ISSN:0020-9309    

DOI:10.1002/iroh.19950800402

出版商:Akademie Verlag, Berlin    

年代:1995

数据来源: WILEY

摘要:

AbstractAn accompanying technical use of ecological effects from pelagic food‐web interactions (biofiltration) or from sediment (nutrient remobilization) can speed up recovery of lake ecosystems and can make restoration programs more effective after external load reductions. At present the comprehensive use of multiple ecotechnological controls for water quality is limited because our knowledge of the many complex interactions, indirect effects and above all the long‐term effects of such operations is insufficient. Beginning in the 1960s we started long‐term limnological analyses of the trophic interactions between community structure and the flow of matter under “manipulated” conditions in whole‐lake experiments at Lake Stechlin (manipulated water circulation and waste heat), Lake Haussee (biomanipulation) and Lake Fuchskuhle (lake‐dividing). This paper summarises changes in abiotic and biotic structures and functions of the manipulated lake ecosystems and discusses the possibilities and limitations of “whole‐

ISSN:0020-9309    

DOI:10.1002/iroh.19950800403

出版商:Akademie Verlag, Berlin    

年代:1995

数据来源: WILEY

摘要:

AbstractEcotechnology aims at the implementation of such a complex physical, chemical and/or biological ecosystem structure, which leads to a maximum capacity of the ecosystem to improve the water quality by ecosystem‐internal mechanisms. Numerous ecological control variables can be used in ecotechnology, however only mortality caused by predation, feeding or grazing on all trophic levels provides the possibility of a top‐ down control of the community structure. There are two contrasting concepts regarding the efficiency of top‐down control: (1) the “cascading trophic interactions” hypothesis (Carpenteret al., 1985), which postulates that changes at the top of the food web are transmitted down to primary producers, and (2) the “bottom‐up/top‐down” hypothesis (McQueenet al., 1986), which predicts that top‐down effects are strong at the top but weaken near the bottom of the food web. This paper describes an examination of these concepts by summarizing the effects of strong (Bautzen reservoir) and extremely strong (Lake Gräfenhain) enhancement of the stock of piscivorous fish. Both investigations refer to long‐term whole‐lake experiments. The results seem to confirm the “bottom‐up/top‐down” hypothesis. Effects at the top are strong, although sustained effects regarding dominance ofDaphniaare achieved only at an “optimum” (relatively low but not zero) density of zooplanktivorous fish. Far below the optimum density an efficient invertebrate predator was able to compensate almost completely the fish predation pressure on largeDaphnia.On the other hand, the optimum density can easily be exceeded during periods when high numbers of 0+ fish occur. Especially the effective control of 0+ fish of the intentionally enhanced piscivorous species is a key problem. At the bottom of the “classical” food web, the effects are restricted to a change of the phytoplankton compositions (mean biomass is not reduced).The contradiction between the latter results and other findings from lakes having lower phosphorus loadings (e. g. Stenson, 1988) can be solved only if the “bottom‐up/top‐down” hypothesis is combined with the hypothesis of a “biomanipulation efficiency threshold of the P‐loading” (Benndorf, 1987). The latter hypothesis predicts that the desired reduction of mean phytoplankton biomass as a strong top‐down effect at the bottom of the food web can be expected only below a threshold of the P‐loading. Below this threshold a set of biomanipulation‐induced indirect effects on phosphorus metabolism causes a reduction of the in‐lake P‐concentration. Consequently, sustained reduction of the phytoplankton biomass by biomanipulation can be achieved only by P‐limitation, which is an indirect bottom‐up effect induced by top‐down control of the food web. Taking into consideration the combination of the “bottom‐up/top‐down” and “P‐threshold” hypothesis, an attempt is made to predict the effects of biomanipulation regarding phytoplankton and water tra

ISSN:0020-9309    

DOI:10.1002/iroh.19950800404

出版商:Akademie Verlag, Berlin    

年代:1995

数据来源: WILEY

摘要:

AbstractThe effects of a decreased sewage release from a cellulose mill on the hypertrophic Bleiloch reservoir were studied. The waste water treatment reduced the concentration of yellow substances in the reservoir and resulted in a more light‐coloured waterbody. It is estimated that the changes in the light attenuation in the Bleiloch reservoir after 1989 can be described as eutrophication. Selected physical, chemical, and biological parameters from 1994 show the effect of changes.Three large pelagic enclosures (diameter 10 m, length 20 m) were installed in the reservoir to assess effects of artifical mixing on phytoplankton biomass and composition. Two circulation techniques have been used in the enclosures (relase of compressed air at the bottom of the enclosure and mechanical mixing, where water was pumped from the surface downward).The investigation demonstrate that the magnitude of seasonal peaks of chlorophyll were depressed in the mixed enclosures during circulation. The results were discussed in comparison with a reference enclosure without mixing and the waterbody of the reservoir. Cryptophytes and other flagellates achieved dominance during mixing in the “air”‐enclosure, while diatoms were the most abundant species in the „pump”︁‐enclosure. The development of filamentous cyanobacteria, which are significant indicators of eutrophication, was disturbed in the enclosures. They were outcompeted by cryptophytes, movable chlorophytes and diatoms.Both mechanical pump and compressed air can be used to control excessive algal growth. Further studies on the dynamics of phytoplankton to artifical mixing are suggested. The results of further studies should design anin situexperiment in the reservoir to reduce algal growth by light limitation.Further on a dense duckweed cover spreads over the surface of the Bleiloch reservoir, which influences the light regime in the waterbody. Therefore factors influencing the duckweed growth were analysed. Special attention was focused on the influence of the pH, consequences of the mixing in the waterbody and the role of

