3,204 research outputs found
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Impact of earthworms on trace element solubility in contaminated mine soils amended with green waste compost
The common practice of remediating metal contaminated mine soils with compost can reduce metal mobility and promote revegetation, but the effect of introduced or colonising earthworms on metal solubility is largely unknown. We amended soils from an As/Cu (1150 mgAs kg−1 and 362 mgCu kg−1) and Pb/Zn mine (4550 mgPb kg−1 and 908 mgZn kg−1) with 0, 5, 10, 15 and 20% compost and then introduced Lumbricus terrestris. Porewater was sampled and soil extracted with water to determine trace element solubility, pH and soluble organic carbon. Compost reduced Cu, Pb and Zn, but increased As solubility. Earthworms decreased water soluble Cu and As but increased Pb and Zn in porewater. The effect of the earthworms decreased with increasing compost amendment. The impact of the compost and the earthworms on metal solubility is explained by their effect on pH and soluble organic carbon and the environmental chemistry of each element
Impact of the earthworm Lumbricus terrestris (L.) on As, Cu, Pb and Zn mobility and speciation in contaminated soils
To assess the risks that contaminated soils pose to the environment properly a greater understanding of how soil biota influence the mobility of metal(loid)s in soils is required. Lumbricus terrestris L. were incubated in three soils contaminated with As, Cu, Pb and Zn. The concentration and speciation of metal(loid)s in pore waters and the mobility and partitioning in casts were compared with earthworm-free soil. Generally the concentrations of water extractable metal(loid)s in earthworm casts were greater than in earthworm-free soil. The impact of the earthworms on concentration and speciation in pore waters was soil and metal specific and could be explained either by earthworm induced changes in soil pH or soluble organic carbon. The mobilisation of metal(loid)s in the environment by earthworm activity may allow for leaching or uptake into biota
Managing urban socio-technical change? Comparing energy technology controversies in three European contexts
A {\em local graph partitioning algorithm} finds a set of vertices with small
conductance (i.e. a sparse cut) by adaptively exploring part of a large graph
, starting from a specified vertex. For the algorithm to be local, its
complexity must be bounded in terms of the size of the set that it outputs,
with at most a weak dependence on the number of vertices in . Previous
local partitioning algorithms find sparse cuts using random walks and
personalized PageRank. In this paper, we introduce a randomized local
partitioning algorithm that finds a sparse cut by simulating the {\em
volume-biased evolving set process}, which is a Markov chain on sets of
vertices. We prove that for any set of vertices that has conductance at
most , for at least half of the starting vertices in our algorithm
will output (with probability at least half), a set of conductance
. We prove that for a given run of the algorithm,
the expected ratio between its computational complexity and the volume of the
set that it outputs is . In comparison, the best
previous local partitioning algorithm, due to Andersen, Chung, and Lang, has
the same approximation guarantee, but a larger ratio of between the complexity and output volume. Using our local
partitioning algorithm as a subroutine, we construct a fast algorithm for
finding balanced cuts. Given a fixed value of , the resulting algorithm
has complexity and returns a cut with
conductance and volume at least ,
where is the largest volume of any set with conductance at most
.Comment: 20 pages, no figure
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Crystallization of calcite from amorphous calcium carbonate: earthworms show the way
No abstract available
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Do earthworms impact metal mobility and availability in soil? A review
The importance of earthworms to ecosystem functioning has led to many studies on the impacts of metals on earthworms. Far less attention has been paid to the impact that earthworms have on soil metals both in terms of metal mobility and availability. In this review we consider which earthworms have been used in such studies, which soil components have been investigated, which types of soil have been used and what measures of mobility and availability applied. We proceed to review proposed reasons for effects: changes in microbial populations, pH, dissolved organic carbon and metal speciation. The balance of evidence suggests that earthworms increase metal mobility and availability but more studies are required to determine the precise mechanism for this. (C) 2009 Elsevier Ltd. All rights reserved
Microbial Degradation of the Leachable and Lignocellulosic Components of Leaves and Wood from \u3cem\u3eRhizophora mangle\u3c/em\u3e in a Tropical Mangrove Swamp
Preparations of uniformly [14C] labeled mangrove leaves and specifically radiolabeled [14C-lignin] lignocelluloses and [14C -polysaccharide]lignocelluloses from mangrove leaves and wood were used in experiments to determine the microbial rates of mineralization of the leachable and lignocellulosic components of mangrove detritus in aerobic and anaerobic sediments of a tropical mangrove swamp. The bulk of the leachable fraction from mangrove leaves was mineralized relatively rapidly and was assimilated into microbial biomass with high efficiency (30 %). In contrast, rates of mineralization of the lignocellulosic component of mangrove leaves and wood were 10fold lower than mineralization rates of the leachable fraction. The polysaccharide component of the lignocelluloses was mineralized at rates 2 times higher than rates of mineralization of the lignin component, indicating that mangrove detritus becomes relatively enriched in lignin-derived carbon with time. Anaerobic rates of mineralization of the leachable and lignocellulosic components of mangrove leaves and wood were 10 to 30 times lower than respective aerobic mineralization rates, suggesting a very long residence time for mangrove detritus in anaerobic sediments. Comparison of the rates of degradation of mangrove detritus in sediments from a mangrove swamp and a salt marsh demonstrated that the lignocellulolytic potential in sediments of the two marine ecosystems are similar, but that lignocellulose from mangroves is less biodegradable than lignocellulose from the salt-marsh plants, Spartina alterniflora and Juncus roemerianus
Insulin release: synchronizing beta cells in the pancreas
The secretion of insulin from the pancreas relies on both gap junctions and subpopulations of beta cells with specific intrinsic properties
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Impacts of epigeic, anecic and endogeic earthworms on metal and metalloid mobility and availability
The introduction of earthworms into soils contaminated with metals and metalloids has been suggested
to aid restoration practices. Eisenia veneta (epigeic), Lumbricus terrestris (anecic) and Allolobophora
chlorotica (endogeic) earthworms were cultivated in columns containing 900 g soil with 1130, 345, 113
and 131 mg kg1 of As, Cu, Pb and Zn, respectively, for up to 112 days, in parallel with earthworm-free
columns. Leachate was produced by pouring water on the soil surface to saturate the soil and generate
downflow. Ryegrass was grown on the top of columns to assess metal uptake into biota. Different
ecological groups affected metals in the same way by increasing concentrations and free ion activities in
leachate, but anecic L. terrestris had the greatest effect by increasing leachate concentrations of As by
267%, Cu by 393%, Pb by 190%, and Zn by 429% compared to earthworm-free columns. Ryegrass
grown in earthworm-bearing soil accumulated more metal and the soil microbial community exhibited
greater stress. Results are consistent with earthworm enhanced degradation of organic matter leading
to release of organically bound elements. The degradation of organic matter also releases organic acids
which decrease the soil pH. The earthworms do not appear to carry out a unique process, but increase
the rate of a process that is already occurring. The impact of earthworms on metal mobility and
availability should therefore be considered when inoculating earthworms into contaminated soils as
new pathways to receptors may be created or the flow of metals and metalloids to receptors may be
elevated
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