Desiccation time and rainfall control gaseous carbon fluxes in an intermittent stream

Droughts are recognized to impact global biogeochemical cycles. However, the implication of desiccation on in-stream carbon (C) cycling is not well understood yet. We subjected sediments from a lowland, organic rich intermittent stream to experimental desiccation over a 9-week-period to investigate temporal changes in microbial functional traits in relation to their redox requirements, carbon dioxide (CO2) and methane (CH4) fluxes and water-soluble organic carbon (WSOC). Concurrently, the implications of rewetting by simulated short rainfalls (4 and 21 mm) on gaseous C fluxes were tested. Early desiccation triggered dynamic fluxes of CO2 and CH4 with peak values of 383 and 30 mg C m−2 h−1 (mean ± SD), respectively, likely in response to enhanced aerobic mineralization and accelerated evasion. At longer desiccation, CH4 dropped abruptly, likely because of reduced abundance of anaerobic microbial traits. The CO2 fluxes ceased later, suggesting aerobic activity was constrained only by extended desiccation over time. We found that rainfall boosted fluxes of CO2, which were modulated by rainfall size and the preceding desiccation time. Desiccation also reduced the amount of WSOC and the proportion of labile compounds leaching from sediment. It remains questionable to which extent changes of the sediment C pool are influenced by respiration processes, microbial C uptake and cell lysis due to drying-rewetting cycles. We highlight that the severity of the dry period, which is controlled by its duration and the presence of precipitation events, needs detailed consideration to estimate the impact of intermittent flow on global riverine C fluxes.

WOODY COMPONENT STRUCTURE OF A RIPARIAN FOREST IN AN INTERMITTENT STREAM IN THE SEMI-ARID REGION OF PARAÍBA, BRAZIL

Objetivou-se analisar os aspectos estruturais da vegetação ciliar de um curso d´água intermitente no semiárido paraibano. Foram estabelecidas 51 parcelas contíguas de 10 X 20 m (1,02 ha), distribuídas em três faixas paralelas ao longo do curso d’água. Utilizou-se como critérios de inclusão amostrar os indivíduos arbustivo-arbóreos, vivos e mortos ainda em pé, com diâmetro do caule ao nível do solo (DNS) ≥ 3 cm e altura total ≥ 1 m. Na área foram amostrados 1.864 indivíduos, com área basal total de 14,8 m2. As três espécies mais importantes em VI foram: Cenostigma pyramidale (Tul.) E. Gagnon & G.P. Lewis, Combretum leprosum Mart. e Croton blanchetianus Baill. A altura e o diâmetro médio dos indivíduos amostrados foram respectivamente: 4,8 m e 10,1 cm. Os valores de diversidade e equabilidade foram 2,77 nats.ind.-1 e 0,72 respectivamente.

An Assessment of the Functional and Ecological Aspect of Novel Intermittent Stream Valves for Spraying Seed Potatoes

It is important to protect potatoes from insects and diseases at an early stage of their development. Pesticides are necessary to prevent loss caused by Colorado potato beetles feeding on potato leaves. Nowadays, there are attempts to reduce the use of chemical agents to the minimum necessary level. This article describes the construction of a novel valve that applies chemicals in an intermittent stream during potato treatment. Thus, it is possible to reduce the emission of chemicals to the natural environment. The article also describes the research site where the valve was tested, provides the results of laboratory investigations on different types of sprayer nozzles and their validation. Apart from that, the degree of the seed potato surface covering with the dressing was assessed in order to select the right sprayer nozzle and working pressure. The results of field tests of the seed dresser prototype with novel nozzles showed that they effectively dressed seed potatoes while saving 2 L (50%) of the chemical per hectare. Fissure sprayers achieved the highest degree of covering (up to 78%) with the first version of the valve (without auxiliary airflow). When the innovative valve (the second solution with auxiliary airstream) was applied at a distance of 50 mm from the seed potato fall path S, the highest degree of coverage with the dressing substance (up to 88%) was observed for the ejector sprayer. When the distance between the valve and the seed potato fall, path S was increased from 50 to 100 mm, the degree of surface coverage was lower for both of the valves used in the tests.