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The colonization of freshwater lakes by invasive alien species is increasingly alarming primarily owing to nutrient loads from the watersheds. For the sustainable management of invasive weeds, preventive methods, such as watershed management and sustainable agricultural practices, are recommended. Watershed protection activities by the upstream local community are believed to be effective measures to reduce nutrient loading to the receiving water bodies and hence help prevent the spread of water hyacinth. However, their willingness and potential contributions determine the effectiveness of watershed management activities. The objective of this study is, therefore, to evaluate the preferences and contributions (willingness to pay and willingness to contribute labor) of the local community for the management of water hyacinth in Lake Tana (Ethiopia). A contingent valuation method for a hypothetical market "prevention of water hyacinth infestation of Lake Tana through watershed management program" was used to collect data from 560 randomly selected households. A multivariable interval regression model was used to identify factors affecting the contribution of local people. The mean yearly willingness to pay and to contribute labor of the respondents was 435.4 Ethiopian Birr (US$ 10) and 22.4 man-days, respectively. The place of residence (rural/urban), educational level, private farm plot area, annual income, and water hyacinth-related conference participation significantly influenced the willingness to pay. Similarly, the willingness to contribute labor was strongly associated with place of residence, location, educational level, and household family size. The economic value derived from this study reflects community preferences, which could be an input for informed and evidence-based decision-making regarding the prevention of weed expansion and sustainable use of ecosystem services. Therefore, local, regional, and national authorities are advised to mobilize the local community to contribute labor and/or money so as to halt the expansion of the weed., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Modeling of suspended sediment emission into freshwater lakes is challenging due to data gaps in developing countries. Existing models simulate sediment concentration at a gauging station upstream and none of these studies had modeled total suspended solids (TSS) emissions by inflowing rivers to freshwater lakes as there are no TSS measurements at the river mouth in the upper Blue Nile basin. In this study a 10year TSS time series data generated from remotely sensed MODIS/Terra images using established empirical relationship is applied to calibrate and validate a hydrology model for Lake Tana in Upper Blue Nile Basin. The result showed that at a monthly time scale TSS at the river mouth can be replicated with Nash-Sutcliffe efficiency (NS) of 0.34 for calibration and 0.21 for validation periods. Percent bias (PBIAS) and ratio of the root-mean-square error to the standard deviation of measured data (RSR) are all within range. Given the inaccessibility and costliness to measure TSS at river mouths to a lake the results found here are considered useful for suspended sediment budget studies in water bodies of the basin., (Copyright © 2015 Elsevier B.V. All rights reserved.)

We investigated the magnitude of reservoir sedimentation upstream and its sediment-shadow effect on a large downstream-linked lake, Lake Tana (Ethiopia). To better understand the reservoir-induced reductions of fluvial sediment downstream, sediment budgets for two scenarios were developed. The results indicated that reservoir sedimentation is extremely high, with annual storage capacity losses (1–4.2%) exceeding the global average. Consequently, unless mitigation measures are implemented, the reservoirs' dead storage volume will be filled with sediment in less than 42% of their designed life expectancy. The sediment-trapping conditions created by the reservoirs will also reduce sediment inflow from tributaries into the lake by 15–52%, overbank sedimentation on floodplains by 33–48%, and sediment deposition in Lake Tana by 16–54% annually. Overall, under the current environmental set-up, the ongoing and planned reservoir constructions could extend the expected useful lifetime of Lake Tana from 918 to 2022 years. [ABSTRACT FROM AUTHOR]

