166 research outputs found
Aeration, tillage effects on
Few land management practices have the potential to
impact upon soil aeration as directly or rapidly as tillage.
Indeed, often, the reason for performing tillage is to modify
or improve soil physical properties including aeration. The
problems associated with inadequate aeration have been
comprehensively reviewed elsewhere (1, 2). Important
effects of limited soil aeration in crop production are:
altered nutrient dynamics, a shift from oxidative to
reductive chemical/biological reactions, impaired plant
growth, and changes in gas equilibria affecting both soil and
ambient atmospheres. For example, consider the soil
nitrogen cycle which aeration effects via its influence on
denitrification and gaseous nitrogen losses, decreased
nitrogen mineralization rate and a reduction in nodulation
and symbiotic fixation by leguminous plants (3). If the
oxygen supply is sufficiently limited, and anerobosis sets in,
then the products of reduction reactions may accumulate to
toxic levels. In addition, a depleted oxygen supply may
constrain root form and function, such as water and nutrient
uptake, and therefore plant shoot performance even when
many other soil physical factors are favorable (4).
Unfortunately, relatively short periods of oxygen shortage
can seriously compromise crop performance if they
coincide with critical stages of crop growth (1). Finally,
there are the effects of gas sources and sinks in the soil and
transformations of soil gaseous components, and the
exchange between soil and above ground air, on the
atmosphere, e.g., diminished soil aeration may enhance the
emission of greenhouse gases (5).
While the tillage-related literature is voluminous, little
of it directly addresses soil aeration. Of necessity, this
short article critiques only research which has measured
aeration status directlyâparticularly indices of concentration
and rateâand will make little or no attempt to draw
inferences about the effect of tillage on soil aeration from
studies reporting other related soil characteristics.
Although bulk density, moisture content, and pore size
distribution are related to soil aeration, and so may be
indicative of aeration status, their direct relevance to a
nuanced understanding of soil aeration is problematical.
For instance, measurements of pore space convey little
about pore continuity, tortuosity, or stability (6), whereas
these effects are largely integrated de facto in measurements
of oxygen diffusion rate (ODR)
Subsoiling and surface tillage effects on soil physical properties and forage oat stand and yield
Much of New Zealand's agriculture integrates animal and crop production on poorly drained,
easily compacted soils. We hypothesized that soil properties affecting forage oat (Avena sativa,
cv Awapuni) establishment on land compacted by 15 years of conventional cropping might be
influenced by various subsoiling and surface tillage combinations. Plots on a Moutoa silty clay
(Typic Haplaquoil) were paraplowed (P), deep subsoiled (V), shallow subsoiled (5), or were left
as non-subsoiled controls (C). Subsequently, the surface 15 cm was surface-tilled (T) using a
power rotary-tiller and firmed with a Cambridge roller or were not tilled (N). Oats were then sown
with a cross-slot drill. Subsoiling greatly reduced soil strength. Cone indices showed disruption to
40cm with P, 36 cm for V, and 30 cm for S. Approximately 60% of profile cone indices to a depth
of 0.5 m from subsoiled treatments were less than 1.5 MPa, compared to approximately 30% for C.
T slightly improved strength distribution in non-subsoiled controls but had little effect in subsoiled
treatments. Subsoiling without T continued to show improved profile cone index cumulative
frequency 233 days after subsoiling, Subsoiling after T in this high rainfall climate eliminated
most of the separation in cumulative frequency of soil profile cone index values by two weeks
after T. T reduced emergence from 142 to 113 plants per square meter and reduced yield from
5318 to 3679 kg ha-1. Forage yield increased from 3974 to 4674 kg ha-1 with subsoiling. Soil
porosity, saturated and slightly unsaturated hydraulic conductivities (KSAT and K_40 ) and air
permeability were highly variable but generally increased with subsoiling. Oxygen diffusion rate
(ODR) (using Pt microelectrodes) was also variable, but N and C treatments had consistently
lower ODRs than T or subsoiled treatments. Generally, subsoiling without T produced better soil
conditions and oat crop performance than the prevailing New Zealand practice of T without subsoiling
Synthetic- and bio-polymer use for runoff water quality management in irrigation agriculture
Low concentrations of synthetic- or bio-polymers in irrigation water can nearly eliminate
sediment, N, ortho- and total-P, DOM, pesticides, micro-organisms, and weed seed from runoff. These
environmentally safe polymers are employed in various sensitive uses including food processing, animal
feeds, and potable water purification. The most common synthetic polymer is anionic, high purity
polyacrylamide (PAM), which typically provides 70-90% contaminant elimination. Excellent results are
achieved adding only 10 ppm PAM to irrigation water, applying 1 -2 kg ha. -1 per irrigation, costing
12 kg -1 . Biopolymers are less effective. Using twice or higher concentrations, existing biopolymers
are ,r=60% effective as PAM, at 2 - 3 times the cost. A half million ha of US irrigated land use PAM for
erosion control and runoff protection. The practice is spreading rapidly in the US and worldwide. Interest
in development of biopolymer surrogates for PAM is high. If the supply of cheap natural gas (raw material
