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Selection and Use of Aquatic Vegetation by Migratory Waterfowl in North Central TexasSmith, JoEtta Kaye 05 1900 (has links)
Assessment of aquatic plant selection by waterfowl has been conducted during the winters of 1997-2000 on 49 0.2-0.79 ha research ponds in north central Texas. Ponds were categorized by dominant plant species into eight habitat types. Census with waterfowl species identification were performed to investigate impacts of aquatic vegetation and water depth on waterfowl. Eighteen waterfowl species were observed. Peak migration occurred in late December/early January. Mixed native ponds and mixed native/hydrilla ponds were the most frequently selected habitat types. The study included correlation analysis between pond water levels and waterfowl use. Full ponds received greatest use followed by half full ponds, while almost empty ponds received minimal use. Time activity budgets were conducted on waterfowl utilizing mixed native and hydrilla ponds to compare waterfowl time partitioning on native aquatic vegetation versus hydrilla. Although only minor differences were found in time budgets, social status appears to be strongly related to habitat selection. Ducks on native ponds were paired (86%), conversely no ducks on hydrilla ponds were paired. Hydrilla pond although frequently utilized, were populated by lower status birds mostly single hens.
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Desempenho de lagoas de maturação utilizando macrófitas aquáticas e chicaneamento / Performance of maturation ponds using aquatic plants and bafflesPolisel, Kleber Castilho 30 September 2005 (has links)
As lagoas de estabilização têm sido, por suas características operacionais e baixos custos de implantação, consideradas como a opção mais viável para tratamento de águas residuárias em pequenas e médias comunidades. O sistema composto por lagoa anaeróbia e facultativa em série é o mais empregado no Brasil. Com o avanço no monitoramento das lagoas de estabilização que se iniciou na década de 90, no caso do Estado de São Paulo pela SABESP, e que hoje se encontra bastante estruturado, periódico e confiável, nota-se que esses sistemas apesar de projetados seguindo as técnicas mais recentes, não possuem a eficiência esperada quando em operação. Tornam-se então prementes os estudos no sentido de melhorar o desempenho dos sistemas existentes e fornecer subsídios para novos projetos de lagoas de estabilização. Este trabalho estudou a utilização de chicaneamento nas lagoas de estabilização verificando a influência das chicanas no comportamento hidrodinâmico e desempenho desses sistemas além da utilização de macrófitas aquáticas no processo de tratamento de águas residuárias. Concluiu-se que mesmo com aumento de eficiência de remoção de DQO, 'DBO IND.5', nitrogênio Kjedahl e amoniacal, para ambos os casos: lagoa com aguapé e lagoa com lentilha dágua, os inúmeros problemas operacionais e aumento de custos que surgiram da aplicação das macrófitas aquáticas tornam desaconselhável o uso de aguapé e lentilha dágua em lagoas de tratamento de esgoto. Com relação ao chicaneamento o sistema que mais se aproximou dos valores teóricos, com relação ao tempo de detenção hidráulico e número de dispersão (d), foi a lagoa com chicaneamento longitudinal, melhorando o comportamento hidráulico do sistema, podendo ser considerado uma medida simples e de baixo custo para incrementar a eficiência de lagoas de estabilização / Due to the operational characteristics and low investment costs stabilization ponds have been considered as the most viable option for wastewater treatment in small and medium size communities. Anaerobic and facultative ponds in series are the most used in Brazil. With the progress of monitoring of the stabilization ponds, that was initiated in the decade of 1990 in the State of São Paulo by SABESP, it was observed that these systems do not possess the expected efficiency when in operation, although they were designed following the best available knowledge at that time. Thus, new studies were direct to improve the performance of the existing systems and to supply subsidies for new projects of stabilization ponds. This research examines, separately, the use of baffles and macrophytes in a pilot scale stabilization pond verifying the influence of these elements on the hydrodynamic behavior and performance of the wastewater treatment. It was concluded that although there is an increase in removal efficiency of DQO, 'DBO IND.5', nitrogen Kjedahl and ammoniacal, the several operational problems and increase of costs that had appeared with the application of water hyacinths and duckweed in the pond, it is not recommended to use these aquatic plants in sewer treatment. Concerning the use of baffles the system that came closer to the theoretical values, in relation to the hydraulic time of detention and number of dispersion (d), was the pond with longitudinal baffles. These baffles improved the hydraulic behavior of the system and are a simple measure and of low cost to develop the efficiency of stabilization ponds
