Christian Prat

Erosion extension of indurated volcanic soils of Mexico by aerial photographs and remote sensing analysis

In the northern part of Michoacan State in Mexico, between the Patzcuaro and Cuitzeo lakes, we used aerial photographs and Spot satellite data, to define the spatial and temporal extensions of soil erosion over indurated volcanic material called tepetates. Segmentation techniques combined with graphic mask were applied over the aerial photographs in order to obtain the extension of eroded areas for 1975, 1995 and 2000. An unsupervised classification was performed over various band combinations of Spot. The eroded areas were checked and improved with ground control points. The results show that there are no more eroded areas today than 25 years ago. There is, however, an evolution of the eroded areas; some of them have disappeared while others have become larger. A change in land use intensity explains the regression of eroded area in the north and the augmentation of eroded surfaces in the south. The result obtained with Spot imagery classification allows discrimination of four different erosion degrees, where only one could be distinguish with aerial photographs. However, it is not possible to distinguish outcropping tepetates and outcropping andesit with Spot. As well, additional socioeconomic studies and studies over spectral signatures of eroded materials in relation with their mineral contents are in process.

Tracing sediment sources in a tropical highland catchment of central Mexico by using conventional and alternative fingerprinting methods

Land degradation is intense in tropical regions where it causes for instance a decline in soil fertility and reservoir siltation. Two fingerprinting approaches (i.e. the conventional approach based on radionuclide and geochemical concentrations and the alternative diffuse reflectance infrared Fourier transform spectroscopy method) were conducted independently to outline the sources delivering sediment to the river network draining into the Cointzio reservoir, in Mexican tropical highlands. This study was conducted between May and October in 2009 in subcatchments representative of the different environments supplying sediment to the river network. Overall, Cointzio catchment is characterized by very altered soils and the dominance of Andisols and Acrisols. Both fingerprinting methods provided very similar results regarding the origin of sediment in Huertitas subcatchment (dominated by Acrisols) where the bulk of sediment was supplied by gullies. In contrast, in La Cortina subcatchment dominated by Andisols, the bulk of sediment was supplied by cropland. Sediment originating from Potrerillos subcatchment characterized by a mix of Acrisols and Andisols was supplied in variable proportions by both gullies and rangeland/cropland. In this latter subcatchment, results provided by both fingerprinting methods were very variable. Our results outline the need to take the organic carbon content of soils into account and the difficulty to use geochemical properties to fingerprint sediment in very altered volcanic catchments. However, combining our fingerprinting results with sediment export data provided a way of prioritizing the implementation of erosion control measures to mitigate sediment supply to the Cointzio reservoir supplying drinking water to Morelia city. Copyright

Tracing sediment sources in a tropical highland catchment of central Mexico by using conventional and alternative fingerprinting methodsTracing sediment sources in a tropical

Land degradation is intense in tropical regions where it causes for instance a decline in soil fertility and reservoir siltation. Two fingerprinting approaches (i.e. the conventional approach based on radionuclide and geochemical concentrations and the alternative diffuse reflectance infrared Fourier transform spectroscopy method) were conducted independently to outline the sources delivering sediment to the river network draining into the Cointzio reservoir, in Mexican tropical highlands. This study was conducted between May and October in 2009 in subcatchments representative of the different environments supplying sediment to the river network. Overall, Cointzio catchment is characterized by very altered soils and the dominance of Andisols and Acrisols. Both fingerprinting methods provided very similar results regarding the origin of sediment in Huertitas subcatchment (dominated by Acrisols) where the bulk of sediment was supplied by gullies. In contrast, in La Cortina subcatchment dominated by Andisols, the bulk of sediment was supplied by cropland. Sediment originating from Potrerillos subcatchment characterized by a mix of Acrisols and Andisols was supplied in variable proportions by both gullies and rangeland/cropland. In this latter subcatchment, results provided by both fingerprinting methods were very variable. Our results outline the need to take the organic carbon content of soils into account and the difficulty to use geochemical properties to fingerprint sediment in very altered volcanic catchments. However, combining our fingerprinting results with sediment export data provided a way of prioritizing the implementation of erosion control measures to mitigate sediment supply to the Cointzio reservoir supplying drinking water to Morelia city. Copyright