for PAM synthesis) diminishes, industries may seek alternative polymers. Also "green" perceptions and
preferences favor biopolymers for certain application
Synthetic- and Bio-polymer use for runoff water quality management in irrigated agriculture
Low concentrations of synthetic- or bio-polymers in irrigation water can nearly eliminate sediment, N,
ortho- and total-P, DOM, pesticides, micro-organisms, and weed seed from runoff. These environmentally safe
polymers are employed in various sensitive uses including food processing, animal feeds, and potable water
purification. The most common synthetic polymer is anionic, high purity polyacrylamide (PAM), which typically
provides 70-90% contaminant elimination. Excellent results are achieved adding only 10 ppm PAM to irrigation
water, applying 1-2 kg ha-lper irrigation, costing 12 kg-1. Biopolymers are less effective, but show promise; they
include starch co-polymers, microfibril suspensions, chitin, polysaccharides and protein derivatives. Using twice or
higher concentrations, existing biopolymers are ~60% effective as PAM, at 2-3 times the cost kg-1. A half million ha
of US irrigated land use PAM for erosion control and runoff protection. The practice is spreading rapidly in the US
and worldwide. Interest in development of biopolymer surrogates for PAM is high. If the supply of cheap natural gas
(raw material for PAM synthesis) diminishes, industries may seek alternative polymers. Also "green" perceptions and
preferences favor biopolymers for certain applications. More complete history, user/technical information and
bibliography are found at
Middle to late Pleistocene palaeoecological reconstructions and palaeotemperature estimates for cold/cool stage deposits at Whittlesey, eastern England
Fossiliferous beds in a complex sequence of late Middle to Late Pleistocene deposits at Whittlesey, eastern England, provided a rare opportunity for a multidisciplinary study of the palaeoecology of cool/cold stage deposits from different glacial stages. The fossiliferous sediments investigated form part of the River Nene 1st Terrace. Three of the four fossil assemblages investigated pre-date the last interglacial stage (Ipswichian/Eemian/marine oxygen isotope stage (MIS) 5e), whereas the other dates to part of the MIS 3 interstadial complex (Middle Devensian/Weichselian). Pollen, plant macrofossil, molluscan, coleopteran, ostracod, foraminifera and vertebrate data are available to a greater or lesser extent for each cool/cold stage assemblage, and they broadly present the same ecological picture for each one: a continuum from low-energy permanent to non-permanent aquatic habitats through marshland with associated waterside taxa, together with flood influxes of fluvial, riparian and ruderal taxa. Although each fossil assemblage records cool/cold climatic conditions, to a greater or lesser extent, these conditions are more apparent in the insect and ostracod faunas. In comparison with results published for the Last Glacial Maximum (LGM) stadial in The Netherlands, palaeotemperature estimates based on ranges of mutual agreement between independent coleopteran and ostracod methods for the three pre-Ipswichian/Eemian assemblages indicate minimum mean July air temperatures that are from +1° to +3 °C warmer, but January values that embrace the â8 °C estimate for the LGM. There is, however, a disparity between the coleopteran and ostracod palaeotemperature estimates for the Middle Devensian/Weichselian fossil assemblage, which are based on two different sample stratigraphic levels; the lower, coleopteran assemblage is indicative of very cool, continental climates, whereas the stratigraphically slightly higher ostracod assemblage suggests a climatic amelioration. Lack of numerical age-estimates prevents a robust stratigraphical interpretation, but the youngest pre-Ipswichian/Eemian fossil assemblage could date to the MIS 7â6 transition, at a time when cooling possibly preceded glacially driven sea-level fall. It is apparent from the rich coleopteran data that some continental cold-indicator taxa also appeared in pre-Ipswichian/Eemian cold stages and therefore assignment of continental cold-indicator taxa to particular Devensian/Weichselian intervals should be undertaken with care
Defining the stock structure of northern Australia's threadfin salmon species
The requirement for Queensland, Northern Territory and Western Australian jurisdictions to ensure sustainable harvest of fish resources relies on robust information on the resource status. In northern Australia management of inshore fisheries that target blue threadfin (Eleutheronema tetradactylum) and king threadfin (Polydactylus macrochir) is independent for each of these jurisdictions. However, the lack of information on the stock structure and biology of threadfins means that the appropriate spatial scale of management is not known and assessment of the resource status is not possible. Establishing the stock structure of blue and king threadfin would also immensely improve the relevance of future resource assessments for fishery management of threadfins across northern Australia. This highlighted the urgent need for stock structure information for this species
Georges Bank : a leaky incubator of Alexandrium fundyense blooms
