Rodrigo Studart Corrêa

Unprecedented carbon accumulation in mined soils: the synergistic effect of resource input and plant species invasion

Opencast mining causes severe impacts on natural environments, often resulting in permanent damage to soils and vegetation. In the present study we use a 14-year restoration chronosequence to investigate how resource input and spontaneous plant colonization promote the revegetation and reconstruction of mined soils in central Brazil. Using a multi-proxy approach, combining vegetation surveys with the analysis of plant and soil isotopic abundances (delta13C and delta15N) and chemical and physical fractionation of organic matter in soil profiles, we show that: (1) after several decades without vegetation cover, the input of nutrient-rich biosolids into exposed regoliths prompted the establishment of a diverse plant community (> 30 species); (2) the synergistic effect of resource input and plant colonization yielded unprecedented increases in soil carbon, accumulating as chemically stable compounds in occluded physical fractions and reaching much higher levels than observed in undisturbed ecosystems; and (3) invasive grasses progressively excluded native species, limiting nutrient availability, but contributing more than 65% of the total accumulated soil organic carbon. These results show that soil-plant feedbacks regulate the amount of available resources, determining successional trajectories and alternative stable equilibria in degraded areas undergoing restoration. External inputs promote plant colonization, soil formation, and carbon sequestration, at the cost of excluding native species. The introduction of native woody species would suppress invasive grasses and increase nutrient availability, bringing the system closer to its original state. However, it is difficult to predict whether soil carbon levels could be maintained without the exotic grass cover. We discuss theoretical and practical implications of these findings, describing how the combination of resource manipulation and management of invasive species could be used to optimize restoration strategies, counteracting soil degradation while maintaining species diversity.

Risk of nitrate leaching from two soils amended with biosolids

High concentrations of N and P in biosolids are one of the strongest appeals for their agronomic use. However, it is essential to understand the fate of N in soils treated with biosolids for both plant nutrition and managing the environmental risk of NO3−-N leaching. This work aims to evaluate the risk of nitrate leaching from a sandy Podosol soil and from a clay Ferrosol soil, each one amended at the range 0.5–8.0 dry Mg/ha rates of freshly tertiary sewage sludge, composted sludge, limed sludge, heating-dried sludge and solar-irradiated sludge. Results showed that for similar biosolids application rates NO3−-N accumulated up to 3 times as much in the Ferrosol than in Podosol soil. However, there was a fixed 20% NO3−-N loss from the 20 cm amended-Ferrosol topsoil, whilst the N-nitrified expected to leach down from 20 cm amended-Podosol topsoil layer ranged from 42% to 76% of the accumulated NO3−-N, depending on the biosolid type. After all, NO3−-N expected to leach from Podosol soil ranged from 0.6 (heating-dried sludge) to 3.9 times (limed sludge) relative to Ferrosol soil at similar biosolid application rates. Nevertheless, the risk of NO3−-N groundwater contamination caused by biosolids applied at 0.5−8.0 dry Mg/ha rates could be considered very low.

Sobrevivência e crescimento de seis espécies arbóreas submetidas a quatro tratamentos em área minerada no cerrado

Among many human activities developed in areas of Brazilian savanna, mining is one that causes significative damage to the environment. Natural sucession on such sites is extremely slow and therefore revegetation works are necessary. This work aims to evaluate survival and growth of six tree species under four treatments grown on an exploited gravel mine in the Brazilian Federal District. The four treatments were drawn from the combination of mulching around tree seedlings and the establishment of Stylosanthes spp on the area surface. A control was established on a nearby unexploited for comparison reason. Results show a higher survival rate and growth of tree seedlings established on the exploited site than on the control-site which kept intact soil. There were no significant differences for survival and growth among trees established on the gravel mine under the four treatments - combined mulching and/or herbaceous layer on gravel mine surface.Among many human activities developed in areas of Brazilian savanna, mining is one that causes significative damage to the environment. Natural sucession on such sites is extremely slow and therefore revegetation works are necessary. This work aims to evaluate survival and growth of six tree species under four treatments grown on an exploited gravel mine in the Brazilian Federal District. The four treatments were drawn from the combination of mulching around tree seedlings and the establishment of Stylosanthes spp on the area surface. A control was established on a nearby unexploited for comparison reason. Results show a higher survival rate and growth of tree seedlings established on the exploited site than on the controlsite which kept intact soil. There were no significant differences for survival and growth among trees established on the gravel mine under the four treatments combined mulching and/or herbaceous layer on gravel mine surface.

Biosolids effectiveness to yield ryegrass based on their nitrogen content

Biosolids have been reported to increase yields and supply plant nutrients. However, complying with health and environmental standards is necessary before applying biosolids to land. Thus, sludge stabilization is required to make biosolids safe enough for their agricultural use. Side effects of stabilization processes on agronomic features of sewage sludge are not quite known, although their understanding is essential for biosolids management. Based on a model equivalent to the Mitscherlich equation, effects of the most common processes for sludge stabilization were evaluated (composting, liming, heat-drying and solar irradiation) in relation to the agronomic effectiveness of biosolids to yield Lolium perenne L. on two tropical soils, with NH4H2PO4 as a reference. Sewage stabilization processes have affected the ability of biosolids to promote plant growth. Their effectiveness was usually higher than fertilizer in a Spodosol and lower in an Oxisol. Solar-irradiated sludge presented the highest effectiveness among the biosolids and reached peak yields at the lowest application rate independent on soil type. Biosolids could efficiently substitute fertilizers and even yield more plant dry matter than the NH4H2PO4 reference, depending on the biosolid and soil type.

