Search

Rainfall is generally partitioned into throughfall, stemflow, and interception in ecosystems. Stemflow variability can affect the hydrology, ecology, and soil chemistry patterns. However, the influence of canopy structure and rainfall characteristics on stemflow production in sugarcane plantations which are important for renewable energy production remain poorly understood. By using funnels attached to the sugarcane stems, the present study determined the stemflow amount during the period of sugarcane growth and its relationship with plant development. Approximately, 14% of gross rainfall reached the soil as stemflow, and the funneling ratios was 60. In general, it was observed a positive relationship between stemflow rates with both leaf area index and plant height. This was attributed to an increasing number of acute branching angles of the sugarcane leaves as well as high stem tillering and density. However, at the end of growth cycle, stemflow rate was lower than in previous periods which can be attributed to changes in sugarcane canopy such as stems inclination and lodging, reducing the effectiveness of water conveyance along the stem. Our study showed the need to include stemflow to better understand the hydrology of sugarcane plantations.

Extreme climatic events may be translated into a higher frequency of both dry and wet years. Frequent droughts pose a challenge to water supply in terms of both quantity and quality. In order to cope with this, there has to be a documentation on the concentration of chemicals in water during such events. The southeast region of Brazil experienced a major drought event in 2014 leading to number of social, economic, and environmental impacts. The objective of the present paper is to understand the effect of an extreme drought on dissolved organic and inorganic carbon concentrations of the Piracicabal river, which is under high human pressure. Concentrations of both dissolved organic (DOC) and inorganic carbon (DIC) were monitored daily, for 30 days, during a dry month in 2014. DOC values found here were at least twice those observed in the river in non-extreme conditions. Rain events within this drought led to significant differences in discharge, DOC, and DIC. We built a dilution-concentration model which described an exponential relationship between discharge and both carbon forms. This indicated that drastic changes in concentrations of DOC and DIC are expected during such events. Our results may also apply to a number of regions in the world especially those of the developing countries where rivers are highly subjected to sewage impact.

© 2019 Elsevier B.V. Soil erosion leads to land degradation and translocation of soil particles together with associated particulate organic carbon (POC)and nutrients, thereby influencing the global carbon cycle. In the present study, we estimated the contribution of POC delivered to a first-order stream from upslope sugarcane fields and a riparian forest in southeast Brazil. The results show that the amount of surface runoff and soil erosion generated in the riparian forest is significantly lower than in the upslope sugarcane field. However, the contribution of the forest to the total stream bed POC was above 70%, even though most sediments delivered to the stream originated from the upland sugarcane fields. The discrepancy between sediment and POC delivery from both land uses is a consequence of the presence of preferential runoff pathways from the agricultural fields, through the buffer strips, to the stream. This disconnection between the main sources of sediment and POC to the first-order stream is a potentially important mechanism influencing the transfer of POC from upslope areas to waterways. This mechanism should be considered in order to more reliably assess fluxes of OC from upslope areas to first-order streams in landscapes where arable land is separated from streams by a semi-natural buffer zone with permanent vegetation. ispartof: CATENA vol:181 status: published

Sugarcane is an annual crop with a dynamic canopy that changes over time mainly because of genetic adaptation. There is uncertainty about the temporal trends of throughfall (TF) in this important commercial crop. In the present paper, we used troughs to measure TF in a third and fourth ratoon and subsequently in a fourth and fifth ratoon. Additional measurements were carried out in an adjacent riparian forest. There were no significant differences between cycles of sugarcane, growth phases and riparian forest. The TF results for ratoon crop and riparian forest in 2011/2012 were 76% and 79.5% of gross rainfall, respectively, while in 2012/2013, they were 79% and 78%, respectively. However, TF was remarkably lower in the riparian forest relative to ratoon from the second half of the culm formation and elongation phase (280 days after harvest) until harvest. Copyright © 2016 John Wiley & Sons, Ltd.

Since an understanding of how runoff is generated is of great importance to soil conservation, to water availability and to the management of a watershed, the objective of this study was to understand the generation of surface runoff in a watershed covered by sugarcane and riparian forest. Nine surface runoff plots were set up, evenly distributed on the lower, middle and upper slopes. The lower portion was covered by riparian forest. We showed that the average surface runoff coefficient along the slope in the present study was higher than in other studies under different land uses. Furthermore, the surface runoff was higher under sugarcane compared to the riparian forest, especially after sugarcane harvesting. Besides land cover, other factors such as the characteristics of rainfall events, relief and physical soil characteristics such as soil bulk density and saturated hydraulic conductivity influenced the surface runoff generation.

