I am researching the use of several stormwater techniques known to reduce runoff to provide future developers and municipal officials with tools to meet the stormwater post-construction runoff standards laid out in Phase II of the Clean Water Act. Specifically, I am looking at Smart Growth, Low Impact Development, Open Space Design, and Green Infrastructure. Phase II states that any new development or re-development equaling one acre or greater must be able to capture and infiltrate the first inch of rain to fall on site following 72 hours with no measurable precipitation. There is no one way to solve the problem of stormwater management; therefore we must implement an integrated approach which synthesizes these design theories to effectively manage stormwater. I used the La Rue site on Kingston Pike just before Cherokee Blvd. as a testing ground for my hypothesis. I will proceed with two design scenarios for this project. The first scenario encompasses designing the site as if it were in the pre development stages. I will keep the same building square footage, but rearrange the footprints in a more efficient layout for stormwater management. The second scenario will be a retrofit of the site to comply with Phase II standards. Though it is not a current requirement of Phase II, many professionals believe in the coming years the EPA will require the retrofit of existing developments to meet these standards. In this scenario, the building footprints will remain exactly as they are but any other features will be malleable (infrastructure, vegetation, grading, etc.). Another component in this thesis will be to determine which design theories are best suited to each scenario. My pre-investigation belief is that for the pre-development scenario, I will be able to implement parts of all four theories. For the retrofit, I believe that I will be limited mostly to Low Impact Development and Green Infrastructure. Though, it is possible that I may still be able to fit in some principles of the Smart Growth and Open Space Design (reduce impervious footprints, reduce road widths, etc.).

Orientadores: Maria Aparecida Azevedo Pereira da Silva, Maria Regina Bueno Franco / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-09T03:53:03Z (GMT). No. of bitstreams: 1 Sampaio_KarinadeLemos_D.pdf: 3249314 bytes, checksum: c77f7bb03d18a2359d110d8fa3068a70 (MD5) Previous issue date: 2007 / Resumo: Durante a etapa de concentração de sucos, juntamente com a água, são também perdidos compostos voláteis responsáveis pelo aroma e sabor característicos da fruta. Esses voláteis podem, no entanto, ser recuperados por condensação, gerando um subproduto conhecido como water phase. Quando submetida à destilação fracionada, a water phase recuperada durante o processamento de sucos pode gerar essências naturais (GRAS), de alto valor agregado, as quais, ao serem incorporadas a sucos e refrescos, aumentam a qualidade sensorial desses produtos. Infelizmente, as water phases geradas por empresas brasileiras de sucos tropicais como caju, maracujá, etc são subaproveitadas. Isso ocorre devido ao conhecimento insuficiente tanto da composição dos voláteis presentes nas mesmas, como das condições de destilação a que devem ser submetidas para a elaboração de essências. Assim, os objetivos do presente estudo foram: i) identificar por cromatografia gasosaespectrometria de massas (CG-EM) o perfil de voláteis presentes em waterphase de caju gerada por indústria nacional de suco, determinando por CG-olfatometria (CGO), a importância odorífera de cada volátil identificado e, ii) através de destilação fracionada de water phase de caju gerada por empresa nacional, elaborar essências naturais, caracterizando a qualidade sensorial das mesmas, bem como o perfil de voláteis. Três tipos de materiais foram analisados: i) water phase de caju gerada durante a concentração de suco utilizando-se recuperador de aromas; ii) um condensado aquoso obtido por simples condensação da água evaporada durante a etapa de concentração do suco de caju e, iii) nove essências naturais GRAS geradas através da destilação fracionada de uma water phase de caju, utilizando-se coluna de fracionamento a 1 atm de pressão atmosférica e temperatura de 98 ºC, com condensação a ¿ 6 ºC. Os compostos voláteis presentes nas amostras foram isolados através de extração líquido-líquido com diclorometano e concentrados sob fluxo de nitrogênio. Após avaliação sensorial por equipe treinada, os isolados foram analisados por cromatografia gasosa (CG) utilizando-se um cromatógrafo gasoso Varian modelo 