Gabriela Cuevas

Chemical fractionation of heavy metals in a soil amended with repeated sewage sludge application

Abstract A sequential extraction method (KNO 3 , NaOH, Na 2 -EDTA, HNO 3 ) was used to determine the soil fraction of Zn, Cd, Cu, Ni, Pb, and Cr in different plots treated with sewage sludges. The sludges were applied to cropland from 1983 to 1991. Soil samples were collected after the 1st and 5th-year of the last sludge application. Sludge applications increased the INOR-fraction for Zn, Cd, and Cu. Cu was the only element found in the EXCH-fraction. Pb and Cr were found mainly in the RES-fraction. Ni was found in the INOR and OM-fractions. All the metals increased in the more resistant fractions. Sewage sludge applications changed the metals distribution of the soil and this effect has continued for at least 5 years.

Plant and Soil Responses to the Application of Composted MSW in a Degraded, Semiarid Shrubland in Central Spain

Composted municipal solid waste (MSW) was assessed as a soil amendment material for restoring the canopy cover of a degraded soil in an area with a Mediterranean climate. Four rates (0, 40, 80 or 120 Mg ha−1) of MSW were surface-applied to a calcareous soil in central Spain and the effects on soil properties and the native plant community recorded over the next five years. Soil N, P and K levels increased significantly after application. Soil organic carbon (OC) increased with the amount of MSW applied, but the differences were small and inconsistent. Soil total Zn, Pb, Ni and Cu increased in the MSW-treated soils compared to the controls, but levels were still below the maximum allowed by Spanish legislation. DTPA-extractable soil Zn and Cu were the only heavy metals studied that increased with MSW application, but their concentrations were still adequate for plant growth. Total aerial plant biomass yields and canopy cover increased with MSW amendment compared to the control treatment. Plant production increased three fold in the amended plots in the first years and than declined with time, although no consistent trends were observed. The percentage canopy cover ranged from approximately 82 to 100 % in the MSW treatments and from 43 to 49% in the control throughout the study period. Native plant species richness decreased slightly with increasing MSW rates. Differences in the plant communities developing on the control and MSW-treated plots were observed, with a reduction in perennial species and an increase in annual species after five years. Plant tissue N, P, K, Zn and Cu levels generally increased with the MSW rate. Thus, MSW application have a positive effect on the soil chemical characteristics and on the native vegetation without causing environmental damage. MSW may therefore be of use in the rehabilitation of ecosystems similar to that studied.

Effects on run-off water quantity and quality of urban organic wastes applied in a degraded semi-arid ecosystem.

Biosolids and composted municipal solid wastes were surface-applied (0 and 80 Mg ha(-1)) to a degraded soil in a semi-arid environment to determine their effects on the quantity and quality of run-off water. Three and 4 years after application, a simulated rainfall was performed (intensity=942.5 ml min(-1) and kinetic energy=3.92 J m(-2)) on 0.078 m(2) plots using a portable rainfall simulator. The run-off from the different treatment plots was collected and analysed. The type of treatment was highly related to infiltration, run-off and sediment production. The biosolid-treated plots showed the minimum value of total run-off, maximum time to the beginning of run-off and maximum run-off ratio (the relationship between total rainfall and run-off). The MSW-treated plots showed values intermediate between biosolid-treated plots and control plots. Soil losses were also closely related to treatment type. Control plots showed the maximum sediment yield, MSW-treated plots showed intermediate values, and biosolid plots the minimum values for washout. The concentrations of NH(4)-N and PO(4)-P in the run-off water were significantly higher in the treated plots than in control plots. The highest PO(4)-P value, 0.73 mg l(-1), was obtained in the soil treated with biosolids; NO(3)-N concentration also increased significantly with respect to the control and MSW treatments. NH(4)-N concentrations of 15.6 and 15.0 mg l(-1) were recorded in the soils treated with biosolids and MSW, respectively, values approximately five times higher than those obtained in run-off water from untreated soil. However, the concentrations of all these constituents were lower than threshold limits cited in water quality standards for agricultural use. With the exception of Cu, all trace metals analysed in the run-off water were below detection limits.

Composted MSW Effects on Soil Properties and Native Vegetation in a Degraded Semiarid Shrubland

Three rates of dried composted MSW (40, 80 and 120 Mg ha−1) were surface applied to a degraded semiarid shrubland site near Madrid in central Spain. Various soil and plant parameters were determined one year after its application. MSW amendment had an effect on soil chemistry and nutrient levels. Available P and K, concentration of N-NO3 and EC. increased significantly after the MSW application. The concentration of total soil heavy metals, Zn, Pb, Cd, Ni, Cr and Cu rose with the application of MSW as compared with the control plot, but these increases were only significant in total Zn, Pb and Cu. Zn and Cu amounts of DTPA-extractable soil were also significantly higher in the amended soil. Total plant cover increased significantly in the plots treated with low and intermediate MSW rates. Total biomass production increased as compost rates were added but this rise is not proportional to the amount of MSW added. The degraded soil used in this study may require MSW rates up to 80 Mg ha−1 to improve soil chemical properties as well as to produce minimal changes in the native vegetation.

An Accuracy Index with Positional and Thematic Fuzzy Bounds for Land-use/Land-cover Maps

This paper proposes a comprehensive framework for the accuracy assessment of taxonomically diverse LULC maps. A widely accepted difficulty in assessing such maps is associated with the vagueness in the interpretation of complex landscapes. For every class of the map, this method quantified the thematic and positional fuzziness of accuracy, induced by this difficulty. The labeling protocol consisted of a fuzzy comparison between the map and a reference maplet, for which degrees of positional and thematic tolerance can be user-defined. The construction of reference maplets permitted a flexible analysis (comparable with the assessment of other maps) of the positional fuzziness of the reference dataset and of the vagueness of the assessment process, while the alternate evaluation protocol, based on traditional point like data collection, did not allow such analysis.

Local deforestation patterns in Mexico - An approach using geographiccally weighted regression

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Identifying Local Deforestation Patterns Using Geographically Weighted Regression Models

This study aimed at identifying drivers and patterns of deforestation in Mexico by applying Geographically Weighted Regression (GWR) models to cartographic and statistical data. We constucted a nation-wide multidate GIS database incorporating digital data about deforestation from the Global Forest Change database (2000–2013); along with ancillary data (topography, road network, settlements and population disribution, socio-economical indices and government policies). We computed the rate of deforestation during the period 2008–2011 at the municipal level. Local linear models were fitted using the rate of deforestation as dependent variable. In comparison with the global model, the use of GWR increased the goodness-of-fit (adjusted R2) from 0.20 (global model) to 0.63. The mapping of GWR models’ parameters and its significance, anables us to highlight the spatial variation of the relationship between the rate of deforestation and its drivers. Factors identified as having a major impact on deforestation were related to topography, accessibility, cattle ranching and marginalization. Results indicate that the effect of these drivers varies over space, and that the same driver can even exhibit opposite effects depending on the region.