Effective Preciptation, Soil Loss and Plant Cover Systems in the Caatinga Biome, Brazil

Abstract

-The objective of this work was to evaluate the influence of anthropic activities on the effective precipitation (eP) and soil loss in watersheds under different land uses in a tropical dry forest region. The experimental area was located in the central part of the State of Ceará, Brazil. The land uses evaluated were: fallow Caatinga (FC), thinned Caatinga (TC) and deforested Caatinga followed by a burning procedure and pasture cultivation (DBP). The areas were monitored in the rainy season (January to May, 2010), when 57 natural rainfalls occurred, totaling 941 mm of precipitation. The eP and sediment productions were quantified by the sum of all occurrences during the study period, and the soil loss was represented by suspended and dragged sediments. The eP was 15.13 mm and sediment produced was 167.81 kg ha -1 in FC conditions. The eP values was smaller (11.28 mm) in the watershed with TC, which had soil loss sum of 42.04 kg ha -1 . The largest annual eP was found in the DBP area, with 112.88 mm yr -1 of accumulated water depth, which also showed the greater annual soil loss (3114.97 kg ha -1). The greatest interference of plant cover in the two variables evaluated occurred in the first precipitation events, when the plants were not yet fully developed.Keywords: Water erosion. Semiarid region. Surface runoff. PRECIPITAÇÃO EFETIVA E PERDAS DE SOLO EM DIFERENTES SISTEMAS DE COBERTURAVEGETAL NO BIOMA CAATINGA RESUMO -O presente estudo objetivou investigar a influência da ação antrópica na precipitação efetiva (Pe) e nas perdas de solo em microbacias submetidas a diferentes usos do solo em região de floresta tropical seca. A área experimental está localizada na parte central do estado do Ceará, Brasil. Os usos do solo investigados foram: Caatinga em Pousio (CP), Caatinga Raleada (CR) e manejo de Desmatamento da Caatinga seguido de Queima e cultivo de Pastagem (DQP). O monitoramento foi realizado na estação chuvosa (janeiro a maio) de 2010, com uma ocorrência de 57 eventos naturais de chuva, totalizando 941 mm precipitados. Na quantificação da Pe e produção de sedimentos foi feito um somatório para todos os eventos ocorridos no período de estudo e nas perdas de solo consideraram-se os sedimentos em suspensão e em arraste. Em condições de pousio, a Pe e a produção de sedimentos foram de 15,13 mm e 167,81 kg ha -1 respectivamente. Os menores valores de Pe (11,28 mm) ocorreram na microbacia cujo uso da terra era o CR, cujas perdas de solo totalizaram 42,04 kg ha -1 . No uso da terra DQP foi registrada a maior Pe anual com 112,88 mm ano -1 de lâmina escoada acumulada, bem como as maiores perdas de solo anual (3.114,97 kg ha -1 ). A maior inferência da cobertura vegetal nos dois processos investigados ocorreu para os primeiros eventos, quando o estrato herbáceo ainda não estava desenvolvido.Palavras-Chave: Erosão hídrica. Semiárido. Escoamento superficial.

Influence of seasonal vegetation dynamics on hydrological connectivity in tropical drylands

“…In contrast, high magnitude events which occurred over very wet (six events), and wet (10 events) vegetation density scenarios had the hillslope connectivity processes buffered (Santos, Andrade, Medeiros, Palácio, & Araújo Neto, 2017). This behaviour represents the typical hillslope dryland processes where pre-rainy season rains generate a small portion of the total annual runoff, but are responsible for substantial erosion volume due to the significant exposure of the soils (Lima et al, 2013;Palácio et al, 2016;Santos, Andrade, Medeiros, Palácio, & Araújo Neto, 2017). Simultaneously, it is important to emphasize the highly variable monthly rainfall behaviour, indicating that the vegetation fluctuation analysis should be done by the precipitation behaviour not by fixed seasons or months.…”

“…Different C‐factors for each density class in each rainfall/vegetation scenario enable understanding of how the natural Caatinga dynamics affect the potential connectivity. In this way, the C‐factor was defined, based on the literature (Anache et al, 2017; Andrade et al, 2017; C. A. Lima et al, 2013; Palácio et al, 2016) for the different NVDI responses (Table 3): bare land and sparse vegetation (0.5), savanna (0.11), shrubland (0.04), dry forest (0.0167), and rain forest (0.0004). To understand the vegetation seasonality impact on the connectivity the IC models were run for each vegetation scenario, allowing the creation of five connectivity scenarios.…”

“…based on research on runoff, infiltration, erosion, sediment transport, models and experimental plots effects of different vegetation, including Caatinga areas and similar vegetation stages/ densities and rainfall seasons(Figueiredo et al, 2016;Santos, et al, 2013;Palácio et al, 2016) for the different NVDI responses (Table3): bare land and sparse vegetation (0.5), savanna (0.11), shrubland (0.04), dry forest (0.0167), and rain forest (0.0004). To understand the vegetation seasonality impact on the connectivity the IC models were run for each vegetation scenario, allowing the creation of five connectivity scenarios.T A B L E 2…”