Dynamics of the relative nitrogen and phosphorus concentrations in a reservoir situated in a semi-arid zone (Sahela, Morocco)

B. Mhamdi, A. Azzouzi, M. Mhamdi and T. Sime-Ngando ()

Water Resources Management: An International Journal, Published for the European Water Resources Association (EWRA), 2007, vol. 21, issue 6, 983-995

Abstract: Fluctuations in total nitrogen and phosphorus concentrations and in the N/P ratio (i.e. in terms of mass) were measured at the entry and exit of the Sahela Reservoir (Morocco) throughout an annual cycle. Particulate N and P concentrations in sedimenting particles in the reservoir itself were also measured. The results obtained showed that the spring floods were a major source of N and P inputs, this being especially pronounced for phosphorus that was present mainly in particulate form. In all the compartments of the reservoir analysed, the N/P ratios were high (means between 81 and 314), especially in summer (the only season when the reservoir was emptied) when the supply of P was apparently limited by the drought. However, the values of this ratio in the sedimenting particles remained lower (mean=21), at levels characteristic of natural communities. This implies that the reservoir's biological communities preferentially store phosphorus, no doubt to maximise their activity in an environment where a large proportion of this element is not bioavailable. Furthermore, it appeared that the quantity of particulate N and P sequestrated by the sediments and the total quantities of N and P leaving the reservoir were greater than the inputs of these nutrients, underlining the importance of lateral and internal nutrient supplies. One spot measurement, made in a single month, showed that nutrient release activity from the sediments was in fact quite considerable. Copyright Springer Science + Business Media B.V. 2007

Keywords: Reservoirs; Nutrient dynamics; Nutrient flows; Nitrogen; Phosphorus; N/P ratio (search for similar items in EconPapers)
Date: 2007
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DOI: 10.1007/s11269-006-9068-5

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