3600, equipado com detector de ionização de chama (DIC) e coluna capilar com fase estacionária DB-Wax. A identificação dos compostos foi conduzida através de um cromatógrafo gasoso da marca SHIMADZU modelo 17-A, equipado com detector de massas QP-5000 e operando nas seguintes condições: voltagem de ionização de 70eV (ionização por impacto de elétrons), velocidade de scan de 1 scan s ¿1 e varredura realizada entre 35 e 350 m/z. Os isolados da water phase e de uma das essências foram submetidos à CG-olfatometria (CGO), onde cinco julgadores treinados utilizando a técnica tempo-intensidade Osme, avaliaram os odores presentes nos efluentes cromatográficos dos citados isolados. Os resultados revelaram na water phase a presença de 64 compostos voláteis, dos quais 52 apresentaram impacto odorífero no efluente cromatográfico. Cerca de 38% dos compostos voláteis eram ésteres, 23% álcoois e 15% ácidos. Os voláteis de maior impacto odorífero presentes na water phase foram: ácido 3-metil butanóico (descrito como vômito, chulé), 2- metil butanóico (vômito, chulé), ácido acético (abacaxi cozido, remédio), acetofenona (queijo, cera), 2-hidroxi hexanoato de etila (caju), 2-metil-4-pentenal (verde, fruta), heptanol (caju, fruta), trans-3-hexen-1-ol (verde, fruta), 3-metil-1-butanol (chulé, álcool isoamílico); trans-2-butenoato de etila (fruta, caju), 2-metil butanoato de etila (fruta, caju), octanol (perfume, flor), trans-2-hexenal (maria fedida, verde), cis-3-hexen-1-ol (grama, doce), 2-etil-1-hexanol (verde, erva), isovalerato de etila (caju, doce) , 2-etil acrilato de metila (maria fedida, verde) e octanoato de etila (grão, terra molhada). Assim, a presente water phase, por conter muitos voláteis odoríferos de aromas desejáveis em uma essência de fruta, possuía grande potencial para gerar essências naturais de caju de boa qualidade sensorial. No condensado aquoso foram identificados 27 compostos voláteis, sendo 40% álcoois, 27% ácidos e 23% ésteres. A grande quantidade de álcoois e ácidos aliado a pequena quantidade e concentração de ésteres presentes no condensado aquoso demonstram que o mesmo é uma matéria prima menos favorável para a produção de essências, mas ainda assim, passível de ser explorada para esse fim. Todas as essências elaboradas apresentaram baixa intensidade de aroma de caju. O isolado da essência com maior intensidade de aroma de caju entre as 9 elaboradas possuía 61 compostos voláteis, dos quais 36 apresentaram importância odorífera no efluente cromatográfico. Dos 32 voláteis identificados, 33% eram álcoois, 23% terpenos, 14% ésteres, 11% aldeídos. Dentre eles, os de maior impacto odorífero foram: carvona (descrita como grama, sauna), 2-metil- 1-butanol (caju fermentado, fermentado), linalol (mamão, perfume), 2-hidroxi-4-metil pentanoato de etila (caju, fruta), cis-geraniol (essência de caju, fruta, flor), nonanal (grama, verde), 3-metil-1-butanol (caju fermentado, ardido), octanol (perfume, fruta), 2-etil-1- hexanol (grão, óleo de amêndoa), crotonoato de etila (caju, fruta). O alto caráter ¿doce/alcoólico¿ reportado nesta essência pela equipe sensorial, em detrimento do aroma característico de caju, pode ser atribuído à grande proporção de álcoois e terpenos presentes na mesma, em detrimento dos ésteres, que normalmente são responsáveis por notas de aromas ¿frutais¿ em essências. Dentre outros fatores, a baixa proporção de ésteres nesta essência, pode ser atribuída à perda, degradação, ou oxidação dos mesmos durante o processo de destilação fracionada da essência, realizada a alta temperatura e pressão atmosférica. A temperatura de condensação utilizada durante o processo de destilação (-6°C) também pode não ter sido suficientemente baixa para recuperar estes compostos na essência. De um modo geral, os resultados da presente pesquisa revelam que ainda que empresas brasileiras estejam gerando water phase com grande potencial para elaboração de essências naturais de caju, o processo de destilação fracionada dessas water phases, embora não possa ser considerado complexo, não é trivial, e requer otimização. Pesquisas adicionais explorando condições de destilação a menores temperaturas e pressões são cruciais para a adequada transformação das water phases nacionais em essências GRAS de alta qualidade sensorial / Abstract: During the juice concentration step, volatile compounds responsible for the aroma and flavour characteristics of the fruit are lost together with the water. These volatiles can however be recovered by condensation, producing a sub-product known as the water phase. When submitted to