Trenching

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Thomas J Overbye - One of the best experts on this subject based on the ideXlab platform.

  • a graph theoretic approach for addressing Trenching constraints in wind farm collector system design
    Power and Energy Conference at Illinois, 2013
    Co-Authors: S Dutta, Thomas J Overbye
    Abstract:

    This paper addresses the topic of automatically computing cable layout designs of large scale wind farms. A network of cables in a wind farm's electrical collector system collects power generated by turbines and brings to the wind farm substation. Frequently, sections of the land area of a large wind farm are restricted for excavating and burying these cables, i.e. Trenching. Such restrictions might arise from the landowners, presence of water bodies etc. It is important to take into consideration these real-life constraints in the process of automating designs of optimal wind farm electrical collector systems. This paper presents a graph-theory based methodology for addressing these Trenching constraints in optimal collector system designs. The developed methodology has been tested on a real-life large wind farm.

  • optimal wind farm collector system topology design considering total Trenching length
    IEEE Transactions on Sustainable Energy, 2012
    Co-Authors: S Dutta, Thomas J Overbye
    Abstract:

    This paper addresses the optimal cable layout design of a collector system in a large-scale wind farm. The objective is the minimization of total Trenching length which is the sum of lengths of all branches of the collector system tree. A graph-theoretic minimum spanning tree algorithm has been used as a starting algorithm, and improvements and modifications have been proposed to cater to the constraints and characteristics of a wind farm collector system. The contribution of this paper is three-fold. First, an algorithm has been proposed to further improve the results of the minimum spanning tree algorithm by creating external splice locations separate from the wind turbine locations in computing the cable layout configuration. Second, an algorithm has been proposed to compute the minimum Trenching length layout configuration under the constraint of a prespecified maximum number of turbines connected to a feeder cable. Third, an algorithm has been developed to automatically compute the direction and magnitude of power flow on the different cables and to assign cable sizes accordingly.

Edmund V J Tanner - One of the best experts on this subject based on the ideXlab platform.

  • a new approach to Trenching experiments for measuring root rhizosphere respiration in a lowland tropical forest
    Soil Biology & Biochemistry, 2010
    Co-Authors: Emma J Sayer, Edmund V J Tanner
    Abstract:

    Soil respiration in tropical forests is a major source of atmospheric CO2. The ability to partition soil respiration into its individual components is becoming increasingly important to predict the effects of disturbance on CO2 efflux from the soil as the responses of heterotrophic and autotrophic respiration to change are likely to differ. However, current field methods to partition respiration suffer from various methodological artefacts; root–rhizosphere respiration is particularly difficult to estimate. We used trenched subplots to estimate root–rhizosphere respiration in large-scale litter addition (L+), litter removal (L−) and control (CT) plots in a lowland tropical semi-evergreen forest in Panama. We took a new approach to Trenching by making measurements immediately before-and-after Trenching and comparing them to biweekly measurements made over one year. Root–rhizosphere respiration was estimated to be 38%, 17% and 27% in the CT, L+, and L− plots, respectively, from the measurements taken immediately before and one day after Trenching in May–June 2007. Biweekly measurements over the following year provided no estimates of root–rhizosphere respiration for the first seven months due to decomposition of decaying roots. We were also unable to estimate root–rhizosphere respiration during the dry season due to differences in soil water content between trenched and untrenched soil. However, biweekly measurements taken during the early rainy season one year after Trenching (May–June 2008) provided estimates of root–rhizosphere respiration of 39%, 24% and 36% in the CT, L+, and L− plots, respectively, which are very similar to those obtained during the first day after Trenching. We suggest that measurements taken immediately before and one day after root excision are a viable method for a rapid estimation of root–rhizosphere respiration without the methodological artefacts usually associated with Trenching experiments.

