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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Effects of irradiation and temperature on shoot growth and development in Blue holly (Ilex x meserveae) /

Kosiba, Andrea, January 2005 (has links) (PDF)
Diss. (sammanfattning) Alnarp : Sveriges lantbruksuniversitet, 2005. / Härtill 4 uppsatser.
42

Semen and sperm characteristics of swamp buffalo (Bubalus bubalis) bulls for artificial insemination in Thailand, in relation to season /

Koonjaenak, Seri, January 2006 (has links) (PDF)
Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv. / Härtill 5 uppsatser.
43

Systematika a proměnlivost zdravínku jarního Odontites vernus (Bellardi) Dumort. v České republice / Systematics and variation of Red Bartsia, Odontites vernus (Bellardi) Dumort. in the Czech Republic

BAĎUROVÁ, Tereza January 2012 (has links)
The Master's thesis studied the Odontites vernus group in the Czech Republic. The group was presented by two different taxa based on the seasonal types and the ploidy levels: an early flowering tetraploid Odontites vernus subsp. vernus (2n = 4x = 40) and a late-flowering diploid Odontites vernus subsp. serotinus (2n = 2x = 18). Plants from 33 populations were sampled for measuring the ploidy level and 27 morphological characters for morphological analysis. Two ploidy levels were confirmed in the Czech Republic and a new late flowering tetraploid taxon (2n = 4x = 40) was found. The three taxa were separated from each other based on the seasonal variation, ploidy level, morphology and ecology.
44

VariaÃÃo sazonal dos componentes da alga marinha vermelha Gracilaria birdiae (Plastino & Oliveira) / Seasonal variation of the components of the red seaweed Gracilaria birdiae (Plastino & Oliveira)

Juliana Gomes Pereira 06 March 2009 (has links)
Algas marinhas sÃo seres classificados no reino protista, predominantemente aquÃticos e com grande capacidade adaptativa. Encontradas em todas as regiÃes do planeta, as algas desempenham importante papel ecolÃgico e econÃmico, representando um grande potencial de biorrecursos. A alga marinha vermelha Gracilaria birdiae, coletada durante doze meses, foi submetida à extraÃÃo aquosa a 100 ÂC de polissacarÃdeos e apresentou rendimento superior a 50 %, com exceÃÃo nos meses de fevereiro, setembro e novembro de 2007 ( 49,5%, 41,8% e 49,4% respectativamente). O teor de sulfato foi obtido por microanÃlise e nÃo variou significativamente ao longo dos meses analisados, apresentando valor mÃdio de 1,35%. O grau de sulfataÃÃo mÃdio encontrado foi de 0,15. O conteÃdo protÃico nas amostras tambÃm nÃo apresentou variaÃÃo considerÃvel, tendo mÃdia de 0,5%, entretanto, no mÃs de abril o conteÃdo protÃico aumentou cerca de 3 vezes do valor mÃdio encontrado. As doze amostras foram caracterizadas quimicamente por cromatografia de permeaÃÃo em gel (GPC), espectroscopia na regiÃo do infravermelho (FT-IR) e por ressonÃncia magnÃtica nuclear (RMN). Os cromatogramas de GPC das amostras apresentaram semelhanÃas e caracterÃsticas tÃpicas de polissacarÃdeos das algas vermelhas. Em geral, foram observados um pico principal, em aproximadamente 7,58 mL e um ombro em aproximadamente 9,2 mL de volume de eluiÃÃo, com exceÃÃo dos meses de agosto, outubro e novembro de 2007, que apresentaram cromatogramas com pico principal em aproximadamente 8,27 mL de volume de eluiÃÃo, detectados pelo Ãndice de refraÃÃo. Os polissacarÃdeos investigados apresentaram