fractionated distillation, the water phase recovered during juice processing can produce natural essence (GRAS), of high economic value, which, on being incorporated into juices and soft drinks, can increase the sensory quality of these products. Unfortunately, the water phases produced by Brazilian companies producing tropical juices such as cashew and passion fruit juices are under-used, due to a lack of knowledge of the composition of the volatiles present and of the distillation conditions to which they should be submitted to elaborate the essences. Thus the objectives of the present study were: i) identify the profile of the volatiles present in the cashew water phase produced by a national juice industry using gas chromatography-mass spectrometry (GC-MS), determining the odoriferous importance of each volatile identified using GC-olfactometry, and ii) elaborate natural essences by way of fractionated distillation of the cashew water phase produced by a national company, characterising their sensory quality and the profile of the volatiles. Three types of material were analysed: i) the cashew water phase produced during juice concentration using an aroma recovery unit; ii) an aqueous condensate obtained by the simple condensation of the water evaporated off during the cashew juice concentration step, and iii) nine natural GRAS essences produced by the fractionated distillation of a cashew water phase, using a fractionation column at 1 atm of atmospheric pressure and a temperature of 98ºC, with condensation at ¿6ºC. The volatile compounds present in the samples were isolated by liquid-liquid extraction using dichloromethane and concentrated in a flow of nitrogen. After a sensory evaluation by a trained panel, the isolates were analysed by gas chromatography (GC) using a Varian model 3600 gas chromatograph equipped with a flame ionisation detector (FID) and a capillary column with a DB-Wax stationary phase. The compounds were then identified using a Shimadzu model 17-A gas chromatograph equipped with a QP-5000 mass detector operating under the following conditions: ionisation voltage of 70eV (ionisation by electron impact), scanning velocity of 1 scan s-1 scanning between 35 and 350 m/z. Compounds isolated from the water phase and from one of the essences were submitted to GC-olfactometry (GC-O), where five trained judges evaluated the odours present in the chromatographic effluent of the above cited isolates using the Osme time-intensity technique. Sixty-four volatile compounds were found in the water phase, of which 52 presented an odoriferous impact on the chromatographic effluent. About 38% of the volatile compounds were esters, 23% alcohols and 15% acids. The following volatiles of the water phase showed the greatest odoriferous impact: 3-methyl butanoic acid (described as smelling of vomit, smelly feet), 2- methyl butanoic acid (vomit, smelly feet), acetic acid (cooked pineapple, medicinal), acetophenone (cheese, wax), ethyl 2-hydroxy hexanoate (cashew), 2-methyl-4-pentenal (greens, fruity), heptanol (cashew, fruity), trans-3-hexen-1-ol (greens, fruity), 3-methyl-1- butanol (smelly feet, isoamyl alcohol); ethyl trans-2-butenoate (fruity, cashew), ethyl 2- methyl butanoate (fruit, cashew), octanol (perfume, flowery), trans-2-hexenal (stinky insect, greens), cis-3-hexen-1-ol (grass, sweet), 2-ethyl-1-hexanol (greens, herbal), ethyl isovalerate (cashew, sweet), methyl 2-ethyl acrylate (stinky insect, greens) and ethyl octanoate (grainy, wet earth). Thus since the water phase contained so many odoriferous volatiles with desirable aromas for a fruit essence, it showed considerable potential to produce natural cashew essence with good sensory quality. Twenty-seven volatile compounds were identified in the aqueous condensate, of which 40% were alcohols, 27% acids and 23% esters. The larger amounts of alcohols and acids allied to the smaller amount and concentration of esters present in the aqueous condensate, indicated that this was a less favourable raw material for the production of essences, although possibly still of some use for such ends. All the essences elaborated presented a low intensity of cashew aroma. The isolate from the essence with the greatest intensity of cashew aroma amongst the 9 elaborated had 61 volatile compounds, of which 36 presented odoriferous importance in the chromatographic effluent. Of the 32 volatiles identified, 33% were alcohols, 23% terpenes, 14% esters and 11% aldehydes. Amongst these, those with greater odoriferous impact were: carvone (described as smelling of