Sewage, agricultural runoff, and atmospheric deposition have greatly increased the amount of nutrients (largely nitrogen (N) and phosphorus (P)) in surface water nationwide. Excess nutrients are associated with algal blooms and dissolved oxygen depletion in many water bodies, but linkages between nutrients and dissolved oxygen have been largely correlative. Biochemical oxygen demand (BOD) is a regulated water quality parameter that is aimed at describing the amount of oxygen consumed during the decomposition of organic matter. Despite the awareness that excess nutrients are linked to dissolved oxygen in rivers, few studies in the nutrient criteria literature discuss BOD measurements or how nutrients may impact BOD. Accordingly, I used factorial experiments to test the effect of inorganic nutrients (as N, P and N+P) and dissolved organic carbon on BOD measurements in Utah streams. The study was carried out from January through summer baseflow in 2011, allowing me to evaluate the effects of spatial and temporal variation of ambient nutrient concentration on oxygen demand. The study design included measurements in streams above and below nutrient point-sources (publicly owned treatment works) and several reference sites. I used classification and regression trees to identify thresholds of TN and TP that separate BOD response to nutrients into statistically distinct groups. My results show that seasonal variation affected BOD levels. As temperatures rose and water levels increased during peak runoff, I observed the highest BOD response to nutrient additions. I also found a significant correlation between BOD and ambient nutrient concentrations during that time period. I identified potential nutrient-related thresholds that could be used to assign numeric criteria that would protect designated uses. The threshold values I found for TN and TP were 0.56 mg/L and 0.09 mg/L, respectively. My results suggest that BOD may be sensitive to nutrient inputs and my experimental approach could be used as one line of evidence to support nutrient criteria related to aquatic life uses.

Submitted by Ronildo Prado (ronisp@ufscar.br) on 2017-08-22T13:00:56Z No. of bitstreams: 1 DissRMFS.pdf: 2091397 bytes, checksum: 9416d9552b0e519672969fe9b02432ff (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-08-22T13:01:05Z (GMT) No. of bitstreams: 1 DissRMFS.pdf: 2091397 bytes, checksum: 9416d9552b0e519672969fe9b02432ff (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-08-22T13:01:12Z (GMT) No. of bitstreams: 1 DissRMFS.pdf: 2091397 bytes, checksum: 9416d9552b0e519672969fe9b02432ff (MD5) / Made available in DSpace on 2017-08-22T13:01:18Z (GMT). No. of bitstreams: 1 DissRMFS.pdf: 2091397 bytes, checksum: 9416d9552b0e519672969fe9b02432ff (MD5) Previous issue date: 2017-03-10 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Reservoirs located in tropical regions are main carbon (C) sources to the atmosphere, and bacterial metabolism is a key process that regulates those emissions. However, studies on the environmental drivers of bacterial metabolism in tropical reservoirs are scarce. By measuring metabolic rates and the limnological parameters in four cascading reservoirs that form a trophic state gradient, we determined the environmental drivers of bacterial metabolism in a tropical region, and compared them with those found in the literature (mainly from temperate regions). Our multiple regression models selected variables related to the trophic state as the main drivers of bacterial production (BP) and bacterial growth efficiency (BGE). On the other hand, bacterial respiration (BR), and consequently bacterial carbon demand (BCD), were weakly and negatively correlated to dissolved organic carbon (DOC), contrasting with the literature data. BR was always high, especially in less productive reservoirs where planktonic communities were limited by phosphorus. Nutrient limitation, high temperatures and high incident light intensity increased the environmental hostility, and cells must invest more energy in maintenance mechanisms, which directs the metabolism towards BR. This was observed in the reservoirs studied, especially in the more oligotrophic environments (Nova Avanhandava and Três Irmãos) where BR was higher and ECB lower. Our results indicate that the regulatory mechanisms of bacterial metabolism may vary according to latitude. / Reservatórios de regiões tropicais são fontes de carbono (C) para a atmosfera e o metabolismo bacteriano é um processo fundamental na regulação dessas emissões. No entanto, estudos que elucidem os fatores ambientais que determinam o metabolismo bacteriano em reservatórios tropicais são ainda escassos. Neste estudo foram medidas taxas metabólicas e parâmetros limnológicos em quatro reservatórios em cascata que formam um gradiente de estado trófico, com o intuito de determinar os reguladores do metabolismo bacteriano em uma região tropical e compará-los com dados obtidos a partir da literatura disponível (principalmente de regiões temperadas). Nossos modelos de regressão múltipla selecionaram variáveis relacionadas ao estado trófico como os principais reguladores da produção bacteriana (PB) e da eficiência de crescimento bacteriano (ECB). Foi encontrada uma relação fraca e negativa entre a respiração bacteriana (RB) e o carbono orgânico dissolvido (COD), diferente dos dados da literatura. As taxas de RB foram sempre elevadas, especialmente em reservatórios menos produtivos, nos quais as comunidades planctônicas estavam limitadas por fósforo. A escassez de nutrientes, as elevadas temperaturas e a alta intensidade de luz incidente aumentam o grau de hostilidade, e as células devem investir mais energia em mecanismos de reparação, o que direciona o metabolismo para a RB. Isso foi observado nos reservatórios estudados, especialmente, nos ambientes mais oligotróficos (Nova Avanhandava e Três Irmãos) nos quais a RB foi mais elevada e a ECB mais baixa. Nossos resultados indicam que os mecanismos reguladores do metabolismo bacteriano podem variar de acordo com a latitude. / FAPESP: 14/14139-3 / FAPESP: 11/50054-4