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Assembleia de peixes associada a bancos de macrófitas aquáticas no rio Areias, reservatório da Usina de Lajeado, Tocantins, Brasil: composição e distribuiçãoAraújo, Alice Ferreira 20 March 2017 (has links)
As macrófitas aquáticas colonizam principalmente os braços de reservatórios e ou áreas protegidas da ação do vento e das correntezas. Estudos a cerca da ictiofauna associada a banco macrófitas aquáticas demonstram que a presença desse tipo de vegetação é fundamental na seleção de habitats pelos peixes. O objetivo deste trabalho é caracterizar a composição taxonômica, riqueza e diversidade da ictiofauna associada à macrófitas aquáticas no rio Areias. As coletas foram realizadas trimestralmente entre os meses de janeiro a outubro de 2016, em bancos de macrófitas aquáticas misto. Foram coletados 1.333 indivíduos, pertencentes a 21 espécies, distribuídas em cinco ordens e 11 famílias. Os Characiformes caracterizaram como a ordem dominante em todo o período do estudo. Sendo que as espécies Hyphessobrycon moniliger, Hemigrammus ora e Hemigrammus rodwayi foram as mais capturadas. / The macrophytes aquatic colonize mainly the arms of the reservoirs and / or areas protected from the action of the wind and of the currents. Studies about the fish fauna associated with the bank macrophytes aquatic demonstrate that the presence of this type of vegetation is fundamental in the selection of habitats by the fish. The objective of this work is to characterize the composition, taxonomic, and richness and diversity of the fish fauna associated with the macrophyte water in the river Areias. The collections were carried out quarterly between the months of January to October 2016, banks of macrophytes aquatic mixed. Were collected 1.333 individuals, belonging to 21 species, distributed in five orders and 11 families. The Characiformes were characterized as the dominant order throughout the period of the study. Being that the species Hyphessobrycon moniliger, Hemigrammus ora and Hemigrammus rodwayi were the most captured.
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Levantamento florístico e distribuição de macrófitas aquáticas na Represa Guarapiranga, São Paulo, Brasil / Floristic composition and distribution of aquatic macrophytes in the reservoir Guarapiranga, São Paulo, BrazilRodrigues, Maria Estefânia Fernandes 10 August 2011 (has links)
O objetivo desse trabalho foi verificar a composição e distribuição de macrófitas aquáticas no reservatório Guarapiranga, além de contribuir para o conhecimento taxonômico das espécies. Foram realizadas coletas mensais de Julho/2008 a Junho/2009, em 20 bancos de macrófitas distribuídos ao longo de todo reservatório. Em cada banco foram coletadas e registradas as espécies presentes e coletadas amostra superficial da água para análise em laboratório do fósforo total e clorofila \"a\". In situ, foram tomadas medidas de temperatura da água, pH, CE, OD e DS. Para verificar a distribuição e relação das macrófitas com variáveis ambientais foram realizadas análises de similaridade e correspondência canônica. A comunidade de macrófitas do reservatório é composta por 133 espécies, pertencentes a 89 gêneros, distribuídos em 45 famílias, sendo 127 de Angiospermas, 5 de Samambaias e 1 de Hepática, neste trabalho é apresentado uma chave de identificação e descrições para as espécies presentes na área de estudo. Através das análises estatísticas observamos dois principais agrupamentos: o primeiro constituído de 4 bancos de macrófitas localizados no Braço Embu-Guaçu, caracterizados pela presença de macrófitas enraizadas com folhas flutuantes e submersas e com melhor qualidade de água e o segundo constituído de outros bancos com predomínio de espécies emergentes e flutuantes e água com maior carga de poluentes. A área de cobertura da espécie Polygonum ferrugineum diminuiu com elevação do nível da represa, enquanto a área de cobertura de macrófitas flutuantes livres (Pistia stratiotes e Salvinia herzogii) aumentou. Foi possível concluir que a Represa Guarapiranga possui uma elevada riqueza de macrófitas aquáticas, cuja composição específica é diferente entre os braços e corpo central. / The aim of this study was to investigate the composition and distribution