grass, sauna), 2-methyl-1-butanol (fermented cashew, fermented), linalool (papaya, perfume), ethyl 2-hydroxy-4-methyl pentanoate (cashew, fruity), cis-geraniol (cashew essence, fruity, flowery), nonanal (grass, greens), 3-methyl-1- butanol (fermented cashew, pungent), octanol (perfume, fruit), 2-ethyl-1-hexanol (grainy, almond oil), ethyl crotonoate (cashew, fruit). The highly ¿sweet/alcoholic¿ character of this essence as reported by the sensory panel, in detriment of a characteristic cashew aroma, can be attributed to the high proportion of alcohols and terpenes present, in detriment of esters, which are the compounds normally responsible for the fruity notes of essences. Amongst other factors, the low proportion of esters in this essence could be attributed to their loss during the fractionated distillation of the essence, carried out at high temperatures and atmospheric pressure. In general the results of the present study revealed that even if Brazilian companies are producing cashew water phase with great potential for the elaboration of natural cashew essences, the fractionated distillation process of these water phases, although not complex, is not trivial and requires optimisation. Additional research is crucial, exploring distillation conditions at lower temperatures and pressures for an adequate transformation of these national water phases into GRAS essences with high sensory quality / Doutorado / Consumo e Qualidade de Alimentos / Doutor em Alimentos e Nutrição

In this paper we formulate a nonlocal density functional theory of inhomogeneous water. We model a water molecule as a couple of oppositely charged sites. The negatively charged sites interact with each other through the Lennard–Jones potential (steric and dispersion interactions), square-well potential (short-range specific interactions due to electron charge transfer), and Coulomb potential, whereas the positively charged sites interact with all types of sites by applying the Coulomb potential only. Taking into account the nonlocal packing effects via the fundamental measure theory, dispersion and specific interactions in the mean-field approximation, and electrostatic interactions at the many-body level through the random phase approximation, we describe the liquid–vapour interface. We demonstrate that our model without explicit account of the association of water molecules due to hydrogen bonding and with explicit account of the electrostatic interactions at the many-body level is able to describe the liquid–vapour coexistence curve and the surface tension at the ambient pressures and temperatures. We obtain very good agreement with available in the literature MD simulation results for density profile of liquid–vapour interface at ambient state parameters. The formulated theory can be used as a theoretical background for describing of the capillary phenomena, occurring in micro- and mesoporous materials.

A liquid Cooled below its normal freezing temperature is known as a supercooled liquid. On further cooling, supercooled liquids crystallize to thermodynamically stable, ordered structures. Alternatively, if the cooling rate is fast enough, the crystallization may be avoided altogether. Below a particular temperature during rapid cooling the liquid will solidify into a disordered, amorphous phase -also known as the glassy phase of matter. This particular temperature is termed the ”glass transition temperature” (Tg). Unlike a crystalline solid, a glass is neither a thermodynamically stable phase nor does it possess long range molecular ordering. Very slow structural relaxation (in the time scale of ∼ 100 s) is always present in the glassy phase. Thus, this phase is often referred to as a metastable phase of matter. Experimental and theoretical studies related to the behavior of supercooled liquids are the subject matter of many investigations for the last few decades [1]. These studies find their applications in diverse fields such as geology, cryopreservation, glaciology and atmospheric science. However, properties of supercooled liquids and the corresponding amorphous phase are not completely understood at present, particularly for hydrogen bonded (H-bonded) systems. This thesis concerns both the crystallization and the glass formation process of H-bonded systems. The systems of interest are water, the commonly accepted universal solvent, and the aqueous binary mixture of glycerol and water. The technique of molecular probing is often used to study the cooperativety and rotational diffusion of supercooled liquids and for determination