This text deals with the impact of irrigation water use on groundwater environment and soil salinity in Ethiopia.
Irrigation systems have been under pressure to produce more with lower supplies of water. Various innovative practices can gain an economic advantage while also reducing environmental burdens such as water abstraction, energy use, pollutants, etc. Farmers can better use technological systems already installed, adopt extra technologies, enhance their skills in soil and water management, tailor cropping patterns to lower water demand and usage, reduce agrochemical inputs and more.
Water scarcity has been defined as the point at which the aggregate impact of all users impinges on the supply or quality of water under prevailing institutional arrangements to the extent that the demand by all sectors, including the environment, cannot be satisfied fully.
TABLE OF CONTENT
ABSTRACT
1. INTRODUCTION
2. Literature Review
3. Summary, Conclusion and Recommendation
4. REFERENCE
ABSTRACT
In Ethiopia where agriculture is the backbone of its economy while arid and semi-arid climatic zones occupy over 60% of the total land area. Irrigation systems have been under pressure to produce more with lower supplies of water. A side from the positive impact of irrigation on increasing crop production, in the downstream part of a river basin, irrigation can cause salinity to build up with the increasing depth of the ground water. Poor irrigation agriculture in arid and semiarid regions results in land degradation through soil salinity and sodic soil developments in different parts of the world. Except for water lost through evapotranspiration, agricultural water is recycled back to surface water and/or groundwater. However, agriculture is both cause and victim of water pollution. Water quality related problems in irrigated agriculture are identified as salinity, sodicity, specific ion toxicity. Regarding irrigation schemes and quality of irrigation water as well a drainage facility; there are no force full binding rules and regulations that enforce designers and owners to practice to incorporate.
Key Word: Impact of irrigation, Soil salinity, Freshwater, Agriculture ,
1. INTRODUCTION
Irrigation systems have been under pressure to produce more with lower supplies of water. Various innovative practices can gain an economic advantage while also reducing environmental burdens such as water abstraction, energy use, pollutants, etc. (Svendsen, 2007). Farmers can better use technological systems already installed, adopt extra technologies, enhance their skills in soil and water management, tailor cropping patterns to lower water demand and usage, reduce agrochemical inputs, etc.
Water scarcity has been defined as the point at which the aggregate impact of all users impinges on the supply or quality of water under prevailing institutional arrangements to the extent that the demand by all sectors, including the environment, cannot be satisfied fully (UN Water, 2006). Hence scarcity is a consequence of demand, supply and governance. The OECD (2012) suggested that by 2050 global demand for potable water may increase by 55 per cent (UN Water, 2006). There are three key influences on future global water demand: (i) population growth; (ii) increasing wealth; and (iii) changing diet preferences. Most of the projected global population increase will take place in developing countries already suffering water, food and health problems. The world population is expected to increase to 9.3 billion by 2050 and 10.1 billion by 2100 (Hoekstra, 2013). At the same time there is also expected to be increased income growth for many countries (OECD, 2012). Income growth in developing countries (IGDC) is associated with increased water consumption because of changes in water demand for food production, as well as for sanitation. Meanwhile economic growth in emerging economies and improved living standards are also set to change the use of water for lifestyle purposes. To support these changes in lifestyle and consumption patterns increasing water demand by agricultural and energy industries are likely (OECD, 2012). This is referred to as the water–food–energy nexus (Kumar et al. 2013). As well as income growth influencing lifestyle preferences it is also expected to change diet preferences. Demand in many regions is forecasted to shift from predominantly cereal-based consumption to increase in vegetable oils and meat, which are higher water-intensive commodities. Livestock pasture to support meat production typically requires greater water use per kg production than poultry, while cereal production requires less. Food and feed crop demands are predicted to nearly double in the next.
