Your search found 10 records
1 Yilak, D. L.; Tilahun, S. A.; Schmitter, Petra; Nakawuka, Prossie; Enku, T.; Kassawmar, N. T.; Steenhuis, T. S. 2015. Determining the groundwater potential for agricultural use in Ethiopian Highlands [Abstract only] Paper presented at the 10th Alexander von Humboldt Conference 2015 on Water-Food-Energy River and Society in the Tropics. EGU Topical Conference Series, Addis Ababa, Ethiopia, 18-20 November 2015. 2p.
Agriculture ; Groundwater irrigation ; Groundwater recharge ; Water levels ; Water use ; Highlands ; Irrigation water ; Water levels ; Watersheds ; Sustainability ; Case studies / Ethiopia / Ethiopian Highlands / Robit-Bata watershed / Lake Tana
(Location: IWMI HQ Call no: e-copy only Record No: H047278)
(0.01 MB)
The Ethiopian government has declared the Lake Tana - Beles region to be a growth corridor and irrigation development is one of the priorities. Since the dry season river flow is limited, groundwater has the greatest potential for increasing irrigation in the near future. The main drawback is lack of information on sustainable groundwater use and specifically the ground water potential. Therefore the objective of this research is to calculate the annual groundwater recharge. The study was conducted in Robit-Bata, an experimental watershed of 911 ha, located at the south-eastern edge of Lake Tana. Farmers have excavated more than 300 hand dug wells for irrigation use from which, we used 50 wells for water table fluctuation observations for one year starting from April, 2014. Daily Precipitation was recorded for the same period. The annual recharge was estimated using the water – level fluctuation method. Specific yield was defined as the difference of porosity and field capacity of the subsurface formation. The annual average areal groundwater recharge was 640 mm/year, which is 41% of the rainfall and ranged from 50mm to 390mm per week for the various locations in the watershed. The greatest recharge amounts were found in the plains at the foot of the hills and river course areas consisting mostly weathered basalt rock. At those locations the groundwater rose steadily during the rainy monsoon phase. Smaller amount of recharge occurred both near the top of the hills with tough rock formation and in the, flat areas near to stream with sandy and clay deposits and groundwater at, shallow well depth. Our study indicates that the current use of the groundwater seems sustainable. Further research is required for optimized utilization of the limited groundwater resources for irrigation development to meet the food security of the community.
2 Hussein, M. A.; Muche, H.; Schmitter, Petra; Nakawuka, P.; Tilahun, S. A.; Langan, Simon; Barron, Jennie; Steenhuis, T. S. 2019. Deep tillage improves degraded soils in the (sub) humid Ethiopian highlands. Land, 8(11):1-15. [doi: https://doi.org/10.3390/land8110159]
Agricultural production ; Deep tillage ; Soil degradation ; Humid zones ; Highlands ; Watersheds ; Conventional tillage ; Hardpans ; Sediment ; Rain ; Runoff ; Soil loss ; Soil moisture ; Infiltration ; Maize ; Crop yield / Ethiopia / Robit-Bata Watershed
(Location: IWMI HQ Call no: e-copy only Record No: H049375)
(2.40 MB) (2.40 MB)
Intensification of rainfed agriculture in the Ethiopian highlands has resulted in soil degradation and hardpan formation, which has reduced rooting depth, decreased deep percolation, and increased direct runoff and sediment transport. The main objective of this study was to assess the potential impact of subsoiling on surface runoff, sediment loss, soil water content, infiltration rate, and maize yield. Three tillage treatments were replicated at five locations: (i) no tillage (zero tillage), (ii) conventional tillage (ox-driven Maresha plow, up to a depth of 15 cm), and (iii) manual deep ripping of the soil’s restrictive layers down to a depth of 60 cm (deep till). Results show that the posttreatment bulk density and penetration resistance of deep tillage was significantly less than in the traditional tillage and zero-tillage systems. In addition, the posttreatment infiltration rate for deep tillage was significantly greater, which resulted in significantly smaller runoff and sedimentation rates compared to conventional tillage and zero tillage. Maize yields were improved by 6% under deep tillage compared to conventional tillage and by 29% compared to no tillage. Overall, our findings show that deep tillage can be effective in overcoming some of the detrimental effects of hardpans in degraded soils.
