ALBERT — All Library Books, journals and Electronic Records Telegrafenberg

1

Electronic Resource

Seasonal variation of phytoplankton community structure and nitrogen uptake regime in the Indian Sector of the Southern Ocean (1998)

Mengesha, Semeneh ; Dehairs, Frank ; Fiala, Michel ; [et al.]

Springer

Polar biology 20 (1998), S. 259-272

add to mindlist on the mindlist

Details

ISSN: 1432-2056

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract This study investigates the dynamics of phytoplankton communities and nitrogen uptake in the Indian sector of the Southern Ocean during spring and summer. The study area is oligotrophic (Chl a stocks 〈50 mg m−2); nevertheless, a large spatial variation of phytoplankton biomass and community structure was observed. During both seasons the phytoplankton community in the seasonal ice zone showed higher biomasses and was mainly composed of large diatom cells. However, in the permanently open ocean zone the community had low biomass and was chiefly composed of nano- and picoflagellates. In the polar front zone, although biomass was higher, the community structure was similar to the open ocean zone. The results suggest that the variation in phytoplankton community structure on a larger scale resonates with gradients in water column stability and nutrient distribution. However, significant changes in biomass and nutrient stocks but little change in community structure were observed. Absolute nitrogen uptake rates were generally low, but their seasonal variations were highly significant. During spring the communities displayed high specific nitrate uptake (mean rate = 0.0048 h−1), and diatoms (in the seasonal ice zone) as well as nano- and picoflagellates (in the permanently open ocean zone and polar front zone) were mainly based on new production (mean ƒ-ratio = 0.69). The transition to summer was accompanied by a significant reduction in nitrate uptake rate (0.0048 h−1 → 0.0011 h−1) and a shift from predominantly new to regenerated production (ƒ-ratio 0.69 → 0.39). Ammonium played a major role in the seasonal dynamics of phytoplankton nutrition. The results emphasize that, despite a large contrast in community structure, the seasonal dynamics of the nitrogen uptake regime and phytoplankton community structure in all three subsystems were similar. Additionally, this study supports our previous conclusion that the seasonal shift in nitrogen uptake regime can occur with, as well as without, marked changes in community structure.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s003000050302

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

2

Electronic Resource

Effect of organic complexation on the behaviour of dissolved Cd, Cu and Zn in the Scheldt estuary (1997)

Baeyens, Willy ; Goeyens, Leo ; Monteny, Frank ; [et al.]

Springer

Hydrobiologia 366 (1997), S. 81-90

add to mindlist on the mindlist

Details

ISSN: 1573-5117

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Samples from the Scheldt estuary have been assayed for dissolved Cd, Cuand Zn using differential pulse anodic stripping voltammetry, either astotal (after UV irradiation) or labile concentrations. Under theseexperimental conditions, labile concentrations ranged between51–65% of total Cu, 16–66% of total Zn and53–91% of total Cd. The metal–organic interactions wereassessed by evaluating (a) the distribution coefficient Kd forthe distribution of the metals between the liquid phase (complexation) andtheir binding to particulate matter, and (b) the competitive effect exertedby inorganic complexing ligands using a multi–element interactionmodel. The proportion of organically bound metals (strong and labile) wasestimated, in this speciation scheme, to range from 86 to 99% for Cu,from 90 to 96% for Zn, and from 10 to 35% for Cd. From thedissolved organic carbon distribution in the Scheldt (≤ 10 mg Cl-1 and taking into account competition from major cations Caand Mg, free ligand concentrations available for heavy metal complexationwere estimated to be ≤ 0.15 mg C l-1. With these values,conditional stability constants for the chelation of Cu, Zn and Cd werecalculated assuming either a single-step or a two-step complexation in thedissolved phase. Given the assumptions made in these models, stabilityconstants in the range of 107.8–1010.6 forCu, 107.0–109.1 for Zn and106.9–108.9 for Cd were obtained. Therelevance of these data to previous in vitro and in situ studies isdiscussed taking into consideration current concepts of metal bindingaffinity for organic ligands.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1003176327686

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

3

Electronic Resource

Biogeochemical behaviour of Cd, Cu, Pb and Zn in the Scheldt estuary during the period 1981–1983 (1997)

Baeyens, Willy ; Elskens, Marc ; Gillain, Gérard ; [et al.]