of aquatic macrophytes in the Guarapiranga reservoir and contribute to the taxonomic knowledge of the species. Field work were performed monthly from June/2008 to May/2009, in 20 stands of macrophytes distributed throughout the reservoir. In each stand, the present species were recorded and collected and water temperature, pH, electric conductivity, dissolved oxygen and Secchi disk transparency were measured. Additionally, superficial water sample were collected for total phosphorus and chlorophyll \"a\" analysis in the laboratory. To investigate the distribution of macrophytes and its relationship with environmental variables, similarity and canonical correspondence analysis were performed. The aquatic macrophytes community of the reservoir was composed of 133 species belonging to 89 genera distributed in 45 families being 127 angiosperms, 5 ferns and 1 liverwort. This work presents an identification key and descriptions for the species present in study area. The statistical analysis showed a cluster of four macrophytes stands located in the branch Embu-Guaçu, characterized by the presence of rooted macrophytes with floating leaves and submerged and with a better quality of water.Another cluster was formed by the other groups of macrophyte stands that were dominate by floating and emergent species, where we observed higher load of pollutants in the water. The coverage area of the species Polygonum ferrugineum decreased with the increase in the water level of the reservoir, while the coverage of the free-floating species (Pistia stratiotes and Salvinia herzogii) increased. In conclusion, Guarapiranga has a great aquatic macrophytes species richness, with different specific composition in the branches and in the central body.
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Desenvolvimento do aerênquima em raízes de Cebatopteris richardii brongn. (PTERIDACEAE) submetidas a estresse hídricoGarcia, Juliana Bittencourt January 2016 (has links)
O aerênquima é um tecido vegetal com grandes lacunas de ar que podem ter função de circulação de gases e/ou sustentação de órgãos, estando presente nas raízes e órgãos aéreos de plantas aquáticas ou sob alagamento, podendo ainda ser formado em decorrência de algum estresse. Ceratopteris richardii é uma planta aquática, de hábito anfíbio que apresenta aerênquima em seus órgãos vegetativos. Dessa forma, esse trabalho buscou analisar a formação de aerênquima nas raízes e pecíolo desta espécie frente a uma situação de restrição hídrica e verificar sua plasticidade fenotípica. Vinte indivíduos de C. richardii foram cultivados e submetidos a um tratamento com diferentes concentrações de PEG 6000. Em todas as amostras analisadas, foi observada a formação de aerênquima. A análise qualitativa mostrou diferença entre os tratamentos, porém, a análise estatística revelou que as diferenças não são significativas para o número amostral empregado. Variações de crescimento do esporófito revelaram que a espécie de estudo modificou algumas características de desenvolvimento em resposta a restrição hídrica. Tais resultados revelam importantes características para esta espécie, que parece aclimatar-se a situação de estresse a qual foi submetida. Com base nisso, sugere-se ampliar estes estudos para elucidar questões relacionadas a formação de aerênquima e o ambiente, seja para esta espécie ou de outro grupo taxonômico. / Aerenchyma is a plant tissue with large air gaps that may have gas circulation function and / or sustain organs. This structure is present in roots and aerial organs of water plants and in plants under flooding it may also be formed during some stress. Ceratopteris richardii is an aquatic plant, with amphibious habit that has aerenchyma in their vegetative organs. Thus, the aim of this study is analyze the aerenchyma formation in roots and stem of this specie under water restriction situation and verify their phenotypic plasticity. Twenty specimen of C. richardii were cultured and subjected to treatment with different concentrations of PEG 6000. In all samples, were observed aerenchyma formation. Qualitative analysis showed differences among treatments, however, the statistical analysis revealed that the differences are not significant for the sample size. Sporophyte growth variations revealed that the specie of study modified some growth characteristics in response to water restriction. These results reveal important characteristics for C. richardii, which seems to acclimatize the stress situation which has submitted. On the base that, it is suggested further studies to become clearer the relation between aerenchyma formation and environment, even to either this species or another taxonomic group.
