Artemia Occurrence, Salinity and Ionic Rates in Saline Crater Lakes of Western Uganda (original) (raw)
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This study, carried out between November 2003 and February 2005, aimed to investigate the temporal trends of conductivity, ions, nutrient concentrations and phytoplankton biomass expressed as chlorophyll a in the Kenyan Rift Valley saline-alkaline lakes namely Nakuru, Bogoria and Elmentaita. The influence of environmental variables on phytoplankton biomass has always been of much interest in understanding phytoplankton dynamics. Being shallow and endorheic, these lakes’ chemical, physical and biological properties were found to be strongly influenced by the hydrologic cycle within their catchment area. The lakes are characterised by high nutrient concentrations but with low Ntot: Ptot ratios. Significant differences between surface and near-bottom samples for water temperature, chlorophyll a and some nutrients were found in these lakes. A stepwise Discriminant Analysis with lakes as defined groups resulted in a significant model with SRP, nitrate-N, conductivity and light supply being of major importance. A significant correlation between specific conductivity and total alkalinity (Kendalls τ = 0.85, n = 132) was calculated. While L. Bogoria showed the least temporal variation in conductivity-(65-73 mS cm−1), larger variations were observed in L. Elmentaita (21-77 mS cm−1). Na+ and K+ form the main cations with Cl−, HCO3− and CO32 being the major anions in all the three lakes. Flouride was detected in high quantities (mean values L. Bogoria 72 meq 1−1, L. Nakuru 17 meq 1−1 and L. Elmentaita 71 meq 1−1). A PCA followed by multiple regression analysis with chlorophyll a as dependent variable showed that nitrate-N, conductivity, phosphorus and light supply were the key variables influencing algal biomass in these lakes.
Major ion chemistry in a tropical African lake basin
Freshwater Biology, 1981
SUMMARY. The amount of water lost by seepage from Lake Naivasha, calculated as the residual in the water budget, was 5 (1973), 11 (1974) and 20% (1975) of the total water loss. Direct measurements of seepage in nearshore shallows indicated that water entered the lake via ground-water seepage in the northern portion and left the lake in the southern portion. Naivasha lies in a topographic closed basin but is hydrologically a seepage lake; it is distinctive among the lakes lying in the endorheic rift valleys of Ethiopia, Kenya and Tanzania because the water is fresh.The mean chemical composition (mg l−1) of bulk precipitation collected on two transects across the rift valley near L. Naivasha and at three stations near Nairobi was: Na, 0.54, K, 0.31; Ca, 0.19; Mg, 0.23; SO4, 0.72 and Cl, 0.41. The major inflow, the Malewa River, was largely a solution of bicarbonate (1.15 m-equiv, l−1), sodium (9 mg l−1) and calcium (8 mg l−1) and carried a total dissolved solid load (kg ha−1) of 62 (1973) and 120 (1974). Total dissolved solids, sodium, calcium and bicarbonate concentrations were inversely related to discharge.Among the standing waters in the Naivasha basin, sodium and bicarbonate are predominant and the mean total dissolved solute content (mg l−1) increased from a low under the northern papyrus swamp (217) to intermediate values in L. Naivasha (329), the nearshore lagoons (367) and Crescent Island basin (394) to a high in Oloidien Lake (831). Ion ratios and stability field diagrams indicated that calcite is formed in the Crescent Island basin and Oloidien Lake. Calcite was detected in the sediments of the two basins. Ion ratios also indicated that sulphate was retained in the sediments of the northern papyrus swamp.Several factors combine to keep L. Naivasha's water fresh. A large fraction of the water supplied to the lake comes from dilute rivers and rain. The lake does not lie in a closed basin, but loses water and solutes via seepage. Exchanges with sediments both in the pelagic and littoral regions of the lake are the major routes for solute movement and biochemical sedimentation is a major factor in removal of silica. Both geochemical and biochemical sedimentation account for much of the potassium, calcium, magnesium and bicarbonate removal. Only low levels of the conservative ions, sodium and chloride, are taken up by the sediments, while very low levels of sulphate and fluoride are actually released.
Journal of The World Aquaculture Society, 2004
Abstract.–From July 1998 to June 2000 four thalassohaline aquatic environments along the Colombian Caribbean coast (Manaure, Galerazamba, Salina Cero, and Tayrona) were surveyed monthly to determine the influence of salinity, percent 02 saturation, pH, temperature, and nutrients (NO2-, NO3- and PO4-3) on Artemia (Crustacean, Anostracan) biomass production and cyst production potential. The effects of the regularly measured physicochemical parameters on biomass and cyst production potential were analyzed using univariate analysis of variance (SPSS VI 0.0). The influence of physicochemical parameters on biomass production was not significant (P > 0.05). In contrast, there was a significant interaction (P<0.05) of salinity, percent 02 saturation, and nitrate (used as a proxy for chlorophyll a) on cyst production potential. In addition, for all four locations nitrate levels were directly proportional to salinity. This might be explained by the fact that in saltworks numerous organisms are trapped and slowly die as salinity increases progressively in the evaporating basins; thus, organic matter accumulates and decomposes. Consequently, the concentration of the nitrogenous compounds, first nitrite and later nitrate, increases through time as salinity increases. Moreover, decreasing nitrate levels seem to increase cyst production potential; thus supporting the notion that when insufficient food is available cyst production increases.