Os processos hidrológicos afetam os processos biogeoquímicos, pois o movimento da água nos vários compartimentos do agroecossistema promove a redistribuição dos nutrientes, como o nitrogênio (N) e o carbono orgânico dissolvido (COD). O carreamento desse N e COD nos corpos hídricos se dão, normalmente, via escoamento superficial trazendo implicações negativas à sua qualidade. Em culturas anuais, como a cana-de-açúcar, há exigência de grande quantidade de fertilizantes inorgânicos e orgânicos que têm o N e o COD como os principais elementos. A floresta ripária desempenha funções relacionadas à geração do escoamento direto em microbacia e a retenção de nutrientes. Este trabalho tem como objetivo realizar o balanço hídrico e determinar o fluxo de N e COD em duas microbacias com cobertura de cana-de-açúcar, sendo que, uma microbacia apresenta floresta ripária próxima ao riacho em conformidade com a legislação vigente (Cana com floresta ripária - CCF) e a outra não apresenta floresta ripária nessas condições (Cana sem floresta ripária - CSF). Para tanto as microbacias foram instrumentalizadas para medir e coletar simultaneamente dados hidrológicos e amostras de chuva (entradas) e dos riachos (saídas) para análises de N e COD. As vertentes estudadas nas microbacias foram subdivididas em três porções: inferior, intermediária e superior, sendo que a primeira, na microbacia CCF encontra-se exclusivamente em floresta ripária. O monitoramento hidrológico ocorreu semanalmente no primeiro ano de estudo, e quinzenalmente no segundo. Já o monitoramento biogeoquímico das entradas e saídas ocorreu semanalmente. Para realizar o balanço de massa foram computadas as entradas via fertilizantes inorgânicos e orgânicos na cultura. A precipitação foi de 1200 mm no primeiro ano de estudo e 1350 mm no segundo, sendo cerca de 80% das mesmas de baixa intensidade (0-5 mm h-1). A interceptação foi de aproximadamente 25% da precipitação tanto pela cana-de-açúcar quanto pela floresta ripária. Os resultados de Ksat na área de cana-de-açúcar apontaram para a existência de camadas de impedimento próxima à superfície e como consequência os coeficientes de escoamento superficial foram superiores a outros usos do solo encontrados na literatura, bem como em relação à floresta ripária. Com isso, o fluxo direto representou cerca de 40% do deflúvio. A microbacia CCF não apresentou maior eficácia na diminuição do fluxo direto como era esperado, possivelmente, devido aos canais preferenciais gerados pelo lançamento pontual de água dos terraços. Os fluxos de entrada naturais de NID, NOD e COD nas microbacias foram relativamente baixos, sendo a principal via os fertilizantes (acima de 95%). As saídas desses elementos e compostos também foram baixas denotando que, possivelmente, as saídas dos mesmos nas microbacias se dão via queima pré-corte, ocorrida no primeiro ano de estudo, biomassa coletada e desnitrificação. Há evidências do papel da floresta ripária, presente em maior extensão na microbacia CCF, na diminuição do fluxo de N e COD dissolvidos nos riachos Hydrological processes affect biogeochemical processes, because the movement of water in many compartments of the agroecossystem promotes elements redistribution. The transport of nitrogen (N) and dissolved organic carbon (DOC) in streams occur generally through runoff bringing negative implications for their water quality. Annual crops, such as sugarcane, require large amounts of inorganic and organic fertilizers that present N and DOC in their composition. Riparian forests play important roles related to quickflow generation and nutrient retention. These forests might maintain water quality in watersheds. In the present study, we determined the water balance and the fluxes of N and DOC in two watersheds covered by sugarcane. The first watershed presented riparian forest next to the creek in accordance with Brazilian legislation (CCF), and other watershed presented no riparian Forest in these conditions (CSF). The watersheds were instrumented to measure and collect hydrological data simultaneously and rain samples (inputs), and the streams (outputs) for N and DOC analysis. Each slope of the watersheds was divided into three parts: downslope, middleslope and upslope. All slopes parts, except the downslope at CCF, were covered by sugarcane. Downslope part CCF was under riparian forest. The hydrological monitoring occurred on a weekly basis during the first year and biweekly in the second year. The biogeochemical monitoring occurred on a weekly basis. To accomplish the mass balance the inputs of inorganic and organic fertilizers in the plantation were also computed. In first year, the rainfall was 1200 mm and in the second was 1350 mm. Around 80% of such precipitation was low intensity (0-5 mm h-1). The interception loss was approximately 25% of the rainfall either by sugarcane as the riparian forest. The Ksat results in the area of sugarcane showed the existence of impeding layers near the surface and consequently the overland flow coefficients were higher than other land uses available in the literature as well as in relation to riparian forest area. Thus, quickflow represented about 40% of the streamflow. The watershed CCF was not more effective in reducing the quickflow as expected, possibly due to preferential channels caused by the punctual release of water from the terraces. The natural input of NID, NOD and DOC in the watersheds were relatively low, with the fertilizers as the main source (above 95%). The outputs of these elements and compounds were also low denoting that the main outputs occur potentially by sugarcane pre-harvest burning, occurred in the first year, biomass harvested and denitrification process. However, there is evidence of the role of riparian forest, present to a greater extent in the watershed CCF, decreasing the output of N and DOC dissolved in streams