of the glass transition temperature. For the present set of work, a molecular probe technique called spin probe ESR is extensively used. Electron paramagnetic resonance or electron spin resonance (EPR/ESR) measures the electronic energy level separation and is well known for the high sensitivity. All of the systems studied in the present set of work are diamagnetic. This issue is circumvented by dissolving paramagnetic spin probe molecules, which are usually organic free radicals with one N-O group, into the systems. Spin probes are added in very low concentrations (~10-3M) to minimize the effect on the host system and also to avoid mutual interactions between them. The unpaired electron delocalized in the direction of the N-O bond serves as the paramagnetic center required for an ESR experiment. The splitting of electron energy level due to the external magnetic field (Zeeman splitting) can give rise to resonance absorption of energy if exposed to a microwave of appropriate frequency. There is also a magnetic coupling (hyperfine) between the spin of the unpaired electron and nuclear spin of the nearby nitrogen atom. The hyperfine coupling splits each electron energy levels, to the first order, symmetrically into three levels. The transitions between these levels -subject to appropriate selection rules -give rise to the ESR spectrum [2]. The spectral shape in a magnetic field sweep ESR experiment appears complex if randomly oriented spin probes are dispersed in an amorphous or polycrystalline solid matrix. The high degree of mobility in probe molecules, present in a liquid solution, can average out the individual anisotropy of magnetic tensors to get a spectrum of three equally spaced liens. Experiments can be performed spanning a spin probe reorientation timescale of 10-7-10-12 s typically in the temperature range of 4.2 -300K. In chapter one we have given a brief overview of the supercooled liquids and the phase transitions related to the present work. Particular emphasis has been given to the dynamical features of the supercooled liquid close to its glass transition temperature and their classification based on the degree of ’fragility’ [3]. Brief general introductions of the systems studied in each of the following chapters are also provided. Then, the details of ESR spectroscopy and a quantum mechanical picture of the method of spin probe ESR have been discussed [4]. A separate section has been devoted to the numerical and analytical methods used to analyze the spectrum to extract information related to the spin probe dynamics [5]. The chapter concludes with a description of the ESR spectrometer. In chapter two we have studied the glass transition and dynamics of the supercooled water by the method of spin probe ESR. The vitrification has been done by direct exposure of the bulk water sample, doped with the spin probe TEMPOL, to the liquid helium flow. The vitrified matrix turns into the ultraviscous liquid above the putative glass transition temperature of ~136 K which further transforms to cubic ice (Ic) above TX ~150 K. The supercooled fraction of water, along with the spin probes which are treated as impurities by the crystallized surroundings, remain trapped inside the veins or triple junctions of the ice grains which serve as the interfacial reservoir of impurities in a polycrystalline ice matrix. The spectra for the entire temperature range have been analyzed with the help of in-depth computation by modelling the reorientation of TEMPOL in terms of the jump angle θs and the rotational correlation time τ [5]. This model, based on a homogeneous mobility scenario of the spin probe, works nicely except in the temperature range of 140-180 K. Dynamical heterogeneity (DH) is apparent in this temperature range and a more mobile (fast) component, as compared to the one corresponding to the very slow dynamics of TEMPOL at lower temperatures (slow), is observed. The relative weight of the fast and the slow component changes with temperature and above ~180 K the entire spectrum changes into the motionally narrowed triplet. The temperature dependence of the slow component of τ shows a change in slope at a temperature close to the putative glass transition temperature of water. The fast component of τ exhibits a fragile, i.e. non-Arrhenius character at high temperature with a crossover to a strong, i.e. Arrhenius behavior below ~225 K, close to the hypothesized fragile-to-strong crossover (FSC) for water at TFSC ~228 K. The breakdown of the Debye-Stokes-Einstein (DSE) law is observed when the τ values