Gerardo Ojeda

• PhD
• Research Associate at Universidad Nacional Abierta y a Distancia

The CO2 emission rates have been continuously incremented during the last decades. To mitigate it, a method to store carbon in terrestrial ecosystems is the addition of biochar to soil. After its application to soil, biochar suffers an ageing process, able to deteriorate its functional properties as soil improver. However, at present, it is not cle...

Industrial metal-rich sludge can improve soil properties, but it is potentially toxic to soils and adjacent aquatic systems. The soil-sludge-water interactions influence metals bioavailability over time, a phenomenon mostly regulated by the still debatable "sludge physical protection" or "sludge delayed release" hypotheses. The present study aimed...

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...

The impact of conversion process parameters in pyrolysis (maximum temperature, inert gas flow rate) and hydrothermal carbonization (maximum temperature, residence time and post-washing) on biochar and hydrochar properties is investigated. Pine wood (PW) and corn digestate (CD), with low and high inorganic species content respectively, are used as f...

Increasing temperatures and changes in the intensity and frequency of precipitations may impact the ability of tropical high-elevation Andean ecosystems (Paramos) to store and retain carbon (C). We, therefore, examined how warming and fluctuations in soil moisture could influence soil CO2 emissions from heterotrophic respiration (RH, the result of...

Purpose Biochar is a carbon-rich product, able to enhance soil fertility and mitigate CO2 emissions. While biochar effects on agriculture are becoming known, its impact elsewhere, e.g., on estuarine ecosystems, has yet to be assessed. The main aim of the present study was to determine the effect of biochar on sediment–water retention, CO2 emissions...

To reclaim a limestone quarry, 200 and 400 Mg/ha of municipal sewage sludge were mixed with an infertile calcareous substrate and spread as mine soil in 1992. Soil samples were taken 1 week later and again after 17 yr of mine soil rehabilitation so as to assess changes in the amount and persistence of soil organic carbon (SOC). Sludge application i...

Today biochar is considered a stable-carbon source that is able to improve soil quality. However, although biochar effects on some soil properties are already becoming well known, its impact on complex soil hydrological functions has yet to be better assessed. The main objectives are: (a) to determine the impact of different biochar amendments on i...

Transforming a shrubland into a dehesa system may be useful for recovering certain productive and regulatory functions of ecosystems such as grazing potential, soil erosion control, and also for reducing the risk of wildfire. However, the productivity of the herbaceous cover and tree development in the transformed system may be limited by soil fert...

The main aim of this study is to analyze the influence of 4-nonylphenol (NP) on soil water retention and biological activity. Two doses of 4-nonylphenol (25 and 50 mg kg−1) were tested in a loam soil with and without peat amendment. In general, one week after the start of the experiment, the soil water content retained at −0.75 MPa of soil suction...

Sewage sludge application to soils is regulated by its total metal content. However, the real risk of metals is determined by the fraction that is biologically available. The available fraction is highly related to the strength of metal binding by the matrix, which is a dynamic process. The evaluation of the fate of metals in time can contribute in...

Biochar is an organic material produced via the pyrolysis of C-based biomass, which is increasingly being recognized by scientists and policy makers for its potential role in carbon sequestration, reducing greenhouse gas emissions, waste mitigation, and as a soil amendment. Recent studies indicated that biochar improves soil fertility through its p...

This study aimed to evaluate short-term earthworm-induced changes in the availability of metals applied to soil directly (metal-spiked) or via an organic matrix (sludge-amended). A laboratory experiment was performed using destructive sampling of microcosms filled with agricultural soil. A concentration gradient of industrial sludge contaminated pr...

The main objective of this study was to analyse how different sewage sludges influence soil wetting and drying dynamics. Three composted and three thermally-dried municipal sludges from different wastewater plants located in Catalonia (NE Spain) were mixed with a mine-soil obtained from a limestone quarry. Measurements of the time required to reach...

We have evaluated the effects of improving substrate fertility on the growth and reproduction of a P. halepensis plantation in a restored limestone quarry on a stony calcareous regolith (R plots). The natural substrate was supplemented by adding a 0.2 m layer of a fine textured soil (RS plots) or a sewage sludge amended soil (RSS plots). The treatm...

The recycling of suitable organic wastes can enhance soil fertility via effects on soil physical, chemical and biological properties. To compare the effects of digested (DS), thermally dried (TDS) and composted dewatered (CDS) sewage sludge on soil microbiological properties, an experiment was conducted at field sites for more than one year (401 d)...

Composting or thermally-drying sludges are becoming commonly used in soil rehabilitation of degraded land. Sludge amendments increase soil organic matter, but can reduce soil wettability due to hydrophobic compounds. The main objective of this study is to analyse how composted and thermally dried sludges influence soil wettability and water retenti...

Three types of sewage sludge from the same wastewater treatment plant but processed in different ways (composted, fresh and thermally dried) were applied in doses equivalent to approximately 10 Mg of dry matter per hectare to the surface of a loamy soil in order to improve its physical condition. The effect of this organic amendment on the structur...

Anaerobically-digested sludge called fresh sludge (F), composted sludge (C) and thermally-drying sludge (T), all from the same batch, were applied to the surface of a calcareous Udic Calciustept with loamy texture. Dosage equivalent was 10 t ha(-1) of dry matter. The concentration of mineral nitrogen (ammonium and nitrate) in the soil was measured...

Sludge from the same waste-water treatment plant, processed in different ways, was applied superficially to plots of a soil developed on marls (Udic calciustept) at doses equivalent to 10 t ha−1 of dry matter. The concentration of mineral nitrogen (ammonium, nitrate) in runoff waters was measured to assess the effects of composting and thermally dr...

The impact of three types of surface applied sewage sludge from the same lot (fresh, composted, and thermally dried) on the water retention properties of a loam soil (Udic Calciustept) and a loamy sand soil (Typic Haplustalf) from central Catalonia (NE Spain) was investigated using fractal analysis. First, we proposed a composite fractal model that...

In order to promote the transformation of a burnt Mediterranean forest area into a dehesa system, 10 t ha−1 of dry matter of the same sewage sludge in three different forms: fresh, composted and thermally-dried, were added superficially to field plots of loam and sandy soils located on a 16 per cent slope. This application is equivalent to 13ċ8 t h...

Three types of sewage sludge were applied to a calcareous loam soil and a neutral pH, sandy surface texture soil. All sludge came from the same batch, secondary treatment by anaerobic digestion (fresh sludge, 20% dry matter) and were subjected to composting with pinewood splinters (composted sludge, 66,5% dry matter) or were thermally dried (therma...

We report soil water desorption modifications during air drying in a soil amended with six different sewage sludges (composted or thermally dried). The time required to change water retention from wilting point (-1.5MPa) to dryness (ψ = -25 MPa) was increased by composted sludges but not by thermally dried sludges, although both sludges were able t...