130,546 research outputs found
Denitrification and benthic metabolism in lowland pit lakes: The role of trophic conditions
No full textOver recent decades, a great number of pit lakes have been formed, as a result of sand and gravel quarrying in river floodplains that are often also heavily exploited for agriculture. These lakes can act as nutrient filters and regulate the nitrogen pollution resulting from agricultural fertiliser use. In this paper we report the main outcomes of a study of the major nitrogen pathways in five pit lakes of differing trophic status, located along a lowland stretch of the Po river (Northern Italy). Benthic nitrogen fluxes and denitrification rates were determined in the hypolimnion and denitrification and reactive nitrogen assimilation by microphytobenthos in the littoral zone. We tested the hypothesis that lake depth and trophic status can impair denitrification and/or reactive nitrogen assimilation, compromising the function of the lakes as nutrient filters. In the studied lakes, denitrification and reactive nitrogen assimilation by primary producer communities accounted for substantial nitrogen removal rates, which were among the highest reported in the literature. Benthic nitrogen fluxes and denitrification varied between and within lakes, with depth. The littoral zone and surface waters also supported primary production, favouring nitrogen assimilation and temporal retention in the primary producer biomass. In all lakes, denitrification rates decreased from littoral to hypolimnetic sites. Denitrification rates and net nitrogen assimilation also diminished from oligotrophic to eutrophic conditions. To some extent, in eutrophic lakes there was a transfer of primary production from the benthos to the water column and the benthic system became heterotrophic, reducing the capacity for net nitrogen removal. Overall these results highlight that floodplain pit lakes can provide ecosystem services formerly supplied by natural wetlands. An important factor for management is the development of extensive littoral and shallow water zones, which are critical for maximising the nitrogen removal
Band structure of a two-dimensional ferromagnetic antidot lattice
No full textThe spin wave band structure of a two-dimensional square array of NiFe circular
antidots having diameter of 120 nm and periodicity of 800 nm has been investigated by
using Brillouin light scattering technique and micromagnetic calculations based on the
dynamical matrix method [1]. The external magnetic field was applied in the plane and
perpendicularly to the transferred wave vector. Extended and localized spin modes
having a propagative nature were found. Opening of bandgaps is interpreted in terms of
Bragg diffraction of spin waves from the antidot lattice and this effect is explained by
studying the behaviour of the internal field as shown in Fig.1. The mean internal field is
larger along the vertical rows of antidots and smaller between the antidots (see panel (a)
for extended modes and (c) for localized modes). By developing an analytical model
according to which the mean internal field is represented by means of a rectangular step
function characterized by a region 1 corresponding to vertical rows of antidots and a
region 2 between the antidots (see panels (b) and (d)), the relevant scattering potential
for Bragg reflection is not provided by the holes themselves, but by the concomitant
internal field inhomogeneity between holes [2]. This is in contrast to antidots in
photonics and electronics where the back-reflection is directly caused by the presence of
holes. The research leading to these results has received funding from the European
Community's Seventh Framework Programme (FP7/2007-2013) under Grant
Agreement n228673 (MAGNONICS).
[1] L. Giovannini, F. Montoncello, and F. Nizzoli, Phys. Rev. B 75, 024416 (2007).
[2] R. Zivieri, S. Tacchi, F. Montoncello, L. Giovannini, F. Nizzoli, M. Madami, G.
Gubbiotti, G. Carlotti, S. Neusser, G. Duerr, and D. Grundler, Phys. Rev. B 83, (2012)
Nitrogen and phosphorous budgets during a farming cycle of the Manila clam Ruditapes philippinarum: An in situ experiment
No full textMicrophytobenthos activity and fluxes at the sediment-water interface: interactions and spatial variability
No full textSeasonal nitrogen and phosphorus dynamics during benthic clam and sospende mussel cultivation
No full textEffects of suspended mussel and infaunal clam cultivation on sediment characteristics, and benthic organic and inorganic nitrogen and phosphorus fluxes were compared in a shallow coastal lagoon. The two species had different impacts on sediment features, but both created "hotspots" of nutrient fluxes with annual N and P regeneration rates being 4.9 and 13.5 (mussel) and 4.5 and 14.9 (clams) fold greater than those of unfarmed control sediments. Mussel farming also caused considerable nutrient regeneration within the water column with the mussel ropes contributing similar to 25% of total inorganic N and P production and at times dominating the sediments (e.g. 95% of SRP production in summer and 45% of DIN production in winter). Such nutrient regeneration rates seriously question the proposal that suspension-feeding bivalves act as a eutrophication buffer, especially during summer when nutrient regeneration rates are maximal, but other nutrient sources (freshwater run-off and unfarmed sediments) are at their lowest. (C) 2011 Elsevier Ltd. All rights reserved
Impact of clam and mussel farming on benthic metabolism and nitrogen cycling with emphasis on nitrate reduction pathways.