altas massas molares , variando de 0,11 x 104 a 8,51 x 105 g/mol. Os espectros de infravermelho das doze amostras de polissacarÃdeos apresentaram perfis semelhantes, com as bandas caracterÃsticas de agarocolÃides, mais especificamente, do tipo agarana. Espectros de RMN foram empregados para a caracterizaÃÃo estrutural das amostras ao longo do ano e, revelaram que a estrutura do polissacarÃdeo à composta por segmentos de (1→ 3)-β-D-galactopiranosil ligada a (1→4)-α-L-anidrogalactopiranosil. O estudo da variaÃÃo sazonal da composiÃÃo centesimal, em geral, nÃo apresentou variaÃÃo acentuada. Com relaÃÃo à quantidade de proteÃnas solÃveis e a atividade hemaglutinante no extrato protÃico, o estudo da variaÃÃo sazonal revelou uma pequena variaÃÃo no teor de proteÃnas solÃveis, com valor mÃximo (0,94 mgP/mL) em novembro/06 e mÃnimo no mÃs de dezembro/06 (0,39 mgP/mL). Em geral, a atividade hemaglutinante observada em Gracilaria birdiae à fraca, porÃm, ela esteve presente em concentraÃÃes variÃveis ao longo de todo o perÃodo estudado, com exceÃÃo no mÃs de dezembro/06, independente do conteÃdo protÃico total e solÃvel encontrado. / Seaweeds are classified in the kingdom protist, predominantly aquatic and with great adaptive capacity. Found in all regions of the planet, algae play an important role ecological and economic, representing a great potential for bioresources. The red seaweed Gracilaria birdiae, collected during twelves months, was submitted to aqueous extraction of polysaccharides at 100ÂC, showed yield exceeding 50 %, except in February, September and November 2007 (49,5%, 41,8% and 49,4% respectively). The sulfate content was obtained by microanalysis and it not vary significantly over the months examined averaging 1,35%. The sulfate degree was 0.15. The protein content in the samples also showed no considerable variation, with average of 0,5%, howevwr in April, the protein content increased about 3 times the average found. The twelve samples were chemically characterized by Gel Permeation Chromatography (GPC), Infrared (FT-IR) and Nuclear Magnetic Resonance (NMR) spectroscopy. The GPC chromatograms of the samples showed similarity and typical characteristics of polysaccharides from red algae. In general, we observed a main peak, at approximately 9,2 mL volume of eluition, with the exception of August, October and November 2007, which showed chromatograms with main peak at approximately 8,7 mL volume of eluition, detected by a refractive index. The polysaccharides investigated showed hight molecular weight, ranging from 0.11 x 104 and 8.51 x 105 g/mol. The infrared spectra of the twelve samples of polysaccharides presented similar profiles, with bands characteristics of agarocolloids, more specifically agaran-like, with evidence of protein. NMR were employed to the structural characterization of the samples throughout the year and revealed that the structure of polysaccharides is composed by (1→3)-β-D-galactopyranosyl linkage to (1→4)-α-L-anhydrogalactopyranosyl segments. The study of seasonal variation in proximate composition, in general, showed no marked variation. Regarding the amount of soluble protein in the crude extract, the study of seasonal variation showed a small variation in the content of soluble protein, with maximum value (0,94 mgP/mL) in November/06 and minimum (0,39 mgP/mL) in December/06. The hemagglutinating activity during the period of one year, except in December/06.
45

