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Due to perceived shortcomings in some aspects of hazard assessment for chemicals administered to aquatic systems, experiments were conducted to determine the effects of copper on various ecological parameters in artificial streams and microcosms. Effects investigated were colonization and growth of periphyton communities in artificial streams, community composition and nutritional content of periphyton in these streams, leaf conditioning and nutritional content in laboratory microcosms, and nutritional suitability of these leaves to a shredding macroinvertebrate. Main effects observed in periphyton growth experiments were significant reduction in substrate colonization due to copper treatment, which led to significantly lower standing biomass in treated streams. Observed growth rates were generally similar between control streams and copper treated streams. Light treatments did not affect periphyton responses to copper. Community composition of the periphyton was affected by 2.5 μg/L copper. Periphyton phosphorus and nitrogen contents were not affected by copper treatment. Conditioning rate of leaves was significantly decreased by 50 μg/L copper treatments in some cases. Leaf phosphate and nitrogen contents were not significantly affected by copper treatment. Significant differences in nutritional suitability of copper-treated leaves to a shredding macroinvertebrate were not detected. These experiments suggest that aquatic primary producers are more sensitive to copper than heterotrophs. Additionally, adverse effects on periphyton were observed at concentrations well below measures of chronic toxicity to organisms dependent on periphyton as a trophic resource and the chronic criteria for copper. As such, greater emphasis should be placed on the sensitivities of periphyton communities in future copper criteria determination. / Ph. D.

Currently, protocols for investigating the effects of chemical pollutants on periphyton communities under natural conditions are statistically flawed and/or potentially harmful to the ecosystems in which the studies are conducted. Toxicant-releasing substrates have been proposed to allow the delivery of different levels of chemical pollutants to replicate microbial communities in situ while minimizing the amount of toxicant released into the aquatic ecosystems under investigation. The purpose of this research was to compare the copper-induced responses of laboratory periphyton communities in artificial streams to those generated using standard, laboratory toxicity testing protocols during a summer and winter experiment. Chemical-releasing substrates were successfully used to deliver copper to periphyton communities in a predictable manner, over a broad range of doses, and at fairly constant rates during one week exposure periods. / Master of Science

Pigment-based chemotaxonomy uses relative amounts of photosynthetic pigments (biomarkers) within algae samples to determine the algal class composition of each sample. Chemotaxonomy has been applied successfully to phytoplankton communities, but its efficacy for periphyton has not yet been established. This study examined the ability of simultaneous linear equations (SLE), CHEMTAX, and the Bayesian Compositional Estimator (BCE) to determine algal class composition in Florida Everglades periphyton. The methods were applied to artificial datasets, mixed lab cultures of known composition, and Everglades periphyton samples for which microscopic biovolume data was available. All methods were able to return accurate sample compositions for artificial data and mixed lab cultures. Correlation between pigment methods and microscopic results for natural periphyton samples was poor. SLE and CHEMTAX returned similar results for all samples while BCE performed less well. / by Jamie L. Browne. / Thesis (M.S.)--Florida Atlantic University, 2010. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.

