1,721,099 research outputs found
Changes in carbon and nitrogen stocks following conversion of plantation forest to dairy pasture on Vitrands (Pumice Soils), New Zealand
Full text linkBetween 1990 and 2010 some New Zealand plantation forests underwent deforestation to establish dairy farms. The main area of land-use conversion to pasture is to the north of Lake Taupo in the Central North Island (Figures 1 and 2). Pinus radiata (radiata pine) plantations were established in the late 1920s-early 1930s because the Vitrands (Pumice Soils) predominant in the Central North Island were deficient in Co and other trace elements, causing a fatal stock disease in sheep and cattle known as ‘bush sickness’. Bush sickness was subsequently rectified in the mid-1930s with the regular addition of Co, so pastoral farming became viable. The high price of milk solids has recently led to renewed interest in dairying. Recent studies have shown carbon can accumulate following deforestation and establishment of pasture (Fearnside and Barbosa, 1998; Murty et al. 2002; Hedley et al. 2009). However, more information on the rate of accumulation of carbon after deforestation is needed. Increases in soil carbon can improve physical and chemical soil properties, and is an important store of global carbon
Impacts of conversion from forestry to pasture on soil physical properties of Vitrands (Pumice Soils) in central North Island, New Zealand
Full text linkTens of thousands of hectares of land have been converted from plantation forest to pasture in the central North Island of New Zealand between 2000 and 2010. The land use change was driven by the perceived better long term returns from dairy farming compared with forestry. Pumice Soils (NZ Soil Classification, equivalent to Vitrands in Soil Taxonomy) in the central North Island are formed on pumice deposited mainly from the AD 232 ± 5 Taupo volcanic eruption. The texture of Pumice Soils (Figure 1) varies from silt to coarse gravel and they have weak structure and erode easily when disturbed. Water holding capacity may be low but increases as the organic matter content of the topsoil is built up
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Carbon dosing of denitrifying bioreactors to remove nitrate from agricultural drainage
Full text linkSeveral studies have demonstrated that denitrifying woodchips bioreactors effectively remove nitrate from a broad spectrum of wastewater. Even though bioreactors have a comparatively small spatial footprint and are straightforward to construct, the low long-term nitrate removal efficiency they provide compared to other mitigation options, such as constructed wetlands, may limit their utilization by catchment managers and landowners. This thesis investigated the use of external carbon dosing in bioreactors to improve nitrate removal and quantified some potential adverse effects of carbon dosing on bioreactors and downstream aquatic environments. Through observations ranging from field to mesocosm experiments, this thesis sought to (1) determine whether and to what extent external carbon dosing could improve nitrate removal in bioreactors and (2) assess the potential adverse effects of carbon dosing, such as reduced hydraulic performance and pollution swapping.
The first component of the study evaluated the carbon dosing of a pilot-scale (58 m³) bioreactor treating drainage waters from a 0.65 ha paddock on a dairy farm. The effects of carbon dosing on the bioreactor's nitrate removal rates were assessed following a constant dosage of 8% (v/v) methanol solution at 10 mL min⁻¹ to the bioreactor's inlet distributor. Sulfate reduction and losses of added methanol from the bioreactor’s outlet were quantified as the potential adverse effects of external carbon dosing. Methanol dosing increased seasonal nitrate removal rates to 8 g N m⁻³ day⁻¹ in 2020 and 5 g N m⁻³ day⁻¹ in 2021 (with a halved dosing rate), compared to 1 g N m⁻³ day⁻¹ in the undosed bioreactor in 2018. Even under nitrate-limiting conditions, the added methanol was effectively removed in the bioreactor, with a mean removal rate of 106 g CH₃OH-C m⁻³ day⁻¹
. Methanol concentrations decreased by order of magnitude along the bioreactor (lengthwise) and never exceeded 50 mg CH₃OH-C L⁻¹ at the outflow. The added carbon caused sulfate reduction with a mean removal rate of 8.5 g SO4²⁻-S m⁻³ day⁻¹ in 2020 (higher dosing rate) and 0.5 g SO4²⁻-S m⁻³ day⁻¹ in 2021 (halved dosing rate). Carbon dosage at a continuous rate was shown to be a viable method for increasing nitrate removal while minimizing capital and operational costs. The simplicity of this approach is a significant advantage, and it could be used by a variety of industries, including farmers.