Estrutura da comunidade e produção dos copépodes pelágicos dos recifes da APA Costa dos Corais (Tamandaré, PE, Brasil)

FIDELIS, Valdylene Tavares Pessoa 27 February 2014 (has links)
Submitted by Caroline Falcao (caroline.rfalcao@ufpe.br) on 2017-05-22T16:05:26Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) PDF_Pessoa, V.T._Tese de doutorado (2).pdf: 1505257 bytes, checksum: 1b505fd37853f0c9b450bb8b1256ebb2 (MD5) / Made available in DSpace on 2017-05-22T16:05:26Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) PDF_Pessoa, V.T._Tese de doutorado (2).pdf: 1505257 bytes, checksum: 1b505fd37853f0c9b450bb8b1256ebb2 (MD5) Previous issue date: 2014-02-27 / O objetivo deste trabalho foi analisar a estrutura da comunidade e estimar produção dos copépodes pelágicos do ambiente recifal em diferentes escalas temporais. As amostras foram coletadas em uma estação fixa dentro da baía Tamandaré durante a maré vazante, ao longo de quatro ciclos lunares, durante os períodos seco (novembro/dezembro de 2010) e chuvoso (julho/agosto 2010) e durante os períodos diurnos e noturnos. Foram coletados dados de pluviometria, temperatura, salinidade, material particulado em suspensão e clorofila-a. As amostras de plâncton foram obtidas através da utilização de arrastos subsuperfíciais horizontais usando uma rede cônica (malha de abertura de 200 μm). O material coletado foi fixado e as amostras foram analisadas por contagem, identificação, classificação por estágio de desenvolvimento, sexo e medição das espécies de copépodes presentes nas subamostras. Foram realizados cálculos de densidade, diversidade, riqueza e a frequência de ocorrência para todas as espécies de copépodes pelágicos. A partir das medidas do prossomo dos copépodes foi calculado o peso dos organismos e subsequentemente foram feitos os cálculos de biomassa e das taxas de crescimento e finalmente dos dados de produtividade. As análises realizadas sugerem que a comunidade de copépodes pelágicos do mesozooplâncton associada aos recifes de Tamandaré é regida por fatores ambientais totalmente associados a variações sazonais, principalmente pela pluviosidade, MPS e também pela salinidade. Foram identificados 22 espécies para região, e as espécies que mais frequentes e abundantes ao longo de todo estudo foram: Acartia lilljeborgi, Paracalanus quasimodo, Temora turbinata, Pseudodiaptomus acutus e Calanopia americana. Os valores densidade (694,6 ± 239,4 e 260,7 ± 481,2 ind.m-3 seco e chuvoso), biomassa (1452,02 ± 1072,40 e 200,43 ± 200,27 μg C m-3 seco e chuvoso) e produção (360,640 ± 261,60 e 50,147 ± 50,12 μg C m-3 dia-1 seco e chuvoso) foram significativamente diferentes entre os períodos seco e chuvoso, com maiores valores observados no período seco. Em relação aos turnos diurno/noturmo também existe diferenças significativas para os valores de densidade, biomassa e produção, e os maiores valores foram registrados durante a noite. Portanto, pode-se concluir que assim como a estrutura da comunidade, a produção estimada das principais espécies de copépodes pelágicos de um ambiente recifal é influenciada pelas variações sazonais e nictemeral. Existe influencia das fases da lua, sobre a estrutura da comunidade considerando cada período individualmente e estes dados foram corroborados pelas análises estatísticas ANOVA e PERMANOVA aplicados aos dados de densidade total e das espécies, respectivamente. Em relação aos dados de biomassa e produção, analisados de forma geral, as variações dos ciclos lunares não parecem influenciar de forma significativa a produtividade das espécies de copépodes da região. / The aim of this study was to analyze the community structure and to estimate the production of pelagic copepods on the reef environment at different time scales. Samples were taken at one station in the Tamandaré bay at ebb tide, along four lunar cycles, during dry (November and December 2010) and rainy periods (July and August 2010) and during the days and nights. Data of rainfall, temperature, salinity, suspended particulate matter (SPM) and chlorophyll-a were collected. The plankton samples were obtained through the use of subsurface horizontal hauls with a plankton net (mesh size of 200 μm). The material was fixed and the samples were analyzed by counting, identification, classification by stage of development, sex and measurement of copepod species present in the subsamples. Calculations of density, diversity, richness and frequency of occurrence were performed for all species of pelagic copepods. From the measurements of the copepod prosome, the weight of the organisms was obtained and subsequently the biomass and growth rates, and ultimately the productivity data, were calculated. The performed analysis suggest that the pelagic copepods community of the mesozooplankton associated with the reefs of Tamandaré is regulated by environmental factors entirely associated with seasonal variations, mainly rainfall, SPM and also by salinity. For the region, 22 species were identified, and the most frequent and abundant species throughout the study were: Acartia lilljeborgi, Paracalanus quasimodo, Temora turbinata, Pseudodiaptomus acutus and Calanopia americana. The values of density (694.60 ± 239.40 and 260.70 ± 481.20 ind. m-3 dry and rainy seasons), biomass (1,452.02 ± 1,072.40 and 200.43 ± 200.27 μg C m-3 dry and rainy seasons) and production (360.64 ± 261.60 and 50.14 ± 50.12 μg C m-3 day-1 dry and rainy seasons) were significantly different between the dry and rainy seasons, with higher values being observed in the dry season. Regarding the period of the day, there are also significant differences in the values of density, biomass and production, and the highest values were recorded during the night. Therefore, it can be concluded that, as well as the community structure, the estimated production of the main species of pelagic copepods on a reef environment is influenced by seasonal and nictemeral variations. There is influence of the moon phases on the structure of the community, considering each period individually. This result was corroborated by the ANOVA and PERMANOVA statistical analysis applied to the data of total and species density, respectively. Regarding biomass and production data, analyzed in general, the variations of lunar cycles do not seem to significantly influence the productivity of copepod species in the region.
46

Estudos das variações sazonais e intrapopulacional dos metabólitos secundários majoritários das folhas de \'Eremanthus glomerulatus Less\' (Asteraceae) / Study of the seasonal and intrapopulational variations of the secondary metabolites from the leaves of Eremanthus glomerulatus Less (Asteraceae).

