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  • 1
    Electronic Resource
    Electronic Resource
    Impact of submerged macrophytes on fish-zooplanl phytoplankton interactions: large-scale enclosure experiments in a shallow eutrophic lake (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 33 (1995), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. The impact of changes in submerged macrophyte abundance on fish-zooplankton-phytoplankton interactions was studied in eighteen large-scale (100 m2) enclosures in a shallow eutrophic take. The submerged macrophytes comprised Potamategon pectinatus L., P. pusillus L. and Callitriche hermaphroditica L. while the fish fry stock comprised three-spined sticklebacks, Gasterosteus acuteatus L., and roach, Rutilus rutilus L.2. In the absence of macrophytes zooplankton biomass was low and dominated by cyclopoid copepods regardless of fish density, while the phytoplankton biovolume was high (up to 38 mm31) and dominated by small pennate diatoms and chlorococcales. When the lake volume infested by submerged macrophytes (PVI) exceeded 15–20% and the fish density was below a catch per unit effort (CPUE) of 10 (approx. 2 fry m−2), planktonic cladoceran biomass was high and dominated by relatively large-sized specimens, while the phytoplankton biovolume was low and dominated by small fast-growing flagellates. At higher fish densities, zooplankton biomass and average biomass of cladocerans decreased and a shift to cyclopoids occurred, while phytoplankton biovolume increased markedly and became dominated by cyanophytes and dinoflagellates.3. Stepwise multiple linear regressions on log-transformed data revealed that the biomass of Daphnia, Bosmina, Ceriodaphmia and Chydorus were all significantly positively related to PVI and negatively to the abundance of fish or PVI x fish. The average individual biomass of cladocerans was negatively related to fish, but unrelated to PVI. Calculated zooplankton grazing pressure on phytoplankton was positively related to PVI and negatively to PVI x fish. Accordingly the phytoplankton biovolume was negatively related to PVI and to PVI x zooplankton biomass. Cyanophytes and chryptophytes (% of biomass) were positively and Chlorococcales and diatoms negatively related to PVI, while cyanophytes and Chlorococcales were negatively related to PVI x zooplankton biomass. In contrast diatoms and cryptophytes were positively related to the zooplankton biomass or PVI x zooplankton.4. The results suggest that fish predation has less impact on the zooplankton community in the more structured environment of macrophyte beds, particularly when the PVI exceeds 15–20%. They further suggest that the refuge capacity of macrophytes decreases markedly with increasing fish density (in our study above approximately 10 CPUE). Provided that the density of planktivorous fish is not high, even small improvements in submerged macrophyte abundance may have a substantial positive impact on the zooplankton, leading to a lower phytoplankton biovolume and higher water transparency. However, at high fish densities the refuge effect seems low and no major zooplankton mediated effects of enhanced growth of macrophytes are to be expected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2427.1995.tb01166.x
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  • 2
    Electronic Resource
    Electronic Resource
    Pike (Esox lucius L.) stocking as a biomanipulation tool 1. Effects on the fish population in Lake Lyng, Denmark (1997)
    Springer
    Hydrobiologia 342-343 (1997), S. 311-318 
    Details
    ISSN: 1573-5117
    Keywords: biomanipulation ; pike stocking ; predation ; 0+planktivores ; pike mortality ; pike/perch interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract From 1990–1993 juvenile pike (Esox lucius) were stockedeach spring in the eutrophic Lake Lyng (9.9 ha, max. depth 7.6 m,mean depth 2.4 m) in densities between 515 and 3616 pikeha−1. In 1989–90 the fish population consisted mainly ofroach (Rutilus rutilus), rudd(Scardinius erythrophthalmus), perch (Percafluviatilis) and ruffe (Gymnocephalus cernuus), andtotal fish biomass was estimated at 477 kg ha−1. Prior tostocking pike was not present in the lake. Following the first year ofstocking, the density of roach, rudd and ruffe fry expressedas catch per unit effort decreased significantly by 64 to 97%.In 1991 ruffe disappeared completely. The pike stocking did notaffect the density of perch significantly.The growth of pike was high and also the growth of perchincreased significantly from 1990 to 1991 (p〈0.001) and from1991 to 1994 (p〈0.001). We found a linear negativerelationship between stocking density of pike in May or June and theabundance of juvenile planktivorous fish (r 2=0.85, p〈0.05) in the littoral zone in August. No relationship was found inthe pelagic zone (r 2=0.21, p〉0.4). Pikesurvival was low in late August/early September. We suggest that growthof the piscivorous perch increased due to increased Secchi depthand a continuous high density of 0+ planktivores in the pelagiczone of the lake during the years of pike stocking, possibly caused bybehaviourial changes and the forcing of the 0+ planktivoresinto the pelagic zone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1017032616642