Le mercure (Hg) est un polluant métallique préoccupant de par sa toxicité et son omniprésence dans les écosystèmes aquatiques. Sous sa forme méthylée, il est capable de se bioaccumuler dans les organismes et d’être bioamplifié le long de la chaîne trophique. La méthylation du Hg est un processus biotique principalement attribué aux microorganismes sulfato-réducteurs (MSR). La rhizosphère des plantes aquatiques a été récemment identifiée comme un compartiment privilégié de la méthylation du Hg dans certains écosystèmes tropicaux et boréaux. Les objectifs de cette étude étaient de déterminer l’influence des plantes aquatiques sur la biogéochimie et la bioaccumulation du Hg et le rôle que jouent les MSR dans ce processus au sein des écosystèmes aquatiques landais. L’utilisation de traceurs isotopiques stables du Hg a permis d’identifier le compartiment « plantes aquatiques » comme un lieu privilégié des transformations des espèces mercurielles (méthylation/ déméthylation du Hg) et comme la principale source de méthylmercure (MeHg) dans ces écosystèmes tempérés. La combinaison des approches moléculaires (T-RFLP, clonage, séquençage) et culturales (isolement, détection de MeHg par biosenseur) a démontré l’implication de MSR du genre Desulfovibrio dans le processus de méthylation du Hg au sein de la rhizoplane aquatique. D’après une expérience menée en microcosmes utilisant un traceur isotopique du Hg, le MeHg formé au niveau de la rhizosplane aquatique serait biodisponible pour la chaîne trophique. Cette dernière observation est à relier à des concentrations en Hg significatives, observées in situ, pour certains poissons de fin de chaîne alimentaire. / Mercury (Hg) is a metallic pollutant worrying because of its toxicity and ubiquity in aquatic ecosystems. Its organic form is easily bioaccumulated in organisms and biomagnified along food webs. Hg methylation is a biotic process mainly attributed to sulfate-reducing prokaryotes (SRP). The rhizoplane of aquatic plants has recently been identified as the principal compartment involved in Hg methylation in some tropical and boreal ecosystems. The objectives of this study were to determine the influence of aquatic plants on the biogeochemistry and bioaccumulation of Hg and the role of SRP in this process in the aquatic ecosystems of the Landes (South Western France). The use of Hg stable isotopic tracers allowed to identify the "aquatic plants" compartment as the main place for Hg species transformations (methylation / demethylation of Hg) and the main source of methylmercury (MeHg) in these temperate ecosystems. The combination of molecular (T-RFLP, cloning, sequencing) and cultural (isolation, MeHg detection by biosensor) approaches demonstrated the involvement of populations related to the genus Desulfovibrio in the process of Hg methylation in the aquatic rhizoplane. According to an experiment conducted in microcosms using a Hg isotopic tracer, MeHg formed in the aquatic rhizoplane seems to be bioavailable to the food chain. This last observation is linked to significant Hg concentrations, observed in situ, for some carnivorous fishes (end of the food chain).

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Esta dissertação consiste de dois capítulos, cada um correspondendo a um estudo realizado de modo independente. Em um córrego de Mata Atlântica, Rio de Janeiro, Brasil, foram estudados efeitos de herbívoros e de controles ambientais no perifíton. No primeiro trabalho foram testados os efeitos do camarão Potimirim glabra, um engenheiro do ecossistema, nos parâmetros metabólicos de comunidades perifíticas (Produção, Respiração, Metabolismo Líquido da Comunidade e razão Produção:Respiração). O tratamento de inclusão de Potimirim produziu resultados inversos aos esperados, com aumento da clorofila e massa seca das comunidades perifíticas, levantando dúvida com relação à eficácia dos tratamentos. Nenhuma das variáveis metabólicas esteve relacionada aos tratamentos. Considera-se que efeitos artefato da gaiola utilizada na inclusão dos camarões podem ter prejudicado o efeito esperado de remoção de material pelos camarões. Os resultados podem indicar, entretanto, que para o efeito de herbívoros os parâmetros clorofila e massa seca sejam mais sensíveis e variáveis que os metabólicos para as comunidades estudadas. São recomendados futuros trabalhos com metodologias que reduzam os efeitos artefato, tais como exclusão de herbívoros com cercas elétricas. No segundo trabalho, foram estudados os estoques, a distribuição e os controles da biomassa perifítica para o córrego. Entre os substratos estudados, a areia apresentou os maiores estoques, com 5 vezes mais clorofila e 20 vezes mais massa seca que os substratos pedra e folha. Diferenças entre trechos com diferentes densidades do camarão herbívoro Potimirim glabra revelaram para o substrato pedra menores valores de massa seca para os locais onde o camarão é mais numeroso. Entre as variáveis ambientais, apenas a profundidade esteve relacionada aos dados de biomassa nos substratos pedra e areia. A comparação dos dados deste estudo com trabalhos anteriores pode indicar que distúrbios provocados por enchentes podem alterar os estoques e os padrões de distribuição para este córrego. / This dissertation consists of two chapters, each corresponding to an independent study. In an Atlantic Rainforest stream, Rio de Janeiro, Brazil, the effects of herbivores and of environmental controls on periphyton were studied. In the first experiment I tested the effects of the shrimp Potimirim glabra, an ecosystem engineer, on the metabolic parameters of periphytic communities (Production, Respiration, Net Daily Metabolism and Production:Respiration ratio). The Potimirim inclusion treatments produced results opposite to the expected, with higher chlorophyll and dry mass of the periphytic communities. This lead to doubt of the efficacy of the treatments. None of the metabolic variables was related to the treatments. It is considered that artificial effects of the cage used in the shrimp inclusion may have changed the expected effect of material removal by the shrimps. The results may hint, however, that the chlorophyll and dry mass parameters may be more sensitive to and variable with the effects of herbivores than the metabolic parameters in the studied communities. Future work is recommended with methods that reduce artificial effects, such as herbivore exclusion using electric fences. In the second experiment, stocks, distribution and controls of periphytic biomass were studied for the stream. Among the studied substrates, sand presented the highest stocks, with 5 times more chlorophyll and 20 times more dry mass than the rock and leaf substrates. Differences among reaches with different densities of the herbivore shrimp Potimirim glabra revealed for the stone substrate smaller dry mass values in the reaches where the shrimp is more abundant. Among environmental variables, only depth was related to biomass, in the substrates rock and sand. The comparison of data in this study with previous work may hint that disturbances caused by spates may change stocks and distribution patterns for this stream.