Juliano Geraldo Amaral 22 February 2008 (has links)
O trabalho buscou investigar as variações sazonais de metabólitos secundários em Eremanthus glomerulatus Less (Asteraceae). Embora não ser utilizada para fins medicinais esta espécie contem substâncias biologicamente ativas. Para este estudo, foram selecionados dez indivíduos de uma mesma população localizada na região do município de Ibiraci - MG, que durante um período de aproximadamente dois anos (06/2000 a 04/2002) tiveram um de seus ramos coletados mensalmente. Visando a análise das folhas destes ramos uma metodologia para extração e análise de seus metabólitos secundários majoritários por CLAE-UV foi desenvolvida e utilizada para determinação de suas variações sazonais. A identificação destes metabólitos se deu principalmente pelas técnicas hifenadas CLAE-DAD-EM e CLAE-DAD-EM/EM. Os metabólitos que não puderam ser identificados por estas ferramentas foram isolados do extrato etanólico foliar desta espécie e identificados por RMN de 1H e 13C e EM. Durante este estudo foi verificado que o envelhecimento das folhas resulta em uma significativa redução no conteúdo de todos os seus metabólitos secundários. Também foi possível identificar nove metabólitos secundários pertencentes as classes dos ácidos cafeoilquínicos, derivados fenólicos e flavonóides, dos quais foram isolados três, sendo dois ainda não relatados na literatura. Quanto a variação sazonal pode-se verificar que os indivíduos apresentam perfis metabólicos bem semelhante com diferenças quantitativas mas praticamente não apresentando variações qualitativas entre os indivíduos. Pode-se observar também que há um metabolismo bem diversificado no qual nem sempre todos os indivíduos apresentam aumento de produção de um mesmo metabólito em determinada estação do ano. Apesar das variáveis é possível definir o outono e a primavera como as estações que durante o estudo apresentaram os melhores índices de produção de praticamente todos os metabólitos analisados. Por fim pode-se concluir que as variações sazonais em E. glomerutalus são significativas e que são determinantes para definir a época de futuras coletas para posteriores estudos químicos ou farmacológicos. / This study was performed to investigate the seasonal intrapopulational variations of the secondary metabolites in Eremanthus glomerulatus Less (Asteraceae). Although this species is not used for medicinal purposes, it contains biologically active substances. For this study, ten individuals from the same population located in the region of Ibirici city, Minas Gerais state, had one of their lbranches collected monthly for about two years (from 06/2000 to 04/2002). Aiming the analysis of the leaves from the branches, a methodology on UV-HPLC was developed and used for the extraction and analysis of major secondary metabolites to determine the seasonal variations. The identification of the metabolites has occurred mainly by the HPLC-DAD-MS and HPLC-DAD-MS/MS hyphenated techniques. The metabolites that could not be identified by these methods were isolated from ethanolic extract of leaves of these species and identified by NMR 1H and 13C and MS. During this study it was noticed that the aging of the leaves results in a significant reduction on the rate of all the secondary metabolites. It was also possible to identify nine secondary metabolites belonging to caffeoylquinic acids, phenolical derivatives and flavonoids, from which, three compounds were isolated, however two compounds wasnt described in the literature. Relating to the seasonal variation, it was possible to verify that the individuals present similar metabolic profiles with quantitative differences but practically without qualitative difference. It was also possible to observe that there is a diversified metabolism in which not all individuals present an increase in the production of the same metabolite on a specific season. Despite these variations, it is possible to define autumn and spring as the seasons that presented the best rates of production on practically all the analyzed metabolites. Finally, it is possible to conclude that the seasonal variation of E. glomerutalus is significant and decisive to define the right time for future collection for further chemical and pharmacological studies.
47

The Ecological Succession of Mosquitoes Inhabiting Waste Tires in a Subtropical Swamp and Upland Forest in Central West Florida

Dinh, Emily Thuong Nguyen 01 February 2016 (has links)
Literature has not yet seen a contribution involving the description of successional patterns of mosquitoes (Diptera: Culicidae) inhabiting discarded automobile tires in sylvan areas nor an investigation into the macro- and micro-environmental factors that may influence the seasonal shifts in species composition and abundance in that respective habitat. Waste tires in undeveloped forests are a hazard to human and animal health because they can support a population of vector mosquitoes. Locating productive waste tire mosquito habitats is problematic in wooded areas but is crucial for diminishing pathogen transfer in areas where humans have regular access to forests because of possible zoonotic disease transmission. The intentions of this study were 1) to describe the ecological succession patterns of mosquitoes in waste tires in a subtropical wetland and upland forest and 2) to create a database on which regressive geo-spatiotemporal models locating unidentified productive waste tires in sylvan zones can be built. The entomological research conducted here did not confirm the hypothesis that Aedes albopictus (Skuse) would be the dominant species in all the tires at all the study sites. There appeared to be seasonal trends in mosquito production despite the general constant warmth and rainfall levels year-round in subtropical Tampa, Florida. However, the findings of this research indicates that climatic conditions alone do not sufficiently explain spatiotemporal variation in mosquito populations. Rather, the effects of weather are heterogeneous at the microcosmic level, which has a more direct impact on ecological interactions between the different species found here and their abiotic environment.
48

