Seasonal characterization of the nutrients state in Oualidia Lagoon (Moroccan Atlantic coast)

The nutrient cycle in Oualidia lagoon, on the Atlantic Moroccan coast, was studied at both spatial and temporal scales, covering spring and summer conditions. Water samples were collected bimonthly at high tide from March to August during years 2011 and 2012 at six stations distributed throughout the lagoon. The physico- chemistry (temperature, salinity, dissolved O2) and nutrient enrichment of the lagoon surface water were monitored. The average nutrient concentration of surface water were 14.4 μmol.l-1 and 28.1 μmol.l-1 for NH4+, 20.4 μmol.l-1 and 19.9 μmol.l-1 for PO43- and 3.7 μmol.l-1 and 7.6 μmol.l-1 for NO2- in 2011 and 2012, respectively. Strong seasonal differences of nutrient distribution at the different stations were noticed. Temperature, salinity and dissolved O2 were correlated with nutrient concentrations, all parameters showing low spatial (inter-station) variability. Hydrological conditions exert a major control on the nutrient cycling in the lagoon. Results of this study are important to increase the richness on the scientific knowledge of nutrient dynamics along the Moroccan Atlantic coast, particularly in the semi-enclosed lagoons that are important transitional systems.Peer reviewe

The influence of hydro-chemical parameters on microphytoplankton distribution along Oualidia lagoon, Moroccan Atlantic

Microphytoplankton and environmental parameters were monitored and analyzed bimonthly (twice a month) over an annual cycle (June 2011 to May 2012) at six stations in Oualidia lagoon. The present study is conducted to assess the relationship between physicochemical parameters and microphytoplankton assemblages, which can serve as a method to assess the quality of paralic ecosystem. The assessment results revealed a seasonal variation of nutrients concentrations. Spatial variation of temperature, salinity and concentration of dissolved oxygen was noticed. Two microphytoplankton classes were dominant: Bacillariophyceae and Dinophyceae. The phytoplankton diversity and abundance were characterized by a pronounced sea- sonal pattern. Canonical correspondence analysis between environmental variables and dominant taxa of phytoplankton indicated the tidal influence on microphytoplankton distribution in Oualidia lagoon. Concentrations of nitrite, salinity, pH and temperature showed a positive correlation with dinoflagellates and diatoms indicating their importance in microphytoplankton growth and sustenance. Concentrations of orthophosphates developed negative correlation with microphytoplankton. Finally, fifteen taxa were identified that may present a risk of inducing harmful blooms (Pseudo-nitzschiasp., Dinophysisacuminata, D. acuta, D. caudata, D. fortii. D. sacculus, Phalacromarotundatum, Gonyaulaxpolygramma, Lingulodiniumpolyedra, Ostre- opsissp., Pelagodiniumsp., Gyrodiniumspirale, Heterocapsasp., Prorocentrumcordatum and P. micans)

Assessment of physico-chemical parameters of freshwater in the Sidi Abderrahmane reservoir, Safi, Morocco

The purpose of the study was to assess the water quality in the Sidi Abderrahmane freshwater reservoir (Safi, Morocco). The monitoring data used in the study included physical, chemical, and biological characteristics. The spatial and temporal characteristics of these parameters was evaluated by collecting water samples fortnightly from May 2011 to December 2012 in three stations chosen to represent different parts of the reservoir. Ten parameters considered as indicators of water properties were analysed: temperature, dissolved oxygen, pH, electric conductivity, transparency, orthophosphorus, ammonium, nitrites, nitrates, and chlorophyll a. The results show that nutrient concentrations were among the highest (mean concentrations: PO43− = 0.64 mg l−1, NH4+ = 1.08 mg l−1) recorded for Moroccan freshwater reservoirs. Our data indicated that the Sidi Abderrahmane is a destratified reservoir that it is relatively warm (mean temperature: 22.42 ± 4.88 °C); a polymictic reservoir in a semi-arid climate. Fertilisers applied in the surrounding orchards affect significantly affect nutrient levels in the waterbody, particularly PO43− and NH4+ in autumn. The water column is seasonally homogeneous, as a result of wind-induced mixing, and our tests showed no anoxia throughout the study period. With suitable hydraulic conditions (short residence time, short outflow/inflow ratio, good oxygenation, and homogeneity), the Sidi Abderrahmane water body could reduce the stratification time and improve water quality