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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of organic chemistry 31 (1966), S. 3363-3365 
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 2 (1972), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: It this study the use of Sephadex G-25, Sephadex LH-20 and CPG-10-75 for the separation of soluble humic compoutids frotn fresh water is tested.It is shown by Sephadex G-25 gel filtration that differences in molecule-size distribution of soluble humic compounds in one lake at different titnes and between lakes can be predicted by E250 and E365 measurements.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 16 (1986), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY. 1. The main source of P, Fe and DOC in the humic Lake Tjeukemeer is superfluous water pumped from surrounding peaty polders. Most particulate P is intracellular but almost all particulate Fe is abiotic.2. The size and molecular weight of the P, Fe and DOC (mainly fulvic acids (FA)) were determined by ultrafiltration and Sephadex G-100 gel filtration. Throughout the year most dissolved P and Fe was in colloids 〉35 nm with apparent molecular weight between 30,000 and 150.000. The bulk of FA occurred in particles 〈35nm.3. Calculating the atomic ratios of P, Fe and organic C in the different size classes revealed that Fe-FA chelates are a minor species of the Fe pool. Less than 10% of the fulvic acids occurred as Fe-FA chelates.4. Based on their apparent size and molecular weight, the Fe-FA chelates are colloidal aggregates, probably with the formula Fen-1(FA)n.5. About 50% of the dissolved P had the same size as the Fe-FA aggregates. These aggregates were only noticeable in winter when humus-rich polder water was flushed through the lake. During the rest of the year the dissolved Fe and P consisted mainly of acid-labile inorganic colloids which might have been organically coated.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 4 (1974), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: In this paper the effect of a fulvic acid fraction on the growth of a Pseudomonas sp. from fresh water is reported. The presence of fulvic acid in the culture medium caused an increase in the cell yield and in the cell yield per μl O2 taken up by the Pseudomonas. The observed stimulating effect has been explained in terms of co-metabolism of fulvic acid by the Pseudomonas.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 24 (1990), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY. 〈list xml:id="l1" style="custom"〉1 The concentrations of total and dissolved (〈0.2 μm) Fe, Mn, Cu, Co, Zn and Al in the Dutch reservoir, the Tjeukemeer, were recorded fortnightly between 1984 and 1986.2 Due to its reservoir function, the Tjeukemeer receives water that is relatively rich in Fe and Mn from its peaty drainage area in winter. In summer, water that is relatively rich in Cu and Zn from lake IJsselmeer, which is flushed by a tributary of the River Rhine, flows into the lake. Therefore trace metal loads, as estimated from annual mean concentrations and hydraulic data, are climate-dependent.3 In wet years, such as 1985, the annual Fe, Mn, Cu and Zn loads may be 3.1,0.2,0.001 and 0.009 gm−2, respectively. In dry years, such as 1984 and 1986, the Fe and Mn loads may be less than one quarter while the Cu and Zn loads may double. Especially in wet years comparable Cu and Zn inputs occur by deposition.4 Despite the dependence of trace metal loads on the climate-dependent water regime. Principal Component Analysis indicated no strong relation between the total Cu, Co, Zn and Al concentrations in lake water and hydrological tracers such as Cl− and UV absorbance. Instead, wind speed appeared to be more strongly connected with the dynamics of these metals. Thus in the shallow Tjeukemeer, internal trace metal loading due to wind-induced resuspension starts to dominate the contributions of external loads to the total metal concentrations at wind speeds exceeding 3ms−1.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 19 (1988), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY. 1. Sephadex gel filtration of filtered water from small, Finnish forest lakes demonstrated abiotic movement of 33P from added PO4 to two higher molecular weight fractions. This movement was most pronounced in waters with high humic content which also had high iron content. The two fractions which took up 13P had nominal molecular weights of 〉 100,000 and 10,000-20,000.2. An equilibrium existed between free PO4 and the two fractions. However, one fraction, at least, appeared to exist in two phases, with one phase in rapid equilibrium with free PO4 but the other in only slow equilibrium.3. Additions of ferric iron up to 1 mg Fe l−1 to the filtered lake water stimulated movement from free PO4, provided high concentrations of humic materials were present. In the absence of humic materials even 0.1 mg Fe 1−1 would precipitate all added 33PO4.4. The high molecular weight P was only partially reactive with standard molybdate reagents. Exposure of the high molecular weight P to sunlight caused a small release of PO4 under the experimental conditions employed.5. Possible implications for biological phosphorus demand of such sequestration of free PO4 by humic materials in combination with iron are discussed.