ISSN:0020-9309    

DOI:10.1002/iroh.19950800405

出版商:Akademie Verlag, Berlin    

年代:1995

数据来源: WILEY

ISSN:0020-9309    

DOI:10.1002/iroh.19950800406

出版商:Akademie Verlag, Berlin    

年代:1995

数据来源: WILEY

摘要:

AbstractThe Reservoir‐administration of Saxony continuously investigates the development of water quality in its numerous reservoirs. 25 of these reservoirs are used for drinking water supply. About 40 reservoirs have considerable importance for recreation and fishing.The following priorities of water quality management are based on the results of scientific investigations:protection against eutrophicationprevention of increase of nitrate concentrationsprotection against polutants, especially pesticides, heavy metals, hydrocarbons, mineral oilsacidification of watersThe objectives of the water quality of the Saxonian reservoirs refer to EU‐guidelines, to DVGW‐guidelines, to the drinking water ordinance of FRG, to guidelines of LAWA and to the actual knowledge of limnology.The evaluation of the most important reservoirs in the period from 1991 to 1994 shows the following result:These objects can be achieved by two main strategies:the reduction of the external loadingthe control by means of the internal ecological mechanismsTo investigate the loadings of the reservoirs and the sources of the nutrients mass balances particularly for phosphorus and nitrogen were based on periodic analyses. From these mass balances the strategies of water qualilty management were derived. An important consequence in this conection is the following:“The protection of the water is a basic requirement to the security of water quality”Therefore, the reduction of external loading is the main field of the strategy. In the case of high nutrient loaded reservoirs, par example eutrophic waters, a combination with the strategy of internal control, particularly with the biomanipulation is c

ISSN:0020-9309    

DOI:10.1002/iroh.19950800407

出版商:Akademie Verlag, Berlin    

年代:1995

数据来源: WILEY

摘要:

AbstractThe nutrient elimination was investigated in the underwater pre‐dam Haselbach (UWHA) situated in the mouth region of the Saidenbach reservoir (Saxony, Germany). The pronounced thermal stratification with the depth of the thermocline determined by the top height of the underwater dam (4,8 m below surface) resulted in epilimnetic inflow and hydraulic short circuit between inlet and main basin of the reservoir in summer. A simple model was developed for the approximation of nutrient elimination. Epilimnetic nitrate was used as a quasi‐conservative discharge tracer. Compared with a “normal” pre‐dam of the same size, the estimated mean phosphorus elimination of less than about 20% in UWHA was low. However, the UWHA proved to be an efficient settling basin for allochthonous part

ISSN:0020-9309    

DOI:10.1002/iroh.19950800408

出版商:Akademie Verlag, Berlin    

年代:1995

数据来源: WILEY

摘要:

AbstractThe drinking water reservoir Dröda (Feilebach) is the main and the most important drinking water resource in the destrict Vogtland (Saxonia). Since the establishment of this object the water has got a high nitrate load. In a short period the limit of nitrate for drinking water was exceeded.In the first part there is given a short survey of the general quality of the water of this reservoir, later the nitrate examinations over 25 years are demonstrated. Nearly a every year rhythm and long term trends are noticeable. The yearly variations are mainly based on the seasonal differences of the import of nitrate. The long term trends are interpreted as an effect of the change in agricultural utilization. A small dependence on the yearly rainfall is recognizable. Finally, possibilities are shown to decrease the nitrate load

ISSN:0020-9309    

DOI:10.1002/iroh.19950800409

出版商:Akademie Verlag, Berlin    

年代:1995

数据来源: WILEY

摘要:

AbstractActivated sludge systems can be operated to select bacteria which accumulate phosphorus as polyphosphate. By these means, phosphate can be removed without the addition of chemical precipitants. This contribution presents results of experiments with a bench‐scale purification plant for domestic sewage. The goal was to find the concentrations of relevant metal cations at which the biological P removal may be affected by competing chemical (precipitation) or physical (adsorption) processes. For this goal, increasing amounts of iron and calcium, respectively, were added into the pilot plant.During the addition of iron, the proportion of chemically (iron‐) bound phosphorus increased from 10 to more than 50%. The P‐release rate substantially decreased with increasing amount of added iron. An addition of small amounts of iron enhanced the long‐term stability of the P elimination as a whole.During the experimental period with addition of calcium, the proportion of Ca‐bound phosphorus increased from 1 to 2% to almost 15%. In batch experiments a measurable Ca‐phosphate precipitation took place at a pH value of at least 8.0 and a Ca‐concentration of at least 100 mg/l. The increase in hardness of the influent waste water didn't produce any positive effect on the stability of the enhanced biological phosphorus removal.The metal ions Ca2+, Mg2+and K+serve as counter‐ions in the polyhosphate chains. They were identified and quantified by X‐ray spectrometry in combination with scanning transmission electron microscopy. A release of Mg2+and K+occured simultaneously with the degration of polyphosphates (PP). The PP bound to Ca was no

ISSN:0020-9309    

DOI:10.1002/iroh.19950800410

出版商:Akademie Verlag, Berlin    

年代:1995

数据来源: WILEY

ISSN:0020-9309    

DOI:10.1002/iroh.19950800411

出版商:Akademie Verlag, Berlin    

年代:1995

数据来源: WILEY