Soil Carbon Sequestration Resulting from Biosolids Application

Carbon (C) sequestration in soils through the increase of the soil organic carbon (SOC) pool has generated broad interest to mitigate the effects of climate change. Biosolids soil application may represent a persistent increase in the SOC pool. While a vast literature is available on the value of biosolids as a soil conditioner or nutrient source in agricultural systems, there is still limited knowledge on soil sequestration mechanisms of biosolids-borne C or the main factors influencing this capacity. The emerging challenges posed by global environmental changes and the stringent needs to enhance C storage call for more research on the potential of soil biosolids incorporation as a sustainable C storage practice. This review addresses the potential of C sequestration of agricultural soils and opencast mines amended with biosolids and its biological regulation.

Downward Movement of Potentially Toxic Elements in Biosolids Amended Soils

Potentially toxic elements (PTEs) in soils are mainly associated with the solid phase, bound to the surface of solid components, or precipitated as minerals. For most PTEs, only a small portion is dissolved in the soil solution. However, there is an interest in following the fate of mobile PTEs in the environment, for a growing amount of evidence indicates that downward movement of PTEs may occur in biosolids amended soils, leading to groundwater contamination. Therefore, it is crucial to understand the factors that control the release of these elements after land application of biosolids, in order to overcome problems related to downward movement of PTEs in the soil profile.

Chemical fertility of a substrate treated with sewage sludge and domestic residue compost.

O aproveitamento de residuos urbanos como fontes de materia orgânica e nutrientes contribui para diminuir a pressao das sociedades modernas sobre o meio ambiente. Por outro lado, a incorporacao de materia orgânica e um meio de se criarem condicoes edaficas para o estabelecimento de plantas em solos degradados e substratos expostos. Este trabalho visou avaliar a fertilidade e a cobertura vegetal (Paspalum notatum var. saurae Parodi) de um substrato exposto a superficie, tratado com doses crescentes (0 - 76 Mg ha-1, base seca) de lodo de esgoto ou composto de residuos domesticos. Os resultados indicam que o lodo de esgoto foi capaz de aumentar a CTC e as concentracoes de N, P e Zn no substrato enquanto nao houve incrementos significativos desses nutrientes no substrato tratado com o composto de residuos domesticos. A cobertura vegetal do substrato variou de 68 a 96% nos tratamentos com lodo (resposta assintotica) e entre 22 e 67% nos tratamentos com composto (resposta linear), de acordo com a dose aplicada. Valores de CTC e concentracoes de N, P e Zn explicaram 94% da variacao da cobertura vegetal sobre a superficie da area.

Biosolid Application to Agricultural Land—a Contribution to Global Phosphorus Recycle: A Review

Abstract Phosphorus (P) is an essential nutrient required for plant development. Continuous population growth and rising global demand for food are expected to increase the demand for phosphate fertilizers. However, high–quality phosphate rock reserves are progressively becoming scarce. Part of the increased pressure on P resources could be alleviated by recycling P present in biosolids. Therefore, it is crucial to understand the dynamics of P in biosolid–amended soils, the effects of residual biosolid–borne P in soils, the way in which microorganisms may control P dynamics in biosolid–amended soils and the environmental implications of the use of biosolids as a source of P. Further research is needed to maximize biosolid–borne P uptake by crops and minimize its loss from biosolid–amended soils. The analysis of the microbiological control of P dynamics in biosolid–amended soils indicates interactions of biosolid P with other nutrients such as carbon (C) and nitrogen (N), suggesting that harmonization of the current regulation on the use of biosolids in agriculture, mainly based on total N and pollutant contents, is needed to better recycle P in agriculture.

Levantamento florístico do estrato lenhoso das áreas mineradas no Distrito Federal

Approximately 0.6% of the Federal District in Brazil is degraded by mining. To indicate native woody species for revegetation works, a floristic survey was carried out in abandoned mined sites. Seventy- eight native and 14 exotic cerrado species were found on the sites. However, only eight species showed to be constant in such environment (frequency > 50%).Eighteen other species presented frequencies between 25 and 50% and the remaining 74% were considered accidental to mined areas left to primary succession (frequency 50%) plus the eighteen accessory-species (frequencies between 25 and 50%), which account for 78.9% of the woody- layer abundance, can be indicated for revegetation works of mined areas in the Brazilian cerrado.

Biosolids Soil Application: Why a New Special on an Old Issue?

1Department of Natural Resources and Environment, School of Agriculture, University of Buenos Aires, Avenue San Martin 4453, Buenos Aires 1417 DSE, Argentina 2Department of Ecology, University of Brasilia, Campus Darcy Ribeiro, Caixa Postal 04.401, 70910-970 Brasilia, DF, Brazil 3Department of Plant, Soil and Environmental Sciences, University of Florence, P. le delle Cascine 28, 50144 Florence, Italy 4 Foundation for Environmental Studies Centre of the Mediterranean (CEAM), C/Charles R. Darwin 14, Parque Tecnologico, 46980 Paterna, Spain 5Department of Biology and Medicine, Tula State University, Lenin Avenue 92, Tula 300012, Russia