Author Posting. © The Author(s), 2012. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 103 (2014): 163-173, doi:10.1016/j.dsr2.2012.11.002.A series of oceanographic surveys on Georges Bank document variability of populations of the toxic dinoflagellate Alexandrium fundyense on time scales ranging from synoptic to seasonal to interannual. Blooms of A. fundyense on Georges Bank can reach concentrations on the order of 104 cells l-1, and are generally bank-wide in extent. Georges Bank populations of A. fundyense appear to be quasi-independent of those in the adjacent coastal Gulf of Maine, insofar as they occupy a hydrographic niche that is colder and saltier than their coastal counterparts. In contrast to coastal populations that rely on abundant resting cysts for bloom initiation, very few cysts are present in the sediments on Georges Bank. Bloom dynamics must therefore be largely controlled by the balance between growth and mortality processes, which are at present largely unknown for this population. Based on correlations between cell abundance and nutrient distributions, ammonium appears to be an important source of nitrogen for A. fundyense blooms on Georges Bank.We appreciate financial support of the National Oceanic Atmospheric Administration (grant NA06NOS4780245 for the Gulf of Maine Toxicity (GOMTOX) program) and the Woods Hole Center for Oceans and Human Health through National Science Foundation grants OCE-0430724 and OCE-0911031 and National Institute of Environmental Health Sciences grant 1P50-ES01274201
Anthropogenic Space Weather
Anthropogenic effects on the space environment started in the late 19th
century and reached their peak in the 1960s when high-altitude nuclear
explosions were carried out by the USA and the Soviet Union. These explosions
created artificial radiation belts near Earth that resulted in major damages to
several satellites. Another, unexpected impact of the high-altitude nuclear
tests was the electromagnetic pulse (EMP) that can have devastating effects
over a large geographic area (as large as the continental United States). Other
anthropogenic impacts on the space environment include chemical release ex-
periments, high-frequency wave heating of the ionosphere and the interaction of
VLF waves with the radiation belts. This paper reviews the fundamental physical
process behind these phenomena and discusses the observations of their impacts.Comment: 71 pages, 35 figure
Effects of cleaning methods upon preservation of stable isotopes and trace elements in shells of Cyprideis torosa (Crustacea, Ostracoda): implications for palaeoenvironmental reconstruction
The trace element (Sr/Ca and Mg/Ca) and stable isotope (ÎŽÂčâžO and ÎŽÂčÂłC) geochemistry of fossil ostracod valves provide valuable information, particularly in lacustrine settings, on palaeo-water composition and palaeotemperature. The removal of sedimentary and organic contamination prior to geochemical analysis is essential to avoid bias of the results. Previous stable isotope and trace element work on ostracod shells has, however, employed different treatments for the removal of contamination beyond simple âmanualâ cleaning using a paint brush and methanol under a low-power binocular microscope. For isotopic work pre-treatments include chemical oxidation, vacuum roasting and plasma ashing, and for trace element work sonication, chemical oxidation and reductive cleaning. The impact of different treatments on the geochemical composition of the valve calcite has not been evaluated in full, and a universal protocol has not been established. Here, a systematic investigation of the cleaning methods is undertaken using specimens of the ubiquitous euryhaline species, Cyprideis torosa. Cleaning methods are evaluated by undertaking paired analyses on a single carapace (comprising two valves); in modern ostracods, whose valves are assumed to be unaltered, the two valves should have identical geochemical and isotopic composition. Hence, when one valve is subjected to the chosen treatment and the other to simple manual cleaning any difference in composition can confidently be assigned to the treatment method. We show that certain cleaning methods have the potential to cause alteration to the geochemical signal, particularly Mg/Ca and ÎŽÂčâžO, and hence have implications for palaeoenvironmental reconstructions. For trace element determinations we recommend cleaning by sonication and for stable isotope analysis, oxidation by hydrogen peroxide. These methods remove contamination, yet do not significantly alter the geochemical signal
Local festivals, social capital and sustainable destination development: experiences in East London
This paper explores the nature of social capital arising from engagement in local festivals and the implications of this for the social sustainability of an emerging destination. Two case studies are developed from a longitudinal research project which investigates local festivals staged in the Hackney Wick and Fish Island area adjacent to Queen Elizabeth Olympic Park in East London, UK between 2008 and 2014. This area has been directly affected by extensive development and regeneration efforts associated with the staging of the London 2012 Olympic Games. The two festivals considered here respond to the challenges and opportunities arising for local people as the area changes. One festival aims to foster a sense of community by creating shared experiences and improving communication across diverse groups. The other draws together the cultural community, links them to the opportunities arising as the area emerges as a destination, and attracts visitors. These festivals increase social capital in the area, but its distribution is very uneven. The accrual of social capital exacerbates existing inequalities within the host community, favouring the âhavesâ at the expense of the âhave notsâ. There are tensions between the development of social capital and social sustainability in this emerging destination
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