3 Tilahun, S. A.; Yilak, D. L.; Schmitter, Petra; Zimale, F. A.; Langan, Simon; Barron, Jennie; Parlange, J.-Y.; Steenhuis, T. S. 2020. Establishing irrigation potential of a hillside aquifer in the African highlands. Hydrological Processes, 34(8):1741-1753. [doi: https://doi.org/10.1002/hyp.13659]
Aquifers ; Highlands ; Sloping land ; Groundwater table ; Groundwater recharge ; Irrigation water ; Wells ; Water budget ; Water storage ; Water availability ; Water levels ; Hydrometeorology ; Monitoring ; Infiltration ; Runoff ; Discharges ; Rain ; Watersheds ; Small scale systems ; Farmer-led irrigation ; Models / Africa South of Sahara / Ethiopia / Lake Tana / Robit Bata Watershed
(Location: IWMI HQ Call no: e-copy only Record No: H049535)
https://onlinelibrary.wiley.com/doi/epdf/10.1002/hyp.13659
https://vlibrary.iwmi.org/pdf/H049535.pdf
https://vlibrary.iwmi.org/pdf/H049535.pdf
(3.92 MB) (3.92 MB)
Feeding 9 billion people in 2050 will require sustainable development of all water resources, both surface and subsurface. Yet, little is known about the irrigation potential of hillside shallow aquifers in many highland settings in sub-Saharan Africa that are being considered for providing irrigation water during the dry monsoon phase for smallholder farmers. Information on the shallow groundwater being available in space and time on sloping lands might aid in increasing food production in the dry monsoon phase. Therefore, the research objective of this work is to estimate potential groundwater storage as a potential source of irrigation water for hillside aquifers where lateral subsurface flow is dominant. The research was carried out in the Robit Bata experimental watershed in the Lake Tana basin which is typical of many undulating watersheds in the Ethiopian highlands. Farmers have excavated more than 300 hand dug wells for irrigation. We used 42 of these wells to monitor water table fluctuation from April 16, 2014 to December 2015. Precipitation and runoff data were recorded for the same period. The temporal groundwater storage was estimated using two methods: one based on the water balance with rainfall as input and baseflow and evaporative losses leaving the watershed as outputs; the second based on the observed rise and fall of water levels in wells. We found that maximum groundwater storage was at the end of the rain phase in September after which it decreased linearly until the middle of December due to short groundwater retention times. In the remaining part of the dry season period, only wells located close to faults contained water. Thus, without additional water sources, sloping lands can only be used for significant irrigation inputs during the first 3 months out of the 8 months long dry season.