Evaluation and Selection of Indicators for Land Degradation and Desertification Monitoring: Methodological Approach

An approach to derive relationships for defining land degradation and desertification risk and developing appropriate tools for assessing the effectiveness of the various land management practices using indicators is presented in the present paper. In order to investigate which indicators are most effective in assessing the level of desertification risk, a total of 70 candidate indicators was selected providing information for the biophysical environment, socio-economic conditions, and land management characteristics. The indicators were defined in 1,672 field sites located in 17 study areas in the Mediterranean region, Eastern Europe, Latin America, Africa, and Asia. Based on an existing geo-referenced database, classes were designated for each indicator and a sensitivity score to desertification was assigned to each class based on existing research. The obtained data were analyzed for the various processes of land degradation at farm level. The derived methodology was assessed using independent indicators, such as the measured soil erosion rate, and the organic matter content of the soil. Based on regression analyses, the collected indicator set can be reduced to a number of effective indicators ranging from 8 to 17 in the various processes of land degradation. Among the most important indicators identified as affecting land degradation and desertification risk were rain seasonality, slope gradient, plant cover, rate of land abandonment, land-use intensity, and the level of policy implementation.

Evaluation and selection of indicators for land degradation and desertification monitoring: types of degradation, causes, and implications for management

Indicator-based approaches are often used to monitor land degradation and desertification from the global to the very local scale. However, there is still little agreement on which indicators may best reflect both status and trends of these phenomena. In this study, various processes of land degradation and desertification have been analyzed in 17 study sites around the world using a wide set of biophysical and socioeconomic indicators. The database described earlier in this issue by Kosmas and others (Environ Manage, 2013) for defining desertification risk was further analyzed to define the most important indicators related to the following degradation processes: water erosion in various land uses, tillage erosion, soil salinization, water stress, forest fires, and overgrazing. A correlation analysis was applied to the selected indicators in order to identify the most important variables contributing to each land degradation process. The analysis indicates that the most important indicators are: (i) rain seasonality affecting water erosion, water stress, and forest fires, (ii) slope gradient affecting water erosion, tillage erosion and water stress, and (iii) water scarcity soil salinization, water stress, and forest fires. Implementation of existing regulations or policies concerned with resources development and environmental sustainability was identified as the most important indicator of land protection.

Influence of conservation tillage and soil water content on crop yield in dryland compacted alfisol of Central Chile

En Chile, las zonas de clima mediterraneo se caracterizan por suelos altamente degradados y compactados por erosion, lo que requiere el uso de sistemas de labranza conservacionista para mitigar la erosion hidrica, asi como incrementar el contenido de agua en el suelo. Se evaluo una rotacion avena (Avena sativa L. cv. Supernova-INIA) - trigo (Triticum aestivum L. cv. Pandora-INIA) establecida bajo los siguientes sistemas conservacionistas: cero labranza (Nt), Nt + curvas de nivel (Nt+Cp), Nt + franjas vivas (Nt+Bh) y Nt + subsolado (Nt+Sb), las que fueron comparadas al sistema de labranza convencional (Ct), para evaluar su influencia en el contenido de agua en el suelo (SWC) en el perfil (10 a 110 cm profundidad), la compactacion del suelo y su interaccion con el rendimiento del cultivo. Las parcelas experimentales fueron establecidas 3 anos seguidos (2007 al 2009) en un Alfisol compactado. Al final de la temporada, el SWC disminuyo 44 a 51% en los sistemas conservacionistas y 60% en el sistema convencional. El sistema de labranza y la profundidad tuvieron un efecto significativo (p < 0.05) en el SWC; Nt+Sb presento un menor contenido de agua entre los 10 y 30 cm y similar al resto de los sistemas conservacionistas entre los 50 y 110 cm, sin embargo, superior a Ct. Aunque los sistemas conservacionistas mostraron un mayor SWC, la alta compactacion afecto los rendimientos. Cero labranza + subsolado redujo la compactacion del suelo e incremento significativamente el rendimiento en grano (similar a Ct en las temporadas 2008 y 2009). Estos resultados nos muestran que la eleccion de un sistema conservacionista en suelos compactados de la region mediterranea, requiere mejorar la estructura del suelo para obtener mejores rendimientos e incrementar el contenido de agua en el suelo.

