10 research outputs found
Primary versus diagenetic origin of Blue Lias rhythms (Dorset, UK): evidence from sulphur geochemistry
In vitro studies on sulphate reduction and acidification in sediments of shallow soft water lakes
Derivation of organic carbon reactivity in a redox-stratified aquifer—hydrogeochemical modelling of kinetically driven reaction systems
Modeling nitrogen cycling in a coastal fresh water sediment
Increased nitrogen (N) loading to
coastal marine and freshwater systems is occurring
worldwide as a result of human activities.
Diagenetic processes in sediments can change
the N availability in these systems, by supporting
removal through denitrification and burial of
organic N (Norg) or by enhancing N recycling. In
this study, we use a reactive transport model
(RTM) to examine N transformations in a
coastal fresh water sediment and quantify N
removal rates. We also assess the response of
the sediment N cycle to environmental changes
that may result from increased salinity which is
planned to occur at the site as a result of an
estuarine restoration project. Field results show
that much of the Norg deposited on the sediment
is currently remineralized to ammonium. A
rapid removal of nitrate is observed in the
sediment pore water, with the resulting
nitrate reduction rate estimated to be 130 lmol
N cm–2 yr–1. A model sensitivity study was
conducted altering the distribution of nitrate
reduction between dissimilatory nitrate reduction
to ammonium (DNRA) and denitrification.
These results show a 40% decline in sediment N
removal as NO3 – reduction shifts from denitrification
to DNRA. This decreased N removal
leads to a shift in sediment-water exchange
flux of dissolved inorganic nitrogen (DIN)
from near zero with denitrification to 133 lmol
N cm–2 yr–1 if DNRA is the dominant pathway.
The response to salinization includes a shortterm
release of adsorbed ammonium. Additional
changes expected to result from the
estuarine restoration include: lower NO3 –
concentrations and greater SO4
2– concentrations
in the bottom water, decreased nitrification
rates, and increased sediment mixing. The
effect of these changes on net DIN flux and N
removal vary based on the distribution of
DNRA versus denitrification, illustrating the
need for a better understanding of factors
controlling this competition
Pregabalin and pain after total knee arthroplasty: a double-blind, randomized, placebo-controlled, multidose trial â€
Formation of siderite-Mg-calcite-iron sulphide concretions in intertidal marsh and sandflat sediments, north Norfolk, England
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Pollination and other ecosystem services produced by mobile organisms: a conceptual framework for the effects of land-use change
Many ecosystem services are delivered by organisms that depend on habitats that are segregated spatially or temporally from the location where services are provided. Management of mobile organisms contributing to ecosystem services requires consideration not only of the local scale where services are delivered, but also the distribution of resources at the landscape scale, and the foraging ranges and dispersal movements of the mobile agents. We develop a conceptual model for exploring how one such mobile-agent-based ecosystem service (MABES), pollination, is affected by land-use change, and then generalize the model to other MABES. The model includes interactions and feedbacks among policies affecting land use, market forces and the biology of the organisms involved. Animal-mediated pollination contributes to the production of goods of value to humans such as crops; it also bolsters reproduction of wild plants on which other services or service-providing organisms depend. About one-third of crop production depends on animal pollinators, while 60-90% of plant species require an animal pollinator. The sensitivity of mobile organisms to ecological factors that operate across spatial scales makes the services provided by a given community of mobile agents highly contextual. Services vary, depending on the spatial and temporal distribution of resources surrounding the site, and on biotic interactions occurring locally, such as competition among pollinators for resources, and among plants for pollinators. The value of the resulting goods or services may feed back via market-based forces to influence land-use policies, which in turn influence land management practices that alter local habitat conditions and landscape structure. Developing conceptual models for MABES aids in identifying knowledge gaps, determining research priorities, and targeting interventions that can be applied in an adaptive management context