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  • 3
    Electronic Resource
    Electronic Resource
    Top-down control in freshwater lakes: the role of nutrient state, submerged macrophytes and water depth (1997)
    Springer
    Hydrobiologia 342-343 (1997), S. 151-164 
    Details
    ISSN: 1573-5117
    Keywords: top-down control ; shallow lakes ; trophic structure ; trophic cascade ; macrophytes ; zooplankton ; fish ; biomanipulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Based on data from 233 Danish lakes, enclosure experiments, full-scaleexperiments and published empirical models we present evidence that top-downcontrol is more important in shallow lakes than in deep lakes, excepting lakeswith a high abundance of submerged macrophytes. The evidence in support is: (1)That at a given epilimnion total phosphorus concentration (TP) the biomass offish per m2 is independent of depth, which means that biomassper m3is markedly higher in shallow lakes. (2) That the biomass of benthic invertebratesis higher in shallow lakes, which means that the benthi-planktivorous fish areless dependent on zooplankton prey than in deep lakes. By their ability to shiftto zooplankton predation their density can remain high even in periods whenzooplankton is scarce and they can thereby maintain a potentially high predationpressure on zooplankton. (3) That the possibilities of cladocerans to escapepredation by vertical migration are less. (4) That the zooplankton:phytoplanktonmass ratio per m2 is lower and presumably then also thegrazing pressure onphytoplankton. (5) That nutrient constraints appear to be weaker, as evidenced bythe fact that at a given annual mean TP, summer TP is considerably higher inshallow lakes, especially in eutrophic lakes lacking submerged macrophytes. (6)That negative feedback on cladocerans by cyanobacteria is lower as cyanobacterialdominance is less frequent in shallow lakes and more easily broken (at least inNorthern temperate lakes), and (7) That top-down control by benthi-planktivorousfish is markedly reduced in lakes rich in submerged macrophytes because theplants serve as a refuge for pelagic cladocerans and encouragepredatory fish at the expense of prey fish. We conclude that manipulation of fishand submerged macrophytes may have substantial impact on lake ecosystems, inparticular in shallow eutrophic lakes. On the contrary, if the conditions formore permanent changes in plant abundance or fish community structure are lackingthe feed-back mechanisms that endeavour a return to the original turbid state willbe particularly strong in shallow lakes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1017046130329
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  • 4
    Electronic Resource
    Electronic Resource
    Biomanipulation as an Application of Food-Chain Theory: Constraints, Synthesis, and Recommendations for Temperate Lakes (1998)
    Springer
    Ecosystems 1 (1998), S. 558-574 
    Details
    ISSN: 1435-0629
    Keywords: Key words: biomanipulation; lake; restoration; food chain; phosphorus; nutrient; fish; cyprinid.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: ABSTRACT The aim of this review is to identify problems, find general patterns, and extract recommendations for successful biomanipulation. An important conclusion is that the pelagic food chain from fish to algae may not be the only process affected by a biomanipulation. Instead, this process should be viewed as the “trigger” for secondary processes, such as establishment of submerged macrophytes, reduced internal loading of nutrients, and reduced resuspension of particles from the sediment. However, fish reduction also leads to a high recruitment of young-of-the-year (YOY) fish, which feed extensively on zooplankton. This expansion of YOY the first years after fish reduction is probably a major reason for less successful biomanipulations. Recent, large-scale biomanipulations have made it possible to update earlier recommendations regarding when, where, and how biomanipulation should be performed. More applicable recommendations include (1) the reduction in the biomass of planktivorous fish should be 75% or more; (2) the fish reduction should be