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Systems management of Glenbrook Lagoon, New South WalesKeogh, Andrew James, University of Western Sydney, Hawkesbury, Faculty of Science and Technology, School of Applied and Environmental Sciences January 1996 (has links)
Glenbrook Lagoon, an 8 hectare lake receiving rainfall runoff from a residential catchment, is experiencing nutrient enrichment problems expressed as excessive aquatic plant presence. This study aims to assess the relative nutrient contribution of the total system compartments, including catchment loading, water column, aquatic plants and surface sediment. This information is utilised in the formulation of management strategies which may produce a sustainable nutrient reduction and general improvement in the system. The total nutrient content of the aquatic system was determined to be high in comparison with the present nutrient loading from the catchment. The ideal management case considers nutrient reduction of the surface sediment compartment firstly, followed by the aquatic plant community, with the water column and catchment influence as relatively low priority compartments. Various strategies for managing these are proposed. The total system benefits of the ideal management case are reductions in nutrients, aquatic plant biovolume and suspended solid loading. Unavoidable constraints placed upon the ideal management case include the excessive aquatic plant presence restricting accessability to the surface sediment for dredging. The resulting best management case requires aquatic plant eradication prior to sediment management, with the total system benefits associated with the ideal management case being retained. / Master of Science (Hons)
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Carbon acquisition in variable environments: aquatic plants of the River Murray, Australia.Barrett, Melissa S. January 2008 (has links)
This thesis considers the implications of changes in the supply of resources for photosynthesis, with regard for modes of carbon acquisition employed by aquatic plants of the River Murray. Carbon supplies are inherently more variable for aquatic plants than for those in terrestrial environments, and variations are intensified for plants in semi-arid regions, where water may be limiting. In changeable environments the most successful species are likely to be those with flexible carbon-uptake mechanisms, able to accommodate variations in the supply of resources. Studies were made of plants associated with wetland habitats of the Murray, including Crassula helmsii, Potamogeton tricarinatus, P. crispus and Vallisneria americana. The aim was to elucidate the mechanisms of carbon uptake and assimilation employed, and to determine how flexibility in carbon uptake and/or assimilation physiology affect survival and distribution. Stable carbon isotopes were used to explore the dynamics of carbon uptake and assimilation, and fluorescence was used to identify pathways and photosynthetic capacity. The studies suggest that physiological flexibility is adaptive survival in changeable environments, but probably does not enhance the spread or dominance of these species. V. americana is a known bicarbonate-user, and it is shown here that it uses the Crassulacean Acid Metabolism (CAM) photosynthetic pathway under specific conditions (high light intensity near the leaf tips) concurrently with HCO[subscript]3 - uptake, while leaves deeper in the water continue to use the C[subscript]3 pathway, with CO₂ as the main carbon source. However, V. americana does not use CAM when under stress, such as exposure to high light and temperature. The diversity of carbon uptake and assimilation mechanisms in this species may explain its competitive ability in habitats associated with the Murray. In this way it is able to maximise use of light throughout the water column. In shallow, warm water, where leaves are parallel to the surface, CAM ability is likely to be induced along the length of the leaf, allowing maximal use of carbon and light. The amphibious C. helmsii is shown to use CAM on submergence, even where water levels fluctuate within 24 hours. This allows continued photosynthesis in habitats where level fluctuations prevent access to atmospheric CO₂. It appears that stable conditions are most favourable for growth and dispersal, and that the spread of C. helmsii is mainly by the aerial form. Carbon uptake by P. tricarinatus under field conditions is compared with that of P. crispus to demonstrate differences in productivity associated with aqueous bicarbonate and atmospheric CO₂ use. P. tricarinatus uses HCO[subscript]3 - uptake to promote growth toward the surface, so that CO₂ can be accessed by floating leaves. Atmospheric contact provides access to light and removes the limitation of aqueous diffusive resistance to CO₂, thereby increasing photosynthetic capacity above that provided by submerged leaves. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1320380 / Thesis (Ph.D) -- University of Adelaide, School of Earth and Environmental Sciences, 2008
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Batch Operation of Pilot-Scale Salty Water Constructed Wetlands in Dapeng BayChen, Hsiao-Hua 11 June 2008 (has links)
Recently, the use of constructed wetlands to treat nutritions and containing wastewater, has quite been in vogue. However, since salts aquacultural wastewater contains massive nutrients and salts, the common aquatic plant species are not suitable to treat it. Therefore the purpose of this research is mainly to use pilot-scale salty water constructed wetland systems operated under batch conditions to removal efficiency of nutrients.
