent 97.5% of its surface area. Fifteen elements (Cr, Cu, Ba, As, Sb, Hg, Sn, Mn, Fe, Al, Zn, Ni, Co, Cd and Pb) have been analysed by (ICP–AES) after a partial acid extraction. The content of analysed elements has been correlated to some soil parameters such as organic matter, pH, and granulometric fractions. Results of the statistical analyses have shown a large variety and complexity in some of these relationships. The main factors for variation in the heavy metal contents are both the soil type and the lithology. Gypsisols and Calcisols developed on sedimentary rocks have the lowest contents while Leptosols overlying metamorphic and igneous rocks have the highest contents. The spatial distribution of heavy metal contents shows a large variability with the highest contents in the mountain ranges (Iberian and Pyrenees) and the lowest in the plains of the central Ebro valley.

Sediment sources and siltation in mountain reservoirs : a case study from the Central Spanish Pyrenees

Abstract Based on a 137 Cs -derived chronology, we reconstruct the depositional history of the Barasona reservoir in the Esera–Isabena Basin, Central Pyrenees (Spain). Most of the sediments were delivered to the Barasona reservoir during flood events. Comparative mineralogical studies of the Esera and Isabena river channels and the Barasona reservoir sediments help to identify sediment sources and areas of high sediment yield risk, and to establish erosion and sediment transport processes in the watershed. Changes in the mineralogical composition of the sediments can be used to discriminate the relative contribution of the Esera and Isabena rivers during flood periods. Three main periods in the siltation history of the Barasona reservoir were distinguished: (1) From dam construction (1932) to the early 1950s, the reservoir was flushed every year using the lower gates, and average sediment accumulation was very low (1.5 cm/yr). (2) During the 1950s and 1960s, the sedimentation rate increased and reached the highest values: 15 cm/yr, 24.6 cm/yr and 18.2 cm/yr in the Esera river mouth, the northern and the southern areas of the reservoir, respectively. Both changes in the exploitation regime (no annual flushes) and climate variability (increased flood frequency and river inflow) caused this increase in sediment delivery and accumulation. (3) The third period was initiated by the enlargement of the dam in 1972. The new sedimentary dynamics in the reservoir caused a general decrease in the sedimentation rate (11.6 cm/yr in the southern areas; 10 cm/yr in the Esera mouth) that was especially noticeable in the northern areas, where the accumulation rate was reduced to 3.7 cm/yr. An increase in channel erosion processes during this period contributed to the transport of sediments to the inner areas of the reservoir.

Lateglacial and Late Holocene environmental and vegetational change in Salada Mediana, central Ebro Basin, Spain

The Salada Mediana lacustrine sequence, central Ebro Basin, Spain (41330@10AN, 0344@W, 350 m a.s.l.) provides an example of the potential and limitations of saline lake records as palaeoclimate proxies in the semi-arid Mediterranean region. Sedimentary facies analyses, chemical stratigraphy, stable isotopes (d18O and d13C) of authigenic carbonates, d13C values of bulk organic matter and pollen analyses from sediment cores provide paleohydrological and vegetation change reconstructions for the Lateglacial and Late Holocene in the central Ebro basin. A preliminary chronology is based on 210Pb and 14C AMS dates. The lacustrine sequence is composed of three sedimentary Sections. The Lower Section was deposited in a permanent saline to brackish lake. This stage represents the most humid period in the record and it was accompanied by the expansion of temperate trees (particularly Corylus). The Middle Section was deposited in an ephemeral playa-lake complex. Frequent subaerial exposure conditions favour the colonisation of the playa lake #oor by Chenopodiaceae during a low water table period. This interval re#ects the most arid conditions in the Salada Mediana record, including the current environment. A secondary temperate tree expansion occurred after the maximum aridity period. Aquatic plants and cyanobacterial mats spread in the lake during periods of raised water tables.This paleohydrological and vegetational evolution attests to large changes in e!ective moisture during the Lateglacial in the semi-arid northeastern Spain. The abundance of Corylus during the Lateglacial indicates that refugia for temperate trees were located along the Ebro valley during the Last Glacial Maximum. The Holocene sediments in the Salada Mediana records have been eroded, and the Upper Section represents deposition during the last few centuries. ( 2000 Elsevier Science Ltd and INQUA. All rights reserved.

Use of biosolids to restore the natural vegetation cover on degraded soils in the badlands of Zaragoza (NE Spain)

Abstract In the semiarid central Ebro valley, the soils of the badlands surrounding Zaragoza city exhibit severe degradation features. Nevertheless, poor land management practices and limiting climatic and edaphic factors make the natural regeneration of the soil difficult. The use of sewage sludge as amendment for land rehabilitation is increasingly being considered as a technical solution to reverse this environmental degradation and to restore the original vegetation cover. This paper describes the changes produced on the natural vegetation cover after application of digested sewage sludge (biosolids) to three soil types. Experiments were conducted on plots with two different slope levels by applying different rates of biosolids. When increasing rates of biosolids were applied, the biomass yield increased proportionally, although differences among the different soil types and the level of the slope were observed. To avoid undesirable side-effects, mainly referred to soil pollution (salinity and toxic levels of metals), each case has to be individually studied. Therefore, prior to application both characterisation of biosolids and determination of the most suitable application rates to be used are required.