A side from the positive impact of irrigation on increasing crop production, in the downstream part of a river basin, irrigation can cause salinity to build up with the increasing depth of the ground water. In Ethiopia, despite significant efforts by the government and other stakeholders, water management in irrigated areas is hampered by constraints in policy, institutions, technologies, capacity, infrastructure, and markets (Awulachew et al. 2010). As reported by (Ruffeis et al.2007) most of the established or proposed irrigation schemes are found in the arid and semi-arid lowlands of Ethiopian’s major river basins. The challenge for sustainable irrigation is more substantial in these arid and semi-arid regions, where large production areas are impacted by soil salinity, inadequate subsurface drainage, and water logging (Wichelns and Qadir 2015). As a result, the potential benefits of irrigation are great, the actual achievement in many irrigated areas of the country is substantially less than the potential due to poor water management leading to waterlogging, salinity and related problem (Hordofa et al. 2008).According to the database developed by (Awulachew et al. 2007), there were 791 irrigation schemes in the country. From personal observation and informal communication with regional irrigation authorities, majority of the irrigation projects located in the arid and semi-arid. The visible influence of the groundwater environment on soil resulting from irrigation can only be observed at the advanced stages of salinity buildup, when expensive measures must be implemented. Irrigation also can cause upstream and downstream problems, such as water shortages downstream, drainage problems, and the drainage of contaminants. Thus, in order to prevent soil salinization, it is very important to assess the impact of irrigation on the groundwater environment in arid and semiarid regions.
This article presents the finding of a study undertaken to assess the status-quo and significant environmental impacts of large- scale irrigation in Ethiopia. The main focus of this report is put on the environmental impacts of irrigation on natural resources with special emphasis on soil quality, water quality and downstream impacts, hydrology and potential interference with ecosystems.
In several studies a number of different environmental impacts have been identified which are directly caused by irrigation projects. Sectorial guidelines to conduct environmental impact assessments of irrigation projects (FAO, MoWR) use checklists which include the pertinent environmental impacts. These potential impacts are grouped into impact categories such as economic, socio-economic, natural resource and ecological impacts. This article puts its focus on impacts on natural resources and ecosystems which are closely related to in-field impacts on soil, water quality, hydrological issues and destruction of ecosystems due to irrigation development
Sound irrigation agriculture contributes towards achieving food security and livelihood improvements for the increasing population through enhancement of agricultural productivity. Lessons from the past indicate that the development of a sound irrigated agriculture depends on a catena, or chain of related factors, involving soils, waters, crops and man. Failure of any one of these links can bring hardship or even disaster to an irrigation enterprise (Tessema, 2011). Poor irrigation agriculture in arid and semiarid regions results in land degradation through soil salinity and sodic soil developments in different parts of the world. Hence, the study of arid lands and salt affected soils has been an important topic for modern agricultural management and particularly for poor countries like Ethiopia where agriculture is the backbone of its economy while arid and semi-arid climatic zones occupy over 60% of the total land area (Awulachew et al., 2007).The total land area affected by salinity and sodicity in Ethiopia estimated at about 11 thousand ha and soils have been reported to occur for the most part of the rift valley zone (FAO, 1985a; Tadesse and Bekele, 1996). Nowadays, soil salinity has become important problem in irrigated soils of Awash River basin in central and Eastern Ethiopia. The effect of the quality of irrigation water on soil properties has been discussed by many researchers (Richards, 1984; Westcott and Ayers, 1985; Kinfe, 1999). Water quality related problems in irrigated agriculture are identified as salinity, sodicity, specific ion toxicity.
1.1. Statement of the Problem
High salt concentrations prevent the uptake of water by plants causing crop–yield reductions. This occurs when salts accumulate in the root zone to such an extent that the crop is no longer able to extract sufficient water from the salty soil solution, resulting in water stress for a significant period if water uptake is appreciably reduced, the plant slows its rate of growth. The plant symptoms are similar in appearance to those of drought. In addition to these, salt affected soils are not only the result of the saline soils but also attributed to application of low quality irrigation water. All waters used for irrigation caries varying amounts of dissolved salts and other constituents. Some dissolved constituents can improve crop growth if present in small to moderate amounts; otherwise can harm soils and restrict plant growth if they are present in excessive amount. Due to the above facts and indication of salt in the immediate upstream area (district) along the gullies, intermittent streams and deep wells dug for domestic use made us to assess the salinity hazard for soils and water of Awash basin irrigation project.
1.2. Likely to improve
Irrigation agriculture is the activity that always accomplished to increase the level of production and productivity as well to improve livelihoods of a given country. This brings positive and negative effect on the environment and a lot of Theses, Dissertation, Research institute, Universities, and NGO’s have been done on the effects (both positive and negative) of the sector and give their recommendation according to their findings.The aim this review was to review, identify impact of irrigation water on ground water environment and soil salinity.