Springer

Hydrobiologia 366 (1997), S. 15-44

add to mindlist on the mindlist

Details

ISSN: 1573-5117

Keywords: Scheldt estuary ; trace metals ; 1981–1983 ; dissolved ; particulate ; biogeochemistry

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Cu, Zn, Cd and Pb have been analysed in suspendedmatter and water samples from the Scheldt estuary,collected during five cruises between May 1982 and May1983. In order to evaluate the overall metal behaviourin the estuary, continuous longitudinal profiles ofthe total, the particulate and the dissolved metalconcentrations are discussed in relation to variousspecific physico-chemical parameters. By means ofcorrelation and multi-regression techniques, severalestuarine processes could be identified which dominateand/or control the behaviour of the individual tracemetals in three distinct areas of the Scheldt estuary. The behaviour of the four selected metals was foundto show some common features, but is besides this alsocharacterised by many individual and specificproperties. The total metal concentrations seem toco-vary well with the turbidity in the maximumturbidity zone between salinities 2 and 10 psu. In thedownstream area a dilution profile is observed for thetotal metal concentrations of Cu and Cd as well as forthe dissolved concentrations of all metals. Dissolved metal production rates are high for Cu andCd, but much lower for Zn and Pb, confirming thedifferent longitudinal dissolved metal profiles. ForCu and Cd these dissolved metal profiles arecharacterised by a broad mobilisation area, coveringthe whole middle estuary. Pb on the other hand, showsa more confined mobilisation area, and for Zn no sucharea was found. During winter the dissolved metalproduction rates seem to be controlled, predominantly,by desorption processes. During summer dissolved metalproduction is correlated mainly to the dissolvedoxygen content, suggesting the domination of redoxprocesses solely or in combination with desorptionprocesses. In some cases, co-existent with nearly zerooxygen concentrations, removal of dissolved metals wasobserved, possibly reflecting precipitation reactions. Longitudinal particulate metal profiles all show anegative deviation versus the dilution profile. Cu andCd provide the higher deviations, characterised by anarrow enrichment zone preceding a broad mobilisationarea. Finally, all particulate metal profiles appearedto correlate well with POC, when expressed involumetric units.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1003168125869

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

4

Electronic Resource

The impact of the Scheldt input on the trace metal distribution in the Belgian coastal area (results of 1981–1983 and 1995–1996) (1997)

Baeyens, Willy ; Elskens, Marc ; Van Ryssen, Ramses ; [et al.]

Springer

Hydrobiologia 366 (1997), S. 91-108

add to mindlist on the mindlist

Details

ISSN: 1573-5117

Keywords: Trace metals ; North Sea ; coastal waters ; fluxes ; residual flows ; river inputs

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Offshore fluxes of Cu, Zn, Cd, Pb and Hg were calculated based onresidual flow patterns and salinity gradients along the Belgian coast. Theresidual flow lines along the Belgian coast are more or less parallel to thecoast except in the area where the north-easterly flowing watermass comingfrom the Channel encounters the south-westerly-oriented Scheldt outflow,forming a residual hydrodynamical front. From the steady-state salinitypattern, diffusion coefficients perpendicular to the residual flow werededuced; they ranged from 21 to 108 m2 s-1. Offshore fluxes of dissolved and particulate trace metals based on diffusiveand mixing processes are calculated. The steady state profiles of dissolvedmetals show a dilution effect in the coastal waters, reaching an almostconstant concentration in the marine watermass in the 1981–1983dataset. The ratios of the Scheldt input of trace metals to the totaldissolved offshore flux vary from 38 to 55% (1981–1983),depending on the kind of metal, and from 55 to 91% (1995–1996).The ratio of the Scheldt input to the dissolved metal flow parallel to thecoast, is in both periods (1981–1983 and 1995–1996), smallerthan 1%. The steady-state concentration profiles of particular metalsversus salinity are fairly constant in the coastal-estuarine and marinewatermasses, but decrease very abruptly from the first to the secondwatermass. Assuming a conservative behaviour of the particular metals,offshore fluxes and the resulting concentration increases agree fairly wellwith the observed values. The ratios of the Scheldt input to the particulatetrace metal offshore flux vary between 30 to 46% (1981–1983)and 13 to 37% (1995–1996). The contribution of the Scheldtestuary to the flows parallel to the coast ranges from 1.6 to 2.9%(1981–1983) and from 0.6 to 1.6% (1995).