The pilot-scale have nine pools, the influent was from discharge channels containing aquacultural wastewater and community sewage near by Dapeng Bay. The experiment designs altogether has four stages.In the first stage to the third stage, the HRT was continued at 7 days. Last stage, the HRT was continued at one month. Experimental period has used waste brick bat, oyster shell, 9mm stone and mix stone (9mm stone and 3mm stone mix) as filter medium. The 9mm stone pool and mix stone pool coordinates differently to test the stage planter differently to plant the species. The plant aspect has Avicennia marina(L2¡BL3 pool ), Lumnitzera racemosa and Phragmites australis. (First, the second stage plants the Phragmites australis , the third stage starts to plant Lumnitzera racemosa).
The experimental results showed that the filter media used with the mix stone presented the highest removal efficiency for the nutrients,whice the oyster shell exhibited the lowest removal efficiency for the nutrients. The oyster shell system was also found nutrients releaseal to the system. For using plants to remove the nutrients, we found that plants, did not show better performace than the systems without plants(p¡Ö0.05). However, for the condition of vegetation, the plant species of Avicennia marina exhibited the best performace.
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Habitat ecology and long-term development of the macrophyte vegetation of north-west German streams and rivers since the 1950sSteffen, Kristina 28 May 2013 (has links)
Diese Arbeit behandelt die Charakterisierung der Habitate und die Langzeit-Entwicklung über sechs Jahrzehnte der Makrophytenvegetation nordwestdeutscher Bäche und Flüsse, um zum Wissen über die Ökologie aquatischer Makrophyten beizutragen und sie als Bioindikatoren zu nutzen. Siebzig Bäche und Flüsse der Regionen Ems-Hunte Geest, Lüneburger Heide, Allerflachland, nördliches Harzvorland, Fuß des Weser-Leine Berglandes und ostholsteinisches Hügelland sind Bestandteil der Studie, wobei der Schwerpunkt auf der überregionalen Betrachtungsebene liegt. Aus der Analyse der Zusammensetzung und Verbreitung der Makrophytengesellschaften im Zusammenhang mit Gewässergröße und physikalischen und chemischen Wasser- und Sedimenteigenschaften schlossen wir, dass Gewässertiefe und Fließgeschwindigkeit von den gemessenen Variablen den größten Einfluss auf die heutige Gesellschaftszusammensetzung haben, gefolgt vom Gehalt pflanzenverfügbaren Phosphors im Sediment. Es ist jedoch nicht auszuschließen, dass vor der im Untersuchungsgebiet seit den 1950ern stattfindenden, starken Intensivierung der landwirtschaftlichen Nutzung, als noch ausgeprägtere Gradienten bei den Nährstoffgehalten der Fließgewässer existiert haben, chemische Größen einen stärkeren Einfluss auf die Makrophytenvorkommen hatten als heute.
Mittels semi-permanenter Dauerflächen haben wir den Vegetationswandel zwischen den 1950ern und 2010 untersucht und einen dramatischen Rückgang der Artenvielfalt festgestellt (der Gesamtartenpool sank um 27.5 % von 51 auf 37 Hydrophytenarten, die Artenzahl pro Aufnahmefläche um 19.4 % von 4.7 auf 3.8 Arten), begleitet von einem umfassenden Bestandsumbau vom Vorherrschen wurzelnder (v.a. potamider) Arten zur Dominanz freischwimmender (v.a. lemnider) Arten. Oligotraphente Arten wie Potamogeton gramineus und P. polygonifolius sind in den Probeflächen ausgestorben und die mesotraphenten Arten Myriophyllum alterniflorum und Ranunculus peltatus in ihrer Auftretenshäufigkeit um mehr als 50 % zurückgegangen, während die eutraphenten Arten Myriophyllum spicatum und Spirodela polyrhiza um mehr als 100 % zugenommen haben. In den Artmerkmalen Blattausdauer und spezifische Blattfläche (SLA) wurden Änderungen festgestellt: In den historischen Makrophytenbeständen der 1950er waren immergrüne Arten und Arten mit dünnen Blättern oder solchen mit viel arenchymatischem Gewebe häufig (große SLA), während die rezenten Bestände von 2010 durch sommergrüne Arten und solche mit robuster Struktur (geringe SLA) gekennzeichnet sind. Die Veränderungen in der Arten-zusammensetzung waren am tiefgreifendsten in der Region Ems-Hunte Geest, wo weitläufige Niedermoore durch Entwässerung insbesondere seit der Eindeichung des Dümmer Sees (1953) intensiv bewirtschaftetem Agrarland gewichen sind, und weniger ausgeprägt in der Lüneburger Heide, einer der wenigen Tieflandsregionen Deutschlands, in der noch Fließgewässer mit kaum durch den Menschen veränderter Struktur zu finden sind.