Tropical regions hold the planet´s most biodiverse ecosystems. Despite its importance to biodiversity and conservation, anthropogenic activities are degrading these ecosystems, with unknown consequences for its functioning and structure. In between the several ecosystems through the tropics, freshwater ecosystems call attention, due to its small fraction of area comparing to terrestrial ecosystems, that represent an enormous importance for human surviving and developing. Headwater streams constitute the majority of water bodies in a catchment, and therefore, it is essential for the health of the entire freshwater ecosystems. Several headwater streams are inserted in agricultural lands, suffering from the pressures from agricultural intensification. Therefore, this thesis was developed aiming to understand what are the main pressures that tropical headwater streams has been suffering, worldwide and locally in the Corumbataí river basin. The first chapter will contribute to understanding what are the main issues that tropical streams have been experiencing, focusing on agricultural multiple stressors and climate change effects. The second chapter analyzes how the conversion of low-intensity pasturelands to high-intensity bioenergy crops changes the water quality parameters in streams located in the Corumbataí river basin and also examines how important are the riparian forests in the headwater zone to provide better water quality in bioenergy crops. The third chapter investigates how water quality and climatic characteristics affect benthic biofilm community dynamics in tropical headwater streams in the Corumbataí river basin. The results have shown the existence of several knowledge gaps about tropical streams, mainly related to the effects of climate change, multiple stressors and the lack of policies and mitigation strategies for climate change. In relation to water quality, we found that the conversion of low-intensity pastures to high-intensity bioenergy crops are degrading water quality. Riparian forests in the springhead zone have demonstrated to be essential in providing water quality in bioenergy crops, especially in the wet season. The benthic biofilm community seems to be controlled mainly by climate characteristics and not by nutrient availability as observed in temperate streams. Therefore, a climate change scenario, the benthic biofilm will be strongly affected, with consequences in the functioning of tropical headwater streams. To reduce the negative impacts of intensive agriculture and climate change, we recommend the implementation of riparian forests, with special attention to the springhead area and also the implementation of best agricultural practices in tropical agriculture to ensure the sustainability of tropical freshwater resources. As regiões tropicais possuem os ecossistemas mais biodiversos do planeta. Apesar da sua importância na manutenção da biodiversidade, as atividades antrópicas estão degradando esses ecossistemas, gerando consequências negativas para sua estrutura e funcionamento. Entre os diversos ecossistemas tropicais, as águas doces chamam a atenção por ocupar uma pequena área em comparação com ecossistemas terrestres, porém, representam grande importância para a sobrevivência e desenvolvimento humano. Os riachos de cabeceira representam a maior parte dos corpos aquáticos em uma microbacia e, portanto, sua conservação é essencial para a saúde de toda a rede de drenagem de água doce. Diversos riachos de cabeceira estão inseridos em ecossistemas agrícolas, sofrendo as consequências da agricultura intensiva. Nesse sentido, esta tese foi desenvolvida com o intuito de entender quais são os principais impactos que os riachos de cabeceira tropicais vêm sofrendo, globalmente e localmente na bacia do rio Corumbataí (SP, Brasil). O primeiro capítulo contribui para entender quais os principais problemas que riachos tropicas estão sofrendo, focando nos múltiplos estressores advindos da agricultura e efeitos de mudanças climáticas. O segundo capítulo analisa como a conversão de pastos para cultivo de cana de açúcar modifica a qualidade da água em riachos da bacia do rio Corumbataí e também analisa o quão fundamentais são as florestas nas áreas de nascente para manter a qualidade da água em plantios de cana de açúcar. O terceiro capítulo analisa como a qualidade da água e características climáticas influenciam biofilmes bentônicos em riachos de cabeceira na bacia do rio Corumbataí. Os resultados demonstraram a existência de diversos tópicos que necessitam de maior entendimento, principalmente relacionados às mudanças climáticas e estressores múltiplos e a falta de políticas e estratégias de mitigação para os efeitos de mudanças climáticas. Em relação à qualidade da água, demonstrou-se que a conversão de pastos para cultivo de cana de açúcar reduz a qualidade da água. A presença de florestas nas nascentes demonstrou ser essencial na manutenção da qualidade da água em plantios de cana. Os biofilmes bentônicos demonstraram ser controlados principalmente por características sazonais e não pela disponibilidade de nutrientes como observado em riachos temperados. Portanto, essa comunidade será severamente afetada diante das mudanças climáticas, com consequências no funcionamento de riachos de cabeceira tropicais. Para reduzir os efeitos negativos da agricultura intensiva e das mudanças climáticas, recomenda-se a implementação de florestas ripárias, com especial atenção às áreas de nascentes. Também se recomenda a implementação de boas práticas agrícolas na agricultura para garantir a sustentabilidade dos recursos hídricos tropicais.