No full textThe influences of suspended mussel and infaunal clam cultivation on benthic metabolism and nutrient cycling were compared in Goro lagoon, Italy. Both aquaculture types stimulated benthic metabolism, with sediment oxygen demand (SOD), CO2 and ammonium effluxes of up to 14, 16 and 1.2 mmol m-2 h-1. However, whilst mussel farming preferentially stimulated anaerobic metabolism and sediment reduction, clam farming did not. The mussel ropes were also large oxygen sinks and ammonium sources, with oxygen consumption and ammonium production rates of 1.4 to 1.5 and 0.18 to 0.43 mmol kg-1 h-1. Consequently, the overall impacts of mussel farming on oxygen and nutrient dynamics were much greater than those of clam farming. There were also differences in nitrate-reduction processes and the nitrate sources that fuelled them. In winter, at high water column nitrate concentrations, highest nitrate reduction rates (~320 孯l m-2 h-1) occurred at the mussel farm. Nitrate reduction was driven predominantly by water column nitrate and ~30% of nitrate reduced was recycled to ammonium via dissimilatory nitrate reduction to ammonium (DNRA). At the control and clam farm sites, nitrate reduction rates were lower (~180 孯l m-2 h-1), nitrification supplied ~30% of nitrate and denitrification was dominant. In summer under low nitrate conditions, nitrate reduction was highest (~130 孯l m-2 h-1) at the mussel farm site, but this activity was completely dependent upon water column nitrate and 95% of nitrate was reduced via DNRA. In contrast, at the clam farm station, DNRA was unimportant and nitrification was the major nitrate source for denitrification. Consequently, whilst nitrate reduction processes eliminated fixed N from the clam farm sediments via coupled nitrification-denitrification, the dominance of DNRA at the mussel farm site resulted in a net N input to the sediment compartment. These large differences in the impacts of clam and mussel farming can be explained by the fact that infaunal clams stimulate transfer of both organic matter and oxygen to the sediment, whereas suspended mussels enhance only organic matter inputs.Full Tex
Community metabolism and buffering capacity of nitrogen in a Ruppia cirrhosa meadow.
No full textFluxes of oxygen, inorganic nitrogen (DIN) and denitrification (isotope pairing) were measured from January 1997 to February 1998 via intact cores incubation in a shallow brackish area within the eutrophic Valli di Comacchio (northern Adriatic coast, Italy). Rates were measured in the light and in the dark in sediments colonized by the rooted macrophyte Ruppia cirrhosa and in adjacent sediments with benthic microalgae. Ruppia biomass (25-414 g DW m- 2) exhibited a seasonal evolution whilst that of microphytobenthos (12-66 mg chl a m- 2) was more erratic. Net (NP) and gross (GP) primary productivity was 1.15 and 6.89 mol C m- 2y- 1 for bare and 25.4 and 51.7 mol C m- 2y- 1 for Ruppia vegetated sediments. Nitrogen pools in Ruppia standing stock varied from 43.6 to 631.4 (annual average 201.2) mmol N m- 2; the macrophyte N content was correlated with DIN concentration in the water column. Estimated N pool in microphytobenthos was one order of magnitude lower (from 2.4 to 14.5 mmol N m- 2, annual average 7.2). Theoretical DIN assimilation calculated from NP was 127.8 and 1112.6 mmol N m- 2y- 1 whilst that calculated from GP was 765 and 2282 mmol N m- 2y- 1 for microphytobenthos and Ruppia respectively. Measured annual fluxes of DIN were 974.6 and - 577 mmol N m- 2y- 1 in bare and Ruppia vegetated sediments meaning that the two sites were a source and sink for DIN and that from 25 to 50% of Ruppia annual DIN requirements came from the water column. During the period of this study total denitrification was lower in the macrophyte colonized (92.3 mmol N m- 2y- 1) compared to bare sediments (163.3 mmol N m- 2y- 1) as a probable consequence of higher competition between denitrifiers and phanerogams. At both sites the ratio between denitrification of water column nitrate (DW) and denitrification coupled to nitrification (DN) was >1.6 due to little oxygen penetration in reducing sediments (< 1.2 mm) and scarce nitrification activity. DW (0-35 μmol N m- 2h- 1) was significantly correlated with water column NO3- (2-16 μM). Theoretical DIN assimilation to denitrification ratio varied from 12.0 to 24.8 for Ruppia vegetated and from 0.8 to 4.7 for unvegetated sediments. At Valle Smarlacca, Ruppia may influence nitrogen cycling by incorporating large DIN pools in biomass which is scattered in surrounding areas and fuels intense bacterial activity. With increasing anthropogenic nutrient input and insignificant organic matter export in the open sea the already severe eutrophic conditions are enhanced and may accelerate the decline of the macrophyte meado
Impact of a trout farm on the water quality of an Apennine creek from daily budgets of nutrients.
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