4 Sishu, F. K.; Thegaye, E. K.; Schmitter, Petra; Habtu, N. G.; Tilahun, S. A.; Steenhuis, T. S. 2020. Endosulfan pesticide dissipation and residue levels in khat and onion in a sub-humid region of Ethiopia. In Habtu, N. G.; Ayele, D. W.; Fanta, S. W.; Admasu, B. T.; Bitew, M. A. (Eds.). Advances of science and technology. Proceedings of the 7th EAI International Conference on Advancement of Science and Technology (ICAST 2019), Bahir Dar, Ethiopia, 2-4 August 2019. Cham, Switzerland: Springer. pp.16-28. (Lecture Notes of the Institute for Computer Sciences, Social Informatics and Telecommunications Engineering (LNICST) Volume 308) [doi: https://doi.org/10.1007/978-3-030-43690-2_2]
Pesticide application ; Endosulfan ; Pesticide residues ; Crop production ; Catha edulis ; Onions ; Subhumid zones ; Wet season ; Dry season ; Farmers / East Africa / Ethiopia / Robit Bata Watershed
(Location: IWMI HQ Call no: e-copy only Record No: H049711)
(0.86 MB)
Endosulfan, a mixture of a- and ß-isomers, is used by farmers in the wet and dry season for khat and onion production. Khat leaf samples were collected in farmer fields at intervals of 1 h; 1, 5, 9 and 14 d after application. The dissipation rate of a- and ß-isomers and residue level in khat were compared with residue levels in onion. The extraction was done by using Quick Easy Cheap Effective Rugged and Safe (QuEChERS) method and analyzed by Gas Chromatography – Electron Capture Detector (GC-ECD). Greater residue a- and ß-isomer endosulfan levels were found in khat compared to onion as khat leaves are sprayed repeatedly in two week. Residue levels of khat exceeded the tolerable EU limit of 0.05 mg.kg-1 for leafy vegetables and herbs. For both raw and processed onion sample a- and ßendosulfan residues level were below the tolerable of limit EU regulation for bulb vegetables (i.e. 0. 1 mg.kg-1). The mean half-life for the a-isomer of endosulfan was 3.4 d in the wet season and 3.6 d in the dry season whilst that for the ß-isomer was 5.0 d and 5.4 d respectively. Both isomers dissipated fastest in the wet season under conditions of high humidity and precipitation. The ß-isomer persisted longer and had a lower dissipation rate from plants surface compared to the a-isomer.
5 Setargie, T. A.; Tilahun, S. A.; Schmitter, Petra; Moges, M. A.; Gurmessa, S. K.; Tsunekawa, A.; Tsubo, M.; Berihun, M. L.; Fenta, A. A.; Haregeweyn, N. 2021. Characterizing shallow groundwater in hillslope aquifers using isotopic signatures: a case study in the Upper Blue Nile Basin, Ethiopia. Journal of Hydrology: Regional Studies, 37:100901. [doi: https://doi.org/10.1016/j.ejrh.2021.100901]
Groundwater ; Watersheds ; Shallow wells ; Rain ; Stream flow ; Aquifers ; Runoff ; Dry season ; Irrigation ; Hydrographs ; Stable isotopes ; Case studies / Ethiopia / Upper Blue Nile Basin / Robit-Bata Watershed
(Location: IWMI HQ Call no: e-copy only Record No: H050667)
https://www.sciencedirect.com/science/article/pii/S2214581821001300/pdfft?md5=82c851f6dd4a1f7669a9017af2d7bf8c&pid=1-s2.0-S2214581821001300-main.pdf
https://vlibrary.iwmi.org/pdf/H050667.pdf
https://vlibrary.iwmi.org/pdf/H050667.pdf
(4.32 MB) (4.32 MB)
Study region: Robit-Bata watershed, Upper Blue Nile basin, Ethiopia.
Study focus: Stable isotopes of water (Oxygen-18 and Deuterium) were used as tracers to estimate the contribution of groundwater in shallow hillslope aquifers to streamflow in the Robit-Bata watershed. To assess the spatiotemporal variability of shallow groundwater and develop a hydrograph separation technique, we collected rainfall, shallow groundwater, and streamflow samples and analyzed their d18O and d2 H isotopic compositions. The local meteoric water line (LMWL) and local evaporative line (LEL) of the study area were determined and compared with the global meteoric water line (GMWL). A standard unweighted two-component isotope-based hydrograph separation model was used to determine the percentage contribution of shallow groundwater to streamflow.
New hydrological insights for the region: The LMWL (d2 H = 8.63·d18O + 18.2) mostly showed heavy isotopic enrichment relative to GMWL, and the LEL (d2 H = 5.45·d18O + 6.96) indicated isotopic enrichment compared to Ethiopian lakes. Shallow groundwater responded rapidly to rainfall, with good spatial correlation depending on topographic positions of wells. Pre-event water contributed 90% when the watershed reached maximum storage. This finding gives insight towards the predominant runoff generation process and has significant implications for sustainable dry season irrigation expansion in the area as the sub-surface flow drains out of the watershed from October onwards reducing water tables in the shallow wells.
