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1.
R. D. Gulati 《Hydrobiologia》1990,191(1):173-188
A five-year zooplankton study (1982–86) on three shallow and highly eutrophic lakes in the Loosdrecht area (The Netherlands) did not reveal any significant changes following the considerable reduction in external P-loading (from about 1.0 g to 0.3 g P m–2 year–1) since mid-1984.The recent annual fluctuations in the rotifer and crustacean densities are within the range of those found before the restoration measure became operative. A decrease in the average size of the crustaceans and an absence of large-bodied forms reflects an increased fish predation rather than a change in the quality or quantity of their sestonic food ( < 150 µm) which continues to be dominated by filamentous cyanobacteria and Prochlorothrix hollandica, a prochlorophyte discovered in these lakes recently.  相似文献   

2.
The fish community in the Loosdrecht lakes is dominated by bream, pikeperch and smelt and is characteristic of shallow eutrophic lakes in The Netherlands. The biomasses of the respective fish species amount to ca. 250, 25 and 10 kg ha–1 and correspond to those in Tjeukemeer, another lake in The Netherlands. The average size of bream, however, is much smaller in the Loosdrecht lakes as a consequence of poorer feeding conditions. The zooplankton community in the Loosdrecht lakes is predominantly composed of relatively small species such as Daphnia cucullata, Bosmina coregoni and cyclopoid copepods, whereas in Tjeukemeer, Daphnia hyalina is permanently present in relatively high densities and the other species show a larger mean length. In the Loosdrecht lakes, the absence of D. hyalina and the smaller sizes of the other zooplankton species could be the consequence of a higher predation pressure, in combination with unfavourable feeding conditions for the zooplankton including the low density of green algae and the high density of filamentous cyanobacteria. A biomanipulation experiment in Lake Breukeleveen, one of the Loosdrecht lakes, indicated that feeding conditions were too unfavourable for large zooplankton to develop in spring, when the reduced fish biomass was not yet supplemented by natural recruitment and immigration.  相似文献   

3.
Reduction of the external phosphorus load in 1984 did not lead to recovery of Loosdrecht lakes. Therefore the Provincial Water Authorities of the Province of Utrecht proposed, after consulting the research group Water Quality Research Loosdrecht lakes (WQL), measures to reduce the present external phosphorus loading from 0.35 to 0.1 g Pm–2y–1. Mathematical modelling suggested that such a reduction would benefit the water quality of the lakes. The results of the WQL investigation did not lead to additional measures (dredging, biomanipulation, chemomanipulation).  相似文献   

4.
Modelling phosphorus fluxes in the hypertrophic Loosdrecht Lakes   总被引:2,自引:0,他引:2  
A dynamic, deterministic model is presented to simulate the phosphorus cycle and plankton growth in the shallow, hypertrophic Loosdrecht Lakes (The Netherlands) before and after restoration measures. Besides inorganic phosphorus (SRP) in both the surface water and the interstitial water, the model comprises three algal groups, zooplankton, fish, detritus, zoobenthos and upper sediment (all modelled both in carbon and in phosphorus). Within the model system, the phosphorus cycle is completely closed. Carbon and phosphorus are described independently, so that the dynamics of the P/C ratios can be modelled. Sediment processes are described in a simplified form.Simulated values are largely within the range of observed ones. The detrital fraction of the seston (=phytoplankton+detritus) varies from 50–60% in summer to about 90% in winter. SRP in the surface water is very low during most of the year. Sensitivity for external phosphorus input is larger for algal and detrital P than for algal and detrital C and chlorophyll-a. So the P/C ratio of the seston decreases following restoration measures, as is observed in the lakes, while the much higher P/C ratios of zooplankton and fish remain constant. Phosphorus mobilisation from the sediment decreases with decreasing external input. Adaptation of the model system to the reduced loading takes place within about two years.Sources of uncertainty in the model include the limited knowledge on selective grazing as well as on mortality and mineralisation processes.  相似文献   