Lake Tana, which is the largest Lake in Ethiopia, has been invaded by water hyacinths since 2011. Although the government and the community have devoted considerable time and energy over a long period to removing the invasive weed mechanically and manually, the weed has been increasing significantly. Accurate, reliable, and timely information on the spatiotemporal distribution and extent of water hyacinth is crucial to determine its evolution, propagation, and potentially vulnerable areas of the Lake. Therefore, comprehensive information on the spatial distribution of water hyacinths and their annual and seasonal variability is essential for Lake Tana's water resource planning, development, and management. This study aims to evaluate the spatiotemporal pattern of water hyacinth and its dynamics with seasonal climate variability and impact on evapotranspiration. Landsat 7 ETM+, Landsat 8 OLI, and Sentinel 2 and meteorological datasets were employed. Supervised and manual digitization image classification methods were applied to prepare Land-use/ Land-cover in the Lake. The Mann–Kendall trend test and Pearson correlation coefficient were used to evaluate the trend of water hyacinth and the impact of climate variability on water hyacinth distribution respectively. Besides, the evapotranspiration and water losses were estimated using the FAO-56 Penman–Monteith method. The surface extent of the water hyacinth in Lake Tana has increased by 96% in 2019 from 2011. However, the surface area of the Lake has declined. That means 1603 ha of water surface area has been changed to land surface from 2011 to 2019. The average volume of water loss in Lake Tana was 0.21% of the volume of the Lake from September 2016 to December 2018. [ABSTRACT FROM AUTHOR]

Excess sediment and nutrient losses from intensifying agriculture degrade water quality and boost plant growth. The relationship between circulation patterns, spatial water quality degradation, and water hyacinth infestation is not adequately studied. The objective of this study is, therefore, to investigate the effect of lake circulation patterns on sediment and nutrient distribution and its implication on the spread of water hyacinth in a tropical lake. This study was carried out in Lake Tana, the largest freshwater lake in Ethiopia, where sediment and nutrient concentrations are increasing, and water hyacinths have become a challenge since 2011. The lake circulation pattern was simulated by the Delft3D model based on a bathymetry survey, discharge, and meteorological forcings. To predict the transport path of sediments and dissolved nutrients, an inert tracer was released in the four main river inlets of the lake. Observed lake water level measurements were used to validate the model. Our results show that the lake circulation pattern could explain the transport path of sediment and nutrients and the location of the water hyacinths found in the northeast of the lake. Sediments and nutrients from the largest river, Gilgel Abay, in the southeast of Lake Tana, flow through the two outlets nearby with little sediment deposition due to the relatively short retention time. The phosphorus-rich sediments of the 24 h at 105 °C remaining three main rivers joining the lake at the north and east are transported to the northeast. Thus, the management and control of water hyacinths should focus on the northern and eastern catchment areas of Lake Tana. [ABSTRACT FROM AUTHOR]

Lake Tana, the largest lake in Ethiopia, has been severely threatened by water hyacinth infestation over the last decade, especially along the northeastern shore. Since this invasive weed is extremely difficult to eradicate, sustainable management strategies should be put in place to reduce negative impacts on local ecological and socio-economic systems; this requires a better understanding of the population dynamics. In this paper, we review the seasonal change of water hyacinth coverage in Lake Tana and explore its linkages with various environmental factors. During the rainy seasons, increased nutrient concentrations, humidity, and especially water level can promote the formation of extensive water hyacinth mats. In the dry season, diminishing lake water in surrounding floodplains, along with concomitantly increased temperature and solar radiation, may support seed germination and lead to the next life cycle. Currently, water hyacinth mainly occurs in northeastern Lake Tana due to coastal eutrophication, lake topography and westerlies. Expansion of the infested area is slowing down. However, further spread of water hyacinth is still possible in other parts of the lake basin due to changing climate and environmental conditions. Integrated control methods should be put in place in the near future to prevent water hyacinth infestation in Lake Tana, and upstream basin management is vital to reduce nutrients transportation into the lake as a long-term plan. [ABSTRACT FROM AUTHOR]