Influência da sazonalidade nos constituintes químicos, atividade antimicrobiana e antioxidante das partes aéreas de Baccharis articulata (Lam) Pers e Achyrocline satureioides (Lam.) DC.

Cezarotto, Verciane Schneider 16 September 2009 (has links)
In this study seasonal variation on oil yields and composition, antioxidants activities, toxicity from Artemia salina and antimicrobial activities, from aerial parts of Achyroclines satureoides and Baccharis articulata were investigated. Maximum amount of the hydro-distilled essential oils in spring (0.10%; m/m) and winter (0.43%; m/m) were observed to A. satureioides and B. articulata, respective. Essential oils were analyzed by GC/MS. The compounds a-pinene (28.5 a 41.7%) and (E)- caryophyllene (29.8 a 38.5) were the most abundant component in the all season for A. satureioides. The b-pinene (23.1% a 32.1%), limonene (8.45 a 11.2%), espatulenol (9.31 a 10.9%) and (E)-caryophyllene (4.61 a 7.80%) were the most abundant component for B. articulata. For both species a variation was observed in the total flavonoids content, express in quercetin and antioxidant activity as measurements by DPPH٠ (1,1 diphenyl 2 picrylhydrazyl) free radical-scavenging ability. Regarding to toxicity, the minor CL50 (μg mL-1) was observed in the spring, where the major total flavonoids contents to A. satureioides. To B. articulata, the essential oil and raw methanolic extract were considered non-toxic. Antimicrobial activity measurement of determination of minimum inhibitory concentration (MIC) varied significantly (p<0,05) with different seasons. Autumn and winter were more significant than other season (MIC 37.9 μg mL-1 in autumn and 38.4 μg mL-1 in winter) against bacterial strains Staphylococcus epidermidis ATCC11228; 37.9 μg m -1 (autumn) and 76.8 μg mL-1 (winter) against bacterial strains Bacillus cereus ATCC11778 and 37.9 μg mL-1 (autumn) and 76.8 μg mL-1 (winter) against bacterial strains Klebsiella pneumoniae ATCC13883 to A. satureioides. For B. articulata, the major antimicrobial activity occured in winter (312 μg mL-1) against bacterial strains Bacillus cereus ATCC117, when essential oils showed be effective against bacterial strains Klebsiella pneumoniae ATCC13883 in the concentration of 78.1 μg mL-1. / Neste estudo investigou-se o teor e caracterização dos óleos essenciais, atividade antioxidante, toxicidade frente a Artemia salina e atividade antimicrobiana, das partes aéreas da Achyroclines satureoides e Baccharis articulata de acordo com a variação sazonal. Os resultados demonstraram elevados teores de óleos essenciais, obtidos por hidrodestilação, na primavera (0,10%; m/m) e inverno (0,43%; m/m) para A. satureioides e B. articulata, respectivamente. Após análise dos óleos essenciais por GC/MS, os constituintes majoritários identificados em todas as estações foram a-pineno (28,5 a 41,7%) e (E)-cariofileno (29,8 a 38,5%) para A. satureioides e para B. articulata foram b-pineno (24,0 a 32,1%), limoneno (8,45 a 11,2%), espatulenol (9,31 a 10,9%) e (E)-cariofileno (4,61 a 7,80%). Uma variação sazonal significativa (p<0,05) no teor de flavonóides totais, expressos em quercetina e atividade antioxidante avaliada através do método de capacidade de captura in vitro do radical livre DPPH٠(1,1 difenil 2 picrilhidrazil) pode ser observada em ambas espécies estudadas. Em relação ao ensaio de toxicidade, pode-se verificar que as menores CL50 (μg mL-1) foram obtidas na primavera, onde os teores de flavonóides totais apresentaram-se elevados para A. satureioides, enquanto que o óleo essencial e o extrato bruto metanólico, obtidos das partes aéreas de B. articulata, foram considerados atóxicos. A atividade antimicrobiana avaliada pela determinação da Concentração Inibitória Mínima (CIM) apresentou variação significativa (p<0,05) de acordo com a estação. Os resultados obtidos no outono e inverno foram significativos em relação as demais estações para A. satureioides, com CIM de 37,9 μg mL-1 (outono) e 38,4 μg mL-1 (inverno) frente a cepa de Staphylococcus epidermidis ATCC11228; 37,9 μg m-1 (outono) e 76,8 μg mL-1 (inverno) frente a cepa de Bacillus cereus ATCC11778; e 37,9 μg mL-1 (outono) e 76,8 μg mL-1 (inverno) frente a cepa de Klebsiella pneumoniae ATCC13883. Para B. articulata, o inverno (CIM 312 μg mL-1) foi a estação que apresentou atividade significativa frente a cepa de Bacillus cereus ATCC117, quando o óleo essencial também apresentou-se efetivo na concentração de 78,1 μg mL-1 frente a cepa Klebsiella pneumoniae ATCC13883.
49