5.
In two laboratory-scale enclosures of water from the shallow, eutrophic Lake Loosdrecht (the Netherlands), the predominating filamentous cyanobacteria grew vigorously for 2 weeks, but then their populations simultaneously collapsed, whereas coccoid cyanobacteria and algae persisted . The collapse coincided with a short peak in the counts of virus-like particles. Transmission electron microscopy showed the morphotype Myoviridae phages, with isometric heads of about 90 nm outer diameter and >100-nm long tails, that occurred free, attached to and emerging from cyanobacterial cells. Also observed were other virus-like particles of various morphology. Similar mass mortality of the filamentous cyanobacteria occurred in later experiments, but not in Lake Loosdrecht. As applies to lakes in general, this lake exhibits high abundance of virus-like particles. The share and dynamics of infectious cyanophages remain to be established, and it is as yet unknown which factors primarily stabilize the host–cyanophage relationship. Observations on shallow, eutrophic lakes elsewhere indicate that the cyanophage control may also fail in natural water bodies exhibiting predominance of filamentous cyanobacteria. Rapid supply of nutrients appeared to be a common history of mass mortality of cyanobacteria and algae in laboratory and outdoor enclosures as well as in highly eutrophic lakes. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

6.
A reduction in external phosphorus loading since 1984 to Loosdrecht lakes system by the dephosphorization of the inlet water, yielded only minor effects in Lake Loosdrecht. This reduction measure turned out to have decreased the loading only by a factor of two. A conceptual model was constructed based on laboratory measurements to describe phosphorus flow in the lake ecosystem for the summer of 1987. The role of zooplankton and fish was more important in phosphorus recycling than diffusion at the sediment-water interface. The input and output of phosphorus of the lake were at equilibrium and therefore, further reduction in external loading was needed for recovery. The results of the conceptual model agreed well with the output of the mathematical model PCLOOS. Additional measures such as dredging, flushing, chemomanipulation, or biomanipulation would be ineffective at the present level of external loading. Only a significant further reduction in external input will restore Lake Loosdrecht's water quality over a long period of time.  相似文献   

7.
  1. The model of the International Society of Limnology (SIL) Plankton Ecology working group (hereafter the PEG model) is a verbal model describing the patterns and driving factors of seasonal phytoplankton and zooplankton succession in oligotrophic and eutrophic lakes (Sommer et al., 1986). Despite being a citation classic, tests of the PEG model with respect to differences in zooplankton biomass dynamics between oligotrophic and eutrophic lakes are lacking.
  2. Here, I use the long‐term data from Lake Constance, which during the last 100 year changed from an (ultra‐) oligotrophic lake to a eutrophic lake and back to an oligotrophic lake to analyse trophic status differences in zooplankton biomass seasonality. Using data from one lake allows one to study trophic influences on biomass dynamics without the confounding effects of lake geographical setting and lake morphology, which complicate comparative dynamics in eutrophic versus oligotrophic lakes. However, environmental changes due to other driving factors, for example climate change, may possibly alter biomass dynamics as well.
  3. Data from Lake Constance do not support the differences in zooplankton seasonality in respect to peak timing between eutrophic and oligotrophic lakes suggested by the PEG model. Rather total zooplankton biomass, as well as cladoceran and copepod biomass showed a peak in May/June during all trophic conditions. Biomass dynamics of cladocerans during spring were more strongly influenced by water temperature than by trophic state. Furthermore, analyses of the geographical setting of the lakes considered in Sommer et al. (1986) suggest that the proposed differences in zooplankton seasonality between eutrophic and oligotrophic lakes are at least partially due to the confounding effect of lake altitudinal setting; the oligotrophic lakes were located at higher altitude than the eutrophic lakes.
  4. As a consequence of the results from Lake Constance, and the bias detected in the Sommer et al. (1986) study, a modified PEG model is proposed which considers low water temperature and not food limitation as the most important factor reducing zooplankton growth rate during early spring in both oligotrophic and eutrophic lakes.
  相似文献   