performed efficiently and rapidly (within 1–3 years); (3) efforts should be made to reduce the number of benthic feeding fish; (4) the recruitment of YOY fish should be reduced; (5) the conditions for establishment of submerged macrophytes should be improved; and (6) the external input of nutrients (phosphorus and nitrogen) should be reduced as much as possible before the biomanipulation. Recent biomanipulations have shown that, correctly performed, the method also achieves results in large, relatively deep and eutrophic lakes, at least in a 5-year perspective. Although repeated measures may be necessary, the general conclusion is that biomanipulation is not only possible, but also a relatively inexpensive and attractive method for management of eutrophic lakes, and in particular as a follow-up measure to reduced nutrient load.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100219900051
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  • 5
    Electronic Resource
    Electronic Resource
    Cascading Trophic Interactions from Fish to Bacteria and Nutrients after Reduced Sewage Loading: An 18-Year Study of a Shallow Hypertrophic Lake (1998)
    Springer
    Ecosystems 1 (1998), S. 250-267 
    Details
    ISSN: 1435-0629
    Keywords: Key words: recovery; top-down control; bottom-up control; loading reduction; internal loading; fish; zooplankton; phytoplankton; ciliates; bacteria; size distribution; production.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: ABSTRACT The effects of major reductions in organic matter, total phosphorus (TP), and total nitrogen (TN) loading on the chemical environment, trophic structure, and dynamics of the hypertrophic, shallow Lake Søbygård were followed for 18 years. After the reduction in organic matter loading in 1976, the lake initially shifted from a summer clear-water state, most likely reflecting high grazing pressure by large Daphniaspecies, to a turbid state with extremely high summer mean chlorophyll a (up to 1400 μg L− 1), high pH (up to 10.2), and low zooplankton grazing. Subsequently, a more variable state with periodically high grazing rates on phytoplankton and bacteria was established. Changes in zooplankton abundance and grazing could be attributed to variations in cyprinid abundance due to a fish kill (probably as a consequence of oxygen depletion) and pH-induced variations in fish recruitment and fry survival. The results suggest strong cascading effects of fish on the abundance and size of zooplankton and phytoplankton and on phytoplankton production. A comparatively weak cascading effect on ciliates and bacterioplankton is suggested. Due to high internal loading, only minor changes were observed in lake-water TP after a reduction in external TP loading of approximately 80% in 1982; net retention of TP was still negative 13 years after the loading reduction, despite a short hydraulic retention time of a few weeks. TN, however, decreased proportionally to the TN-loading reduction in 1987, suggesting a fast N equilibration. Only minor improvement in the environmental state of the lake has been observed. We suggest that another decade will be required before the lake is in equilibrium with present external P loading.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100219900020
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  • 6
    Electronic Resource
    Electronic Resource
    Interactions between sediment and water in a shallow and hypertrophic lake: a study on phytoplankton collapses in Lake Søbygård, Denmark (1990)
    Springer
    Hydrobiologia 191 (1990), S. 139-148 
    Details
    ISSN: 1573-5117
    Keywords: phytoplankton collapses ; hypertrophic ; nitrogen ; phosphorus ; sedimentation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Short-term changes in phytoplankton and zooplankton biomass have occurred 1–3 times every summer for the past 5 years in the shallow and hypertrophic Lake Søbygård, Denmark. These changes markedly affected lake water characteristics as well as the sediment/water interaction. Thus during a collapse of the phytoplankton biomass in 1985, lasting for about 2 weeks, the lake water became almost anoxic, followed by rapid increase in nitrogen and phosphorus at rates of 100–400 mg N M−2 day−1 and 100–200 mg P m−1 day−1. Average external loading during this period was about 350 mg N m−2 day−1 and 5 mg P m−2 day−1, respectively. Due to high phytoplankton biomass and subsequently a high sedimentation and recycling of nutrients, gross release rates of phosphorus and nitrogen were several times higher than net release rates. The net summer sediment release of phosphorus was usually about 40 mg P m−2 day−1, corresponding to a 2–3 fold increase in the net phosphorus release during the collapse. The nitrogen and phosphorus increase during the collapse is considered to be due primarily to a decreased sedimentation because of low algal biomass. The nutrient interactions between sediment and lake water during phytoplankton collapse, therefore, were changed from being dominated by both a large input and a large sedimentation of nutrients to a dominance of only a large input. Nitrogen was derived from both the inlet and sediment, whereas phosphorus was preferentially derived from the sediment. Different temperature levels may be a main reason for the different release rates from year to year.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00026048
