Ana Moliner

Soluble organic carbon and pH of organic amendments affect metal mobility and chemical speciation in mine soils

We evaluated the effects of pH and soluble organic carbon affected by organic amendments on metal mobility to find out the optimal conditions for their application in the stabilization of metals in mine soils. Soil samples (pH 5.5-6.2) were mixed with 0, 30 and 60 th a(-1) of sheep-horse manure (pH 9.4) and pine bark compost (pH 5.7). A single-step extraction procedure was performed using 0.005 M CaCl2 adjusted to pH 4.0-7.0 and metal speciation in soil solution was simulated using NICA-Donnan model. Sheep-horse manure reduced exchangeable metal concentrations (up to 71% Cu, 75% Zn) due to its high pH and degree of maturity, whereas pine bark increased them (32% Cu, 33% Zn). However, at increasing dose and hence pH, sheep-horse manure increased soluble Cu because of higher soluble organic carbon, whereas soluble Cu and organic carbon increased at increasing dose and correspondingly decreasing pH in pine bark and non-amended treatments. Near the native pH of these soils (at pH 5.8-6.3), with small doses of amendments, there was minimum soluble Cu and organic carbon. Pine bark also increased Zn solubility, whereas sheep-horse manure reduced it as soluble Zn always decreased with increasing pH. Sheep-horse manure also reduced the proportion of free metals in soil solution (from 41% to 4% Cu, from 97% to 94% Zn), which are considered to be more bioavailable than organic species. Sheep-horse manure amendment could be efficiently used for the stabilization of metals with low risk of leaching to groundwater at low doses and at relatively low pH, such as the native pH of mine soils.

Chemical speciation and mobilization of copper and zinc in naturally contaminated mine soils with citric and tartaric acids.

A one-step extraction procedure and a leaching column experiment were performed to assess the effects of citric and tartaric acids on Cu and Zn mobilization in naturally contaminated mine soils to facilitate assisted phytoextraction. A speciation modeling of the soil solution and the metal fractionation of soils were performed to elucidate the chemical processes that affected metal desorption by organic acids. Different extracting solutions were prepared, all of which contained 0.01 M KNO(3) and different concentrations of organic acids: control without organic acids, 0.5 mM citric, 0.5 mM tartaric, 10 mM citric, 10 mM tartaric, and 5 mM citric +5 mM tartaric. The results of the extraction procedure showed that higher concentrations of organic acids increased metal desorption, and citric acid was more effective at facilitating metal desorption than tartaric acid. Metal desorption was mainly influenced by the decreasing pH and the dissolution of Fe and Mn oxides, not by the formation of soluble metal-organic complexes as was predicted by the speciation modeling. The results of the column study reported that low concentrations of organic acids did not significantly increase metal mobilization and that higher doses were also not able to mobilize Zn. However, 5-10 mM citric acid significantly promoted Cu mobilization (from 1 mg kg(-1) in the control to 42 mg kg(-1) with 10 mM citric acid) and reduced the exchangeable (from 21 to 3 mg kg(-1)) and the Fe and Mn oxides (from 443 to 277 mg kg(-1)) fractions. Citric acid could efficiently facilitate assisted phytoextraction techniques.

Dynamics of pruning waste and spent horse litter co-composting as determined by chemical parameters

Co-composting of pruning waste and horse manure was monitored by different parameters. A windrow composting pile, having the dimensions 2.5m (height) x 30m (length) was established. The maturation of pruning waste and horse manure compost was accompanied by a decline in NH(4)(+)-N concentration, water soluble C and an increase in NO(3)(-)-N content. Organic matter (OM) content during composting followed a first-order kinetic equation. This result was in agreement with the microbiological activity measured by the CO(2) respiration during the process. The correlation at a high level of probability found between the OM loss and CO(2) evolution showed that both parameters could be used to indicate the degree of OM degradation that is the maturity and stability phases of the compost studied. Humification parameters data from the organic matter fractionation did not show a clear tendency during the composting time, suggesting that these parameters are not suitable for evaluating the dynamics of the process.