While field observations showed that carbon dosage could improve nitrate removal, the very variable flows and nitrate concentrations made determining nitrate, sulfate, and methanol removal rates difficult. Therefore, the second component of the thesis was to assess nitrate, sulfate and added carbon removal rates more accurately using mesocosms. An empirical model was also developed to calculate the amount of methanol required to remove specific loads of nitrate. Mesocosm bioreactors were designed to share some characteristics with the field bioreactor (for example, added carbon component and dosage ratio) but diverged in that they were hydrologically regulated to eliminate the impact of transient operating circumstances on bioreactor performance. Carbon dosing increased nitrate removal rates from 7 g N m⁻³ day⁻¹ in the control treatment bioreactors (without methanol addition) to 27 g N m⁻³ day⁻¹ in the methanol-dosed treatment bioreactors. Added methanol was removed in either the absence or presence of nitrate, with mean methanol removal rates of 23 g CH₃OH-C m⁻³ day⁻¹ in nitrate prevailing conditions and 17 g CH₃OH-C m⁻³ day⁻¹ in nitrate limiting conditions. The empirical model suggested that a methanol to nitrate ratio of 0.7 resulted in complete nitrate removal.
In the third component of this thesis research, observations from both mesocosm and full-scale bioreactors were used to assess the hydraulic characteristics of bioreactors under various carbon dosage regimes. Field measurements revealed a decrease in hydraulic conductivity from 4601 m day⁻¹ in 2018 (season without carbon dosing) to 1600 m day⁻¹ in 2021 (second year of dosing). Based on tracer tests of the mesocosm bioreactors, I investigated the effects of added carbon on the internal hydraulic performance of bioreactors. The results of the tracer tests revealed that carbon dosing had no significant effect on the hydraulic parameters of the mesocosm bioreactors (p-value > 0.05).
The findings of this thesis have implications for improving the performance of existing bioreactors or for developing new, externally dosed bioreactors with smaller spatial footprints. The constant dosage strategy, demonstrated in the full-scale bioreactor, was effective in increasing nitrate removal rates while also being safe regarding added carbon losses to the receiving environments. The ease of implementation of the constant dosage strategy could increase take-up from landowners and managers. The thesis also provides an understanding of whether and to what extent carbon dosing affects the hydrology of bioreactors, which can be used to develop new bioreactor designs with less backflow and bypass
Microbial Processes and Nitrate removal in Denitrification Beds
No full textAbstract The anthropogenic abundance of reactive nitrogen (N) forms has increased in the last few decades, increasing food production, but also resulting in increased eutrophication, algae blooms, loss of biodiversity, and greenhouse gas (GHG) emissions, in aquatic and terrestrial ecosystems. Denitrification beds are one approach to return this reactive N back to the atmosphere. These beds are large containers filled with a carbon (C) substrate, often wood byproducts. This substrate acts as a C and energy source for denitrifiers to reduce nitrate (NO₃⁻) from point source discharges into non-reactive dinitrogen (N₂) gas. This study investigated the biological mechanisms, controlling factors and adverse effects of NO₃⁻ removal in a woodchip denitrification bed (176 m x 5 m x 1.5 m) treating glasshouse effluent, and in barrels (0.2 m³) testing alternative carbon substrates for use in denitrification beds (pine and eucalyptus woodchips, sawdust, green waste, maize cobs and wheat straw). Furthermore, different techniques for measuring denitrification rates were compared and an approach for determining reliable NO₃⁻ removal rates in denitrification beds was developed.
