1,518 research outputs found
Nitrogen-alkalinity interactions in the highly polluted Scheldt basin (Belgium)
We present results of one year observations in highly heterotrophic and oxygen-depleted rivers of the polluted Scheldt basin. Monthly measurements revealed a high variability for dissolved inorganic carbon and nitrogen, with the following strong parallelism: highest alkalinity and NH4+ were associated with lowest NO3− and oxygen and vice-versa. In river water incubations, nitrification lowered the alkalinity whereas denitrification raised it; in an anoxic, NO3−-free incubation an increase of alkalinity was observed, partially due to ammonification. A stoichiometric analysis, taking into account the amount of protons produced or consumed by each process involving nitrogen, revealed that monthly variations of NO3− and NH4+ with ammonification, nitrification and denitrification could explain the 28 and 62% alkalinity variations at all stations, except one. The remaining part of the alkalinity variations was attributed to other anaerobic processes (Mn-, Fe- and SO4-reductions). This trend seems to be the result of the whole catchment metabolism (riverine waters and sediments, sewage networks and agricultural soils). The observed HCO3− concentrations in the Scheldt basin were 2–10 times higher than the representative concentrations reported in pristine basins and used in chemical weathering models. This suggests the existence of an anthropogenic source, originating from organic matter decomposition. We conclude that in highly polluted basins, nitrogen transformations strongly influence the acid–base properties of water
Open Issues and Chances for Topological Pyramids
High resolution image data require a huge
amount of computational resources. Image pyramids
have shown high performance and flexibility to reduce
the amount of data while preserving the most relevant
pieces of information, and still allowing fast access to
those data that have been considered less important before.
They are able to preserve an existing topological structure
(Euler number, homology generators) when the spatial
partitioning of the data is known at the time of construction.
In order to focus on the topological aspects let us call this
class of pyramids “topological pyramids”. We consider
here four open problems, under the topological pyramids
context: The minimality problem of volumes representation,
the “contact”-relation representation, the orientation of
gravity and time dimensions and the integration of different
modalities as different topologies.Austrian Science Fund P20134-N13Junta de AndalucĂa FQM–296Junta de AndalucĂa PO6-TIC-0226
Ideas and perspectives: Carbon leaks from flooded land: do we need to replumb the inland water active pipe?
At the global scale, inland waters are a significant source of atmospheric
carbon (C), particularly in the tropics. The active pipe concept predicts
that C emissions from streams, lakes and rivers are largely fuelled by
terrestrial ecosystems. The traditionally recognized C transfer mechanisms
from terrestrial to aquatic systems are surface runoff and groundwater
drainage. We present here a series of arguments that support the idea that
land flooding is an additional significant process that fuels inland waters
with C at the global scale. Whether the majority of CO2 emitted by
rivers comes from floodable land (approximately 10 % of the continents) or
from well-drained land is a fundamental question that impacts our capacity
to predict how these C fluxes might change in the future. Using classical
concepts in ecology, we propose, as a necessary step forward, an update of
the active pipe concept that differentiates floodable land from drained
land. Contrarily to well-drained land, many wetlands (in particular riparian
and littoral wetlands) combine strong hydrological connectivity with inland
waters, high productivity assimilating CO2 from the atmosphere, direct
transfer of litter and exudation products to water and waterlogged soils, a
generally dominant allocation of ecosystem respiration (ER) below the water
surface and a slow gas-exchange rate at the water–air interface. These
properties force plants to pump atmospheric C to wetland waters and, when
hydrology is favourable, to inland waters as organic C and dissolved
CO2. This wetland CO2 pump may contribute disproportionately to
CO2 emissions from inland waters, particularly in the tropics where
80 % of the global CO2 emissions to the atmosphere occur. In future
studies, more care must be taken in the way that vertical and horizontal C
fluxes are conceptualized along watersheds, and 2-D models that adequately
account for the hydrological export of all C species are necessary. In
flooded ecosystems, significant effort should be dedicated to quantifying
the components of primary production and respiration by the submerged and
emerged part of the ecosystem community and to using these metabolic rates in
coupled hydrological–biogeochemical models. The construction of a global
typology of wetlands that includes productivity, gas fluxes and hydrological
connectivity with inland waters also appears necessary to adequately
integrate continental C fluxes at the global scale.</p
VegetaciĂłn acuática y helofĂtica del Sistema IbĂ©rico septentrional, centro de España
VegetaciĂłn acuática y helofĂtica del Sistema IbĂ©rico septentrional, centro de España. En este trabajo, se han reconocido 11 asociaciones y 4 comunidades pertenecientes a las clases fitosociolĂłgicas Potametea y Phragmito-Magnocaricetea. El Sistema IbĂ©rico septentrional constituye un lĂmite meridional para comunidades de Ăłptimo centro-europeo -Caricetum rostratae, Caricetum vesicariae y Comunidad de Sparganium emersum-, asĂ como un lĂmite oriental para comunidades de Ăłptimo atlántico -Ranunculetum omiophylli, Galio broteriani-Caricetum broterianae, Glycerio declinatae-Eleocharitetum-palustris, Glycerio declinatae-Oenanthetum crocatae y Oenantho crocatae-Phalaridetum arundinaceae-
