57 research outputs found
COMBINED USE OF OPEN-AIR AND INDOOR FUMIGATION SYSTEMS TO STUDY EFFECTS OF SO-2 ON LEACHING PROCESSES IN SCOTS PINE LITTER
No full textBoth an open-air fumigation system and a laboratory-based system were used to expose decomposing Scots pine (Pinus sylvestris L.) needles to controlled concentrations of SO2 (arithmetric mean less-than-or-equal-to 48 nl litre-1) during a period, in total, of 301 days. The experimental design involved reciprocal litter transplants from 'clean' to 'polluted' air and vice versa, using the two fumigation systems. The objectives were (1) to observe the effects of SO2 on leachate and litter chemistry, (2) to assess whether pollution-induced changes are reversible in clean air, and (3) to test the suitability of small-scale fumigation chambers (litter microcosms) compared with open-air systems in soil studies.Through the formation of SO4(2-) ions, dry-deposited SO2 exhibited a marked capacity to remove 'base' cations (Ca2+, Mg2+ and K+) from decomposing pine needles, and also to acidify litter leachates (as indicated by proton fluxes from the litter). When litter was transferred from polluted air (48 nl litre-1 SO2, in the open-air system) to either clean or polluted air in the laboratory, the effects of prior exposure to SO2 on leachate composition were still evident even after 86 days: the role of base cation depletion within the litter, caused by SO42- -induced leaching, is discussed.Data for SO42- fluxes in leachates collected from the small-scale chambers indicated that dry deposition velocities for SO2 were not anomalously high within this fumigation system. It is therefore concluded that microcosm studies can provide information complementary to the open-air fumigation approach in soils research.</p
Exploring the "overflow tap" theory: linking forest soil CO2 fluxes and individual mycorrhizosphere components to photosynthesis
No full text"Quantifying soil organic carbon stocks (SOC) and their dynamics accurately is crucial for better predictions of climate change feedbacks within the atmosphere-vegetation soil system. However, the components, environmental responses and controls of the soil CO2 efflux (Rs) are still unclear and limited by field data availability. The objectives of this study were (1) to quantify the contribution of the various Rs components, specifically its mycorrhizal component, (2) to determine their temporal variability, and (3) to establish their environmental responses and dependence on gross primary productivity (GPP). In a temperate deciduous oak forest in south east England hourly soil and ecosystem CO2 fluxes over four years were measured using automated soil chambers and eddy covariance techniques. Mesh-bag and steel collar soil chamber treatments prevented root or both root and mycorrhizal hyphal in-growth, respectively, to allow separation of heterotrophic (Rh) and autotrophic (Ra) soil CO2 fluxes and the Ra components, roots (Rr) and mycorrhizal hyphae (Rm). Annual cumulative Rs values were very similar between years (740 ± 43 g C m-2 yr-1 ) with an average flux of 2.0 ± 0.3 µmol CO2 m-2 s-1 , but Rs components varied. On average, annual Rr , Rm and Rh fluxes contributed 38, 18 and 44 %, respectively, showing a large Ra contribution (56 %) with a considerable Rm component varying seasonally. Soil temperature largely explained the daily variation of Rs (R2 = 0.81), mostly because of strong responses by Rh (R2 = 0.65) and less so for Rr (R2 = 0.41) and Rm (R2 = 0.18). Time series analysis revealed strong daily periodicities for Rs and Rr , whilst Rm was dominated by seasonal (~150 days), and Rh by annual periodicities. Wavelet coherence analysis revealed that Rr and Rm were related to short-term (daily) GPP changes, but for Rm there was a strong relationship with GPP over much longer (weekly to monthly) periods and notably during periods of low Rr . The need to include individual Rs components in C flux models is discussed, in particular, the need to represent the linkage between GPP and Ra components, in addition to temperature responses for each component. The potential consequences of these findings for understanding the limitations for long-term forest C sequestration are highlighted, as GPP via root-derived C including Rm seems to function as a C “overflow tap”, with implications on the turnover of SOC.