Temperature and precipitation trend fluctuations influence the components of the hydrological cycle and the availability of water supplies and result shift in the balance of lake water (lake level). Lake Tana is one of the water resources potential providing many services and threatened by human-induced and natural factors in Upper Blue Nile Basin, Ethiopia. So assessing the impacts of climate change on this water resource is a primary activity for water resource managers, researchers, and stakeholders to understand its potential for the water resource. This study was therefore conducted to examine the implications of the influence of climate change on the water balance of Lake Tana (water level) using potential simulated climate production downscaled by a regional CORDEX climate model powered by GCM-RCM ensembles under the Eastern Africa domain CIMP5 archive (AFR44) and RCP scenarios (RCP4.5, and RCP8.5) for future climate data prediction. Quantile mapping has been used to correct temperature biases, and power transformation was applied for rainfall correction. The performance of the HBV model was evaluated through calibration and validation using objective functions (relative volume error (RVE), Nash-Sutcliffe Efficiency (NSE) and provide RVE of 3.7%, -1.27%, 1.05%, -0.72%, 8.9% and -0.68 during calibration and RVE of -1.5%, 6.93%, -3.04%,8.796%, -5.89% and 8.5% during validation for Gumara, Kiltie, Koga, Gilgel Abay, Megech and Rib respectively. While the model provided NS of 0.79, 0.63, 0.72, 0.803, 0.68 and 0.797 during calibration and NSE of 0.8, 0.64, 0.7, 0.82, 0.801 and 0.82 during validation for Gumara, Kiltie, Koga, Gilgel Abay, Megech, and Rib respectively. The simulated Lake level showed adequate agreement to the observed with NS and RVE of 0.7 and 6.44% respectively. The result showed that lake evaporation and rainfall increase for all future scenarios. The ungauged surface inflow is also increased shortly scenarios while gauged surface inflow increased for RCP4.5 (the 2070s) and RCP8.5 (2040s) and decreased for RCP4.5 (2040s) and RCP8.5 (2070s). The decrease in gauged surface water inflow is due to a decrease in inflow for Gilgel Abay, Koga and Gumara gauged catchments. The results showed that the Lake storage will decrease in all future scenarios of all-time horizons. As the study's revealed climate model minimized the level of uncertainty, especially with the use of more RCMs than GCMs, future studies should therefore use more than one regional climate model and also use fine resolution data like (CMIP 6). [ABSTRACT FROM AUTHOR]

The Blue Nile's source, Lake Tana, is the biggest lake in Ethiopia and offers multiple services to local, regional, and international communities. The first step to effectively, efficiently, and sustainably utilizing the services that the lake may provide is to understand its water balance using accurate estimations of its water balance parameters, including direct rainfall. Direct rainfall to Lake Tana is one of the most important water balance terms of the Lake that needs a precise estimate. This study tries to analyze the spatial and temporal variability of direct rainfall to the Lake and estimate the mean annual and mean monthly direct rainfall amount to the lake using sufficient data and appropriate methodologies. 30 years (1986–2015) monthly and mean annual data from 13 meteorological stations were collected and used to analyses the spatial and temporal variability. Spatial and statistical tools were used for data processing, analysis, and presentation. Five interpolation techniques:- Thiessen polygon, spline, isohyetal, inverse distance weighting, and Kriging were considered and their performances were assessed and compared using evaluation criteria. The results indicate that the Isohytal method is slightly better than the other four methods and it is also easy to implement in a geographic information system (GIS) with Geostatic Analysis in ArcGIS. Further, the analysis has shown that the mean annual direct rainfall to Lake Tana is 1313.43 mm with a standard deviation of 259.01. Besides, it has been seen that there is a significant spatial and temporal variability of direct rainfall on Lake Tana. In terms of spatial variability, the Lake gets maximum direct rainfall in its southeastern part with an annual mean value of 1720 mm and a minimum value in its northwest parts with an annual mean value of 860 mm. In terms of Temporal variability, maximum direct rainfall is estimated in July as 374.11 mm in the Summer season and the minimum is less than 12.3 mm depth in December, January, February, and March in Winter. [ABSTRACT FROM AUTHOR]

This study aimed at assessing the characteristics of water hyacinth biomass in Lake Tana. Explanatory research design was used based on biomass samples and satellite images acquired along with field observation and literature reviews. The results showed that high amount of N and P nutrients, shallow nature of the Lake and suitable climatic conditions of the area are the causes for the weeds' proliferation. The mean NDVI values were -0.542 to 0.828 and -0.628 to 0.877 in the dry and wet seasons, respectively. The spatial distribution of the weed was 2126.9 ha and 592.4 ha during the wet and dry seasons. The weed has recorded a mean leaf length of 9.3 cm, petiole length of 28.1 cm, root shoot ratio of 3.3, leaf blade area of 55.6 cm² and leaf area index of 11343.9 cm². In addition, a mean of 10.9 leaves per plant and 18.6 plants per 0.25m² was found. Furthermore, the biomass analysis revealed 1,990,787.8 tons of wet and 554,523.8 tons of dry water hyacinth biomass can be harvested from the Lake per year. Stakeholders shall work on control of water hyacinth biomass as a short-term measure and reduction of nutrient inflow into the Lake as a long-term measure. [ABSTRACT FROM AUTHOR]

