219 research outputs found
Condições de produção de leituras de estudantes em aulas de química no ensino médio
Pensar a formação de leitores em aulas de Química vai ao encontro de propostas educacionais que visam a formação para a cidadania e o trabalho com o cotidiano dos estudantes, pois possibilita pensar o conhecimento em termos de mudança, do novo, e não apenas do que já está estabelecido, através do trabalho com leituras diversificadas. Entendemos que seja necessário conhecer as concepções dos estudantes a respeito da leitura antes de iniciar o trabalho com textos nas aulas. Dentro dessa compreensão, o presente estudo tem como objetivo apresentar algumas das condições de produção envolvidas nos processos de leitura e formação de leitores em aulas de Química no Ensino Médio. Para tanto, procuramos traçar um perfil dos leitores em aulas de Química, através da elaboração de um questionário sobre leitura, aplicação do mesmo e análise das respostas dos estudantes
Monitoring and modelling of soil–plant interactions: the joint use of ERT, sap flow and eddy covariance data to characterize the volume of an orange tree root zone
Abstract. Mass and energy exchanges between soil, plants and atmosphere control a number of key environmental processes involving hydrology, biota and climate. The understanding of these exchanges also play a critical role for practical purposes e.g. in precision agriculture. In this paper we present a methodology based on coupling innovative data collection and models in order to obtain quantitative estimates of the key parameters of such complex flow system. In particular we propose the use of hydro-geophysical monitoring via "time-lapse" electrical resistivity tomography (ERT) in conjunction with measurements of plant transpiration via sap flow and evapotranspiration (ET) from eddy covariance (EC). This abundance of data is fed to spatially distributed soil models in order to characterize the distribution of active roots. We conducted experiments in an orange orchard in eastern Sicily (Italy), characterized by the typical Mediterranean semi-arid climate. The subsoil dynamics, particularly influenced by irrigation and root uptake, were characterized mainly by the ERT set-up, consisting of 48 buried electrodes on 4 instrumented micro-boreholes (about 1.2 m deep) placed at the corners of a square (with about 1.3 m long sides) surrounding the orange tree, plus 24 mini-electrodes on the surface spaced 0.1 m on a square grid. During the monitoring, we collected repeated ERT and time domain reflectometry (TDR) soil moisture measurements, soil water sampling, sap flow measurements from the orange tree and EC data. We conducted a laboratory calibration of the soil electrical properties as a function of moisture content and porewater electrical conductivity. Irrigation, precipitation, sap flow and ET data are available allowing for knowledge of the system's long-term forcing conditions on the system. This information was used to calibrate a 1-D Richards' equation model representing the dynamics of the volume monitored via 3-D ERT. Information on the soil hydraulic properties was collected from laboratory and field experiments. The successful results of the calibrated modelling exercise allow for the quantification of the soil volume interested by root water uptake (RWU). This volume is much smaller (with a surface area less than 2 m2, and about 40 cm thick) than expected and assumed in the design of classical drip irrigation schemes that prove to be losing at least half of the irrigated water which is not taken up by the plants
Condições de produção de leituras de estudantes em aulas de química no ensino médio
Pensar a formação de leitores em aulas de Química vai ao encontro de propostas educacionais que visam a formação para a cidadania e o trabalho com o cotidiano dos estudantes, pois possibilita pensar o conhecimento em termos de mudança, do novo, e não apenas do que já está estabelecido, através do trabalho com leituras diversificadas. Entendemos que seja necessário conhecer as concepções dos estudantes a respeito da leitura antes de iniciar o trabalho com textos nas aulas. Dentro dessa compreensão, o presente estudo tem como objetivo apresentar algumas das condições de produção envolvidas nos processos de leitura e formação de leitores em aulas de Química no Ensino Médio. Para tanto, procuramos traçar um perfil dos leitores em aulas de Química, através da elaboração de um questionário sobre leitura, aplicação do mesmo e análise das respostas dos estudantes
Time-lapse monitoring of root water uptake using electrical resistivity tomography and mise-à-la-masse: a vineyard infiltration experiment
Abstract. This paper presents a time-lapse application of
electrical methods (electrical resistivity tomography, ERT; and
mise-à-la-masse, MALM) for monitoring plant roots and their activity
(root water uptake) during a controlled infiltration experiment. The use of
non-invasive geophysical monitoring is of increasing interest as these
techniques provide time-lapse imaging of processes that otherwise can only
be measured at few specific spatial locations. The experiment here described was conducted in a vineyard in Bordeaux (France) and was focused on the
behaviour of two neighbouring grapevines. The joint application of ERT and
MALM has several advantages. While ERT in time-lapse mode is sensitive to
changes in soil electrical resistivity and thus to the factors controlling
it (mainly soil water content, in this context), MALM uses DC current
injected into a tree stem to image where the plant root system is in effective
electrical contact with the soil at locations that are likely to be the same
where root water uptake (RWU) takes place. Thus, ERT and MALM provide
complementary information about the root structure and activity. The
experiment shows that the region of likely electrical current sources
produced by MALM does not change significantly during the infiltration time
in spite of the strong changes of electrical resistivity caused by changes
in soil water content. Ultimately, the interpretation of the current source
distribution strengthened the hypothesis of using current as a proxy for
