Long-term effects of gasification biochar application on soil functions in a Mediterranean agroecosystem: Higher addition rates sequester more carbon but pose a risk to soil faunal communities.

Biochar applications can have important implications for many of the soil functions upon which agroecosystems rely, particularly regarding organic carbon storage. This study evaluated the impacts of adding a highly aromatic gasification biochar at different rates (0, 12 and 50 t ha-1) to a barley crop on the provision of crucial soil functions (carbon sequestration, water content, greenhouse gas emissions, nutrient cycling, soil food web functioning, and food production). After natural ageing in the field for six years, a wide range of soil properties representative of the studied soil functions were measured and integrated into a soil quality index. Results showed that C sequestration increased with biochar rate (23 and 68% higher than in the control for the 12 and 50 t biochar ha-1 treatments, respectively). Water content was enhanced at the 50 t ha-1 treatment depending on the sampling date. Despite biochar additions neither abating nor increasing CO2 equivalent emissions (carbon dioxide plus nitrous oxide and methane), the system shifted from being a methane sink (-0.017 ± 0.01 mg CH4-C m-2 h-1 at the 12 t ha-1 treatment), to a net source (0.025 ± 0.02 mg CH4-C m-2 h-1 at the 50 t ha-1 treatment). In addition, biochar ageing provoked a loss of nitrate mitigation potential, and indeed ammonium production was stimulated at the 50 t ha-1 rate. The 50 t ha-1 treatment also adversely affected nematode and collembolan functional diversity. Lastly, biochar did not affect barley yield. The results of the soil quality index indicated that no biochar treatment provided more benefits to our agricultural soil, and, although the 50 t ha-1 treatment increased C sequestration, this was potentially offset by its harmful effects on soil faunal communities. Therefore, application of this biochar at high rates should be avoided to prevent risks to soil biological communities.

Fresh biochar application provokes a reduction of nitrate which is unexplained by conventional mechanisms.

Soil-applied biochar has been reported to possess the potential to mitigate nitrate leaching and thus, exert beneficial effects beyond carbon sequestration. The main objective of the present study is to confirm if a pine gasification biochar that has proven able to decrease soil-soluble nitrate in previous research can indeed exert such an effect and to determine by which mechanism. For this purpose, lysimeters containing soil-biochar mixtures at 0, 12 and 50 t biochar ha-1 were investigated in two different scenarios: a fresh biochar scenario consisting of fresh biochar and a fallow-managed soil, and an aged biochar scenario with a 6-yr naturally aged biochar in a crop-managed soil. Soil columns were assessed under a mimicked Mediterranean ambient within a greenhouse setting during an 8-mo period which included a barley crop cycle. A set of parameters related to nitrogen cycling, and particularly to mechanisms that could directly or indirectly explain nitrate content reduction (i.e., sorption, leaching, microbially-mediated processes, volatilisation, plant uptake, and ecotoxicological effects), were assessed. Specific measurements included soil solution and leachate ionic composition, microbial biomass and activity, greenhouse gas (GHG) emissions, N and O isotopic composition of nitrate, crop yield and quality, and ecotoxicological endpoints, among others. Nitrate content reduction in soil solution was verified for the fresh biochar scenario in both 12 and 50 t ha-1 treatments and was coupled to a significant reduction of chloride, sodium, calcium and magnesium. This effect was noticed only after eight months of biochar application thus suggesting a time-dependent process. All other mechanisms tested being discarded, the formation of an organo-mineral coating emerges as a plausible explanation for the ionic content decrease.

Unmanned aerial system protocol for quarry restoration and mineral extraction monitoring.