Accelerated sediment concentration has become a pervasive feature in developing countries and has substantially impacted lake ecosystem functioning. Despite this, very few comprehensive studies have examined the changes in sedimentation over the time that agriculture intensified greatly with the increasing population. This study aims to fill this gap using historical and recent bathymetric surveys to determine sediment deposition and link these to watershed development. With its unique ecology, Lake Tana that was pristine less than 100 years ago, is one of these systems experiencing increasing sediment concentrations. A detailed bathymetric survey was conducted in late 2017 and compared with bathymetric surveys conducted in 1940, 1987, and 2006. The result shows that in the past 77 years, Lake Tana's depth decreased an average of 28 ± 11 cm, equivalent to nearly 0.9 ± 0.4 Tg (million tons). Sediment deposition was 2.8 ± 2.3 mm a−1 between 1940 and 1987, when the agricultural intensification started. It almost doubled to 5.0 ± 3.7 mm a−1 after that. Spatially, the sediment deposition was most significant in areas near the major river inlets where 2 to 10 km long peninsulas were formed. The increase in sediment deposition is primarily driven by newly formed valley bottom gullies formed after deforestation disturbed the hydrological equilibrium, and watershed outflow increased. [ABSTRACT FROM AUTHOR]

Lake Tana is a shallow inland lake with an average depth of 9 m. It is fresh water lake with the total area of 3150 km2.The lake level has experienced a rapid water level fluctuation in recent years. The study was aimed at analysing the water level fluctuation of Lake Tana. Four Landsat images acquired at different times from the United States Geological Survey have been processed and analysed by using the ERDAS and ARC-GIS softwares to detect changes in the lake area through time. In addition to this, the long-time lake level and climate data obtained from National Metrological Agency were analysed using a linear regression model to complement the lake level change. Focus group discussion, key informant interview and direct observation were held to analyse the impact of lake level fluctuation on the livelihood of the community. The result of the study indicated that more than 180 km2 of Lake Tana area has been converted to farm and other land uses during the last 35 years. The climate variability has been observed for the study period. There was continuous lake level fluctuation because of land-use changes, climate variability and water regulation for hydropower productions. Water level fluctuation of the lake had impacted on land use and its environment. The land use and regulated water at Chara Chara weirs, which are the contributing factors for Lake Tana water level fluctuation, should be managed regularly and critically. Abbreviations: ERDAS, Earth resource dynamic analysis system; GLCF, Global Land Cover Facility; FGD, Focus Group Discussions; IPCC, the Inter-Governmental Panel on Climate Change [ABSTRACT FROM AUTHOR]

Understanding populations' genetic connectivity is critical for conservation and management measures. Most population connectivity studies conducted in aquatic plants have been centered on linearly arranged systems wherein a cline in genetic diversity is expected to the downstream. However, non-linear systems and lakes characterized by hydrological mixing, circulation, and strong discharge might not support this assumption. Considering these processes and the mixed reproductive mechanisms of Cyperus papyrus (L.), we assessed the relative role of hydrological connectivity and vegetative dispersal in shaping the clonal and genetic structure of the species. Four hundred and two papyrus individuals from 13 populations fringing Lake Tana, Ethiopia, were genotyped using 15 microsatellite markers. Despite the genetic bottleneck detected, papyrus populations maintained moderate levels of clonal (R = 0.48) and genetic diversity (HE = 0.40). We found a significant within-lake level of genetic differentiation (F′ST = 0.16; DEST = 0.10). Bayesian analysis assigned individuals to three non-panmictic genetic clusters. Evidences of long-distance vegetative dispersal and asymmetrical contemporary migration were detected among C. papyrus populations. The patterns of the genetic structure, clonal dispersal, and migration rate partly correspond to the surface flow. Overall, hydrological connectivity and vegetative dispersal shape the clonal and genetic structure as well as the connectivity of C. papyrus populations in Lake Tana. [ABSTRACT FROM AUTHOR]