Study focus: Stable isotopes of water (Oxygen-18 and Deuterium) were used as tracers to estimate the contribution of groundwater in shallow hillslope aquifers to streamflow in the Robit-Bata watershed. To assess the spatiotemporal variability of shallow groundwater and develop a hydrograph separation technique, we collected rainfall, shallow groundwater, and streamflow samples and analyzed their d18O and d2 H isotopic compositions. The local meteoric water line (LMWL) and local evaporative line (LEL) of the study area were determined and compared with the global meteoric water line (GMWL). A standard unweighted two-component isotope-based hydrograph separation model was used to determine the percentage contribution of shallow groundwater to streamflow.
New hydrological insights for the region: The LMWL (d2 H = 8.63·d18O + 18.2) mostly showed heavy isotopic enrichment relative to GMWL, and the LEL (d2 H = 5.45·d18O + 6.96) indicated isotopic enrichment compared to Ethiopian lakes. Shallow groundwater responded rapidly to rainfall, with good spatial correlation depending on topographic positions of wells. Pre-event water contributed 90% when the watershed reached maximum storage. This finding gives insight towards the predominant runoff generation process and has significant implications for sustainable dry season irrigation expansion in the area as the sub-surface flow drains out of the watershed from October onwards reducing water tables in the shallow wells.
6 Fenta, H. M; Hussein, M. A.; Tilahun, S. A.; Nakawuka, Prossie; Steenhuis, T. S.; Barron, Jennie; Adie, A.; Blummel, M.; Schmitter, Petra. 2022. Berken plow and intercropping with pigeon pea ameliorate degraded soils with a hardpan in the Ethiopian highlands. Geoderma, 407:115523. [doi: https://doi.org/10.1016/j.geoderma.2021.115523]
Agricultural production ; Intercropping ; Maize ; Pigeon peas ; Soil penetration resistance ; Soil degradation ; Soil analysis ; Hardpans ; Soil moisture ; Tillage ; Rainfed farming ; Runoff ; Water storage ; Highlands ; Smallholders ; Farmers ; Economic analysis ; Crop yield ; Soil chemicophysical properties ; Infiltration ; Sediment ; Watersheds / Ethiopia / Amhara / Robit Bata Watershed
(Location: IWMI HQ Call no: e-copy only Record No: H050790)
https://www.sciencedirect.com/science/article/pii/S0016706121006030/pdfft?md5=1a75bfbda044c2e453917450c6e20dab&pid=1-s2.0-S0016706121006030-main.pdf
https://vlibrary.iwmi.org/pdf/H050790.pdf
https://vlibrary.iwmi.org/pdf/H050790.pdf
(8.62 MB) (8.62 MB)
Closing the yield gap and enhancing efficiency in rainfed maize production systems in Ethiopia requires urgent action in increasing the productivity of degraded agricultural land. The degradation of land through continuous compaction and decline in the organic matter has resulted in a wide-spread formation of a hardpan that restricts deep percolation, prevents plant root development, and, ultimately can lead to increased erosion. Studies exploring practical low-cost solutions to break the hardpan are limited in Ethiopia. The main objective was to evaluate soil mechanical (i.e. modified plow or Berken plow) or biological intervention (i.e. intercropping with pigeon pea) effectiveness to enhance soil water management and crop yield of rainfed maize systems whilst reducing soil erosion and runoff. Five farm fields, each including four plots with different tillage treatments, were monitored during two rainy seasons in 2016 and 2017. The treatments were: (i) farmers practice under conventional (CT) tillage; plots tilled three times using an oxen driven local plow Maresha, (ii) no-till (NT), (iii) Berken tillage (BT), plots tilled three times using an oxen pulled Berken plow, and (iv) biological (CT + Bio), taprooted pigeon pea intercropped with maize on plots conventionally tilled. Results showed that mean tillage depth was significantly deeper in the BT (28 cm) treatment compared to CT and CT + Bio (18 cm) treatments. Measured soil penetration resistance significantly decreased up to 40 cm depth under BT and maize roots reached 1.5 times deeper compared to roots measured in the CT treatment. Under BT, the estimated water storage in the root zone was estimated at 556 mm, 1.86 times higher compared to CT, 3.11 times higher compared to NT and 0.89 times higher compared to CT + Bio. The positive effects on increased water storage and root development resulted in an average increase in maize grain (i.e. 15%, 0.95 t ha- 1 ) and residual above ground biomass (0.3%, 6.4 t ha- 1 ) leading to a positive net benefit of 138 USD ha- 1 for the BT treatment compared to the CT treatment. The negative net benefit obtained under CT and CT+Bio was mainly related to the high labor cost related to plowing, weeding, planting, and fertilizer application whilst in the NT this was related to the significantly lower maize yields. The positive effects in the BT treatment, and to some extent the CT+Bio treatment show great potential for smallholder rainfed maize systems where degraded soils with hardpans and high variability in rainfall prevail.