Auf der syntaxonomischen Ebene zeigte die Anwendung zweier unterschiedlicher pflanzensoziologischer Klassifikationssysteme tiefe Veränderungen in der Struktur der Makrophytengesellschaften über sechs Jahrzehnte auf. Alle dokumentierten Vegetations-bestände konnten einer der Klassen Potamogetonetea, Lemnetea, Phragmitetea oder Fontinalietea zugeordnet werden. Während Batrachietalia/Batrachion und Potamogetonetalia /Potamogetonion-Bestände stark zurückgegangen sind, haben Nymphaeetalia/Nymphaeion-Gesellschaften zugenommen. Die beobachtete Zunahme pflanzensoziologisch schwach charakterisierter Bestände (Fragmentgesellschaften) deutet auf Verluste bei den hoch-spezialisierten Arten hin. Im Schnitt waren sich die rezenten Vegetationsbestände signifikant ähnlicher (SBC=0.25) als die historischen (0.22), was eine Homogenisierung der Fließgewässervegetation Nordwestdeutschlands offenbart.
Beschleunigte Eutrophierungsprozesse in den Gewässern und wasserbauliche Maßnahmen in der intensiv genutzten Kulturlandschaft haben zu einer Uniformierung der Fließgewässerhabitate geführt, worin neben häufigen Störereignissen die Hauptursache für die Verluste in Artenreichtum und Vielfalt der Makrophytenvegetation gesehen werden kann. Weitere Anstrengungen zur Reduzierung der Nährstofffrachten, sowie eine Erhöhung der Habitatheterogenität durch strukturverbessernde Renaturierungsmaßnahmen und ökologisch verträgliche Unterhaltungstechniken und -zeitpunkte sind notwendig, um den Diversitäts-rückgang in der Makrophytenvegetation nordwestdeutscher Bäche und Flüsse aufzuhalten und umzukehren. Eine artenreiche Vegetation ist ein wichtiger Baustein in Fließgewässer-Ökosystemen, deren Funktionsfähigkeit nicht zuletzt auch für das menschliche Wohlergehen von Bedeutung ist.
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The role of Potamogeton crispus L. in the Pongolo River floodplain ecosystem.Rogers, Kevin Hugh. January 1984 (has links)
1. Aquatic macrophytes generally dominate energy and nutrient
transfers in wetland ecosystems. They provide a diverse
habitat for other organisms but each species or life-form,
has a different role in determining ecosystem structure and
function. A multidisciplinary research project on the Pongolo
River Floodplain, Zululand, South Africa, provided a good
opportunity to study the role of a submerged species, Potamogeton
crispus L. in a wetland ecosystem.
2. The role of a plant species in ecosystem structure and functioning
is contingent primarily upon its adaptations to the
interactive biotic and abiotic components of the multifactorial
environment. This role is manifest in the contribution the
species makes both to the sum total of transfers of resources
within the ecosystem and to the nature of the physical and
chemical environment. These contributions can be to both
the conservative energy-matter transfers of the ecosystem and
to the information network which regulates ecosystem functioning.
3. This study set out, using Tete pan as the main field site, to:
i) Characterise the major physical, chemical and biotic
variables of the floodplain ecosystem which are most likely
to affect the acquisition of resources by P. crispus.
ii) Determine the way the species influences the environment.
iii) Assess the species adaptations to environmental characteristics.
iv) Assess transfers of resources from P. crispus to other
ecosystem components, the factors affecting them and the
contributions they make to ecosystem structure and
functioning.
v) Outline the implications of the findings for management of
the ecosystem which is threatened by the construction of an
upstream dam. Annual flooding of the Pongolo river and resultant poor light
climate and fluctuating water levels create an unfavourable
habitat for submerged plant growth in Tete pan during summer.
During autumn through spring, however, stable water levels and
good light penetration are favourable for plant growth. The
duration of favourable and unfavourable periods varies annually,
and on a longer time scale periodic droughts cause the pan to dry
up completely. Nutrient concentrations and salinity of the water
were favourable for freshwater plant growth during the study.