Greenhouse gas emissions from blackwater septic systems in Hanoi,Vietnam / ベトナム・ハノイにおけるし尿腐敗槽からの温室効果ガスの排出

Huynh, Tan Loi 23 September 2020 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22768号 / 工博第4767号 / 新制||工||1745(附属図書館) / 京都大学大学院工学研究科都市環境工学専攻 / (主査)教授 田中 宏明, 教授 清水 芳久, 教授 藤井 滋穂 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM
50

Hur sjöfåglar påverkar undervattensvegetationen i näringsrika sjöar under olika årstider / How waterfowl affect submerged vegetation in eutrophic lakes during different seasons

Karlsson, Emelie January 2020 (has links)
The main diet of herbivorous waterfowl, such as swans, coots, and ducks, consists of submerged macrophytes. The grazing by waterfowl below the surface may affect the biomass and species composition of the submerged plants. The vegetations is, however, also affected by e.g. water turbidity, periphyton growing on the plants and water temperature. This literature study aimed to assess the impact of waterfowl on the biomass and production of submerged vegetation in shallow, eutrophic lakes and how this may vary with the season. The review showed that the density of submerged vegetation biomass varies during the seasons but tends to be highest in the summer. Waterfowl density is usually highest during autumn migration. According to experimental field studies in which waterfowl were excluded from protected areas, showed that protected plants had longer shoots and fewer stumps and, in several studies, also higher biomass, than in areas where waterfowl resided free. Although several studies have shown that waterfowl affect the biomass of macrophytes in different ways, is still uncertain to what degree and whether this has a negative or positive impact on the species composition of vegetation in a longer time perspective. However, alternative state shifts in shallow eutrophic lakes from a clear to a turbid water state have not been shown to be caused by waterfowl. With climate change, the time and place of waterfowl migration and wintering will most probably change. This could lead to altered pressure and seasonality of the grazing by waterfowl on submerged vegetation. / Växtätande sjöfåglars diet består huvudsakligen av undervattensvegetation. Fåglarna betar av växterna oftast under ytan, men undervattensvegetationens biomassa och artsammasättning påverkas inte bara av sjöfåglar, utan också av en rad andra faktorer, till exempel vattnets grumlighet, påväxtalger och vattentemperatur. Syftet med denna litteraturstudie var att undersöka under vilka förutsättningar betning från sjöfåglar har betydelse för undervattensvegetation. Växternas biomassa har visats minska i samband med sjöfåglars födointag, om den huvudsakligen består av vattenväxlighet. Vegetationens täthet varierar under året men uppnår störst täthet under sommaren. Sjöfåglar har visats vara i störst täthet under höstmånaderna, i samband med flyttning. Experimentella studier har genomförts genom att jämföra skyddade områden där sjöfåglar utestängts med öppna områden där sjöfåglar kunnat beta. I de skyddade områdena var växterna generellt längre och hade flera skott. Där fanns också färre stubbar än i de öppna områdena. Flera studier har visat att sjöfåglarna påverkar vegetationens biomassa på olika sätt men det är fortfarande osäkert i vilken grad och om detta över längre tid har en negativ eller positiv påverkan på vegetationens artsammansättning. I och med nutida klimatförändringar kan sjöfåglars tidpunkt och plats för migration och övervintring att förändras. Detta kan leda till att sjöfåglarna inte emigrerar från sjöar och kommer därav med största sannolikhet påverka undervattensvegetationen.

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