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

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. Springer 984 Water Resour Manage (2007) 21:983-995

Influence of Reservoirs on the Concentration of Nutrients in the Water of Mountain Rivers

“…In the world literature, the studies on the influence of storage reservoirs on the chemical composition (including nutrients concentrations) of rivers are focused both on single and numerous reservoirs localised in various regions, diversified in terms of physical and geographical characteristics [4,[6][7][8][9][10][11][12]. Mountain regions show high temporal and spatial diversification of all hydrological processes [13][14][15].…”

Multiannual variations in phytoplankton populations: what distinguished the blooms of Aphanizomenon ovalisporum in Lake Kinneret in 2010 from 2009?

“…Phosphate availability is considered a major limiting factor to phytoplankton growth in Lake Kinneret (Berman, 1988; Markel et al ., 1994; Eckert et al ., 1997) and many other lakes around the world (a few recent publications from diverse environmental conditions include Ogawa, 1988; Rengefors et al ., 2003; Mhamdi et al ., 2007; Fadiran et al ., 2008; Spijkerman, 2008; Aubriot et al ., 2011; Burford and Davis, 2011; Young et al ., 2011). Measurements of the various forms of phosphate are therefore routinely performed as part of monitoring of Lake Kinneret waters.…”

Seasonal and Spatial Distribution and Pollution Assessment of Nitrogen and Phosphorus in Sediments from One of the World’s Largest Tidal Reservoirs

“…Phosphorus and nitrogen concentrations are the limiting variables in the eutrophication process [52]. According to the Nemerow pollution index, comprehensive pollution assessment of nutrients in sediments ranged from unpolluted to slightly polluted, except for the moderate contamination that occurred downstream in winter (Table 1).…”