Mining is an important activity of the primary sector with strong economic and environmental impacts. All over the world, governments have made efforts to regulate mine restoration by monitoring and assessing the evolution of mined sites. Our work aims to synthesize various remote sensing applications into a single workflow in order to obtain cartographic products using Unmanned Aerial Systems (UAS), not only for mine restoration management, but also as a way of monitoring mining activity as a whole. The workflow performs image processing and terrain analysis calculations, which conduct a supervised classification of the land cover. The resulting mapping products include orthoimagery, Digital Surface Models (DSM), land cover maps, volume variation calculations, dust deposition, detection of erosion problems, and drainage network evaluation maps. The data obtained from red-green-blue (RGB) sensors has a spatial resolution of 4-10 cm, providing information that allows the characterization of land covers with an overall accuracy of 91%. In comparison, if using multispectral sensors with the same flight conditions than RGB, image spatial resolution diminishes and land cover characterization accuracy drops to 81%. The resulting digital maps can be fully integrated into Geographic Information Systems (GIS), allowing the quantification of environmental features and spatial changes. Our study provides the basis for creating a large-scale, replicable and ready-to-use workflow suited for monitoring the exploitation of minerals and mine restoration using RGB imagery obtained through drones.

Heavy metal availability assessment using portable X-ray fluorescence and single extraction procedures on former vineyard polluted soils.

The periodic application of copper-based fungicides (Bourdeaux mixture) to vineyards of the Mediterranean region has generated an important pollution source that in some cases requires a quick intervention due to the high bioavailable copper content measured. Despite some vineyards were abandoned 40 years ago, noticeable amounts of Cu and other man-related metals are still nowadays detected in soils. In the present work, the development of a mobility test for the available heavy metal (Cu, Pb, Zn and As) content in soil has been performed using portable X-ray fluorescence (FP-XRF) combined with single leaching test, and was applied to a calcareous soil of a former vineyard area in Catalonia (NE Spain). The combined methodology has provided useful information for fast and detailed risk assessment, in terms of mobility and bioavailability of metals. The anthropogenic contribution was evaluated by means of the Concentration Enrichment Ratios (CER) in soil. The results reflect a clear anthropogenic contribution for Cu, a partial anthropogenic contribution for Pb proceeding from an external pollution source, and a non-significant external contribution for As and Zn. The topsoil concentration ranges for Cu (70-128 mg kg-1) were found to be above the background level and several samples above the regional governmental limits (Generic Reference Levels or GRL values) for soil ecosystem protection and for human health (90 mg kg-1). The present study reveals that the use of FP-XRF equipment constitute a highly valid option for quick decision making during the field location, characterization and quantitative elemental analysis of soil samples for screening of potential pollutants such as heavy metals.

Comparison of biochars derived from different types of feedstock and their potential for heavy metal removal in multiple-metal solutions.

Three different types of feedstocks and their biochars were used to remove Cr(III), Cd(II), Cu(II) and Pb(II) ions from a mixture of multiple heavy metals. The effect of the initial concentration of heavy metals in solution has been analysed, and kinetics modelling and a comparison of the adsorption capacity of such materials have been performed to elucidate the possible adsorption mechanisms. The results show that the adsorption capacity is dependent on the type of feedstock and on the pyrolysis conditions. The adsorption capacity of the biomass types is ranked as follows: FO (from sewage sludge)>> LO > ZO (both from agriculture biomass waste)>> CO (from wood biomass waste). Biochars, which are the product of the pyrolysis of feedstocks, clearly improve the adsorption efficiency in the case of those derived from wood and agricultural biomasses. Complexation and cation exchange have been found to be the two main adsorption mechanisms in systems containing multiple heavy metals, with cation exchange being the most significant. The pore structure of biomass/biochar cannot be neglected when investigating the adsorption mechanism of each material. All the disposal biomasses presented here are good alternatives for heavy metal removal from wastewaters.

Ecological risk assessment of organic waste amendments using the species sensitivity distribution from a soil organisms test battery.

Safe amendment rates (the predicted no-effect concentration or PNEC) of seven organic wastes were estimated from the species sensitivity distribution of a battery of soil biota tests and compared with different realistic amendment scenarios (different predicted environmental concentrations or PEC). None of the wastes was expected to exert noxious effects on soil biota if applied according either to the usual maximum amendment rates in Europe or phosphorus demands of crops (below 2 tonnes DM ha(-1)). However, some of the wastes might be problematic if applied according to nitrogen demands of crops (above 2 tonnes DM ha(-1)). Ammonium content and organic matter stability of the studied wastes are the most influential determinants of the maximum amendment rates derived in this study, but not pollutant burden. This finding indicates the need to stabilize wastes prior to their reuse in soils in order to avoid short-term impacts on soil communities.