The purpose of this research is to analyse how the public, media, government, donors, partners, non-governmental organisations, and civil society, in particular or the stakeholders in general, have participated in the campaign of fighting water hyacinth in Lake Tana. The stakeholders such as researchers, journalists, individuals, youth and practitioners of the environment have begun promoting the problem in different media, concerts, workshops, conferences, and meetings. The major reason is that the length of shoreline infested by the weed has increased alarmingly. Specifically, water hyacinth expansion in Lake Tana is becoming worse. This is the major source of the loss of biodiversity in the lake. However, the multifaceted efforts to save Lake Tana are the highest endeavour to protect against the invasive water hyacinth. Based on the empirical data, the findings show that most of the campaigns are not based on strategic participatory planning. Above all, stakeholders’ participation has not been well institutionalised in Ethiopia. Thus, the stakeholders’ role in environmental management is limited. The efforts are not well planned and sustained. The identification of the water hyacinth problem was delayed. Consequently, minimal attention was given by the stakeholders. [ABSTRACT FROM AUTHOR]

The cryopreservation of the Lake Tana Labeobarbus semen had never been studied before. A combination of three extenders and two cryoprotectants (DMSO and glycerol) were used in Lake Tana Labeobarbus brevicephalus sperm cryopreservation. Among the above described cryo-diluent DMSO 10% had the best performance with all three extenders. Sperm of the L. brevicephalus maintained a higher fertilization rate in the three extenders at a dilution ratio of 1:3 (≥ 85%), exceptionally in Extender 2 DMSO 15% sperm displayed lower value 55.9 ± 0.3%. When pre-frozen cryoprotectants milt diluted at a ratio of 1:9, it provided higher fertilization rates in Extender 1 10% DMSO, Extender 3 glycerol 10% and DMSO 15% (92–97%). Highest equilibration (87.3 ± 1.5%) and post-thaw (83.0 ± 1%) motility were obtained from the diluent, Extender 3 plus DMSO 10%, which proved its suitability for preservation of sperm of the L. brevicephalus. The developed protocol suggests formulating an extending medium comprising of Extender 3 with 10% DMSO, 15% DMSO or Extender 1 with 10% DMSO and the dilution ratio of the cryoprotectant to milt should be 1:3. Two different single-step cooling rates (4 and 10 °C/min) were used. Additional studies should evaluate the viability, survival, and development of larvae produced from cryopreserved sperm. Besides, for sustainable use of sperm suitable oocyte sperm ratios and the feasibility of cryogenic gene banking should be investigated. [ABSTRACT FROM AUTHOR]

This paper surveys some major questions on the evolution of eight piscivorous Barbus species (B. acutirostris, B. dainellii, B. gorguari, B. longissimus, B. megastoma, B. platydorsus, B.truttiformis, and B. macrophtalmus), which together with six other species compose the endemic hexaploid ‘large barb’ species flock of Lake Tana. Preliminary data suggest that the major prey species of these piscivores (up to 90 cm length), in contrast to previous reports, is not Barbus trispilopleura, but at least two other diploid ‘small barb’ species (< 10 cm). Data are collected from 1) the resource partitioning of the piscivores in the field, 2) aquarium experiments on the predator success in catching different prey species and size classes, 3) analyses on allometric growth and diet shifts in the field and 4) molecular genetic data, which will be combined to construct a hypothesis on the process of the evolution of these piscivorous barbs. Being the major target of commercial fisheries, knowledge on these piscivorous fish stocks and their prey species is required for aiming at sustainable fisheries. Preliminary data show a serious decline of fish stocks, most probably largely due to overexploiting their spawning grounds. [ABSTRACT FROM AUTHOR]

