Julio Cesar Neves dos Santos

Land use and trophic state dynamics in a tropical semi-arid reservoir

Water body eutrophication process has been a serious problem around the world, especially in semiarid and arid region where main approach to storage water is reservoir. The aim of this work was to investigate the spatial and seasonal variability in water quality of a reservoir in a semi-arid tropical region with regards to its trophic state, and to identify the sources of nutrient input to the reservoir. Essa pesquisa foi realizada no reservatorio Oros, segundo maior do estado do Ceara-Brasil. This research was developed in the Oros reservoir, the second one most important reservoir in Ceara State, Brazil. Samples were collected bimonthly during the period April 2008 to April 2010, from sex sampling points representing the outlet of tributaries, and one point down of the dam. The study included the following variables: total phosphorus, transparency and chlorophyll-a. Trophic state was evaluated by application of the Carlson modified Trophic State Index (TSI). Maps of the spatial and seasonal dynamics of the water quality in the reservoir were constructed using GIS soft. According to the average values of total phosphorus (> 0.050 mg L -1 ), the waters can be classified as eutrophic. The highest concentrations of chlorophyll-a were found during the dry season, with values ranging from 3.8 to 26.5 µg L -1 , showing high temporal and spatial variations. The waters presented as eutrophic regarding average TSI, at all points sampled. The results indicate a deterioration in water quality and the need for intervention to reduce the release of waste, and thus improve the trophic state of the waters of the Oros reservoir.Water body eutrophication process has been a serious problem around the world, especially in semiarid and arid region where main approach to storage water is reservoir. The aim of this work was to investigate the spatial and seasonal variability in water quality of a reservoir in a semi-arid tropical region with regards to its trophic state, and to identify the sources of nutrient input to the reservoir. Essa pesquisa foi realizada no reservatorio Oros, segundo maior do estado do Ceara-Brasil. This research was developed in the Oros reservoir, the second one most important reservoir in Ceara State, Brazil. Samples were collected bimonthly during the period April 2008 to April 2010, from sex sampling points representing the outlet of tributaries, and one point down of the dam. The study included the following variables: total phosphorus, transparency and chlorophyll-a. Trophic state was evaluated by application of the Carlson modified Trophic State Index (TSI). Maps of the spatial and seasonal dynamics of the water quality in the reservoir were constructed using GIS soft. According to the average values of total phosphorus (> 0.050 mg L -1 ), the waters can be classified as eutrophic. The highest concentrations of chlorophyll-a were found during the dry season, with values ranging from 3.8 to 26.5 µg L -1 , showing high temporal and spatial variations. The waters presented as eutrophic regarding average TSI, at all points sampled. The results indicate a deterioration in water quality and the need for intervention to reduce the release of waste, and thus improve the trophic state of the waters of the Oros reservoir.

Runoff and soil and nutrient losses in semiarid uncultivated fields

Although water erosion is the principle agent responsible for soil degradation, field data on the impacts of erosion, due to high operational costs and measurement difficulties, are scarce, especially in semiarid regions. In this context, the aim of this study was to evaluate runoff and soil and nutrient losses in uncultivated areas in the semiarid region of the state of Ceara in Brazil. The experiment was conducted in a 20 m2 erosion plot that was uncultivated and populated with herbaceous plants. Data were collected during the rainy season from January to May 2009. Monthly water losses from overland flow ranged from 3.4 to 168.9 mm, representing 1.8 to 42.3% of the total monthly rainfall for January and April, respectively. Soil loss from erosion totaled 2,166.6 kg ha-1. In February, soil losses were 834.3 kg ha-1, corresponding to 38.5% of the total value. The rainfall erosivity index (EI30) was 5,716.4 MJ mm ha-1 h-1. The observed high variability of soil losses in individual events was influenced mainly by the antecedent soil water content. Although this study used only one year of observations, the findings are important for land use planning, especially in the semiarid region of Brazil, where datasets are scarce.

