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Title: A Study on Primary Productivity and Nutrients in Abijata Evaporative Concentration Ponds
???metadata.dc.contributor.*???: Dr. Seyoum Mengistu
Wonde, Ayalew
Issue Date: Jun-1997
Publisher: Addis Ababa University
Abstract: Changes in primary productivity and nutrients were studied in- situ in three Abijata evaporative concentration ponds (B, C, D), intake channel (A) and die main lake for seven months from October, 1996 to April, 1997 (9 samplings). Data were also recorded for related physical and meteorological parameters including: temperature, wind speed, light, and water chemistry. Phytoplankton biomass was measured as chl-a. Photosynthesis was estimated by oxygen evolution with the Winkler and Miller methods, and l4C was also used three times for comparison during the study period. The level of pond water fluctuated considerably in response to water influent from the main lake, precipitation and evaporative concentration. In all die studied water-bodies, there was no appreciable stratification in temperature except pond D with greater temperature at the bottom. Intensive wind mixing is a common feature in the ponds. Ionic concentration in pond D exceed by more than 15 times over the channel and pond B. Similar patterns were observed in the composition of major nutrients, except phosphorus. There was strong positive relationship between increasing salinity and alkalinity but inverse relationship with pH and phosphorus was observed. The concentration of dissolved inorganic nitrogen is extremely high ( >14mg/l ) in all water-bodies. No nutrient limitation was found during the study period. A total of 11 phytoplankton genera were identified in the lake, channel and pond B, of which Anabaenopsis represent >50% of the community in number. This persisted as an unialgal population in pond B during the dry months when ionic concentration was also high. Diatoms compose the greater part of the algal community, particularly during the rainy months (March-April,1997) and increased water level. Among diatoms, Navicula and Nitzschia species were dominant at all times, except the dry months. Spirulina platensis was found in lower frequency when compared with reports from earlier studies. Mean chi. a concentration in the main lake, channel and pond B were 8.16, 16.14, 4.23 mg m*3, respectively, much lower than values reported by earlier investigators. Areal photosynthetic rates ranged from 0.2 to 1.05g C m‘2 h'1 in the channel, and 0.042 to 0.414g C m\l in pond B. It is about 5 g C m’2 when extrapolated to daily rate in pond B while in the lake and the channel it does not exceed beyond 11 g C m'2 d 1. This is much lower than the usual rates for African alkaline-saline lakes. The major factors that influence primary productivity during the study period include the higher level of sulphate, declined alkalinity and higher salinity along the concentration gradient. It was found that Miller method is the best technique of estimation of photosynthetic rate in such alkaline-saline waters. These data for primary productivity and nutrients are discussed in relation to their implications for large scale production and control purposes in the ponds.
Description: A Thesis Submitted in (Part) Fulfillment for the Degree of Master of Science in Biology in Addis Ababa University
Appears in Collections:Thesis - Biology

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