Temporal and phenological profiles of open and dense Caatinga using remote sensing:response to precipitation and its irregularities

Caatinga is a typical biome of Brazil's semiarid regions and subject to climate changes.Research is needed on the relation of its features to climate events.This study analyzed the infl uence of rainfall and its irregularities in open and dense woody Caatinga vegetation.Phenological curves were generated by means of Normalized Difference Vegetation Index(NDVI)time profiles in the Grota do Angico Conservation Unit study area in Sergipe State.Rainfall data from 2000 to 2018 were collected and phenological curves generated using various estimate methods that produced the following variables:[start of season,end of season,peak of season position,length of season,mean growing season and maximum seasonal].Rainfall showed a standard intra-annual behavior,with inter-annual variations related to irregularities infl uencing Caatinga response.Dense Caatinga vegetation had higher values of NDVI in all periods,even in anomalous years compared to open Caatinga,in addition to having longer leaf coverage over the year,with an anticipated start and a more extended seasonal end.The analysis of the rainfall regime made it possible to assess its infl uence on the Caatinga and phenological profiles proved to be fundamental to understand periods of physiological change of open and dense Caatinga.These results indicate that dense Caatinga maintains physiological activity longer,which may be associated with greater moisture maintenance in a semiarid region.In addition,because it has a greater leaf cover for longer periods,the soil may be preserved and maintain its characteristics longer,reducing the effects of desertification.The results may be associated with the type of forest management and conservation in this region.The total or partial suppression of individual remnants of Caatinga should be avoided,since the most open areas have lower photosynthetic capacity,affected to a considerable extent from the effects of adverse climatic conditions.Additionally,open Caatinga has a reduced capacity for regenerating naturally and its use by communities in this semiarid region should be limited.

Estimation of aboveground biomass of arboreal species in the semi-arid region of Brazil using SAR(synthetic aperture radar)images

The Caatinga biome is an important ecosystem in the semi-arid region of Brazil.It has significantly degraded due to human activities and is currently a region undergoing desertification.Thus,monitoring the variation in the Caatinga biome has become essential for its sustainable development.However,traditional methods for estimating aboveground biomass(AGB)are time-consuming and destructive.Remote sensing,such as optical and radar imaging,can estimate and correlate with vegetation.Nevertheless,radar imaging is still a novelty to be applied in estimating the AGB of this biome,which is an area with little research.Therefore,this study aimed to use Sentinel-1 images to estimate the AGB of the Caatinga biome in Sergipe State(northeastern Brazil)and to verify its influencing factors.Nineteen sample plots(30 m×30 m)were selected,and the stems of individuals with a circumference at breast height(1.3 m above the ground)equal to or greater than 6.0 cm were measured,and the AGB through an allometric equation was estimated.The Sentinel-1 images from 3 different periods(green,intermediate,and dry periods)were used to consider the phenological conditions of the Caatinga biome.All the pre-processing and extraction of attributes(co-polarized VV(vertical transmit and vertical receive),cross-polarized VH(vertical transmit and horizontal receive),and band ratio VH/VV backscatter,radar vegetation index,dual polarization synthetic aperture radar(SAR)vegetation index(DPSVI),entropy(H),and alpha angle(α))were performed with Sentinel’s Application Platform.These attributes were used to estimate the AGB through simple and multiple linear regressions and evaluated by the coefficients of determination(R2),correlation(r),and root mean squared error(RMSE).The results showed that the attributes individually had little ability to estimate the AGB of the Caatinga biome in the three periods.Combined with multiple regression,we found that the intermediate period presented the equation with the best results among the observed and estimated variables(R^(2)=0.73;r=0.85;RMSE=8.33 Mg/hm^(2)),followed by the greenness period(R2=0.72;r=0.85;RMSE=8.40 Mg/hm^(2)).The attributes contributing to these equations were VH/VV,DPSVI,H,α,and co-polarized VV for the green period and cross-polarized VH for the intermediate period.The study showed that the Sentinel-1 images could be used to estimate the AGB of the Caatinga biome in the green and intermediate phenological periods since the SAR attributes highly correlated with the estimated variable(i.e.,AGB)through multiple linear equations.

Geochemical study of submicron particulate matter(PM1)in a metropolitan area

Air pollution has become a major problem in urban areas due to increasing industrialization and urbanization.In this study ambient concentrations of PM1 and metal concentrations as well as source contributions were identified and quantified by using Positive Matrix Factorization(PMF)in receptor modeling in the Metropolitan Area of Porto Alegre,Brazil.The PM1 samples were collected on PTFE filters from December 2012 to December 2014 in two sampling sites.Major ion and trace element concentrations were assessed.The average concentrations were 12.8 and 15.2μg/m^(3) for Canoas and Sapucaia do Sul sites,respectively.Major ion contributions of PM1 were secondary pollutants such as sulfate and nitrate.Trace elements,especially Cu,Pb,Zn,Cd,and Ni also made important contributions which are directly associated with anthropogenic contributions.Our results show significantly higher levels in winter than in summer.Most of the PM1 and the analyzed PM species and elements originated from anthropogenic sources,especially road traffic,combustion processes and industrial activities,which are grouped in 7 major contributing sources.A back-trajectory analysis showed that the long-range transport of pollutants was not relevant in relation to the contribution to PM1 and metal concentrations.This work highlights the importance of urban planning to reduce human health exposure to traffic and industrial emissions,combined with awareness-raising actions for citizens concerning the impact of indoor sources.

Metal-enriched nanoparticles and black carbon:A perspective from the Brazil railway system air pollution

Having a better understanding of air pollutants in railway systems is crucial to ensure a clean public transport.This study measured,for the first time in Brazil,nanoparticles(NPs)and black carbon(BC)on two groundlevel platforms and inside trains of the Metropolitan Area of Porto Alegre(MAPA).An intense sampling campaign during thirteen consecutive months was carried out and the chemical composition of NPs was examined by advanced microscopy techniques.The results showed that highest concentrations of the pollutants occur in colder seasons and influenced by variables such as frequency of the trains and passenger densities.Also,internal and external sources of pollution at the stations were identified.The predominance of NPs enriched with metals that increase oxidative stress like Cd,Fe,Pb,Cr,Zn,Ni,V,Hg,Sn,and Ba both on the platforms and inside trains,including Fe-minerals as hematite and magnetite,represents a critical risk to the health of passengers and employees of the system.This interdisciplinary and multi-analytical study aims to provide an improved understanding of reported adverse health effects induced by railway system aerosols.