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  • 7
    Electronic Resource
    Electronic Resource
    Eight years of internal phosphorus loading and changes in the sediment phosphorus profile of Lake Søbygaard, Denmark (1993)
    Springer
    Hydrobiologia 253 (1993), S. 345-356 
    Details
    ISSN: 1573-5117
    Keywords: phosphorus ; retention ; sediment ; release ; fractionation ; iron:phosphorus ratio
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract During each of the first 8 years following an 80–90% reduction in external phosphorus loading of shallow, hypertrophic Lake Søbygaard, Denmark in 1982, phosphorus retention was found to be negative. Phosphorus release mainly occurred from April to October, net retention being close to zero during winter. Net internal phosphorus loading was 8 g P m−2 y−1 in 1983 and slowly decreased to 2 g P m−2 y−1 in 1990, mainly because of decreasing sediment phosphorus release during late summer and autumn. The high net release of phosphorus from Lake Søbygaard sediment is attributable to a very high phosphorus concentration and to a high transport rate in the sediment caused by bioturbation and gas ebullition. Sediment phosphorus concentration mainly decreased at a depth of 5 to 20 cm, involving sediment layers down to 23 cm. Maximum sediment phosphorus concentration, which was 11.3 mg P g−1 dw at a depth of 14–16 cm in 1985, decreased to 8.6 mg P g−1 dw at a depth of 16–18 cm in 1991. Phosphorus fractionation revealed that phosphorus release was accompanied by a decrease in NH4Cl-P + NaOH-P and organic phosphorus fractions. HCl-P increased at all sediment depths. The Fe:P ratio in the superficial layer stabilized at approximately 10. Net phosphorus release can be expected to continue for another decade at the present release rate, before an Fe:P ratio of 10 will be reached in the sediment layers from which phosphorus is now being released.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00050760
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  • 8
    Electronic Resource
    Electronic Resource
    Interactions between phytoplankton, zooplankton and fish in a shallow, hypertrophic lake: a study of phytoplankton collapses in Lake Søbygård, Denmark (1990)
    Springer
    Hydrobiologia 191 (1990), S. 149-164 
    Details
    ISSN: 1573-5117
    Keywords: phytoplankton collapses ; hypertrophic lake ; high pH ; phytoplankton ; zooplankton ; fish
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Since 1983 severe phytoplankton collapses have occurred 1–4 times every summer in the shallow and hypertrophic Lake Søbygård, which is recovering after a ten-fold decrease of the external phosphorus loading in 1982. In July 1985, for example, chlorophyll a changed from 650 µg l−1 to about 12 µg 1−1 within 3–5 days. Simultaneously, oxygen concentration dropped from 20–25 mg O2l−1 to less than 1 mg O2l−1, and pH decreased from 10.7 to 8.9. Less than 10 days later the phytoplankton biomass had fully recovered. During all phytoplankton collapses the density of filter-feeding zooplankton increased markedly, and a clear-water period followed. Due to marked changes in age structure of the fish stock, different zooplankton species were responsible for the density increase in different years, and consequently different collapse patterns and frequencies were observed. The sudden increase in density of filter-feeding zooplankton from a generally low summer level to extremely high levels during algae collapses, which occurred three times from July 1984 to June 1986, could neither be explained by changes in regulation from below (food) nor from above (predation). The density increase was found after a period with high N/P ratios in phytoplankton or nitrate depletion in the lake. During that period phytoplankton biomass, primary production and thus pH decreased, the latter from 10.8–11.0 to 10.5. We hypothesize that direct or indirect effects of high pH are important in controlling the filter-feeding zooplankton in this hypertrophic lake. Secondarily, this situation affects the trophic interactions in the lake water and the net internal loading of nutrients. Consequently, not only a high content of planktivorous fish but also a high pH may promote uncoupling of the grazing food-web in highly eutrophic shallow lakes, and thereby enhance eutrophication. A tentative model is presented for the occurrence of collapses, and their pattern in hypertrophic lakes with various fish densities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00026049