root detection. This fact, together with the evidence that current injection
in the soil and in the stem produces totally different voltage patterns,
corroborates the idea that this application of MALM highlights the active
root density in the soil. When considering the electrical resistivity
changes (as measured by ERT) inside the stationary volume of active roots
delineated by MALM, the overall tendency is towards a resistivity increase
during irrigation time, which can be linked to a decrease in soil water
content caused by root water uptake. On the contrary, when considering the
soil volume outside the MALM-derived root water uptake region, the
electrical resistivity tends to decrease as an effect of soil water content
increase caused by the infiltration. The use of a simplified infiltration
model confirms at least qualitatively this behaviour. The monitoring results
are particularly promising, and the method can be applied to a variety of
scales including the laboratory scale where direct evidence of root
structure and root water uptake can help corroborate the approach. Once
fully validated, the joint use of MALM and ERT can be used as a valuable
tool to study the activity of roots under a wide variety of field
conditions
Use of small scale electrical resistivity tomography to identify soil-root interactions during deficit irrigation
Plant roots activity affect the exchanges of mass and energy between the soil and atmosphere. However, it is challenging to monitor the activity of the root-zone because roots are not visible from the soil surface, and root systems undergo spatial and temporal variations in response to internal and external conditions. Therefore, measurements of the activity of root systems are interesting to ecohydrologists in general, and are especially important for specific applications, such as irrigation water management. This study demonstrates the use of small scale three-dimensional (3-D) electrical resistivity tomography (ERT) to monitor the root-zone of orange trees irrigated by two different regimes: (i) full rate, in which 100% of the crop evapotranspiration (ETc) is provided; and (ii) partial root-zone drying (PRD), in which 50% of ETc is supplied to alternate sides of the tree. We performed time-lapse 3-D ERT measurements on these trees from 5 June to 24 September 2015, and compared the long-term and short-term changes before, during, and after irrigation events. Given the small changes in soil temperature and pore water electrical conductivity, we interpreted changes of soil electrical resistivity from 3-D ERT data as proxies for changes in soil water content. The ERT results are consistent with measurements of transpiration flux and soil temperature. The changes in electrical resistivity obtained from ERT measurements in this case study indicate that root water uptake (RWU) processes occur at the 0.1 m scale, and highlight the impact of different irrigation schemes. (C) 2017 Elsevier B.V. All rights reserved
Small-scale characterization of vine plant root water uptake via 3-D electrical resistivity tomography and mise-à-la-masse method
The investigation of plant roots is inherently difficult and often neglected.
Being out of sight, roots are often out of mind. Nevertheless, roots play a key role
in the exchange of mass and energy between soil and the atmosphere, in addition to
the many practical applications in agriculture. In this paper, we propose a
method for roots imaging based on the joint use of two electrical
noninvasive methods: electrical resistivity tomography (ERT) and
mise-à-la-masse (MALM). The approach is based on the key assumption that the
plant root system acts as an electrically conductive body, so that injecting
electrical current into the plant stem will ultimately result in the injection
of current into the subsoil through the root system, and particularly through
the root terminations via hair roots. Evidence from field data, showing that
voltage distribution is very different whether current is injected into the
tree stem or in the ground, strongly supports this hypothesis. The proposed
procedure involves a stepwise inversion of both ERT and MALM data that
ultimately leads to the identification of electrical resistivity (ER)
distribution and of the current injection root distribution in the
three-dimensional soil space. This, in turn, is a proxy to the active (hair)
root density in the ground. We tested the proposed procedure on synthetic
data and, more importantly, on field data collected in a vineyard, where the
estimated depth of the root zone proved to be in agreement with literature on
similar crops. The proposed noninvasive approach is a step forward towards a
better quantification of root structure and functioning.</p
Field observations of canopy flows over complex terrain
The investigation of airflow over and within forests in complex terrain has been, until recently, limited to a handful of modelling and laboratory studies. Here, we present an observational dataset of airflow measurements inside and above a forest situated on a ridge on the Isle of Arran, Scotland. The spatial coverage of the observations all the way across the ridge makes this a unique dataset. Two case studies of across-ridge flow under near-neutral conditions are presented and compared with recent idealized two-dimensional modelling studies. Changes in the canopy profiles of both mean wind and turbulent quantities across the ridge are broadly consistent with these idealized studies. Flow separation over the lee slope is seen as a ubiquitous feature of the flow. The three-dimensional nature of the terrain and the heterogeneous forest canopy does however lead to significant variations in the flow separation across the ridge, particularly over the less steep western slope. Furthermore, strong directional shear with height in regions of flow separation has a significant impact on the Reynolds stress terms and other turbulent statistics. Also observed is a decrease in the variability of the wind speed over the summit and lee slope, which has not been seen in previous studies. This dataset should provide a valuable resource for validating models of canopy flow over real, complex terrain
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