The NO₃⁻-N removal rates of the large denitrification bed averaged 7.6 g N m⁻³ bed volume d⁻¹ and increased with increasing temperature (Q₁₀ = 2.1). Microbial denitrification was the main NO₃⁻ removal mechanism in the denitrification bed and was always limited by C, rather than by NO₃⁻ availability. Dissimilatory nitrate reduction to ammonium (DNRA) and anammox were likely minor processes due to low ammonia (NH₄⁺) and nitrite (NO₂⁻) concentrations throughout the bed. Sulfate (SO₄²⁻) reduction, and methanogenesis, could not compete with NO₃⁻ reduction for C due to continuously high NO₃⁻ concentrations in the bed (>37 mg N L⁻¹). Aerobic processes dominated in the first few meters of the bed and close to the surface, but dissolved oxygen (DO) concentrations decreased rapidly along the bed from the inlet and remained low throughout most of the bed. There were some adverse effects observed in the denitrification bed associated with NO₃⁻ removal. About 4.3% of NO₃⁻-N removed from the bed was released as nitrous oxide (N₂O), but methane (CH₄) emissions from the surface of the bed were very low. A total of 35.4 kg d⁻¹ of carbon dioxide (CO₂) was released from the bed, but was not considered to contribute to a net increase in CO₂ concentrations of the atmosphere as the substrate (woodchips) used in the bed would likely decayed to CO₂ if used for other purposes. A net dissolved organic carbon (DOC) loss from the outlet was not detected. Longevity of the C substrate of the denitrification bed to support denitrification was about 39 years as calculated from the total C losses (CO₂ emissions and release of dissolved CO₂ and DOC from the bed). In a barrel study of different carbon substrates, NO₃⁻ removal was predominantly limited by C availability and temperature (Q₁₀ = 1.2) when NO₃⁻-N concentrations were above 1 mg L⁻¹. All C substrates showed high numbers of denitrification genes (nitrite reductase, nirS and nirK; nitrous oxide reductase, nosZ), providing further support that microbial denitrification was responsible for NO₃⁻ removal. Substrates incubated at 27.1 °C had greater ratio of nir/nosZ genes than substrates incubated at 16.8 °C, which was possibly a partial explanation for higher N₂O production in the warmer barrels. Wheat straw released 10% of NO₃⁻-N removed as dissolved N₂O, while all other carbon substrates released on average about 1.4% of the removed NO₃⁻-N as dissolved N₂O. Methane production occurred when NO₃⁻ concentrations were below 2 mg L-1 in the barrels. Maize cobs removed about 2.5 times more NO₃⁻ than woodchips, but released total organic carbon (TOC) in the outflow and a substantial portion of C was likely consumed by non-denitrifiers. Woodchips had low adverse effects and provided ideal conditions for denitrifiers determined by the relatively high ratio of denitrification gene copies/16S rRNA copies compared to the other C substrates examined.
Investigating different approaches to determine denitrification rates revealed that both the acetylene inhibition method and the copy number of nitrite reductase genes (nirS, nirK) were useful for comparative estimations of NO₃⁻ removal rates between different carbon substrates and temperatures. However, neither approach could be used to quantify actual rates of denitrification. The acetylene inhibition method overestimated the actual NO₃⁻ removal rate by five fold. An in situ push-pull test using enriched ¹⁵NO₃⁻ was useful for determining denitrification rates at one specific point in a denitrification bed but would require multiple testing sites to obtain an average rate of NO₃⁻ removal for the bed. Comparing the ratio of the slopes of natural abundance ¹⁵N-N₂ and ¹⁵N- NO₃⁻ along the length of the bed determined the portion of NO₃⁻ removed by microbial denitrification, but not the denitrification rate. Measurements of dissolved N₂ concentration along the length of the bed were a useful approach to determine denitrification rates. This last approach was rapid and produced relatively accurate rates of NO₃⁻ removal compared to the other approaches conducted in this study. In summary, denitrification beds are an efficient approach for removing NO₃⁻ from point source discharges, but the beds do produce some N₂O. Woodchips could be combined with maize cobs to enhance NO₃⁻ removal rates while keeping adverse effects low in denitrification beds. Measurement of N₂ concentrations along the length and water flow of the bed was the most appropriate approach to determine denitrification rates of denitrifying bioreactors, and may also be useful in other ecosystems with high NO₃⁻ concentration and even flow
- …