  • Trenching increased growth and irrigation increased survival of tree seedlings in the understorey of a semi evergreen rain forest in panama
    Journal of Tropical Ecology, 2007
    Co-Authors: Edmund V J Tanner, Ignacio M Barberis
    Abstract:

    Seedlings in tropical forests are ultimately the source of canopy trees, thus factors controlling their composition and growth potentially influence the composition of the forest. Seedlings are primarily limited by above-ground competition with trees, but below-ground competition is potentially also important. Over 4 y we experimentally reduced below-ground competition by Trenching to 50 cm and reduced drought stress by irrigating in the dry seasons (6 cm every 2 d) in the understorey of a semi-evergreen rain forest in Panama. There were four irrigated plots and four unirrigated, in each plot there were eight subplots (four trenched, four untrenched); 32 seedlings (two per subplot) of each of four tree species were equally allocated to the four treaments; the four species were: Aspidosperma cruenta ; Gustavia superba ; Simarouba amara and Tachigali versicolor . Over all species together, Trenching increased seedling height by 41% and leaf area by 140% over 4 y. The cause was likely to be increased nutrient supply, because the amounts of N, K and Ca were higher in trenched plants, though concentrations were not higher. Irrigation had no significant effect on growth. Irrigation, but not Trenching, reduced seedling mortality. We conclude that below-ground competition was a major limitation for seedling growth for at least some common species ( Gustavia and Tachigali in this experiment). More experiments are necessary to determine whether below-ground competition is also important in other tropical rain forests on fairly fertile soils.

  • gaps and root Trenching increase tree seedling growth in panamanian semi evergreen forest
    Ecology, 2005
    Co-Authors: Ignacio M Barberis, Edmund V J Tanner
    Abstract:

    Although competition between plants is nearly universal in vegetation, we know relatively little about belowground competition and how it interacts with aboveground competition in tropical forests, and almost nothing about such interactions on soils of intermediate fertility in sites with a moderate dry season, despite the fact that such forests are extensive. We investigated this over one year in a Panamanian tropical semi-evergreen rain forest, using tree seedlings (Simarouba amara, Gustavia superba, Tachigali versicolor, and Aspidosperma cruenta; least to most shade tolerant), experimental gaps, and Trenching. Gaps increased growth and decreased mortality; growth increases were: Simarouba 684% (increase in height relative growth rate), Gustavia 411%, Aspidosperma 364%, and Tachigali 324%. Trenching in gaps increased growth in three species (Simarouba 49%, Gustavia 63%, and Aspidosperma 38%) but had very small effects in the understory; Trenching did not affect mortality. We infer that Trenching caused increased growth due to increased nutrients in the wet season, and increased water and/or nutrients in the dry season. Thus, across the tropics, in all but the wettest sites with fertile soils, seedlings of many species will be limited by belowground competition, at least in gaps. This is similar to the pervasive importance of belowground competition in temperate forests.

Alf Ekblad - One of the best experts on this subject based on the ideXlab platform.

  • autotrophic and heterotrophic soil respiration in a norway spruce forest estimating the root decomposition and soil moisture effects in a Trenching experiment
    Biogeochemistry, 2011
    Co-Authors: Daniel Comstedt, Bjorn Bostrom, Alf Ekblad
    Abstract:

    The two components of soil respiration, autotrophic respiration (from roots, mycorrhizal hyphae and associated microbes) and heterotrophic respiration (from decomposers), was separated in a root Trenching experiment in a Norway spruce forest. In June 2003, cylinders (29.7 cm diameter) were inserted to 50 cm soil depth and respiration was measured both outside (control) and inside the trenched areas. The potential problems associated with the Trenching treatment, increased decomposition of roots and ectomycorrhizal mycelia and changed soil moisture conditions, were handled by empirical modelling. The model was calibrated with respiration, moisture and temperature data of 2004 from the trenched plots as a training set. We estimate that over the first 5 months after the Trenching, 45% of respiration from the trenched plots was an artefact of the treatment. Of this, 29% was a water difference effect and 16% resulted from root and mycelia decomposition. Autotrophic and heterotrophic respiration contributed to about 50% each of total soil respiration in the control plots averaged over the two growing seasons. We show that the potential problems with the Trenching, decomposing roots and mycelia and soil moisture effects, can be handled by a modelling approach, which is an alternative to the sequential root harvesting technique.

S Dutta - One of the best experts on this subject based on the ideXlab platform.

  • a graph theoretic approach for addressing Trenching constraints in wind farm collector system design
    Power and Energy Conference at Illinois, 2013
    Co-Authors: S Dutta, Thomas J Overbye
    Abstract:

    This paper addresses the topic of automatically computing cable layout designs of large scale wind farms. A network of cables in a wind farm's electrical collector system collects power generated by turbines and brings to the wind farm substation. Frequently, sections of the land area of a large wind farm are restricted for excavating and burying these cables, i.e. Trenching. Such restrictions might arise from the landowners, presence of water bodies etc. It is important to take into consideration these real-life constraints in the process of automating designs of optimal wind farm electrical collector systems. This paper presents a graph-theory based methodology for addressing these Trenching constraints in optimal collector system designs. The developed methodology has been tested on a real-life large wind farm.