Produção de sedimentos em microbacias hidrográficas semiáridas sobre manejos diferenciados

The aim of this study was to evaluate and compare the sedimentological behavior in two small rural watersheds in the semiarid Northeast of Brazil, examining the influence of human activity on the sediment yields. The studied area is sited in the Alto Jaguaribe basin, more precisely in the Iguatu County, Ceara State. The experimental area was composed of two small watersheds denominated B1 and B2. In watershed B1 a treatment (thinning) was applied, eliminating the plant species with diameters lower than 10 cm. The results showed that the Caatinga clearing practice did have an influence in changing the sediment yield during the first events. It was also found that the magnitude of previous events contributed to an increase in the sediment yields by the subsequent events as a consequence of the sediment deposit in the drainage network. The accumulated sediment yields reached at the end of the 2009 rainfall season values of 1.45 and 1.39 tons ha -1 year -1 for B1 and B2, respectively, with no significant difference at 5%. It was concluded that, even when the effect of treatment on the sediment yields at the beginning of the rainy season is measured, the total sediment yields was not changed by the adoption of clearing. Therefore, it is a management system that can be employed in the land use at semiarid regions.

Similaridade e fatores determinantes na salinidade das águas superficiais do Ceará, por técnicas multivariadas

Tecnicas de estatistica multivariada foram empregadas com o objetivo de identificar a similaridade dos reservatorios superficiais do Ceara, com relacao a salinidade das aguas e identificar os fatores determinantes da qualidade das aguas. Os dados utilizados foram provenientes do banco de dados da Companhia de Gestao dos Recursos Hidricos do Ceara, no periodo de 1998/2009, no total de 807 amostras de 48 reservatorios. Os parâmetros considerados foram: Cl-, Ca2+, Mg2+, Na+, HCO3 -, CE e RAS. A analise de agrupamento hierarquico formou quatro grupos distintos, sendo determinantes os tipos e concentracoes dos sais analisados. Nos grupos 1 e 2 a salinidade da agua e definida principalmente pelas condicoes naturais de solo e clima da regiao e nos grupos 3 e 4, alem desses fatores, a influencia antropica. O emprego da analise de fator/analise de componente principal promoveu a reducao de sete caracteristicas das aguas superficiais do Estado Ceara, para dois componentes, sendo que o primeiro componente explicou 57,28% e o segundo, 26,77% da variância contida nas sete variaveis. Os parâmetros mais representativos na variabilidade da salinidade das aguas foram Cl-, CE, Na+ e Mg2+, relacionados com a solubilidade dos sais.

Effect of Rainfall Characteristics on Runoff and Water Erosion for Different Land Uses in a Tropical Semiarid Region

Rainfall intensity, duration, frequency and magnitude influence both runoff generation and sediment yield. In this study, 176 rainfall events over a five-year period were classified into four regimes based on rainfall depth, duration and 30-minute maximum intensity, using hierarchical cluster analysis in the semiarid region of Brazil. Rainfall Regimes were grouped from higher to lower rainfall depth, longer to shorter duration, and higher to lower I30. Rainfall regime impact on surface runoff and sediment yield was studied in three watersheds under different land use - native tropical dry forest, thinned tropical dry forest, and slash and burn followed by grass cultivation. Thinning of native dry tropical forest reduced surface runoff and sediment yield due to the protective effect of the well-developed herbaceous layer. Runoff generation in the three watersheds showed strong dependence on antecedent soil moisture and the type of rain. Rainfall depth was the major factor for highest sediment yields.

Land use impact on soil erosion at different scales in the Brazilian semi-arid

Erosion and sediment transport processes are strongly dependent on the spatial scale and land use. The objective of this study is to analyse the effects of slash and burn of vegetation followed by grass cultivation for grazing, on the hydrological and sedimentological behaviour at different spatial scales in a semiarid region in Brazil. Rainfall, runoff and soil loss were measured during three years (total of 116 rainfall-runoff events) at three spatial scales: 1 m² and 20 m² plots and 2.8 ha watershed. During the first year (2009) the native dry tropical forest/Caatinga vegetation was maintained, whereas on the following years (2010 and 2011) the original vegetation was cleared using slash and burn techniques to grow pasture (Andropogon gayanus Kunt). Annual runoff coefficient is highest at the 20 m² plot among the investigated scales. Runoff presented the same trend in all years. Sediment yield was strongly influenced by the land cover. Slash, burn and pasture cultivation strongly impacted sediment yield: the first two events after the land cover change yielded roughly ten times more sediment than similar events in the years with native cover and after grass development. The change was most noticeable at the catchment scale due to erosion along the stream, redefining the drainage network.