8.
The state of the environment of the Loosdrecht lakes   总被引:6,自引:6,他引:0  
The Loosdrecht lakes are a system of shallow, interconnected, peat lakes in the centre of The Netherlands. The main environmental functions of the Loosdrecht lakes are nature and recreation. From the point of view of the Dutch policy, a Specific Environmental Quality (Bijzondere Milieukwaliteit) should be set for these lakes.The most serious environmental problem of the area is eutrophication. The Loosdrecht lakes have, by increasing external phosphorus loading, changed, from clear lakes with few macrophytes, followed by a period of abundant characean growth, to turbid lakes dominated by cyanobacteria and detrital matter. Eutrophication was counteracted by use of sewerage systems and dephosporization of the supply water. The resultant decrease in external phosphorus loading did not result in a decrease of turbidity by suspended particles.The eutrophication of the lake ecosystems was described as a series of phases. One of those phases, the status around 1940, has been used as an ecological reference system.By means of a graphical presentation technique, the so-called AMOEBE-approach, the state of the environment of the Loosdrecht lakes has been visualized. Thirty-two ecological parameters, including both biotic and abiotic factors, have been selected and quantified. Concrete target values for these parameters have been derived from historical reports and from Lake Western Loenderveen, located close to the Loosdrecht lakes, but less eutrophic.The general conclusion is that the state of the environment of the Loosdrecht lakes is far from what is required with respect to a Specific Environmental Quality, as many of the selected parameters, like water transparency, total phosphorus, mineral nitrogen, cyanobacteria, bream, pike, macrophytes, birds and otter, deviate by over an order of magnitude from their desired levels.  相似文献   

9.
The present study investigates the zooplankton community dynamics and the abiotic environment in the eutrophic Lake Lysimachia (western Greece). The lake is considered to be recovering from eutrophication after the termination of an urban sewage inflow in 2000, and its waters are replenished constantly from the nearby oligotrophic Lake Trichonis. The results show that, although a decrease in nutrient concentrations was observed compared to the past, the lake still has eutrophic characteristics. This was reflected in the zooplankton community which is typical of those found in eutrophic lakes where rotifers prevail. Similarities among this lake and other nearby lakes were found considering the zooplankton community composition and seasonal variation. However, Lake Lysimachia is inhabited also by a number of different and even unique species (e.g., Moina micrura), suggesting that this ecosystem may be an important biodiversity refuge. Most of the zooplankton species were correlated with water temperature and, to a lesser extent, eutrophication key-water quality variables. Although there are few available data on the zooplankton of the lake, the abundance and composition of the community presenting characteristics indicative of intermediate trophic conditions and suggesting that the lake is probably under a kind of “biological” recovery.  相似文献   

10.
Van Donk  E.  Grimm  M. P.  Gulati  R. D.  Heuts  P. G. M.  de Kloet  W. A.  van Liere  L. 《Hydrobiologia》1990,200(1):291-301
Lake Breukeleveen (180 ha, mean depth 1.45 m), a compartment of the eutrophic Loosdrecht lakes system, was selected to study the effects of whole-lake foodweb manipulation on a large scale. In Lake Loosdrecht (dominated by filamentous cyanobacteria), due to water management measures taken from 1970–1984 (sewerage systems, dephosphorization) the external P load has been reduced from 1.2 g m−2 y−1 to 0.35 g m−2 y−1. The water transparency (Secchi-depthca. 30 cm), however, has not improved. The aim of the food-web manipulation in Lake Breukeleveen was not only to improve the light climate of the lake, but also to study if the successfull effects observed in small lakes (a few ha) can be upscaled. In March 1989 the standing crop of planktivorous and bentivorous fish populations was reduced by intensive fishery, fromca. 150 kg ha−1 toca. 57 kg ha−1. The lake was made unaccessible to fish migrating from the other lakes and it was stocked with large-sized daphnids and 0+ pike. However, water transparency did not increase in the following summer and autumn 1989, which is in contrast with great improvement in the light conditions previously observed in smaller lakes. The main explanations for the negative outcome in Lake Breukeleveen are: 1) the rapid increase of the planktivorous fish biomass and carnivorous cladocerans, predating on the zooplankton community; 2) suppression of the large daphnids by the high concentrations of filamentous cyanobacteria; 3) high turbidity of the lake due to resuspension of bottom material induced by wind, unlike in smaller lakes, and thus inability of submerged macrophytes to develop and to stabilize the ecosystem.  相似文献   

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