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 9 (1979), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY. Curie point pyrolysis mass-spectrometry of freshwater fulvic acids from Tjeukemeer indicates the presence of polysaccharides, amino sugars, proteinaceous material and phenols. These results resemble those of the pyrolysis of soil fulvic acids. However, freshwater fulvic acids may be richer in aliphatic components than those from soil.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 21 (1989), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY. 1. Copper(II) complexation in the eutrophic. humus-rich Lake Tjeukemeer was measured fortnightly for several years by copper titration (Ion Selective Electrode) and by copper solubilization. Additionally, the copper speciation during titration was followed by ultrafiltration.2. The Tjeukemeer showed high ligand concentrations able to complex up to 8.5X10-5 M Cu.3. Scatchard plots and affinity spectra of the titration data allowed the discrimination of at least three different binding sites. In Scatchard plots log K values ranged from 5 to 9, in affinity spectra from 4.5 to 8.4. The highest log K values coincided with relatively low humus concentrations and blooms of algae, mainly Cyanobacteria.5. The ultrafiltration experiments indicated that relatively small size fractions (〈10 nm) have the highest copper binding affinity.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY. 1. The small Lake Negenmad, in the nature reserve ‘De Oude Venen’, was isolated from the canals and lakes of the Frisian lake system. Its chemistry and phytoplankton were monitored 1 year before (1984) and 2 years after (1985–86) isolation. These characteristics were compared with those of the adjacent Lake Veertigmad which was not manipulated.2. The hydrological intervention prevented the inflow of chloride-rich IJsselmeer water into Lake Negenmad and made its water table more dependent on evapotranspiration, precipitation and upwelling water. In comparison with the unmanipulated lake. Lake Negenmad became less saline (c. 50%), more humic (c. 50%) and total dissolved (〈0.2,μm) iron concentration increased dramatically.3. During the 2 years of damming no marked differences in the total nutrient concentrations of either lake were observed. However, the maximum phytoplankton density in the dammed lake was half that in the unmanipulated lake. The lower density may have been caused by low P availability after formation of humus-iron phosphate species.4. Preventing the inflow of water from the Frisian lake system favoured the occurrence in Lake Negenmad of flagellated species (Chrysophyceae, Cryptophyceae) at the expense of filamentous and nuisance-causing cyanobacteria (Oscillutoria, Anabaena, Aphanizomenon spp.).5. The implications of these results for water quality management of reservoirs in peaty areas are briefly discussed.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 17 (1987), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY. 1. The effect of ionic strength on the configuration of aquatic humic substances was studied by gel filtration and dialysis of water from small. Finnish forest lakes of varying colour.2. Sephadex gel filtration of water from the most humic lake gave similar elution profiles of UV absorbance and dissolved organic carbon (DOC). Gel filtration of unconcentrated samples from all three lakes under natural conditions of ionic strength (I = 1.7 × 10−4) and pH (5.5–6.0) gave similar fractionation of humic substances, despite their widely differing colour (30–350 mg Pt l−1) and DOC (5–25mg C l−1).3. Increasing the ionic strength by two orders of magnitude caused considerable retardation on the Sephadex columns of the humic substances, suggesting a decrease in their molecular size and/or shape.4. Dialysis experiments strongly indicated that ionic strength-induced changes in the configuration of the aquatic humic substances are indeed real. Hence it is probable that the elution behaviour of aquatic humic substances on Sephadex gels has previously been wrongly attributed to ionic strength-dependent interactions between the gel and the humic substances.
    Type of Medium: Electronic Resource
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