are combined with the available viscosity data of water to evaluate the DSE ratio, paralleling the SE breakdown which has recently been observed in nanoconfined water [6]. The dynamical heterogeneity is thought to be closely associated with the static structural heterogeneities of supercooled water. The existence of large scale structural fluctuations spanning a range of low-and high-density phases of liquid water have been associated with the heterogeneous dynamics sensed by TEMPOL. Motivated by the Arrhenius like behavior of the slow component, it has been identified with the low density liquid (LDL). The fragile nature of the fast component at high temperature may be identified with that of the high density liquid (HDL) which is the predominant fraction in liquid or weakly supercooled water [6]. Chapter three reports the studies on freezing and dynamics of the supercooled water trapped inside the veins of a polycrystalline ice matrix by dissolving spin probes TEMPO and TEMPOL into it. When a millimolar spin probe aqueous solution is cooled below the freezing point of water, the spin probes -driven by the mechanism described above migrate to the liquid environment inside the ice veins. Local concentration of the probe molecules inside the veins can go up to 1-10 M [7]. Bulk crystallization is evident in differential scanning calorimetry (DSC) studies whereas the liquid environment of the spin probe below the bulk freezing is confirmed by its narrow triplet ESR spectrum. A sudden collapse of this narrow triplet into a single broad line indicates the freezing of the trapped water fraction which usually happens well below the DSC freezing point for both the probes. The spin probe detected freezing point of this interstitial water is found to be largely dependent on the properties and the amount of the dissolved probe molecules. An explanation is sought in terms of the ’destructuring effect’ on the tetrahedral ordering of the water H-bond network by both the high local concentration of the spin probes and the hydrogen bond strength, formed between the water and the spin probe molecules through the polar groups of the latter [8, 9]. These two factors are thought to play important roles in determining the reorientational dynamics of the spin probe molecules, as well. The rotational correlation times of the two probes exhibit a crossover owing to the different mobility of their salvation shells in the more ordered supercooled water. The observed relaxation behavior of this confined water using the probe TEMPO, which has little effect on water H-bond network, is found in agreement with the previous experimental investigations on water confined in a nanochannel [10]. In chapter four, the glass transition, relaxation and the free volume of the glycerol-water (G-W) system are studied over the glycerol concentration range of 5 -85 mol% with TEMPO as the spin probe. G-W mixture is intrinsically inhomogeneous due to the well established phase segregation below a critical glycerol concentration of 40 mol%. In the inhomogeneous regime the water molecules tend to form cooperative domains besides the mesoscopic G-W mixture [11]. Samples are quenched by rapid cooling down to 4.2 K inside the spectrometer cryostat. Spectra were recorded on slow heating of the sample in the temperature range of 130 -305 K. The glass transition temperature is correlated to the sharp transition of the extrema separation of the ESR spectrum. The glass transition temperatures are found to follow a concentration dependence which is closely associated to the mesoscopic inhomogeneities of the G-W system. The steady enhancement in fragility of the G-W system with the addition of water is evident from the temperature dependence of the spin probe correlation time τ for the entire concentration range. In the temperature range of 283 -303 K, the DSE law is followed i.e. the spin probe reorientation process is found to be strongly coupled to the system viscosity. In this regime, the τ values have been used along with the available viscosity data to calculate the effective volume V of the spin probe for the entire concentration range. The spin probe effective volume is a measure of the available free volume of the host matrix. A drastic change in the quantity is seen in the vicinity of the 40 mol% glycerol concentration owing to a similar structural change of the matrix due to the formation of mesoscopic scale inhomogeneities below the critical concentration [12]. The thesis concludes with a discussion about the possible future directions of research.