Nutrients, periphyton and macroinvertebrates were sampled every two months for one year to assess the effects of treated sewage effluent on the Thredbo River and to compare changes in chemical concentrations and the invertebrate community since the introduction of nutrient removal on the Thredbo sewage treatment plant. Chemically, the impact of the effluent was minor and was reduced from levels measured before the addition of nutrient removal to the Thredbo sewage treatment plant. However, the reduction may be the result of higher flows during the study period. Biologically there was no indication of nutrient enrichment during June, August and October, with differences occurring between physically dissimilar sites irrespective of position relative to the sewage effluent inflow. Large increases in periphyton and macroinvertebrates occurred in December, February and April at both open sites and those downstream of the sewage outflow. Previous studies found increases in invertebrate abundance and richness immediately downstream of the sewage inflow, but the impact was greater and extended further downstream than found in this study. Strong correlations between total phosphorus and periphyton biomass and chlorophyll-a indicate phosphorus was a limiting nutrient. Higher periphyton biomass and chlorophyll-a at all sites during the warmer months (especially at open sites with an even cobble substratum), throughout the year, indicates light, temperature and substratum type were as important as phosphorus in controlling algal growth. Low algal biomass during the high flow month of October also indicates the importance of water velocity in controlling periphyton biomass. The structure of the macroinvertebrate community was noticeably different at sites downstream of the effluent discharge, with the exception of the most downstream site, when compared to the upstream sites. The occurrence of high macroinvertebrate numbers and species richness at sites with high periphyton growth and the strong positive correlation between invertebrate grazers and periphyton measurements shows a dependent relationship between invertebrates and periphyton growth. Therefore, the physical factors of light, temperature and substratum characteristics of particular sites in the Thredbo River, may be as important in controlling the benthic community as the levels of nutrient inputs from sewage.

<p>The aim of this thesis was to identify general structuring mechanisms in benthic food webs within the framework of ecological stoichiometry theory. Ecological stoichiometry is defined as the balance of multiple chemical substances in ecological interactions and explicitly considers the combined dynamics of key elements such as carbon (C), nitrogen (N) and phosphorus (P). Ecological stoichiometry theory was developed for pelagic environments, thus it must be tested whether the same mechanisms are applicable to benthic environments. </p><p>In this thesis, ecological stoichiometry theory was used as a framework to investigate nutrient pathways in benthic littoral ecosystems. I conducted one invertebrate field sampling and six experiments. In the experiments, factors such as grazing, light, nutrients and fish presence were manipulated.</p><p>The results showed that stoichiometric variability in consumers could mostly be explained by taxa. However, there was some stoichiometric variability due to sampling season, site, and nutrient enrichment. </p><p>Grazing mostly increased periphyton N and P content, although nutrient recycling effects were dependent on grazer stoichiometry. Grazing changed benthic algal community composition by increasing the proportion of grazing resistant algae species. Additionally, grazing decreased algal diversity, especially under nutrient poor conditions. The manipulation of fish presence revealed that fish affected primary producer biomass and stoichiometry through nutrient recycling. </p><p>The manipulation of abiotic factors, such as light and nutrient addition could affect periphyton nutrient content, biomass and benthic algal chlorophyll a content. The separate addition of N or P led to an increase of the added nutrient in the periphyton. Increased light intensities led to a decreased cellular chlorophyll a content and increased C:nutrient ratios. </p><p>This thesis arrives at the conclusion that periphyton-grazer-predator interactions in the benthic are bound by stoichiometric constraints. Nutrient recycling by benthic invertebrates and fish are important mechanism in benthic littoral ecosystems.</p>