5. Potamoget on crispus on the Pongolo r.iver floodplain is a winter
producing annual which reproduces both sexually (achenes) and
asexually (turions). Winter growth is initiated by turion
germination each year and achenes ensure survival after drought.
If floods continue into autumn young plants remain dormant until
the light climate improves. Individual plants have a life span
of 4 - 5 months but staggered germination of turions from April
to June ensured that the population was present for up to 8
months. Pot amogeton crispus was classified as a competitiveruderal
with multiple regenerative strategies. This life history
enables the species to exploit the favourable period between floods
and survive both summer flooding of unpredictable duration and
intermittent droughts.
6. The major source of nutrfents for P. crispus is the sediment pool
and plant growth brings large amounts of nitrogen and phosphorus
into circulation each year. The rapid completion of the life
cycle ensures that in most years Nand P released to the water
during decay are taken up by other components of the ecosystem
before the next summer floods. Thus, despite a potential for
flushing of nutrient rich water by floods, pans such as Tete
experienced a net gain in nutrients between flood periods during
the study period.
7. Potamogeton crispus was the major primary producer in Tete pan
during this study and although production was seasonal it was
high (126 gm¯³ in comparison to other species reported in the
literature. The presence of an abundant and nutritious food source in the
form of P. crispus turions, attracts a large and diverse
waterfowl population to the floodplain each winter. During
feeding the waterfowl uproot P. crispus plants and remove almost
90% of the turions. This represents a potentially unstable
grazing system as the birds utilize the "residual growth potential"
of the plant population. The hypothesis was formulated that
stability of the grazing system and maintenance of P. crispus
reproduction may be achieved by production of small turions
which are energetically unrewarding for the waterfowl but
form viable propagules. Overall, transfer of nutrients and
organic matter to this grazing food chain represents a small
(<10 % ) proportion of P. crispus production.
9. The growth of P. crispus in Tete pan provides a large surface
area for epiphyton growth which increases in density and species
diversity as plants age. Experiments showed that the host
plant epidermis was invaded by necrotrophic bacteria but grazing
of epiphyton by snails retarded this process in young leaves.
However, as leaves aged the action of the bacteria softened
(conditioned) the host tissues and promoted consumption of the
leaves by snails. The co-existence of epiphyton and host plant
is therefore achieved through a complex set of interacting
attributes of the epiphyton community, the host plant and
grazing animals. Comparisons with previously published
hypotheses of the macrophyte-host relationship indicated that
attempts to find a single controlling factor may be misleading
and that adaptation for co-existence should be sought in a number
of interacting variables.
10. Since conditioning of P. crispus by epiphytes and consumption
of plants by snails follows a succession which reaches a climax
during host senescence, it was important to develop a method of
studying decomposition which included these processes. Experiments
showed that both snails and bacterial conditioning had marked
effects on the rates and pathways of dry matter and nutrient
transfer during decomposition and that no single technique
(eg. litter bags) will permit a thorough understanding of
decomposition processes. Conservative transfers of organic matter, nitrogen and phosphorus
in Tete pan are dominated by the detrital food web with only a
small proportion going to the grazing food chain. The consumption
of P. crispus and its epiphyton by snails in winter and
spring provides the major pathway of allochthonous production to
the benthic detrital aggregate and detrital food web. These
transfers are separated in both time and space from the allochthonous
inputs of C. dacty lon detritus which occur as a result
of decay in the flooded pan margins during summer. The major
input of phosphorus to the pans appears to occur by deposition
of silt during floods but fixation of di-nitrogen by the
epiphyton and in the detrital aggregate greatly exceed flood
related inputs of nitrogen.
12. The continued functioning of the detritus dominated foodweb of
the floodplain pans is dependent upon a sequence of resource
transfers which are dominated, during periods between floods,
by P. crispus and its epiphyton. The processes which regulate
these conservative transfers show characteristics typical of the
information network of cybernetic ecosystem functioning and
hence it was hypothesised that the Pongolo floodplain ecosystem
has the potential to buffer changes in resource input which will
occur now that a dam has been constructed upstream. While the
hydrological regime of the Pongolo river forms the primary
determinant of the floodplain ecosystem, structure and function
management of the system must also account for the "managerial"
role of animals and temperature which initiate and rate regulate
major ecosystem processes. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1984.
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