Clean and accurate soil quality monitoring in mining areas under environmental rehabilitation in the Eastern Brazilian Amazon

Soil quality monitoring in mining rehabilitation areas is a crucial step to validate the effectiveness of the adopted recovery strategy, especially in critical areas for environmental conservation, such as the Brazilian Amazon. The use of portable X-ray fluorescence (pXRF) spectrometry allows a rapid quantification of several soil chemical elements, with low cost and without residue generation, being an alternative for clean and accurate environmental monitoring. Thus, this work aimed to assess soil quality in mining areas with different stages of environmental rehabilitation based on predictions of soil fertility properties through pXRF along with four machine learning algorithms (projection pursuit regression, PPR; support vector machine, SVM; cubist regression, CR; and random forest, RF) in the Eastern Brazilian Amazon. Sandstone and iron mines in different chronological stages of rehabilitation (initial, intermediate, and advanced) were evaluated, in addition to non-rehabilitated and native forest areas. A total of 81 soil samples (26 from sandstone mine and 55 from iron mine) were analyzed by both traditional wet-chemistry methods and pXRF. The available/exchangeable contents of K, Ca, B, Fe, and Al, in addition to H+Al, cation exchange capacity at pH = 7, Al saturation, soil organic matter, pH, sum of bases, base saturation, clay, and sand were accurately predicted (R2 > 0.70) using pXRF data, with emphasis on the prediction of Fe (R2 = 0.93), clay content (R2 = 0.81), H+Al (R2 = 0.81), and K+ (R2 = 0.85). The best predictive models were developed by RF and CR (86%) and when considering pXRF data + mining area + stage of rehabilitation (73%). The results highlight the potential of pXRF to accurately assess soil properties in environmental rehabilitation areas in the Amazon region (yet scarcely evaluated under this approach), promoting a more agile and cheaper preliminary diagnosis compared to traditional methods.

Mine land rehabilitation in Brazil: Goals and techniques in the context of legal requirements

Environmental legislation in many countries demands the rehabilitation of degraded areas to minimize environmental impacts. Brazilian laws require the restitution of self-sustaining ecosystems to historical conditions but ignore the emergence of novel ecosystems due to large-scale changes, such as species invasions, extinctions, and land-use or climate changes, although these novel ecosystems might fulfill ecosystem services in similar ways as historic ecosystems. Thorough discussions of rehabilitation goals, target ecosystems, applied methods, and approaches to achieving mine land rehabilitation, as well as dialogues about the advantages and risks of chemical inputs or non-native, non-invasive species that include all political, economic, social, and academic stakeholders are necessary to achieve biological feasibility, sociocultural acceptance, economic viability, and institutional tractability during environmental rehabilitation. Scientific knowledge of natural and rehabilitating ecosystems is indispensable for advancing these discussions and achieving more sustainable mining. Both mining companies and public institutions are responsible for obtaining this knowledge.

MORFOLOGIA, PROCESSOS DE SEDIMENTAÇÃO E LITOFÁCIES DOS AMBIENTES MORFO-SEDIMENTARES DA PLANÍCIE COSTEIRA BRAGANTINA, NORDESTE DO PARÁ, BRASIL

The Bragança Coastal Plain is located in the Northeastern of Pará, in the Bragança-Viseu CoaxialBasin (Cretaceous), with an approximate surface area of 1,570 Km2. The geometry of the basin and itspaleotopography, associated with recent tectonic movements have controlled the distribution and thethickness of the tertiary and quaternary deposits. This coastal plain constitutes a macrotidal (6 m) depositionalsystem, developed in a hot and humid equatorial climate, with a dry and wet well defined seasons and anannual precipitation averaging 3,000 mm.The geomorphology of the area is subdivided into three main morphologic realms: (1) alluvial plain,with fluvial channel, levees and flood plain; (2) estuarine plain, with an estuarine channel subdivided intoestuarine funnel segment, straight segment, meandering segment and upstream channel, tidal creek and,floodplain and; (3) coastal plain, with salt marsh (inner and outer), tidal plain (supratidal mangroves,intertidal mangroves and sand flats with tidal shoals), chenier, coastal dunes and beach environments.The recent morpho-sedimentary units are separated from highland by a line of inactive cliffs that issituated 25 km from the coastline. This cliffs mark the higher Holocene sea level, very well knowed inbrazilian east coast as Holocenic Transgression (5,100 years B.P.). During this event was deposited a basaltransgressive sequence (S1), constituted by estuarine sand and mud and marine sand. Afterwards, underregressive or stillstand sea level the mangrove deposits prograde over the transgressive sand sheet buildinga prograding sequence (S2). Nowadays, this sequence are being overlain by a recent transgressive sequence(S3).The sedimentary model, based on lithostratigraphy and sedimentary processes, proposed to BragançaCoastal Plain show a complex coastal depositional system, constituted by different sedimentaryenvironments with singular sedimentary, stratigraphic and morphologic characteristics in relation to itsgeometry and spacial distribution of the environments.The morpho-sedimentary unit show that the environments studied from the alluvial plain to coastalplain represent a dynamic area dominated by macrotides and influenced by waves along the shoreline.Therefore, the depositional model proposed is composed by a coastal plain depositional system withfluvial-estuarine-tidal flat environments with dune-beach ridge associated.