Distribution of phytoplankton pigments in nine European estuaries and implications for an estuarine typology
Phytoplankton pigments were studied by LiquidChromatography (HPLC) in nine West Europeanestuaries. Three estuaries, i.e. the Rhine,Scheldt and the Gironde were sampled four timesto cover the different seasons, whereas theother six estuaries were sampled once. Pigmentdistributions in estuaries reflect bothriverine inputs as well as autochthonousblooms. Fucoxanthin was the most commonaccessory photosynthetic pigment showing thatDiatoms were the most common group in thestudied estuaries and were particularlydominant during autumn and winter. In the veryturbid Gironde estuary, degradation processeswere predominant between salinities 1 and 20,while Diatoms, Dinoflagellates and Cryptophytesbloomed above 20 salinity during spring andsummer. This contrasted with the highlyeutrophic but less turbid Scheldt, wherephytoplanktonic blooms occurred at lowsalinities close to the city of Antwerp. In theScheldt, we observed both a tenfold fluctuationof phytoplankton biomass and a fluctuatingpigment diversity index. In contrast,chlorophyll a was always low in theGironde, but we observed large variations ofpigment diversity among samplings duringdifferent seasons. Distribution of pheopigmentsshowed that the maximum turbidity zone (MTZ)was a highly reactive region for heterotrophicphytoplankton degradation. The Scheldt and theThames were the most anthropogenic influencedestuaries contrasting with the Gironde estuarythat has a less urbanised watershed. Anestuarine typology is proposed based on threeclusters emerging from a correspondenceanalysis of pigment variables and variablescharacterising the anthropogenic impact andphysical forcing
Homological computation using spanning trees
We introduce here a new F2 homology computation algorithm based on a generalization of the spanning tree technique on a finite 3-dimensional cell complex K embedded in ℝ3. We demonstrate that the complexity of this algorithm is linear in the number of cells. In fact, this process computes an algebraic map φ over K, called homology gradient vector field (HGVF), from which it is possible to infer in a straightforward manner homological information like Euler characteristic, relative homology groups, representative cycles for homology generators, topological skeletons, Reeb graphs, cohomology algebra, higher (co)homology operations, etc. This process can be generalized to others coefficients, including the integers, and to higher dimension
Homological tree-based strategies for image analysis
Homological characteristics of digital objects can be obtained in a straightforward manner computing an algebraic map φ over a finite cell complex K (with coefficients in the finite field F2={0,1}) which represents the digital object [9]. Computable homological information includes the Euler characteristic, homology generators and representative cycles, higher (co)homology operations, etc. This algebraic map φ is described in combinatorial terms using a mixed three-level forest. Different strategies changing only two parameters of this algorithm for computing φ are presented. Each one of those strategies gives rise to different maps, although all of them provides the same homological information for K. For example, tree-based structures useful in image analysis like topological skeletons and pyramids can be obtained as subgraphs of this forest
Serologic reactivity to leptospira and dengue virus of febrile patients from Guayaquil slums.
Leptospirosis is a zoonosis that occurs throughout the world but is most commonly seen in tropical climates (1). It has risen as a globally important infectious disease as shown in some reports and studies from outbreaks like the 1995 Nicaragua epidemic of severe pulmonary haemorrhage syndrome (SPHS)(2,3), identification of disease among US inner-city homeless population (1,2), the 1998 Lake Springfield Triathlon (2) and 2000 Borneo Eco-Challenge (2,4). Moreover, it was traditionally thought that leptospirosis is only a major health problem in developing, tropical countries (1,4); however, the disease has been under recognized in urban populations of developed countries as well as in temperate rural regions of the world especially during rainy seasons (1,4, 5). But, the real importance of the disease is the incidence related to the lack of sanitary infrastructure. Additionally poorly understood risk factors, pathogenicity, immunopathology are important factors for mortality associated to the disease (1,5,6). Challenges related to prevention are largely dependent on sanitation measures which may be difficult to implement, especially in developing countries, as our country Ecuador (1,6)
EU External Relations: Exclusive Competence Revisited
This Article will focus on the question of exclusive competence in the field of EU external relations, especially in the light of recent developments. After a brief discussion on the origins and development of exclusive competence, a distinction will be made between common commercial policy, which has traditionally been the most important area of an explicit “a priori” exclusive competence, and what is often called an implicit exclusive competence, which, as it is today based on some general criteria enshrined in TFEU Article 3(2), may be called “supervening” exclusive competence. With regard to both categories, the main focus will be on recent developments, notably the impact of the Treaty of Lisbon, which introduced the TFEU and its Articles 2 and 3, as well as the case law of the European Court of Justice (“ECJ” or the “Court”) following the entry into force of the Treaty of Lisbon, on December 1, 2009
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