The population dynamics and demography of Daphnia galeata was analysed in a five year study in the biomanipulated Bautzen Reservoir. Samples were taken two times a week during the period May-July in the pelagic zone of this highly eutrophic water. Major bottom-up and top-down factors were determined during the study period and analysed with regard to their influence on Daphnia dynamics and life history. Field data on fecundity and population structure of D. galeata were combined with results from life table and growth experiments performed under approximately in situ conditions to gain insight into the mechanisms leading to a midsummer decline of this cladoceran species which dominates the zooplankton community in Bautzen Reservoir. Two main patterns of Daphnia dynamics emerged: In years without a midsummer decline the population increased slowly in spring, starting from low densities. High water transparency was observed already during the build-up of the population of D. galeata. Despite considerable fluctuations, Daphnia abundance remained on a high level throughout summer. In years with a midsummer decline the population started from relatively high densities in early May and more than doubled during one week. Peak densities were reached before the clear-water stage emerged. At the end of this period the population declined to low values which lasted for the rest of the summer. Fecundity of the Population of D. galeata declined, whereas the mean egg volume increased at the beginning of the clear-water stage as a result of declining food levels. The size at maturity (SAM) remained high during this period. Additionally, juvenile growth was reduced and the age at maturity was retarded. Survival probability was low for those daphnids born shortly before or during the clear-water stage compared to those born later. It can be concluded from these results that recruitment to adult stages is strongly reduced during the clear-water stage. The end of this period is marked by an alternation in generations. Only at that time can SAM be reduced because the new generation of adults matures at a smaller size, carrying small eggs. A high impact of non-predatory adult mortality can be expected when the population is dominated by a strong peak-cohort during the clear-water stage according to recruitment patterns during the build-up of the population. The most drastic decline both of Daphnia abundance and SAM was observed in those years when the biomass of juvenile fish exceeded 20 kg ha-1 at the end of the clear-water stage. Due to gape-size limitation juvenile fish mainly feed on juvenile daphnids during this period and thus, they reinforce bottom-up effects on the Daphnia population. When fish change their size selection towards adult daphnids at the time when the new generation takes over, this seems to represent the worst case for the Daphnia population. Consequently, the timing between bottom-up effects and the feeding pressure of juvenile fish determines the extent of the decline. - (This manuscript is also available - in the form of a book - from Shaker Verlag GmbH, Postfach 101818, 52018 Aachen, Germany world-wide web address: http://www.shaker.de, electronic-mail address: info@shaker.de. It has been posted on the web sites of Dresden University of Technology with the permission of the publisher)

The population dynamics and demography of Daphnia galeata was analysed in a five year study in the biomanipulated Bautzen Reservoir. Samples were taken two times a week during the period May-July in the pelagic zone of this highly eutrophic water. Major bottom-up and top-down factors were determined during the study period and analysed with regard to their influence on Daphnia dynamics and life history. Field data on fecundity and population structure of D. galeata were combined with results from life table and growth experiments performed under approximately in situ conditions to gain insight into the mechanisms leading to a midsummer decline of this cladoceran species which dominates the zooplankton community in Bautzen Reservoir. Two main patterns of Daphnia dynamics emerged: In years without a midsummer decline the population increased slowly in spring, starting from low densities. High water transparency was observed already during the build-up of the population of D. galeata. Despite considerable fluctuations, Daphnia abundance remained on a high level throughout summer. In years with a midsummer decline the population started from relatively high densities in early May and more than doubled during one week. Peak densities were reached before the clear-water stage emerged. At the end of this period the population declined to low values which lasted for the rest of the summer. Fecundity of the Population of D. galeata declined, whereas the mean egg volume increased at the beginning of the clear-water stage as a result of declining food levels. The size at maturity (SAM) remained high during this period. Additionally, juvenile growth was reduced and the age at maturity was retarded. Survival probability was low for those daphnids born shortly before or during the clear-water stage compared to those born later. It can be concluded from these results that recruitment to adult stages is strongly reduced during the clear-water stage. The end of this period is marked by an alternation in generations. Only at that time can SAM be reduced because the new generation of adults matures at a smaller size, carrying small eggs. A high impact of non-predatory adult mortality can be expected when the population is dominated by a strong peak-cohort during the clear-water stage according to recruitment patterns during the build-up of the population. The most drastic decline both of Daphnia abundance and SAM was observed in those years when the biomass of juvenile fish exceeded 20 kg ha-1 at the end of the clear-water stage. Due to gape-size limitation juvenile fish mainly feed on juvenile daphnids during this period and thus, they reinforce bottom-up effects on the Daphnia population. When fish change their size selection towards adult daphnids at the time when the new generation takes over, this seems to represent the worst case for the Daphnia population. Consequently, the timing between bottom-up effects and the feeding pressure of juvenile fish determines the extent of the decline. - (This manuscript is also available - in the form of a book - from Shaker Verlag GmbH, Postfach 101818, 52018 Aachen, Germany world-wide web address: http://www.shaker.de, electronic-mail address: info@shaker.de. It has been posted on the web sites of Dresden University of Technology with the permission of the publisher)