Recently there are signs of water quality impairment in Lake Tana, the largest fresh water in Ethiopia. The lake is the growth corridor of the government and supports millions of livelihood around. In order to sustain...Recently there are signs of water quality impairment in Lake Tana, the largest fresh water in Ethiopia. The lake is the growth corridor of the government and supports millions of livelihood around. In order to sustain the benefit and maintain the ecosystem of the lake, the lake health has to be kept safe. Therefore monitoring and evaluation of the water quality of lake is very vital. This study focuses on current and previous trends water quality of the lake through measurements and Landsat Images near entry of Gumera River. Statistical analysis of the physical (Turbidity and STD and biological (Cha-a,) and chemical (DPC) water quality parameters were done. Linear and non-linear regression models between water quality parameter and reflectance of Landsat 7 ETM+ images were fitted based on band combinations. Pervious trend in turbidity was analyzed based on the regression models. The results showed that reflectance and turbidity satisfactorily result with an R2 ranging from 0.61 - 0.68. Form 1999-2014 the turbidity of the lake has indicated an increasing trend. Delta development near the entry of Gumera River has been enlarged by 48% because of an increase sediment inflow. The sign in the decreasing water quality of the lake was attributed to the non-point source sediment and nutrient inflow to the lake with high erosion rate from the watersheds. Measures to reduce the non-point source sediment and nutrient inflow by targeting the source areas (hot spots) in the agricultural watersheds need to be priority for stakeholders working on the soil and water conservation. Moreover, reducing the recession agriculture around the lake and wetland management could be crucial for improving lake water quality.展开更多
Agricultural intensification to meet the food needs of the rapidly growing population in developing countries is negatively affecting the water quality. In most of these countries such as Ethiopia, information on surf...Agricultural intensification to meet the food needs of the rapidly growing population in developing countries is negatively affecting the water quality. In most of these countries such as Ethiopia, information on surface and especially groundwater quality is lacking. This limits the measure that can be taken to stop pollution. We, therefore, investigated the spatial and temporal variation of groundwater quality in the upland watershed. Tikur-Wuha watershed was selected because it is located in the Lake Tana watershed, which is seeing the first signs of eutrophication. Groundwater samples were collected from July 2014 to June 2015 from 19 shallow wells located throughout the watershed. Collected water samples were analyzed both in situ and in the laboratory to determine pH, electric conductivity (EC) and total dissolved solid (TDS), concentration of chemicals (nitrate, dissolved phosphorus, calcium, magnesium, aluminum and iron) and Escherichia coli (E. coli). We found that shallow groundwater had greater chemical concentrations and E. coli level in the monsoon rain phase than in the dry phase. Wells located down slope exhibited greater concentrations than mid- and upper-slope positions, with the exception of the nitrate concentration that was less down slope, due to denitrification in the shallow groundwater. Only E. coli level was above the WHO drinking water quality standards. Further studies on groundwater quality should be carried out to understand the extent of groundwater contamination.展开更多
Water is likely the most limiting factor in increasing agricultural production in large parts of Africa. Reference evaporation (ET0) is a key hydrological parameter to use efficiently the scarce supply. Several method...Water is likely the most limiting factor in increasing agricultural production in large parts of Africa. Reference evaporation (ET0) is a key hydrological parameter to use efficiently the scarce supply. Several methods are available for predicting reference evaporation, but the accuracy of any of the methods has not been established for the Ethiopian highlands. The objective of this study is, therefore, to select the best methods for calculating the reference evaporation ET0. For the section, meteorological data of the Bahir Dar station were used, because all data needed for this study including the Class A pan Evaporation were recorded on a daily basis. Pan evaporation was considered as the best estimator of the reference evaporation. The results showed that the FAO-Penman Monteith (using solar radiation, wind speed, temperature and relative humidity) and Enku method (using only maximum daily temperatures) have acceptable daily ET0 ranges and predicted to Class A pan evaporation with correlation coefficients greater than 90% in a monthly basis. Next best was the Thornthwaite’s method with correlation coefficient of 89% with pan evaporation. Piche methods performed relatively well with correlation coefficient of greater than 70%. Blaney-Criddle, Priestley & Taylor, and Hargreaves performed the poorest in predicting pan evaporation. These methods should be recalibrated for local condition and therefore not recommended for use in the Ethiopian highlands. In summary, the FAO-Penman Monteith is recommended for locations where the input data are available;otherwise, the Enku method using maximum daily temperature is best for estimating the reference evaporation.展开更多
