The application of sludge from wastewater in agriculture has increased in recent years, and it is therefore important to assess the effect that such treatment has on both the soil and the plant. The aim of the study described here was to ascertain whether there is a variation in the properties of the soil and to determine if this addition has an impact on the plant.
Materials and methods
The area of investigation was close to the municipality of Villarrubia de los Ojos (Ciudad Real). In this work, six samples were taken from the surface horizon in the studied plot at a depth of 35 cm. A further three samples were taken: (i) a surface horizon of a soil close to the area under investigation but without treatment (control sample), (ii) a sample of sludge from the wastewater treatment plant and (iii) a sample of the mixture used by farmers as fertilizer. Laboratory tests were conducted in accordance with the SCS-USDA (1972) guidelines. Trace element samples were analysed by X-ray fluorescence spectrophotometry (Philips PW 2404).
Results and discussion
The parcel of land studied is dominated by a sandy texture (88.3 % sand), and a decrease in pH was observed in areas in which the mixture (manure + sludge) was added (pH?=?8.0) compared to areas in which fertilizer was not applied (pH?=?8.5). It was observed that the addition of the compound led to an increase in the electrical conductivity of the soil. The trace elements can be organized into two groups based on the results obtained in this study. One group contains the trace elements that were only present in the rows that were treated with the fertilizer. The other group of trace elements was mobilized throughout the whole plot.
Conclusions
The application of sewage sludge on agricultural soils can be very useful as an organic amendment because it produces an increase in soil organic matter. However, sewage sludge must be applied with caution due to the changes in soil chemical properties (for example, pH and E.C.). The use of this type of waste for prolonged periods of time can cause problems of contamination in the soil.
Vines (Vitis vinifera, L.) are a very important agricultural resource for Spain in general and for the Castilla-La Mancha region in particular, providing important productions of wines. Grapes and raisins are used for direct consumption too. In this work, we study analytical constraints regarding metallic trace elements uptake, focusing on Hg, from vines growing in the Almadén mercury mining district, the world's largest producer of this element, inactive nowadays.
Materials and methods
The study started with the analysis of these metals in soils and sets of vines leaves from seven sites located at different distances from the Almadén Hg mine. The samples of soils were dried at ambient temperature for 1 week. They were then sifted (<2 mm) and were stored for subsequent analysis. The leaves were dried and the leaf blade and petiole were separated. About 2 g of each sample were hand milled and analyzed using the same fluorescence spectrometer. Total mercury in soils and vine leaves were determined using a Lumex RA-915+ device, an atomic absorption spectrometer with a pyrolysis unit (RP-91c).
Results and discussion
Results show significant correlations between soil and leaves contents for total and organic mercury (R?=?0.934 and 0.984, respectively). Hg contents range in soil from 2,376 to 0.04 mg/kg in non-polluted places. For the organic fraction, the range varies between 197.49 and 3.15 mg/kg. Total Hg contents measured in leaves were from 5.14 mg/kg (close to dump zone of the mine) to 0.03 mg/kg in the proximity of Carrión de Calatrava, located some 100 km away from Almadén. Mercury reaches maximum in the proximity of known sources of the element: the mining and/or metallurgical areas of Almadén and Almadenejos.
Conclusions
Soils from the study area contain normal contents in trace metals, and these are conditioned by the local geology or urban locations of the area. Trace metals contents in leaves do not show a relationship with soil contents, possibly due to the low bioavailability of these elements in the soils investigated. Mercury is, as expected for this area, an exception to this trend, with very high concentrations that reach maximum values in the proximity of the known sources of the element: the proximity of mining and/or metallurgical areas in Almadén and Almadenejos. 相似文献
The Almadén mining district has suffered long-term extraction activity, and this has left significant areas of decommissioned mining liabilities. Nowadays, the uncontrolled runoff and related erosion and transport of trace metal-enriched soils and sediments affect the whole freshwater ecosystem. The goal of this study was to distinguish geogenic from mining-related sources of trace metals in freshwater sediments, to understand their dispersion in the watershed, and, finally, to evaluate the potential environmental implications for future corrective plans.
Materials and methods
Freshwater surface sediment samples were collected from ten points along the main streams of the watershed (nine inside the mining district and one control point outside the district). Sediments were air dried and analyzed by different standard methods for pH, total major and trace element concentrations, total organic carbon, and grain size. In addition to the determination of the enrichment factor, a multi-statistical approach was applied involving discriminant analysis, Student’s t test, and Mann-Whitney U analysis.
Results and discussion
Sediments inside the district contained high levels of major and trace elements with respect to the control point. The predominance of fine fractions in these sediment samples appears to be one of the most important factors that affects trace metal concentrations. Among the trace elements, not only Hg but also As, Pb, and Zn are discriminative geochemical markers, thus allowing the identification of the different mining sources and their individual or combined impact throughout the district. Furthermore, the high enrichment factors obtained for As, Hg, Pb, and Zn with respect to the local background values highlight the persistent and severe impact from the decommissioned mines on the freshwater surficial sediments and their potential geoavailable risk for aquatic organisms.
Conclusions
The geochemistry of freshwater sediments alone demonstrates that different contamination sources are recognizable within the mining district and these can be related to the specific decommissioned mines. In addition, the discrete sources can be clearly distinguished on the basis of the statistical analysis of the geochemical data. Despite the closure of the mines, stream sediments are still the main repository of trace metals within the district, and they are therefore a potential threat to the freshwater ecosystem.
We investigated the effect that ashes may have on the soil microbial activity. Our hypothesis is that different wood ashes and different proportions of them could have beneficial or detrimental effects depending on the applied dose.
Materials and methods
Dehydrogenase activity and soil oxygen consumption were used to evaluate the potential improvement of soil conditions through the application of two different wood ashes coming from industrial waste. Different ash proportions and time dependence have been used to make comparisons. The respiration curves obtained through a closed-jar incubation experiment were well fitted by a sigmoidal function, the derivative of which yields the time evolution of the consumption rate.
Results and discussion
The results indicate that the dehydrogenase activity and soil oxygen consumption are very sensitive to the presence of ashes in the soil, and the reached values of both are linked to the applied dose of them. In our research, soil oxygen consumption is time and rate dependent of ash application. The curves show that parameter was affected by the ashes in different way, raising the respiration rate, and stretching the biological activity period.
Conclusions
Dehydrogenase activity and soil oxygen consumption are very sensitive to the presence of ashes and can be used to assess their potential use as amendments. The results of this paper can contribute to the required knowledge in order to use ashes in a sustainable way. Ashes coming from olive marc and vine shoots may affect positively the soil respiration and, therefore, the soil fertility, if they are applied in moderate amounts.