7 Sishu, F. K.; Bekele, A. M.; Schmitter, Petra; Tilahun, S. A.; Steenhuis, T. S. 2021. Phosphorus export from two contrasting rural watersheds in the (sub) humid Ethiopian highlands. Frontiers in Earth Science, 9:762703. [doi: https://doi.org/10.3389/feart.2021.762703]
Highlands ; Phosphorus ; Watersheds ; Rural areas ; Runoff ; Soil loss ; Precipitation ; Discharges ; Land use ; Sediment / Africa South of Sahara / Ethiopia / Dangishta Watershed / Robit Bata Watershed
(Location: IWMI HQ Call no: e-copy only Record No: H050851)
https://www.frontiersin.org/articles/10.3389/feart.2021.762703/pdf
https://vlibrary.iwmi.org/pdf/H050851.pdf
https://vlibrary.iwmi.org/pdf/H050851.pdf
(4.00 MB) (4.00 MB)
Establishing worldwide sustainable and phosphorus efficient cropping systems is urgently needed because the supply of suitable phosphate rock is limited, and excess phosphorus in streams causes eutrophication. One of the impediments in the developing world for sustainable P practices is the lack of studies on P transport and its eventual disposition in the environment. One of these regions with few studies is the Ethiopian Highlands, with permeable volcanic soils. The objective was to establish baseline data on P watershed export in the (sub)humid highlands. Two contrasting watersheds were selected near Lake Tana. For 2 years, stream discharge and sediment, total P, dissolved P, and bioavailable particulate P concentrations were determined at the watershed outlet. The first watershed is the 57 km2 Dangishta, with lava intrusion dikes, forcing subsurface flow through faults to the surface and preventing gully formation. Subsurface flow was half of the 1745 mm annual precipitation, and surface runoff and erosion were minimal. The second watershed is the 9 km2 Robit Bata with 1,420 mm precipitation. The banks of several river banks were slumping. The upper part of the watershed generates saturation excess runoff. A hillslope aquifer in the lower part provided interflow. The average sediment concentrations of 10.5 g L-1 in the stream in Robit Bata (11 times that in Dangishta) reflected the sediments from banks slipping in the stream. The hydrology and the soil loss directly affected the phosphorus export. In Dangishta, the total P concentration averaged 0.5 mg L-1 at the outlet. In Robit Bata, the average total P concentration was 2 mg L-1 . The bioavailable particulate P concentration was only twice the concentration in the runoff water. The low phosphorus content of the subsoil slipping in Robit Bata moderated biologically available particulate P at the outlet. Average dissolved P concentrations for both watersheds were around 0.1 mg L-1 in the low range found in temperate climates. It reflects the difference in length of time that phosphorus fertilizers have been applied. Our research concludes that commonly implemented practices such as strengthening river banks and stabilizing gully might not lead to improved water quality in Lake Tana.