CHEMICAL-CHANGES IN DECOMPOSING FOREST LITTER IN RESPONSE TO ATMOSPHERIC SULFUR-DIOXIDE
No full textDecomposing needle and leaf litter, from a pine (Pinus sylvestris L.) stand and a mixed deciduous woodland, respectively, were exposed to arithmetic mean SO2 concentrations of up to 50 nl l-1 (mm3 m-3) in controlled field-based experiments lasting up to 215 d. The objectives of the study were: (1) to evaluate whether SO2 concentrations, known to occur in parts of Europe, could alter the chemical composition of forest litter and leachates, and (2) to use such information to complement results obtained during microbiological studies (Wookey et al., 1991).Dry deposition of SO2 on the litter resulted in the production of sulphate during damp conditions or when the litter was moist. The formation of SO4(2-) and associated H+ ions led to cation exchange processes whereby Mg2+ and Ca2+ in particular were leached from the litter. This resulted in significant (P <0.01) depletion of magnesium and calcium in both litter types, even at the lowest SO2 concentrations tested (15 nl l-1). Incomplete buffering by base cations resulted in acidification of leachates.The magnitude of cation leaching and depletion within the litter was not always linearly related to SO2 or leachate SO4(2-) concentrations, and the role of microbial processes and litter quality as modifiers of such responses is considered.</p
Terrestrial organic carbon storage in a British moorland
No full textAccurate estimates for the size of terrestrial organic carbon (C) stores are needed to determine their importance in regulating atmospheric CO2 concentrations. The C stored in vegetation and soil components of a British moorland was evaluated in order to: (i) investigate the importance of these ecosystems for C storage and (ii) test the accuracy of the United Kingdom's terrestrial C inventory. The area of vegetation and soil types was determined using existing digitized maps and a Geographical Information System (GIS). The importance of evaluating C storage using 2D area projections, as opposed to true surface areas, was investigated and found to be largely insignificant. Vegetation C storage was estimated from published results of productivity studies at the site supplemented by field sampling to evaluate soil C storage. Vegetation was found to be much less important for C storage than soil, with peat soils, particularly Blanket bog, containing the greatest amounts of C. Whilst the total amount of C in vegetation was similar to the UK national C inventory's estimate for the same area, the national inventory estimate for soil C was over three times higher than the value derived in the current study. Because the UK's C inventory can be considered relatively accurate compared to many others, the results imply that current estimates for soil C storage, at national and global scales, should be treated with caution
EFFECTS OF ATMOSPHERIC SULFUR-DIOXIDE ON MICROBIAL ACTIVITY IN DECOMPOSING FOREST LITTER
No full textAt extremely high concentrations, relative to those occurring in the atmosphere, sulphur dioxide (SO2) has known antimicrobial properties. There is also circumstantial evidence, based on field surveys, to indicate that the occurrence and activities of a number of phylloplane fungi and soil microorganisms are correlated with atmospheric concentrations of SO2 occurring in parts of Europe and North America. The results of these studies need to be corroborated by controlled fumigation experiments applying realistic concentrations of SO2. Unfortunately such experiments have been rare.The suggestion that SO2 may be affecting soil microorganisms merits serious consideration because of the fundamental role of these organisms in maintaining soil fertility, especially in forests. Events in the forest litter layer are considered to be particularly important because it forms an interface between the atmosphere and the soil system.The research described in this paper involved exposing leaf litter (from a Pinus sylvestris L. stand and a mixed deciduous woodland) to arithmetic mean concentrations of SO2 of less-than-or-equal-to 0.050-mu-l l-1 in controlled field-based experiments lasting up to 215 days. Fungal cultures, isolated from the pine litter, were also fumigated with less-than-or-equal-to 0.053-mu-l l-1 SO2 in laboratory-based studies.Results showed that arithmetic mean concentrations of SO2 as low as 0.015-mu-l l-1 significantly reduced microbial activity (respiration) in both pine and deciduous litter in the open-air fumigation experiment. Results should also be interpreted in relation to the peak SO2 concentrations (often considerably higher than arithmetic means) to which the litter was exposed. Pure cultures of Cladosporium cladosporiodes (Fres.) de Vries and Coniothyrium olivaceum Bonord, isolated from the litter, were shown to be sensitive to SO2 concentrations of less-than-or-equal-to 0.053-mu-l l-1 in laboratory-based fumigations.It is concluded that the dry deposition of SO2 to forest soils may have important implications for nutrient cycling processes and therefore forest productivity and community structure.</p
Making a CASE for the third space
No full textThis thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonThe Thinking Science programme or CASE (Cognitive Acceleration through Science Education) is a
sequence of thirty lessons that seek to develop pupil reasoning in the context of secondary science. CASE is
based upon the work of Jean Piaget and Lev Vygotsky and was very popular being used by hundreds of
schools, both in the UK and around the world, during the 1990’s and the 2000’s. The lessons and ideas are
still in use today and serve as a lasting legacy for the authors: Philip Adey, Michael Shayer and Carolyn
Yates. This thesis will present an insider’s view of CASE from a teacher who has been using the lessons for
34 years. This perspective will allow the author to articulate an experienced teachers thinking regarding the
principles of CASE. Alongside this an analysis of Vygotskyan psychology, illuminated by Bhabha’s ideas,
will be used to present the concept of the third space as a model to visualise the small group talk taking place
in the CASE classroom.
