J Machı́n’s research while affiliated with Spanish National Research Council and other places

The Salada Mediana lacustrine sequence, central Ebro Basin, Spain (41°30′10″N, 0°44′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 ( and ) of authigenic carbonates, 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 and 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 floor by Chenopodiaceae during a low water table period. This interval reflects 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 effective 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.

Within the Ebro valley, the Zaragoza province contains the largest area of gypsiferous soils in Spain. Previous mapping of the gypsum outcrops has been the starting point for this study of the soils developed on them. In this paper, gypsiferous soils are differentiated according to geological age, lithological facies and other depositional features. The most abundant gypsiferous soils correspond to Tertiary outcrops, where a typical catena includes Leptosols on the crest of the hillslopes, Regosols on the talus and Gypsisols on the valley bottom. Gypsiferous soils, developed on the Triassic Keuper facies and Quaternary materials, occupy a relatively small area. The gypsiferous soils have been mapped at a scale of 1:200 000. A CAD software package has been used for digitizing the soil units. A digital elevation model of the Zaragoza province has been created from the digitized topography. The geographical information system, IDRISI, has been used to integrate all the spatial information generated and to produce maps of the soil types classified according to slope and precipitation. In the Zaragoza province, the gypsiferous soils (Lithic and Eutric Leptosols, Petric, Calcic and Haplic Gypsisols, Gypsic Regosols, Gypsic Solonchaks) occupy a total area of 229 619 ha (13% of the area of the province). 25% of the gypsiferous soils occur within the semiarid area (annual rainfall<400 mm) indicating that climate is the main limiting factor for soil conservation, because of the fragility of gypsiferous soils, special care must be taken with land use operations on the 18 137 ha with slopes above 10°. The knowledge of the distribution of gypsiferous soils in relation to topographic and climatic factors provides an important basis for soil conservation and management.

The abundant gypsiferous soils of the semi-arid central Ebro valley are very sensitive to environmental change. Poor land management practices have caused severe degradation of the soils near the city of Zaragoza, leading to loss of productivity and of ecological function and badland formation on the slopes. The use of sewage sludge for land rehabilitation is increasingly being considered as a technical solution to reverse this environmental degradation and to promote the re-establishment of vegetation cover. This paper describes changes in selected properties of a Gypsisol following the addition of sewage sludge. Experiments investigating the influence of a range of application rates were conducted on 60×100 cm plots. The magnitudes of increase in salinity and decrease in pH were found to be dependent on the sludge application rate. Several beneficial changes were observed including increases in organic matter, organic carbon and nitrogen content as well as in soil moisture and porosity. On the other hand, concentrations of major cations and heavy metals also increase after sewage sludge addition, although, their levels are below the standard limits fixed by the European Union. In order to avoid undesirable side-effects—salinity and toxic concentrations of metals—resulting from the application of sewage sludge to gypsiferous soils in semi-arid environments, it is necessary to characterize the sewage sludge and to determine the most suitable doses. This work highlights the potential of using sewage sludge for land reclamation of degraded soils in semi-arid environments. Nevertheless, the complexity of the processes involved requires further research to ensure the safety of sludge application.

The gypsiferous steppe of Litigio in NE Spain constitutes an enclave of great environmental interest. This characteristic badlands landscape represents a unique semi-arid steppe within Occidental Europe. The ecosystem is very fragile, soils are skeletal, poorly developed and prone to erosion. The xerophytic vegetation is scarce and overgrazing makes its natural regeneration difficult. These physiographic conditions, along with the semi-arid climate and anthropogenic impact, may lead to desertification.Land evaluation is a first step for land use planning and landscape conservation. A raster-based geographical information system was used to integrate the database and to qualitatively assess erosion risks by combining soil types, land classes, land use and slopes. The land use proposed limits agriculture and forestry to specified areas on the thematic maps. Areas vulnerable to erosion are also identified for best landscape conservation.