文摘Recently there are signs of water quality impairment in Lake Tana, the largest fresh water in Ethiopia. The lake is the growth corridor of the government and supports millions of livelihood around. In order to sustain the benefit and maintain the ecosystem of the lake, the lake health has to be kept safe. Therefore monitoring and evaluation of the water quality of lake is very vital. This study focuses on current and previous trends water quality of the lake through measurements and Landsat Images near entry of Gumera River. Statistical analysis of the physical (Turbidity and STD and biological (Cha-a,) and chemical (DPC) water quality parameters were done. Linear and non-linear regression models between water quality parameter and reflectance of Landsat 7 ETM+ images were fitted based on band combinations. Pervious trend in turbidity was analyzed based on the regression models. The results showed that reflectance and turbidity satisfactorily result with an R2 ranging from 0.61 - 0.68. Form 1999-2014 the turbidity of the lake has indicated an increasing trend. Delta development near the entry of Gumera River has been enlarged by 48% because of an increase sediment inflow. The sign in the decreasing water quality of the lake was attributed to the non-point source sediment and nutrient inflow to the lake with high erosion rate from the watersheds. Measures to reduce the non-point source sediment and nutrient inflow by targeting the source areas (hot spots) in the agricultural watersheds need to be priority for stakeholders working on the soil and water conservation. Moreover, reducing the recession agriculture around the lake and wetland management could be crucial for improving lake water quality.
文摘Agricultural intensification to meet the food needs of the rapidly growing population in developing countries is negatively affecting the water quality. In most of these countries such as Ethiopia, information on surface and especially groundwater quality is lacking. This limits the measure that can be taken to stop pollution. We, therefore, investigated the spatial and temporal variation of groundwater quality in the upland watershed. Tikur-Wuha watershed was selected because it is located in the Lake Tana watershed, which is seeing the first signs of eutrophication. Groundwater samples were collected from July 2014 to June 2015 from 19 shallow wells located throughout the watershed. Collected water samples were analyzed both in situ and in the laboratory to determine pH, electric conductivity (EC) and total dissolved solid (TDS), concentration of chemicals (nitrate, dissolved phosphorus, calcium, magnesium, aluminum and iron) and Escherichia coli (E. coli). We found that shallow groundwater had greater chemical concentrations and E. coli level in the monsoon rain phase than in the dry phase. Wells located down slope exhibited greater concentrations than mid- and upper-slope positions, with the exception of the nitrate concentration that was less down slope, due to denitrification in the shallow groundwater. Only E. coli level was above the WHO drinking water quality standards. Further studies on groundwater quality should be carried out to understand the extent of groundwater contamination.
文摘Water is likely the most limiting factor in increasing agricultural production in large parts of Africa. Reference evaporation (ET0) is a key hydrological parameter to use efficiently the scarce supply. Several methods are available for predicting reference evaporation, but the accuracy of any of the methods has not been established for the Ethiopian highlands. The objective of this study is, therefore, to select the best methods for calculating the reference evaporation ET0. For the section, meteorological data of the Bahir Dar station were used, because all data needed for this study including the Class A pan Evaporation were recorded on a daily basis. Pan evaporation was considered as the best estimator of the reference evaporation. The results showed that the FAO-Penman Monteith (using solar radiation, wind speed, temperature and relative humidity) and Enku method (using only maximum daily temperatures) have acceptable daily ET0 ranges and predicted to Class A pan evaporation with correlation coefficients greater than 90% in a monthly basis. Next best was the Thornthwaite’s method with correlation coefficient of 89% with pan evaporation. Piche methods performed relatively well with correlation coefficient of greater than 70%. Blaney-Criddle, Priestley & Taylor, and Hargreaves performed the poorest in predicting pan evaporation. These methods should be recalibrated for local condition and therefore not recommended for use in the Ethiopian highlands. In summary, the FAO-Penman Monteith is recommended for locations where the input data are available;otherwise, the Enku method using maximum daily temperature is best for estimating the reference evaporation.