Since the advent of CASE much of the language it used to describe cognitive development, such as
metacognition, has become common parlance in educational settings. This thesis brings a practitioner
perspective to bear on the principles of CASE and the pupil talk it seeks to generate. Seven CASE lessons
were taught to a secondary, Year 9, class over a period of six months and video recorded. The resulting
lesson plans and transcripts, of small group conversations, enabled the Vygotskian foundations of the CASE
programme to be explored. Bhabha’s notion of the third space was used to categorise talk in a way that is
reflective of the real lives of children and the ideas they carry with them into the classroom. This analysis
enabled an innovative, colour, coding system to be developed to illustrate and track the contours of
children’s talk. This thesis brings a sense of clarity regarding the use of third space theory in educational
settings and bridges a gap in this canon as it takes place in the mainstream secondary classroom within the
context of a core subject. As a result third space talk has now been described and categorised in a way that
allows it to be applied across subjects and in other settings such as special schools.
The Vygotskian concept of a child’s lived experience, perezhivanie, is used to illustrate a possible route for
teacher’s to guide the conversations towards the types of talk supportive of cognitive development. This
research uses the idea of a trigger to show how appropriate challenge can be used to engage learners and this
is uniquely illustrated through the use of a weather map representation of pupil talk. This serves to refresh
CASE and will support and new generation of teachers to better manage the dynamics of small group talk at
a time when the pressure for children, yet again, to be seen and not heard is growing.
The key findings from this study for classroom practitioners can be summarised using the following
headings:
a) Inclusion,
b) Professional choice,
c) Construction talk and,
d) Hope in the zone.
Inclusion points to the fact that pupil funds of knowledge need to be utilised, in the third space, so
that their life-times worth of experiences brought to the classroom are included and acknowledged.
This is true for all learners and the potential of this is supported by the fact that majority of the
pupils highlighted in the transcripts were categorised by the school as SEND.
Professional choice references the fact that choices are made in the planning and conduct of
lessons. To promote thinking teachers can integrate triggers in a way that engages pupils in
intellectual inquiry. Triggers can be included in the lesson conduct or in response to the
conversational turns taken in real-time. Similarly small groups can be orchestrated to develop
construction talk that develops pupils thinking within the two planes described by Vygotsky – the
social and the psychological. If managed utilising the third space then the external interactions with
others support and enhance the inner cognitive life of the individual.
Construction talk is a living vocabulary that verbalises the inner thought life and so is one that
must be inclusive of all forms of talk. The five talk codes reflect the real, honest, messy and playful
conversations taking place in classrooms today as adolescents engage with the cognitive challenges
around which CASE is built. The sensitive use of triggers can engage and guide pupils towards
forms of talk that activate their funds of knowledge and develop both ownership of their talk and a
metacognitive awareness of their thinking.
Hope in the zone – the third space is a theoretical construct that has been successfully used and
applied in a range of educational settings. It has been used here to illuminate construction zone
activity as a powerful time of developmental potential for children facing abstract concepts in
science. Hope in the zone is possible with thoughtful planning and the use of specific classroom
management techniques following the clear pedagogical guidelines for such techniques that are
provided within this thesis.