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1003128411757

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

5

Electronic Resource

Contribution of nitrate to the uptake of nitrogen by phytoplankton in an ocean margin environment (1997)

Elskens, Marc ; Baeyens, Willy ; Goeyens, Leo

Springer

Hydrobiologia 353 (1997), S. 139-152

add to mindlist on the mindlist

Details

ISSN: 1573-5117

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Rates of nitrate and ammonium uptake by phytoplankton were measured fromJuly 1990 to March 1995 in the surface waters at several stations locatedalong the continental margin of the NE Atlantic Ocean. Total inorganicnitrogen assimilation ranged from 2.3 to 95 nM h−1 andexhibited two maxima during the spring bloom and in fall at the beginning ofthe vertical mixing of the water column. Seasonal and spatial changes in thenitrogen uptake regime (f-ratios) were estimated (1) by correcting ammoniumuptake rates with an isotope dilution model, and (2) by evaluating theinhibition of nitrate uptake by ammonium, using a variation of theMichaelis-Menten equation. Overall, nitrate uptake rates paralleled carbonfixation rates, and f-ratios followed the well-known function of nitrate.During spring, new production, sensu Dugdale & Goering (1967), accountedfor 46 to 85% of the total inorganic nitrogen production. It can gainin importance through vertical mixing in fall (0.29 〈 f 〈 0.82), aftera period of predominant regenerated production in summer (0.07 〈 f 〈0.41). Although new production appeared to be quantitatively important onaverage (mean f = 0.53), kinetic data suggested that ammonium wasutilised preferentially throughout the full spectrum of nitrogenconcentrations observed during this study. Moreover, the inhibition ofnitrate uptake by ambient level of ammonium was estimated to range from 8 to50%. Therefore, it is suggested that the supply of regeneratednitrogenous nutrients, combined with feedback mechanisms (preference andinhibition), triggers a switch-over from predominantly new productiontowards regenerated production, even before the complete exhaustion ofnitrate in the surface water. Overall, these results indicate a leading rolefor ammonium in regulating the removal of nitrate in this margin ecosystem.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1003058928157

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

6

Electronic Resource

Use of a simplex technique and contour diagrams for the determination of the reaction rate constants between glutathione and thiram in the presence of NADPH (1988)

Elskens, Marc ; Penninckx, Michel J. ; Vandeloise, Robert ; [et al.]

New York, NY : Wiley-Blackwell

International Journal of Chemical Kinetics 20 (1988), S. 837-848

add to mindlist on the mindlist

Details

ISSN: 0538-8066

Keywords: Chemistry ; Physical Chemistry

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Notes: The Modified Simplex Method (MSM) coupled with contour diagrams is used to determine the rate constants of a kinetic scheme involving three sequential second order processes.Reaction between glutathione and the dithiocarbamate fungicide tetramethylthiuram disulfide produces the oxidized form of glutathione which is then reduced in the presence of NADPH. The concentration of the reducing agent is monitored as a function of time. In the absence of simplifying assumption a closed form solution of the rate equations does not exist. Computed curves of NADPH concentration versus time were generated using the software SIMULCIN.The rate constant values are optimized by the MSM procedure to obtain the best agreement between calculated and experimental data. The significance, validity limits of the estimated rate constants and the relevance of these in vitro data to previous in vivo studies are discussed.

Additional Material: 9 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/kin.550201102

Permalink