Impacto da lixiviação de nitrato e cloreto no lençol freático sob condições de cultivo irrigadoNitrogen and chloride impact on water
Este trabalho objetivou avaliar a influência da antropização e de secas severas na dinâmica da cobertura florestal de um fragmento de caatinga na região semiárida do Brasil, ao longo de 32 anos. Para o cálculo do índice de seca, agrupou-se os valores de precipitação média pondera da anual da série histórica (1988 - 2019) em Decis. A partir do quantitativo de área encontrada nas classes de uso e ocupação (cobertura florestal conservada, cobertura natural campestre, área antropizada e corpos d’água) dos anos extremos secos e chuvosos, procedeu-se à análise estatística multivariada pelo método da análise de agrupamento hierárquico. Os valores médios dos agrupamentos foram submetidos à análise estatística e confrontados pelo teste T de Student (p ≤ 0,05). Foram encontrados três grupos distintos: G1 constituído por anos secos e muito secos da década de 90, o agrupamento 2 formado por anos extremos úmidos e muito úmidos, independentemente do período, e G3 (agrupamento intermediário) constituído tanto por anos típicos secos quanto chuvosos, especificamente de períodos mais recentes (2000 a 2019). Os grupos G2 e G3 contribuíram com as maiores quantitativo de cobertura florestal conservada, 143.176,50 e 144.928,13 ha, respectivamente. Os resultados demonstram que a precipitação pluviométrica está mais estritamente correlacionada com as áreas antropizadas do que propriamente com a regeneração natural da cobertura florestal. A vegetação arbórea-arbustiva do fragmento investigado tem passado por um processo de regeneração natural na década recente (2002 - 2019) em virtude do abandono de áreas anteriormente antropizadas na década de 90. Drought and Anthropogenic Effect on the Dynamics of Forest Cover in a Fragment of Caatinga Phytogeographic Domain A B S T R A C TThe aim of this study was to evaluate the influence of anthropogenic action and severe drought on the dynamics of forest cover in a fragment of caatinga in the semi-arid region of Brazil, over 32 years. To calculate the drought index, the values for weighted mean annual precipitation from an historical series (1988 - 2019) were grouped into deciles. Based on the quantification of the area found in the classes of use and occupation (conserved forest cover, natural rural cover, anthropogenic area and water bodies) for the extreme dry and rainy years, multivariate statistical analysis was carried out using hierarchical cluster analysis. The mean values of the clusters were submitted to statistical analysis and compared by Student's t-test (p ≤ 0.05). Three distinct groups were found: G1, consisting of dry and very dry years from the 1990s; G2, formed by extreme wet and very wet years regardless of the period; and G3 (intermediate group), comprising both dry and rainy years, specifically from more recent periods (2000 to 2019). Groups G2 and G3 contributed the greatest amount of conserved forest cover, 143,176.50 and 144,928.13 ha respectively. The results show that rainfall is more closely correlated with the anthropogenic areas than with the natural regeneration of forest cover. The woody vegetation of the fragment under investigation has undergone a process of natural regeneration during the last decade (2008 - 2016), due to previously anthropogenic areas being abandoned in the 1990s.Keywords: Caatinga, remote sensing, desertification.
Forest management activities influence fine root development, total soil carbon (TSC) and size of aggregates. A field experiment was carried out in Vertisols of two adjacent catchments in a seasonally dry tropical forest (SDTF) to investigate the thinning on fine-root biomass, stock of the total soil carbon and aggregate size. The catchments are located in the State of Ceará, Brazil. The control catchment of 2.1 ha has been under regenerating vegetation for 35 years (RC35), while the second catchment (1.1 ha) was subjected to thinning (TC5) in December of 2008. The analysed variables were: fine-root biomass in the 0-10, 10-20 and 20-30 cm soil layers, TSC and mean weight diameter of the soil aggregates in the 0-20, 20-40 e 40-60 cm layers. The data were submitted to Pearson correlation analysis and compared by paired t-test (P < 0.05). The 0-10 cm layer of the TC5 management stored double the average amount of fine-roots found in the RC35. Under the TC5 management, stocks of soil TSC increased by 237 and 151% in the 20-40 and 40-60 cm layers, respectively, when compared with RC35. Aggregates 2.15 times greater than those found under RC35 management were obtained in the topsoil (0-20 cm) under the TC5 management. The implementation of thinning in a Vertisol of a SDTF emerges as an alternative management to be considered in projects for sustainability in the semi-arid region, contributing to an improvement in soil structure as well as an increase in the stocks of total carbon.
Palavras-chave -Análise de agrupamento. Qualidade de água-classifi cação. Salinidade-água.Abstract -It is constant the risk of contamination in the water table by leachining of salts and toxic waste, such as fertilizer and pesticides. Therefore, it is necessary to understand the dynamics of the quality of waters and devise a plan of sustainable water use consequently a study was conducted at the water table basin located at the Perímetro Irrigado do Baixo Acaraú (DIBAU). The objective of this study was to classify the water quality relative to its hydrochemical composition and to identify the determinants of these qualities samples of water table were collected monthly for 27 months ) contained in these samples were evaluated. The hydrochemical composition was defi ned by the Piper diagram, and the similarity of water quality was performed by multivariable analysis (cluster analysis). The results revealed that waters from the wells analyzed were grouped without presenting any geographical continuity. While sodium and chloride were the elements that determined the four groups obtained. The similarity of water from wells that formed group four resulted in a reduction in the number of wells to be sampled thereby minimizing the costs of monitoring. Although four groups were formed the Piper diagram demonstrated that all the waters were classifi ed as chlorinated sodium. The cluster analysis identifi ed the key elements in each group while the Piper diagram classifi ed the waters without identifying the largest or smallest contribution of a particular element.
A new millennium has begun, and a new paradigm in exploitation of natural resources to generate products has emerged. In this sense, a model in line with local environmental reality and based on the sustainable development goals (SDG) proposed by the UN is required. The document addresses the suitability of natural capitals in the Caatinga phytogeographic domain (CPD) for generating products, encompassing primary (solar energy and rainfall) and secondary (soil and vegetation) natural resources. These resources have well-defined scarcity (water, soil, and vegetation) and abundance (solar radiation) characteristics. Water is scarce due to uncertain rainfall and frequent droughts. Due to their fragility, soils, when shallow and/or with a low organic matter content, are susceptible to erosion and salinization. In turn, vegetation is scarce due to low potential for biomass production (50% of the area has a biomass production below 2 Mg ha-1. As for solar energy, there is no uncertainty regarding its occurrence in the CPD. Moreover, the region has the highest solar radiation intensities in Brazil, with daily averages ranging from 4.8 to 6.0 Kwh m-2 within a year. Therefore, a new model must be adopted, in which socioeconomic development is based on the potential of local natural resources. In short, abundant resources should be prioritized over scarce ones. Furthermore, exploitation must be democratized and not only in the hands of few privileged individuals
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