The outcomes of this research form a practical and easy to apply guide to the use of the third space
as a bridge between pupil knowledge and curricular content and serves to both update and
reposition CASE for a new generation of teachers in a way that is inclusive of all learners. The time
has come for the third space to become more mainstream curricular vehicle. Historically it has been
hard to find and was an idea heavy on metaphor yet light on practical examples of realistic teaching
advice. This thesis shows what it looks and sounds like in the classroom in a way that is inclusive of
all learners. C.S. Lewis said that children are not a distraction from more important work - they are
the most important work. The outcomes of this thesis will help teachers to carry out such work,
work that will outlive CASE and last long beyond my life in the classroom
Role of CH(4) oxidation, production and transport in forest soil CH(4) flux
No full textForest soils are an important sink for atmospheric CH(4) but the contribution of CH(4) oxidation, production and transport to the overall CH(4) flux is difficult to quantify. It is important to understand the role these processes play in CH(4) dynamics of forest soils, to enable prediction of how the size of this sink will respond to future environmental change. Methane oxidation, production and transport were investigated for a temperate forest soil, previously shown to be a net CH(4) consumer, to determine the extent to which physical and biological processes contributed to the not flux. The sum of oxidation rates for soil layers were significantly greater (P</p
The effects of acid nitrogen and acid sulphur deposition on CH4 oxidation in a forest soil: a laboratory study
No full textSieved soil and soil core experiments were performed to determine the potential sensitivity of forest soil CH4 oxidation to oxidised N, reduced N and oxidised S atmospheric deposition. Ammonium sulphate was used to simulate reduced N deposition, HNO3 oxidised N deposition and H2SO4 oxidised S deposition. The effects of NH4+, NO3-, SO42- and H+ on soil CH4 flux were shown to be governed by the associated counter-anion or cation of the investigated ions. Ammonium sulphate, at concentrations greater than those that would be experienced in polluted throughfall, showed a low potential to cause inhibition of CH4 oxidation. In contrast, HNO3 Strongly inhibited net CH4 oxidation in sieved soils and also in soil cores. In addition, soil CO2 production was inhibited and the organic and mineral soil horizons acidified in HNO3 treated soil cores. This suggested that the HNO3 effect on CH4 flux might be indirectly mediated through aluminium toxicity. Sulphuric acid only inhibited CH4 oxidation when added at pH 1. At concentrations more representative of heavily polluted throughfall, H2SO4 had no effect on soil CH4 flux or CO2 production from soil cores, even after 210 days of repeated addition. In contrast to HNO3 additions, acidification of the soil was not marked and was only significant for the mineral soil. The findings suggest that the response of forest soil CH4 oxidation to atmospheric acid deposition is strongly dependent on the form of acid deposition. (C) 2001 Elsevier Science Ltd. All rights reserved.</p
Controlling factors and effects of chronic nitrogen and sulphur deposition on methane oxidation in a temperate forest soil
No full textSoil CH(4) flux rates were determined on 28 occasions between June 1996 and July 1997 in a temperate deciduous woodland in south-west England. The effects of environmental and edaphic factors on flux rates and the effects of chronic deposition of sulphuric acid, nitric acid and ammonium sulphate were investigated. The soil was a consistent net CH4 oxidiser, with mean (n = 10) oxidation rates for plots exposed to ambient throughfall ranging from 44.3 to 110.6 mug CH(4) m(-2) h(-1) between samplings; net CH(4) production was not observed. The annual mean uptake rate differed by only 6% from the annual mean flux calculated from the literature for other studies of >364 d duration in temperate and boreal deciduous woodlands. The CH4 uptake rates were correlated with soil water potential (square-root transformed), temperature and depth of organic horizon (r(2) = 0.78, 0.30 and 0.41, respectively). Soil water potential was the best predictor of net CH(4) oxidation rates and when temperature was added to the regression model no improvement in the r2 was observed. The chronic deposition of sulphuric acid stimulated net methane oxidation (P <0.05), while the chronic deposition of nitric acid and ammonium sulphate had no significant effect. (C) 2001 Elsevier Science Ltd. All rights reserved.</p
Rhizosphere activity and atmospheric methane concentrations drive variations of methane fluxes in a temperate forest soil
No full textAerated soils represent an important sink for atmospheric methane (CH4), due to the effect of methanotrophic bacteria, thus mitigating current atmospheric CH4increases. Whilst rates of CH4oxidation have been linked to types of vegetation cover, there has been no systematic investigation of the interaction between plants and soil in relation to the strength of the soil CH4sink. We used quasi-continuous automated chamber measurements of soil CH4and CO2flux from soil collar treatments that selectively include root and ectomycorrhizal (ECM) mycelium to investigate the role of rhizosphere activity as well as the effects of other environmental drivers on CH4uptake in a temperate coniferous forest soil. We also assessed the potential impact of measurement bias from sporadic chamber measurements in altering estimates of soil CO2efflux and CH4uptake. Results show a clear effect of the presence of live roots and ECM mycelium on soil CO2efflux and CH4uptake. The presence of ECM hyphae alone (without plant roots) showed intermediate fluxes of both CO2and CH4relative to soils that either contained roots and ECM mycelium, or soil lacking root- and ECM mycelium. Regression analysis confirmed a significant influence of soil moisture as well as temperature on flux dynamics of both CH4and CO2flux. We further found a surprising increase in soil CH4uptake during the night, and discuss diurnal fluctuations in atmospheric CH4(with higher concentrations during stable atmospheric conditions at night) as a potential driver of CH4oxidation rates. Using the high temporal resolution of our data set, we show that low-frequency sampling results in systematic bias of up-scaled flux estimates, resulting in under-estimates of up to 20% at our study site, due to fluctuations in flux dynamics on diurnal as well as longer time scales
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