Carbon Mineralization of Pruning Wastes Compost At Different Stages of Composting

To study the carbon mineralization of pruning waste compost, four samples originated from pruning waste, leaves and grass clippings were collected each from a different pilot pile at different stage of the composting process: initial nondecomposed material (C1); two-months old at the end of the biooxidative stage (C2); seven months old during the curing phase (C3) and 12 months old at the end of the curing phase (C4). The CO2-C evolution was measured during 56 days of aerobic incubation. The proportion mineralized from the different composts (% of compost TOC) during the incubation period were: 4.54, 2.43, 1.71 and 1.60 for C1, C2, C3 y C4, respectively. Regardless of compost age, C mineralization occurred in two phases: a first rapid phase (corresponding to the decomposition of the most labile products by microorganisms) and a second, slower phase, during which the most resistant organic products mineralized. During the first stage, the model was fitted to a first-order equation, whereas in the second phase the model was a zero-order equation. Because of the similar results obtained for samples C3 and C4, we can conclude that organic matter had similar microbial stability at both stages and the composting process could be shortened by five months.

Comparison of a gas detection tubes test with the traditional alkaline trap method to evaluate compost stability

Compost stability is an important parameter of compost quality. Among tests proposed to evaluate compost stability, microbial respiration is one of the better accepted tests. Variations in rates of CO2 evolution during composting were studied in two pilot pruning waste piles using a windrow composting system. To measure the CO2 production rate, two methods were compared: the alkaline trap test and gas detection tubes. Both respiration tests indicated increasing compost stability with processing time, but CO2 evolution rates from the alkaline trap method were higher than values from the gas detection tube method. A first-order kinetic equation was used to describe CO2 evolution over time. A linear relationship (r=0.81, p<0.01) was found between the two methods. Although both methods could distinguish unstable compost from stable compost, CO2 detection tubes were easier to use and gave results in a shorter period of time.

Analysis of land-use/land-cover changes in a livestock landscape dominated by traditional silvopastoral systems: a methodological approach

ABSTRACT Remote sensing, which is a common method to examine land-use/land-cover (LULC) changes, could be useful in the analysis of livestock ecosystem transformations. In the last two decades, before Landsat images were free, developing countries could not afford monitoring through remote sensing because of the high cost of acquiring satellite imagery and commercial software. However, Landsat time series nowadays allows the characterization of changes in vegetation across large areas over time. The aim of this study is to analyse the LULC changes affecting forest frontiers and traditional silvopastoral systems (TSPS) in a representative livestock area of Nicaragua. Nearly cloud-free Landsat scenes – a Landsat 5 Thematic Mapper (TM) scene from 1986 and a Landsat 8 Operational Land Imager (OLI) scene from 2015 – have been the data sets used in the study. A process chain following a four-step definition of the remote-sensing process was conceptually developed and implemented based onfree open source software components and by applying the random forest (RF) algorithm. A conceptual LULC classification scheme representing TSPS was developed. Although the imagery shows a heterogeneous surface cover and mixed pixels, it is possible to achieve promising classification results with the RF algorithm with out-of-the-bag (OOB) errors below 13% for both images along with an overall accuracy level of 85.9% for the 2015 subset and 85.2% for the 1986 subset. The classification shows that from 1986 to 2015 (29 years) the intervened secondary forest (ISF) increased 2.6 times, whereas the degraded pastures decreased by 34.5%. The livestock landscape in Matiguás is in a state of constant transformation, but the main changes head towards the positive direction of tree-cover recovery and an increased number of areas of natural regeneration.

Phytoremediation of Degraded Mine Soils Using Organic Amendments and Metal-Tolerant Plants

Mine soils usually contain high levels of metal contamination and poor fertility conditions which limit their restoration and the establishment of vegetation. In this work, we reported our previous results of the use of organic amendments (horse and sheep manure compost and pine bark compost) and metal-tolerant plants (Atriplex halimus, Brassica juncea, and Thlaspi arvense) for the phytoremediation of mine soils. Greenhouse and laboratory experiments were performed with soil samples collected from two abandoned mine sites of Central Spain mixed with 0, 30, and 60 t ha−1 of the organic amendments to evaluate the growth, tolerance, metal accumulation, and translocation of these plants in relation to metal bioavailability and soil conditions affected by the organic amendments. Our results showed that manure reduced metal availability and improved soil fertility due to its high pH, organic matter nature, and nutrient contents, stabilizing metals in soil and allowing a higher plant growth and even a greater amount of metals removed from soils and accumulated in plant tissues, which enhance the phytoremediation capacity of these plants. A. halimus and B. juncea achieved high biomass production and metal accumulation without being severely affected by metal toxicity, but their capacity was insufficient for the phytoextraction of metals in the short to medium term in these soils. However, the use of both species could be a useful and cost-effective practice for the phytostabilization of mine soils in combination with manure amendments.