Runoff curve number for a small forested watershed in a semiarid region of Brazil

Although the Runoff Curve Number method has been developed in the 1950’s, and extensively used worldwide, it has not been so in Brazil, yet. The present study was conducted in a small experimental watershed in the southern central region of Ceara State, Brazil (6°32’S, 39°5’W). The watershed is representative of caatinga, a type of scrubby forest, characteristic of the semiarid northeast in Brazil. The watershed has a mean annual rainfall of 800 mm, being 85% concentrated in the January to May period. All streams are ephemeral, and runoff persists until 24 hours after the causing rainfall event is over. Rainfall and streamflow records (64 rainfall-runoff events) were collected at a station located at the watershed outlet from 2008 to 2011. The representative watershed curve number, was determined by the following methods: a) arithmetic mean; b) geometric mean; c) median and c) asymptotic curve fit. For curve number computation, both unranked and ranked paired rainfall-runoff depth of each event was used. Results showed that the arithmetic mean value of curve number (78.8) is very close to the median value (79.4) and both are larger than the geometric mean (78.0). A smaller value of curve number (76.3), however, was obtained when using the asymptotic approach. The observed curve numbers, ranging from 73.0 to 86, decrease with increasing rainfall depth, and tend to a constant value towards larger rainfall events, which are the events that lead to flooding. The watershed presented a standard response.

CARACTERISTICAS DAS CHUVAS E RESPOSTAS SEDIMENTOLOGICAS EM DIFERENTES USOS DO SOLO NO SEMIÁRIDO

The objective of this work was to evaluated the precipitation characteristics (depth, I30 and erosivity) and their effects on sediment production in three watersheds under different managements of land use 35-year regenerating Caatinga (RC), thinned Caatinga (TC), which underwent thinning of trees with diameter smaller than 10 cm; and deforested Caatinga (followed by burning and pasture) (DC). The experimente was conducted in the central, tropical semiarid region of the State of Ceará, Brazil. The precipitation events, surface runoff and sediment production were monitored from 2010 to 2015. The precipitation characteristics were subjected to Pearsons correlation at 1 and 5% of significance and the events that produced sediments in each watershed were hierarchically grouped by hierarchical cluster analysis technique. Two hundred precipitation events were recorded, with 23 (RC), 18 (TC) and 43 (DC) events producing sediments. The use of thinning (TC) decreased the sediment production by 53.5%, while the deforestation, burn and pasture cultivation (DC) increased soil losses by 14%, compared with the RC. The sediment production was greatly correlated with the I30 in the three watersheds, denoting the erosion process great dependence on the precipitation intensity.

PRECIPITAÇÃO EFETIVA E PERDAS DE SOLO EM DIFERENTES SISTEMAS DE COBERTURA VEGETAL NO BIOMA CAATINGA

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 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 . The largest annual eP was found in the DBP area, with 112.88 mm yr of accumulated water depth, which also showed the greater annual soil loss (3114.97 kg ha). 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.

Measurement of soil erosion on different spatial scales with vegetation cover of caatinga in the northeast of Brazil

Erosion is a phenomenon whose impact on renewable natural resources has been worrying governments and institutions in different parts of the world. To this effect, this study aimed to generate and analyze information obtained in the field, involving the main processes and sources of variation in soil-loss data on different spatial scales in a semi-arid region with a vegetation cover of native caatinga. The study area is located in the semi-arid region of the state of Ceara in Brazil, in the watershed of the upper Jaguaribe River. Studies of erosion and runoff were conducted on three different levels: a watershed with an area of 2.06 ha, an erosion plot of 20 m2 and a plot of 1 m2, all under natural-rainfall conditions. The vegetation of the study area is made up of native caatinga. The study was carried out from 2009 to 2011, with rainfall concentrated in the period of January to June, corresponding to the rainy season in the region. The highest coefficients of runoff were recorded on the scale of the 20m2 plot in relation to the scales of 1m² and the watershed, with the exception of 2009. The highest soil loss in the first two years studied occurred in the watershed in relation to the 20m2 scale. These results were due to the special characteristics of the watershed, where there are places of high sediment yield, these barely being found on the scale of the smaller plot. The transfer soil-loss data measured for small plots, to larger scales cannot be made in a linear fashion.