[en] The aim of the present study is to evaluate the N, P, K nutrients evolution of a biological system by varying the luminous intensity and the pH of the medium. The system is an Aquarium of fresh water (80 L) contains a suit of plants. Experimental procedure focuses on conducting several trials where the system is fed with an amount of inorganic nutrient (K2HPO4) in accordance with a previously established strategy. The luminous intensity and the pH of the medium were varied and the system was checked along the first 24 h and during 4 days. The analytical determination of the studied nutrients, namely phosphate, nitrate and potassium, was accomplished. When the initial concentrations of potassium and phosphate increase a diminution of the nitrate content was observed. In most assays, as the added nutrients consumed, the final nitrate content increased. This shows the interconnection of biogeochemical cycles. With a low luminous intensity, the system only consumed phosphate (aprox. 50%). When this intensity was increased, the phosphate consumption was constant and for the potassium was estimated on 16%. Applying a high luminous intensity and with a low pH value, the phosphate consumption decreased (to 21%) whereas for potassium no changes were registered. The low phosphate consumption when the system presents a inferior pH can be due to the diminution of the rubisco enzyme activity (implied in the Calvin Cycle), this activity decreases when pH is less. This can cause a reduction of the photosynthetic activity as well as of the nutrients consumption. Finally, it was initiated the study of a seawater system. The viability of the analytical methodology previously established for fresh water analysis was evaluated. The seawater matrix requires the optimization of the analytical methods to achieve a reliable determination of the nutrients.

[gl] O presente estudo ten como obxecto avaliar a evolución dos nutrientes de N, P e K nun sistema biolóxico modificando o fotoperiodo e o pH do medio. O sistema en estudo é un acuario plantado de auga doce (80 L). O traballo experimental céntrase na realización dunha serie de ensaios achegando ao sistema unha cantidade fixa dun nutriente inorgánico (K2HPO4), dacordo a unha estratexia previamente establecida. En ditos ensaios modificouse o fotoperiodo e o pH do medio e realizouse un seguimento a corto prazo (24 horas) e outro a longo prazo (4 días). Posteriormente, lévase a cabo a determinación do contido dos nutrientes de interese neste estudo, sendo istos fosfato, nitrato e potasio. Ao incrementar os contidos iniciais de potasio e fosfato observouse unha diminución da concentración doutro nutriente, o nitrato. A medida que se consumen os nutrientes adicionados comprobouse, na maioría dos ensaios, un incremento final do contido en nitrato. Isto amosa a interconexión dos ciclos bioxeoquímicos. Cunha intensidade lumínica baixa observouse so consumo de fosfato (aproximadamente do 50%). Ao incrementar a intensidade lumínica, mantúvose o mesmo consumo de fosfato e para o potasio estimouse nun 16%. Ao diminuir o pH, aplicando unha intensidade lumínica alta, obtívose unha notable diminución do consumo de fosfato (21%) mentras que o consumo de potasio non se veu alterado. O menor consumo de fosfato ao diminuir o pH da auga pode deberse a unha menor actividade do enzima rubisco, implicada no ciclo de Calvin, actividade que diminúe ao descender o pH. Isto provocaría unha menor actividade fotosintética e un menor consumo de nutrientes. Finalmente, iniciouse o estudo dun sistema de auga salgada avaliando a viabilidade da metodoloxía empregada para o seguimento do acuario de auga doce. A complexidade da mostra de auga salgada require futuros estudos para a optimización dos métodos analíticos de determinación dos nutrientes de interese.