The largest freshwater lake in Ethiopia, Lake Tana, has faced ecological disaster due to water hyacinth (Eichhornia crassipes) infestation. The water hyacinth is a threat not only to the ecology but also to the socioeconomic development of the region and cultural value of the lake, which is registered as a UNESCO reserve. This study aims to map the spatiotemporal dynamics of the water hyacinth using high-resolution PlanetScope satellite images and assesses the major environmental variables that relate to the weed spatial coverage dynamics for the period August 2017 to July 2018. The plausible environmental factors studied affecting the weed dynamics include lake level, water and air temperature, and turbidity. Water temperature and turbidity were estimated from the moderate resolution imaging spectroradiometer (MODIS) satellite image and the water level was estimated using Jason-1 altimetry data while the air temperature was obtained from the nearby meteorological station at Bahir Dar station. The results indicated that water hyacinth coverage was increasing at a rate of 14 ha/day from August to November of 2017. On the other hand, the coverage reduced at a rate of 6 ha/day from December 2017 to June 2018. However, the length of shoreline infestation increased significantly from 4.3 km in August 2017 to 23.4 km in April 2018. Lake level and night-time water temperatures were strongly correlated with water hyacinth spatial coverage (p < 0.05). A drop in the lake water level resulted in a considerable reduction of the infested area, which is also related to decreasing nutrient levels in the water. The water hyacinth expansion dynamics could be altered by treating the nutrient-rich runoff with best management practices along the wetland and in the lake watershed landscape. [ABSTRACT FROM AUTHOR]

Water hyacinth is a well-known invasive weed in lakes across the world and harms the aquatic environment. Since 2011, the weed has invaded Lake Tana substantially posing a challenge to the ecosystem services of the lake. The major factors which affect the growth of the weed are phosphorus, nitrogen, temperature, pH, salinity, and lake depth. Understanding and investigating the hotspot areas is vital to predict the areas for proper planning of interventions. The main objective of this study is therefore to predict the hotspot areas of the water hyacinth over the surface of the lake using the geographical information system (GIS)-based multi-criteria evaluation (MCE) technique. The main parameters used in the multi-criteria analysis were total phosphorus (>0.08 mg L−1), total nitrogen (>1.1 mg L−1), temperature (<26.2 °C), pH (<8.6), salinity (<0.011%), and depth (<6 m). These parameters were collected from 143 sampling sites on the lake in August, December (2016), and March (2017). Fuzzy overlay spatial analysis was used to overlay the different parameters to obtain the final prediction map of water hyacinth infestation areas. The results indicated that 24,969 ha (8.1%), 21,568.7 ha (7.1%), and 24,036 ha (7.9%) of the lake are susceptible to invasion by the water hyacinth in August, December, and March, respectively. At the maximum historical lake level, 30,728.4 ha will be the potential susceptible area for water hyacinth growth and expansion at the end of the rainy season in August. According to the result of this study, the north and northeastern parts of the lake are highly susceptible for invasion. Hence, water hyacinth management and control plans shall mainly focus on the north and northeastern part of Lake Tana and upstream contributing watersheds. [ABSTRACT FROM AUTHOR]

Lake Tana is the largest lake in Ethiopia, and its lake outflow is the source of the Blue Nile River that provides vital water resources for many livelihoods and downstream/international stakeholders. Therefore, it is essential to quantify and monitor the water balance of Lake Tana. However, Lake Tana is poorly gauged, with more than 50% of Lake Tana Basin being ungauged from in-situ measurements, making it difficult to quantify the lake inflow from surrounding basins. The lack of in-situ measurements highlights the need for the innovative application of satellite remote sensing. This study explores how freely accessible satellite remote sensing can be used to complement routine weather data to quantify the water balance of Lake Tana and its surrounding catchments. This study particularly investigates whether the outflow from Lake Tana can be estimated with sufficient accuracy as the residual of the lake water balance. Monthly inflow into lake was computed as the total runoff from the surrounding catchments; the runoff was estimated as the residual of the land-based catchment water balance using satellite precipitation improved with an integrated downscaling-calibration procedure, satellite evapotranspiration, and a correction term for changes in land total storage (soil moisture storage and deep percolation). The outflow from Lake Tana was estimated as the residual of lake water balance by combining satellite-based lake precipitation, changes in water storage, and lake inflow with estimated lake evaporation. Evaluation using limited available measurements showed that estimated annual runoff for two gauged subbasins agreed well with measurements, with differences within 4%. The estimated annual outflow from Lake Tana was also close to measured outflow, with a difference of 12%. However, the estimated monthly runoff from catchments and monthly lake outflow were unsatisfactory, with large errors. [ABSTRACT FROM AUTHOR]