8 Sishu, F. K.; Tilahun, Seifu A.; Schmitter, Petra; Steenhuis, T. S. 2023. Investigating nitrate with other constituents in groundwater in two contrasting tropical highland watersheds. Hydrology, 10(4):82. (Special issue: Editorial Board Members’ Collection Series: Integrated Surface Water and Groundwater Resources Management) [doi: https://doi.org/10.3390/hydrology10040082]
Groundwater table ; Nitrates ; Watersheds ; Highlands ; Volcanic areas ; Aquifers ; Wells ; Precipitation ; Rainfall ; Chlorides ; Ammonia ; Fertilizers ; Runoff / Africa South of Sahara / Ethiopia / Lake Tana Basin / Dangishta Watershed / Robit Bata Watershed
(Location: IWMI HQ Call no: e-copy only Record No: H051839)
https://www.mdpi.com/2306-5338/10/4/82/pdf?version=1680523739
https://vlibrary.iwmi.org/pdf/H051839.pdf
https://vlibrary.iwmi.org/pdf/H051839.pdf
(8.28 MB) (8.28 MB)
Nitrate is globally the most widespread and widely studied groundwater contaminant. However, few studies have been conducted in sub-Saharan Africa, where the leaching potential is enhanced during the rainy monsoon phase. The few monitoring studies found concentrations over drinking water standards of 10 mg N-NO3 - L -1 in the groundwater, the primary water supply in rural communities. Studies on nitrate movement are limited to the volcanic Ethiopian highlands. Therefore, this study aimed to evaluate the transport and fate of nitrate in groundwater and identify processes that control the concentrations. Water table height, nitrate, chloride, ammonium, reduced iron, and three other groundwater constituents were determined monthly in the groundwater in over 30 wells in two contrasting volcanic watersheds over two years in the Ethiopian highlands. The first watershed was Dangishta, with lava intrusion dikes that blocked the subsurface flow in the valley bottom. The water table remained within 3 m of the surface. The second watershed without volcanic barriers was Robit Bata. The water table dropped rapidly within three months of the end of the rain phase and disappeared except near faults. The average nitrate concentration in both watersheds was between 4 and 5 mg N-NO3 - L -1 . Hydrogeology influenced the transport and fate of nitrogen. In Dangishta, water was blocked by volcanic lava intrusion dikes, and residence time in the aquifer was larger than in Robit Bata. Consequently, nitrate remained high (in several wells, 10 mg N-NO3 - L -1 ) and decreased slowly due to denitrification. In Robit Bata, the water residence time was lower, and peak concentrations were only observed in the month after fertilizer application; otherwise, it was near an average of 4 mg N-NO3 - L -1 . Nitrate concentrations were predicted using a multiple linear regression model. Hydrology explained the nitrate concentrations in Robit Bata. In Dangishta, biogeochemistry was also significant.