  • optimal wind farm collector system topology design considering total Trenching length
    IEEE Transactions on Sustainable Energy, 2012
    Co-Authors: S Dutta, Thomas J Overbye
    Abstract:

    This paper addresses the optimal cable layout design of a collector system in a large-scale wind farm. The objective is the minimization of total Trenching length which is the sum of lengths of all branches of the collector system tree. A graph-theoretic minimum spanning tree algorithm has been used as a starting algorithm, and improvements and modifications have been proposed to cater to the constraints and characteristics of a wind farm collector system. The contribution of this paper is three-fold. First, an algorithm has been proposed to further improve the results of the minimum spanning tree algorithm by creating external splice locations separate from the wind turbine locations in computing the cable layout configuration. Second, an algorithm has been proposed to compute the minimum Trenching length layout configuration under the constraint of a prespecified maximum number of turbines connected to a feeder cable. Third, an algorithm has been developed to automatically compute the direction and magnitude of power flow on the different cables and to assign cable sizes accordingly.

Marcandre Giasson - One of the best experts on this subject based on the ideXlab platform.

  • partitioning soil respiration examining the artifacts of the Trenching method
    Biogeochemistry, 2018
    Co-Authors: Kathleen Savage, Adrien C Finzi, Eric A Davidson, Rose Abramoff, Marcandre Giasson
    Abstract:

    Total soil respiration (Rt) is a combination of autotrophic (Ra) and heterotrophic respiration (Rh). Root exclusion methods, such as soil Trenching, are often utilized to separate these components. This method involves severing the rooting system surrounding a plot to remove the Ra component. However, soil Trenching has potential limitations including (1) reduced water uptake in trenched plots that increases soil water content, which is one of the environmental controllers of Rt in many ecosystems, and (2) increased available carbon substrate for Rh caused by recently severed dead roots. We present a methodology that utilizes a bayesian modeling framework to quantify the magnitude of artifacts from a large Trenching manipulation experiment. Thus methodology corrects Rh and Ra observations at daily to seasonal time scales. This study finds that the artifacts, due to recently severed roots, persist over a 2 years study period and the artifacts due to altered soil moisture had the greatest impact during drought conditions.

  • Trenching reduces soil heterotrophic activity in a loblolly pine pinus taeda forest exposed to elevated atmospheric co2 and n fertilization
    Agricultural and Forest Meteorology, 2012
    Co-Authors: John E Drake, Andrew C Oishi, Marcandre Giasson, Ram Oren, Kurt H Johnsen, Adrien C Finzi
    Abstract:

    Abstract Forests return large quantities of C to the atmosphere through soil respiration ( R soil ), which is often conceptually separated into autotrophic C respired by living roots ( R root ) and heterotrophic decomposition ( R het ) of soil organic matter (SOM). Live roots provide C sources for microbial metabolism via exudation, allocation to fungal associates, sloughed-off cells, and secretions such as mucilage production, suggesting a coupling between the activity of roots and heterotrophs. We addressed the strength of root effects on the activity of microbes and exo-enzymes by removing live-root-C inputs to areas of soil with a Trenching experiment. We examined the extent to which Trenching affected metrics of soil heterotrophic activity (proteolytic enzyme activity, microbial respiration, potential net N mineralization and nitrification, and exo-enzyme activities) in a forest exposed to elevated atmospheric [CO 2 ] and N fertilization, and used automated measurements of R soil in trenched and un-trenched plots to estimate R root and R het components. Trenching decreased many metrics of heterotrophic activity and increased net N mineralization and nitrification, suggesting that the removal of root-C inputs reduced R het by exacerbating microbial C limitation and stimulating waste-N excretion. This Trenching effect was muted by N fertilization alone but not when N fertilization was combined with elevated CO 2 , consistent with known patterns of belowground C allocation at this site. Live-root-C inputs to soils and heterotrophic activity are tightly coupled, so root severing techniques like Trenching are not likely to achieve robust quantitative estimates of R root or R het .