Firewood extraction affects carbon pools and nutrients in remnant fragments of temperate forests at the Mexican Transvolcanic Belt

Globalmente, los fragmentos forestales representan un almacen importante de carbono, pero estos fragmentos estan bajo una fuerte presion de degradacion; principalmente, debido a la extraccion ilegal de madera para lena y carbon vegetal. El presente estudio evaluo el efecto de la extraccion de lena sobre los almacenes de carbono y la dinamica de nutrientes del suelo en bosques templados de fragmentos remanentes en el centro de Mexico. Se estudiaron cuatro sitios con diferente grado de intensidad de extraccion de lena, donde se midieron el carbono almacenado y el flujo de nutrientes durante dos anos consecutivos. El carbono en la biomasa aerea y en el suelo se redujo con el aumento de la intensidad de la extraccion. El bosque degradado (DF) presento 55 % menos contenido total de carbono que el bosque seminatural (SF). Asi mimo, la produccion de hojarasca tambien se redujo en el DF, pero la descomposicion del mantillo fue mayor en el SF. Como consecuencia, el DF presento menores entradas de carbono organico al suelo. El amonio disponible, el carbono y nitrogeno en la biomasa microbiana del suelo tambien fueron menores en el DF. La conclusion de este trabajo es que la extraccion de lena en los fragmentos forestales en Mexico reduce drasticamente las cantidades de carbono almacenado, los flujos de carbono y nutrientes por medio de la hojarasca, y por tanto, la dinamica de los nutrientes del suelo es afectada.

Extraction of Glomalin and Associated Compounds with Two Chemical Solutions in Cultivated Tepetates of Mexico

Glomalin is a glycoprotein produced by the hyphae of arbuscular mycorrhizal fungi (AMF). The chemical methods usually employed to extract glomalin from the soil obtain something more than this pure glycoprotein, and therefore it would be better to call this fraction soil protein related to glomalin (SPRG) or glomalin associated with humic substances (GAHS). On this account, its isolation is controversial. The SPGR or GAHS has a significant influence on the physical, chemical, and biological properties of soils and could then be considered as an indicator of soil use change. In the present study, the storage of SPRG was evaluated, as well as carbon (C) associated with the latter (CG) and the content of soil organic C (SOC) in cultivated tepetates in the State of Mexico. Tepetates are hardened volcanic tuffs of the fragipan type, ameliorated for agricultural production. The specific objectives of the present study were (1) to evaluate the SPRG levels in tepetates, (2) measure the contribution of carbon (C) made by the SPRG to soil organic C (SOC), and (3) compare the extraction of SPRG with sodium pyrophosphate and sodium citrate. The samples used in this experiment came from 87 tepetate-cultivated plots (0–20 cm) located in the Texcoco River basin, State of Mexico. The levels of SPRG were observed among traces, 2.3 mg g–1 for citrate and up to 5.6 mg g–1 for pyrophosphate. The latter reactive allowed us to extract nearly three times more SPRG and two times more C-SPRG than sodium citrate (P = 0.05) in the tepetates having about 4% of SOC; yet when the latter was less than 0.5%, the extraction levels with both solutions were similar. The SPRG and CG were closely correlated with SOC (r > 0.90). Tepetates have levels of SPRG similar to those observed in arid soils.