9 Sishu, F. K.; Tilahun, Seifu A.; Schmitter, Petra; Steenhuis, T. S. 2024. Revisiting the Thornthwaite Mather procedure for baseflow and groundwater storage predictions in sloping and mountainous regions. Journal of Hydrology X, 24:100179. (Online first) [doi: https://doi.org/10.1016/j.hydroa.2024.100179]
Groundwater table ; Water storage ; Sloping land ; Aquifers ; Highlands ; Watersheds ; Groundwater recharge ; Stream flow ; Water balance ; Precipitation ; Discharge ; Models / Ethiopia / Dangishta Watershed / Robit Bata Watershed
(Location: IWMI HQ Call no: e-copy only Record No: H052843)
https://www.sciencedirect.com/science/article/pii/S2589915524000099/pdfft?md5=fcd021fe86a9e1229d0a54c3a5071e78&pid=1-s2.0-S2589915524000099-main.pdf
https://vlibrary.iwmi.org/pdf/H052843.pdf
https://vlibrary.iwmi.org/pdf/H052843.pdf
(4.69 MB) (4.69 MB)
Hillslope aquifers regulate streamflow and are a critical potable and irrigation water source, especially in developing countries. Knowing recharge and baseflow is essential for managing these aquifers. Methods using available data to calculate recharge and baseflow from aquifers are not valid for uplands. This paper adapts the Thornthwaite and Mather (T-M) procedure from plains to sloping and mountainous regions by replacing the linear reservoir with a zero-order aquifer. The revised T-M procedure was tested over four years in two contrasting watersheds in the humid Ethiopian highlands: the 57 km2 Dangishta with a perennial stream and the nine km2 Robit Bata, where the flow ceased four months after the end of the rain phase. The monthly average groundwater tables were predicted with an accuracy ranging from satisfactory to good for both watersheds. Baseflow predictions were “very good” after considering the evaporation from shallow groundwater in the valley bottom during the dry phase in Dangishta. We conclude that the T-M procedure is ideally suited for calculating recharge, baseflow and groundwater storage in upland regions with sparse hydrological data since the procedure uses as input only rainfall and potential evaporation data that are readily available together with an estimate of the aquifer travel time.
10 Sishu, F. K.; Tilahun, S. A.; Schmitter, Petra; Assefa, G.; Steenhuis, T. S. 2022. Pesticide contamination of surface and groundwater in an Ethiopian highlands’ watershed. Water, 14(21):3446. [doi: https://doi.org/10.3390/w14213446]
Pesticides ; Chemical contamination ; Surface water ; Groundwater ; Water pollution ; Highlands ; Watersheds ; Lakes ; Ecotoxicity ; Aquatic organisms ; Fish ; Human health ; Risk assessment ; Farmers / Africa South of Sahara / Ethiopia / Lake Tana Basin / Robit Bata Watershed
(Location: IWMI HQ Call no: e-copy only Record No: H052844)
https://www.mdpi.com/2073-4441/14/21/3446/pdf?version=1667996326
https://vlibrary.iwmi.org/pdf/H052844.pdf
https://vlibrary.iwmi.org/pdf/H052844.pdf
(4.12 MB) (4.12 MB)
Agricultural intensification in sub-Saharan African countries has significantly increased pesticide applications. Information on pesticide residues and their transport in groundwater and streams is needed to properly manage and reduce any harm to the ecosystem and environment. This information is lacking in the volcanic soils of Ethiopian highlands. Therefore, this study was conducted to assess pesticide concentrations in ground and surface water and their risk to humans and aquatic life. The 9 km2 rural watershed Robit Bata in the Lake Tana Basin was selected. Crops were grown under rainfed and irrigated conditions. Pesticide use was assessed, and groundwater samples were collected from eight wells and surface water samples at the outlet twice in the rain phase and once in the dry phase. Samples were analyzed for chlorpyrifos, dimethoate, (a and ß) endosulfan, profenofos, NO- 3 , and pH. Chlorpyrifos and endosulfan, which are strongly adsorbed and slowly degrading pesticides, were found in nearly all surface and groundwater samples, with maximum concentrations in surface water of 8 µg L-1 for chlorpyrifos and 3 µg L-1 endosulfan. Maximum groundwater concentrations were only slightly lower. The weakly adsorbed and fast degrading pesticides, dimethoate, and profenofos were detected only in the rain phase after spraying in the groundwater, indicating preferential transport to groundwater at depths of up to 9 m. The average concentration was 0.38 µg L-1 for dimethoate in surface waters and 1.24 µg L-1 in groundwater. Profenofos was not detected in surface water. In the groundwater, the average concentration was 0.05 µg L-1 . Surface water concentrations of chlorpyrifos and endosulfan were highly toxic to fish. The World Health Organization banned these pesticides worldwide. It should be phased out for use in Ethiopia to safeguard the ecological health of Lake Tana, which is rich in biodiversity and endemic fish species.
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