238U, 226Ra, 210Pb, 232Th and 40K activities in soil profiles of the Flysch sector (Central Spanish Pyrenees)

Distributions of natural gamma-emitting radionuclides were determined in three soil profiles developed on Tertiary sedimentary materials in mountain landscapes of the Central Spanish Pyrenees. Radioisotope activities (Bq kg(-1)) lie in the range of 0-53 for 238U; 19-33 for 226Ra; 7-75 for 210Pb; 24-48 for 232Th and 335-562 for 40K. 238U and 210Pb activities show an important variability down the soil profiles. 238U was markedly depleted in all upper soil layers and highly enriched in lower layers of two soil profiles. 210Pb exhibits very dissimilar distribution patterns in all three soils. 226Ra and 232Th had quite uniform depth distributions. 40K showed depletion in both upper and lower layers in one soil profile but remained fairly constant in the other two profiles. 238U/226Ra activity ratios (ARs) have been used to assess equilibrium in the 238U decay chain and as indicators of edaphogenesis in the studied soil profiles. Maintenance of initial proportionality in the ratio of 232Th/238U activities has been assessed through ARs of their progenies. Additionally, a variety of soil properties were measured down the soil profiles. Among soils, variation in radionuclide activies may be due to differences in carbonate content, organic matter and/or grain size. In this environment, soil properties differently affect mobilization of natural radionuclides. The association of some radiologic properties with soil layers suggest a relationship between soil processes and radionuclide distribution.

Large 13C enrichment in primary carbonates from Andean Altiplano lakes, northwest Argentina

Abstract We report here extreme 13 C enrichments up to +13‰ PDB in primary calcite and aragonite precipitates in saline, well oxygenated waters from high-altitude lakes in the southern Andean Altiplano, northwestern Argentina. Biological effects, as well as variations in carbon source inputs, and in the exchange rate with atmospheric CO 2 , are commonly considered the main controls on the carbon isotope values of authigenic lacustrine carbonate. We present sedimentological and geochemical evidence that favors physical processes — evaporation effects and CO 2 -degassing — as major controls on 13 C enrichment. We propose that large enrichments may result from the non-equilibrium gas-transfer isotope fractionation during CO 2 -degassing from thermal springs and evaporation effects in arid environments. The dilution effect by large quantities of 14 C-free CO 2 hinders accurate 14 C chronology of these lake records based on lacustrine organic matter and aquatic plants. Our results indicate that geothermal and volcanic CO 2 sources in lake basins located in volcanic settings, and physical fractionation may have a greater significance than commonly accepted to explain lacustrine carbon isotope records.

Responses of a saline lake ecosystem in a semiarid region to irrigation and climate variability- The history of Salada Chiprana, central Ebro basin, Spain

Abstract To adequately manage the fragile and changing environments of semiarid regions it is essential to disentangle human from climate or other environmental impacts over longer timescales than human memory. We investigated sediment cores from Salada Chiprana, a saline lake in the central Ebro basin in Spain, using pollen, charcoal, sedimentological, geochemical and radiometric dating techniques. The sequence indicates a rapid evolution from an ephemeral playa lake during the Late Holocene to a permanent saline lake a few centuries ago. The limnological evolution correlates with changes in agricultural practices and provides evidence of the strong impact of irrigation on the lakes hydrological balance from the XVth century. The work demonstrates that the Salada Chiprana, the only permanent, relatively deep, hypersaline lake in Spain has been created by a long history of human interaction with the landscape.

Patterns of regional hydrological variability in central-southern Altiplano (18°–26°S) lakes during the last 500 years

Abstract Paleohydrological reconstructions based on sedimentological, geochemical, and isotopic records from a lake transect in the central-southern Altiplano (18°–26°S) indicate abrupt moisture fluctuations during the last 500 years. A change to modern conditions occurred in the late 19th century in all the records, from northern Chile (Lago Chungara, 18°15′S) and the Atacama (Laguna Miscanti, 23°45′S) to the southern tip of the Altiplano (Laguna El Peinado, NW Argentina, 26°30′S). A previous drier period shows different patterns of timing, duration, and intensity. In Chungara, the arid period was shorter and occurred during the late 19th and early 20th centuries, while in Miscanti, it occurred earlier and ended at the beginning of the 20th century. In El Peinado, conditions were wetter during the 17–19th centuries and the arid period occurred prior to the 17th century. Other records from the region show abrupt paleohydrological and paleoclimatic changes synchronous with the termination of the Little Ice Age. Despite local differences and dating uncertainties, the Little Ice Age stands out as a significant though complex climatic event in the Andean Altiplano. The discrepancies between the northern and southern Altiplano records during the last few centuries may reflect contrasting responses to external forcing in two areas with different climatic regimes.

