Carbon, nitrogen and phosphorus stoichiometry of rivers in the light of Redfield ratio

Abstract

Abstract. A. Redfield entered the history of hydroecology due to the discovery of a unique stoichiometric ratio of Carbon, Nitrogen and Phosphorus – 106: 16: 1 – in the marine plankton, which it was later named after the author – the Redfield Ratio. Furthermore, A. Redfield established, that the stoichiometric ratio of Carbon, Nitrogen and Phosphorus in seawater is supported on the average level and it is 1017 : 15 : 1. On the basis of established stoichiometric ratios A. Redfield came to the conclusion that exactly Nitrogen is a limiting factor in the marine environment, because the ratio of its average statistical stoichiometric availability in seawater turned out lower than the average stoichiometric utilization of plankton. Also the merit of A. Redfield is the was established by him the carbon and nitrogen forms, which make the greatest contribution to the pool of these elements are available for plankton. After Redfield the studies by the CNP-stoichiometry of water and plankton in marine and ocean ecosystems were carried out by a number of researchers. However, the CNP-stoichiometry of rivers water fell out of the field of view of hydroecologists. The authors of this publication tried to fill this gap. The purpose of the studies was to establish the peculiarities of CNP-stoichiometry of river ecosystems in comparison with marine ecosystems and it determine the contribution of different forms of carbon and nitrogen to the pool of these elements which available for plankton in river water. The research was conducted during the summer low water period (2014) at the at monitoring stations of watershed of the three rivers of the Carpathian region within the Chernivtsi region. It is Dniester, Prut and Siret. Water samples were taken by a bathometer at 16 sites (near 8 forest and 8 meadow floodplains) of each of the 15 monitoring stations. Under laboratory conditions, the nitrate content was determined by the nitrate meter (H-401). Carbonates and hydrogen carbonates was determined by titrimetrically method. Phosphates, ammonia and nitrites was determined by photocolorimetrically method. Like Redfield, the stoichiometric availability of Сarbon and Nitrogen in river water was estimated as the ratio of the molar concentrations of the corresponding elements to the molar Phosphorus concentration. For the first time the features of CNP stoichiometry of the rivers were installed in comparison with the marine stoichiometry. The stoichiometric ratio of total carbon, nitrogen and phosphorus in river water of the Carpathian region is 938C: 59N: 1P and the ratios of their stoichiometric availability to stoichiometric utilization by plankton is 8,9C : 3,7N : 1P. It was shown that stoichiometric availability of energetically favorable for the assimilation by plankton by forms of carbon and nitrogen – СО2 и NH4+ – in the rivers water is greatly reduced, and do not cover the necessary level of stoichiometric utilization of these elements by plankton. It is proved that the greatest contribution in the river water to the pool of stoichiometric available of carbon and nitrogen contributes HCO3-, а азота – NО3- in accordance. It was found that the main limiting factor of growth of and development of plankton in rivers of the Carpathian region appears phosphorus whose balanced share in CNP ratio is an order of magnitude lower than that it need for the utilization by plankton.