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  • 9
    Electronic Resource
    Electronic Resource
    Phosphorus release from resuspended sediment in the shallow and wind-exposed Lake Arresø, Denmark (1992)
    Springer
    Hydrobiologia 228 (1992), S. 91-99 
    Details
    ISSN: 1573-5117
    Keywords: shallow lakes ; resuspension ; internal P-loading ; equilibrium concentration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Wind-induced sediment resuspension occurs frequently in the shallow and eutrophic Lake Arresø, Denmark. The impact of resuspension on internal phosphorus loading was investigated by laboratory experiments studying P-release from the undisturbed sediment surface and by experiments simulating resuspension events. Phosphorus release from undisturbed sediment sampled in May and August was 12 mg and 4 mg m−2 d−1, respectively. During experimental simulation of resuspension, soluble reactive phosphate (SRP) increased by 20–80 µg l−1, which indicates that a typical resuspension event in the lake would be accompanied by the release of 150 mg SRP m−2. The internal P loading induced by resuspension is estimated to be 60–70 mg m−2 d−1, or 20–30 times greater than the release from undisturbed sediment. SRP release during simulation of resuspension was mainly dependent on the equilibrium conditions in the water column and was basically independent of the increase in suspended solids and the duration of resuspension. A second simulation of resuspension conducted 26 hours later, did not result in any further release of SRP from sediment sampled in May. In contrast, there was an additional SRP release from sediment sampled in August, indicating that an exchangable P pool, capable of altering equilibrium conditions, is built up between resuspension events. It is concluded that resuspension, by increasing the P flux between sediment and water, plays a major role in the maintenance of the high nutrient level in Lake Arresø. A relatively high release rate is maintained during resuspension because of the low Fe:P ratio and the high concentration of NH4Cl-extractable P in the sediment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00006480
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  • 10
    Electronic Resource
    Electronic Resource
    Resuspension in a shallow eutrophic lake (1992)
    Springer
    Hydrobiologia 228 (1992), S. 101-109 
    Details
    ISSN: 1573-5117
    Keywords: resuspension ; lakes ; shallow ; modelling ; turbidity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The frequency and the importance of wind-induced resuspension were studied in the shallow, eutrophic Lake Arresø, Denmark (41 km2, mean depth 3 m). During storm events in autumn 1988 lake water samples were collected every 2–8 hours by an automatic sampler at a mid-lake station. The concentration of suspended solids and Tot-P was found to increase markedly. During storms up to 2 cm of the superficial sediment was resuspended, and the concentration of resuspended solids in the water column rose to 140 mg l−1. The resuspended particles had a relatively high settling velocity and on average, a relatively short residence time in the water column of 7 hours. A model which describes the concentration of resuspended solids as a function of wind velocity and of settling velocity of the resuspended particles is presented. Using additional wind velocity data from a nearby meteorological station, the model has been used to calculate the frequency of resuspension events and concentration of resuspended solids for the period from May to November 1988. These calculations show that resuspension occurred about 50% of the time. Average flux of suspended solids from the sediment to the water was 300 g m−2 d−1 and during 50% of the time lake water concentration of suspended solids was more than 32 mg l−1. A relationship between concentration of suspended solids and Secchi-depth is presented. Because of resuspension, Secchi-depth in Lake Arresø is reduced to 0.5 m. Resuspension also had a marked effect on Tot-P concentration in the lake water, and P input to the lake water being totally dominated by resuspension events.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00006481
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