Sediment phosphorus release in a tropical shallow lake under the presence of oxygen

• Autor(a) principal: Oliveira, Jéssica Papera de
• Data de Publicação: 2019
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da UFRN
• Texto Completo: https://repositorio.ufrn.br/jspui/handle/123456789/27415
• topic: CNPQ::ENGENHARIAS::ENGENHARIA SANITARIA; Lake Extremoz; Coastal lake; Fractionation; Sediment; Oxic; Temperature

Phosphorus (P) is a key nutrient in the eutrophication of freshwater and external nutrient sources are considered one of the main causes of P enrichment. To try and control eutrophication, external loading can be reduced. However, P accumulated in the sediment can be cycled back into the water, due to the process of internal loading. Not every form of P in the sediment is likely to be released into the water column, and its release from sediment is influenced by several factors, such as temperature, dissolved oxygen concentration, organisms, pH, and sediment resuspension. P release under anoxic conditions is largely discussed, but oxygen is not the only factor affecting P release. In this study, we evaluate the potential contribution of internal P loading to the eutrophication of Lake Extremoz, which is a well mixed shallow system that has been suffering increasing eutrophication. The quality of its water is relevant as it is used for human consumption. To evaluate internal loading, we have carried out an experiment utilising sediment with lake water, and sediment with deionised water, under conditions similar to the sediment-water interface over a 40-day period. We have also analysed P forms in the sediment per depth range, and before and after the experiment. The main P fraction in the sediment was refractory organic P, and the main mobile fraction was P bound to Fe and Al oxides. Less than half of the P in the sediment is in mobile P forms. During the experiment, temperature varied up to 3.2°C, what led to P release from sediment into the water column, regardless of the aerobic conditions. By the end of the experiment, the majority of the P in the water overlying the sediment was organic (P-Org). In the units that had lake water, P-Org represented 99.5% of the total P. And, in the units that had deionised water, P-Org represented 93.6% of total P. Most of the P flux into the water after the increase in temperature was composed by organic phosphorus. We also saw an increase in organic P forms in the sediment of the experiment. The increase in the temperature, followed by the changes in phosphorus concentrations in the water, mainly P-Org, suggest that the effects of temperature and microorganisms’ metabolism control P flux in the presence of oxygen.