Cattle farming is vital to the economy of the United States. Frequently, cattle are given access to ponds and streams for water. The relative impacts of cattle access in natural water sources on the periphyton community have been rarely investigated. Periphyton is the basis of the aquatic food web, and community composition can serve as a bioindicator of pollution. Thus, my objectives were to quantify the effects of cattle access in aquatic lentic systems on periphyton community structure and biovolume, identify taxa that were associated with cattle access, and identify abiotic mechanisms that might be driving assemblage changes. I conducted my research in 4 cattle-access (CA) and 4 no-access (NA) farm ponds on the University of Tennessee Plateau Research and Education Center from May 2005 – April 2006. Periphyton community composition and water quality were measured every 2 weeks using standard environmental monitoring procedures. I documented 181 new periphyton taxonomic records (7 phyla, 52 families, and 132 genera) in Cumberland County, Tennessee. Periphyton species richness was greatest in NA ponds. Mean biovolume of pollution-sensitive diatoms (e.g., Achnanthidium minutissimum, Cymbella sp., Eunotia sp., Fragilaria crotonensis and Tabellaria fenestrata) was greater in NA ponds. In contrast, pollution-tolerant diatoms (e.g., Gomphonema sp. and Navicula sp.) and non-diatoms (e.g., Oscillatoria sp. and Scenedesmus sp.) were more abundant in CA ponds. Turbidity, pH, conductivity, and concentrations of the total Kjeldahl nitrogen, total phosphorus, potassium, periphyton phosphorus, silicon, iron, magnesium and aluminum were greater in CA ponds. Thus, changes in water quality associated with cattle-access likely mediated changes in the periphyton community. Considering that changes in periphyton community composition can destabilize higher trophic levels, I recommend that cattle farmers take advantage of USDA conservation programs that provide funds for fencing cattle from watersheds and developing alternate water sources. My results also provide evidence that monitoring the periphyton community is a reliable technique to detect water pollution from cattle.

Dietary cadmium (Cd) can contribute significantly to chronic bioaccumulation and toxicity in aquatic organisms. This contribution needs to be quantified so that the relative importance of waterborne and dietary cadmium exposure pathways can be incorporated into protective water quality guidelines and ecological risk assessments. In this research, the contribution of dietary Cd from a natural periphyton diet to chronic (28 d) bioaccumulation and toxicity in the freshwater amphipod Hyalella azteca was quantified using a mechanistically-based saturation bioaccumulation model. Factors that influence dietary Cd bioavailability such as food type, food form, dietary Cd speciation and concentration were investigated. Assimilation efficiency, ingestion rate and the excretion rate constant of dietary Cd were determined for each of these factors. Food nutrition was also considered. Lastly, model predictions of Cd bioaccumulation and toxicity were compared to measurements of tissue concentration and survival when H. azteca were exposed to metal contaminated water and periphyton collected from lakes in the metal mining region of Rouyn-Noranda, Quebec, Canada. In 28 d laboratory experiments where H. azteca bioaccumulated Cd from water and food, dietary Cd was estimated to contribute markedly (21 – 94 %) to bioaccumulated Cd in H. azteca. Effects on chronic survival were best predicted from body concentration rather than water or food exposure concentration. Assimilation efficiency of dietary Cd differed with food type likely as a result of Cd speciation, but did not differ with Cd concentration or food form. Ingestion rate differed with food form while excretion rate constants were unaffected by dietary Cd bioavailability. Predictions of chronic Cd bioaccumulation in H. azteca exposed to field contaminated samples were robust, however the model did not account for effects of water chemistry on Cd bioaccumulation and is thus constrained in its application. Predictions of chronic survival were over-estimated likely due to the additional toxicity caused by the low nutritional quality of the field contaminated periphyton. This research demonstrated that both waterborne and dietary Cd need to be considered in models that assess chronic risk of exposure and effects to H. azteca.