Predicting soil erosion with RUSLE in Mediterranean agricultural systems at catchment scale.

Accurate assessment of soil loss is essential for sustainable agricultural production, management, and conservation planning, especially in productive rain-fed agroecosystems and protected areas. The European Union considers soil as a nonrenewable resource and identifies that soil degradation has strong impacts on soil and water resources. In this work, the Revised Universal Soil Loss Equation model was applied within a geographic information system in the Estaña catchment (Spanish pre-Pyrenees) as representative of a Mediterranean agroecosystem to elaborate a map of soil erosion at high spatial resolution (5 × 5-m cell size). The soil erodibility factor (K) was calculated from three different approaches to evaluate the importance of spatial variations in soil texture, field infiltration measurements (Kfs), and amount of coarse fragments. The average value of estimated soil loss for the whole study area was 2.3 Mg ha−1 year−1, and the highest rates were estimated in crops in steep areas (5.8 Mg ha−1 year−1) and trails (18.7 Mg ha−1 year−1). Cultivated soils with high soil erosion rates (>8 Mg ha−1 year−1) represented 20% of the cultivated area. The average value of soil loss in areas with human disturbances (4.21 Mg ha−1 year−1) was 4.4-fold that estimated for areas with natural vegetation (0.96 Mg ha−1 year−1). Field validation with 137Cs showed that the estimated value of soil loss in barley fields with the K-Kfs-rocks factor improves the model predictions in comparison with those obtained with the K texture and K-Kfs factors. The Revised Universal Soil Loss Equation model predicted a decrease in soil erosion in fields in accordance with the increase of the age of abandonment. Predicted values of soil erosion and measured soil organic matter and stoniness in old abandoned fields agreed with those in areas of natural forest and indicated the recovery of the original conditions of the soil. Statistical analysis highlights that the C factor contributed most of the variability of the values of predicted soil erosion; the K and LS factors contributed in a similar way. The P factor contributed least to the variability of soil erosion. Cultivated soils developed over clay materials in high slope areas are the most susceptible to soil degradation processes in comparison with soils developed over limestones in gentle and medium slope areas. The recovery of terraces in steep fields and conservation of crop residues are proposed as soil conservation practices to reduce the magnitude of soil loss in the study area.

Mobility of natural radionuclides and selected major and trace elements along a soil toposequence in the Central Spanish Pyrenees

Natural gamma-emitting radionuclides (238U, 226Ra, 232Th, 210Pb) and selected major and trace elements (Ca, K, Mg, Na, Fe, Al, Mn, Pb, Ba, Zn, Sr, Li, Co, Ni, Cu, Cr, Cd) were determined in a soil toposequence along a mountain slope of the Tertiary Flysch landscapes in the Central Spanish Pyrenees. A variety of basic properties were also measured from the soil profiles. Mean radioisotope activities (Bq kg−1) range from 22 to 33 for 238U; 25 to 32 for 226Ra; 23 to 33 for 210Pb, and 37 to 46 for 232Th. The radionuclides showed different patterns in their depth distribution, thus 238U and 210Pb had largest differences in concentrations down the soil profiles, whereas 226Ra and 232Th exhibited uniform depth distributions. 238U was depleted in all upper soil layers and enriched in deeper layers. 210Pb exhibits very different depth profiles along the soil toposequence and accumulated at upper layers in three sites. 238U/226Ra activity ratios indicate disequilibrium in the 238U decay chain and reflect the leaching of 238U in contrast with the lack of mobility of 226Ra. The values of 232Th/226Ra indicate that the initial proportionality in the 238U and 232Th decay chains has not been maintained in this toposequence. The relationships between soil properties and gamma-emitting radionuclides suggested the association of 226Ra and 232Th with Fe and Mn oxides. Al, Ca, Fe, and K were the most abundant elements, followed by Mn, Ba, Pb, Sr, Li, and Zn, whereas Co, Cu, Ni, and Cr are as trace elements and Cd was not detected. Correlations between elements suggest association with carbonates (Ca, Sr), silicates and clay minerals (Al, K, Na) and with Fe and Mn oxides (Cr, Cu, Ni, Co, Zn). Along the soil toposequence, Ca, Sr, Mg and Na, K, Al increase at the bottom slope positions, due to highest carbonate contents and abundance of finer soil fractions (clay and silt), respectively. Fe and Mn decrease at the bottom slope because highest contents of Fe and Mn oxides are at upper slope positions. This research is of interest to describe the geochemical cycling of elements in the environment and to assess the processes that affect their mobility in the ecosystems.