Variation of water quality and phytoplankton along different zones of Aswan High Dam Reservoir

Abstract

ABSTRACThis study was carried out at Aswan High Dam Reservoir and focused on the spatial variation of water quality parameters and phytoplankton composition. Water samples were collected from eighteen sampling stations, where six stations for each of the different zones were selected to represent the lacustrine, transition and riverine zones of the reservoir during 2007 and 2008.The results of the environmental factors showed wide variations in their concentrations along the different zones of the reservoir.In this study, chlorophyll a concentration was lower in the lacustrine zone than in the riverine, although turbidity and secchi depth values were all optimal for light availability. This result was influenced by higher abundances in the reservoir phytoplankton assemblages where riverine conditions predominate, by species tolerant to turbulent conditions and typical high mineral turbidity. Calculation of the trophic state index showed that riverine and transition zones are classified as eutrophic, while lacustrine zone is mesotrophic. Phytoplankton composition recorded thirty nine species belonging to Chlorophyceae (19 species), Cyanophyceae (10 species), Bacillariophyceae (7 species), and rare groups including Dinophyceae (2 species) and Eugelnophceae (1 species). Cyanophyceae were the most encountered group in the lacustrine and transition zones, while Bacillariophyceae were most encountered group in the riverine zone. This is due to that Cyanophyceae prefer the steady, transparent and low nutrients water (lacustrine), while Bacillariophyceae prefer flowing, turbid and nutrient-rich water (riverine).Statistical analysis showed that certain environmental factors do affect the phytoplankton growth. The results of the one-way ANOVA revealed that the different environmental factors (DO, water temperature, secchi depth, water velocity, turbidity, nitrate, phosphorus, magnesium, total dissolved solids, and trophic state index) and biotic factors (such as chlorophyll a and phytoplankton groups) were significantly different at the three zones of Aswan High Dam Reservoir (p<0.05). This result supports the speculation of variation in water quality and phytoplankton along the different zones of the reservoir.

Water quality and plankton biota of Osinmo reservoir, Osun State, south-west Nigeria

“…The diversity of phytoplankton in the riverine zone was found to be higher than that in the transitional zone. This result coincides with the findings reported by Salem (2011) from Aswan High Dam reservoir, which he attributed to the dominance of species tolerant of Zoology and Ecology 151 turbulent conditions. According to Wetzel (2001), this could be also the outcome of the lake productivity level, with higher phytoplankton diversity in lakes that are less productive than eutrophic lakes.…”

“…This was the key factor responsible for reduced transparency in Nigerian waters (Adedeji 2011;Adeniyi 1978;Aduwo 2007;Akinbuwa 1999;Holden and Green 1960;Imevbore 1967). High fluctuations in the Secchi disc visibility, as recorded in lacustrine and transitional zones, according to Salem (2011), is due to lower mixing of water in these zones in contrast to the riverine zone, where water current is fast and turbulent. Factors affecting water transparency, according to Bamforth (1958cited Salem 2011, include silting, microscopic organisms and suspended organic matter.…”

“…According to Salem (2011), this could be due to the fast flow of water in the riverine zone, which allowed for replenishment of oxygen compared to nearly nil water velocity in the lacustrine zone of the reservoir. Some of the main factors influencing plankton composition, density and biomass pointed out by Nogueria et al (2010) (water retention time, advection processes, vertical mixture regime, longitudinal and lateral gradients in physical and chemical conditions as well as indirect effects of important meteorological factors such as rainfall and wind) influenced the composition of phytoplankton and zooplankton in Osinmo reservoir.…”

“…Low pH level as a result of influx of water due to heavy rain during the period might have also led to non-availability of Charophyta during this period. The non-availability of Ochrophyta during the early rainy period could be linked to the negative correlation between their abundance and water transparency (Das et al 2011;Salem 2011).…”

Ecological Status of Opa Reservoir, Obafemi Awolowo University, Ile Ife, based on the Abundance and Diversity of its Planktonic Flora

“…The maximum phytoplanktonic abundance, recorded in the lacustrine zone, might be due to stability of certain environmental variables in this zone as a result of reduced water current, restricted movement and higher transparency (Salem, 2011;Adedeji et al, 2015). The lowest abundance in spite of high species richness recorded in April 2013, a period towards the first peak of the rainy season, could possibly be an effect of the washing away of many individual phytoplankton through flooding and their dislodging from littoral vegetation hence species enrichment (Adeniyi and Adedeji, 2007).…”