2. Literature Review
2.1. Mechanism of Salt Accumulation in the Soil
The development of modern irrigation relatively is a recent phenomenon in Ethiopia, where as traditional irrigation has been in existence for long periods. Irrigation has long played a key role in feeding expanding populations and is undoubtedly destined to play a still greater role in the future. It not only raises the yields of specific crops, but also prolongs the effective crop- growing period in area with dry seasons, thus permitting multiple cropping (two or three and sometimes four crops per year) where only a single crop could be grown. Otherwise, the security provided by irrigation, additional inputs needed to intensify production centered pest control, fertilizer, improved varieties and better tillage become economically feasible. Irrigation reduces the risk of these expensive inputs being wasted by crop failure resulting from lack of water (FAO, 1997). According to FAO (1997) 30-40% of world food production comes from an estimated 260 million hectare of irrigated land or one–sixth of the world‘s farmland. Irrigated farms produce higher yield for most crops. FAO (2001) also reports that the role of irrigation in addressing food insecurity problem and in achieving agricultural growth at global level is well established. Clearly, irrigation1 can and should play an important role in raising and stabilizing food production especially in the less developed parts of Africa south of the Sahara. Water uptake by plants can also increase soil salinity. Water percolating through the ground has salts dissolved in it. Plant roots work by taking in water while excluding salts and other non-nutrients. The excluded salts will gradually build up around the roots, and must be periodically “flushed” from the root zone to maintain plant health.
In natural systems, the types of plants found in a specific environment are adapted for naturally occurring soil salinities like saline, sodic and saline sodic, which affect crop water requirements. In many agricultural areas, salts are flushed from the soil by applying irrigation water. The salts that are flushed from the soil either enter groundwater or are discharged to surficial drains. Human activities can also affect salinity levels in ground and surface water. Application of synthetic fertilizers, manures, and wastewater treatment facilities can all contribute salt to surface and groundwater. Nitrogen is a necessary nutrient for plant growth and nitrogen fertilizers are typically in the form of the salt, nitrate. If excess nitrate fertilizer is applied to a field, the nitrate not used by plants can dissolve and move to groundwater. Manure from confined animal facilities is enriched in nutrients and other salts, and canal so increase salinity levels in receiving waters. Domestic wastewater is typically enriched in salts due to household activities such as washing and water softening. Most water treatment facilities cannot remove salt. As a result, discharges from these facilities can increase surface and groundwater salinity(SWRCB, 2016).For appropriate land use and water management in irrigated area, knowledge of the chemical composition of the soil characteristics, water, climate, drainage condition and irrigation methods should be evaluated before implementation of irrigation projects (Al-Ghobari, 2011). With regards to soil studies, a number of surveys have been carried out for different purposes at different times by different institutions. However, the scale and purpose of the studies allow only planning for development undertakings.
2.2. Water Quality as an Issue of Agricultural Production
It is well known that agriculture is the single largest user of freshwater resources, using a global average of 70% of all surface water supplies. Except for water lost through evapotranspiration, agricultural water is recycled back to surface water and/or groundwater. However, agriculture is both cause and victim of water pollution. It is a cause through its discharge of pollutants and sediment to surface and/or ground water through net loss of soil by poor agricultural practices, and through salinization and water logging of irrigated land. It is a victim through use of wastewater and polluted surface and groundwater which contaminate crops and transmit disease to consumers and farm workers. Agriculture exists within a symbiosis of land and water and, as FAO (1990a) makes quite clear, "appropriate steps must be taken to ensure that agricultural activities do not adversely affect water quality so that subsequent uses of water for different purposes are not impaired." According to (FAO, 1993a) summarized the action items for agriculture in the field of water quality as: · establishment and operation of cost-effective water quality monitoring systems for agricultural water uses. Prevention of adverse effects of agricultural activities on water quality for other social and economic activities and on wetlands, inter alia through.
Agriculture, as the single largest user of freshwater on a global basis and as a major cause of degradation of surface and groundwater resources through erosion and chemical runoff, has cause to be concerned about the global implications of water quality. The associated agro-food processing industry is also a significant source of organic pollution in most countries. Aquaculture has now recognized as a major problem in freshwater, estuarine and coastal environments, leading to eutrophication and ecosystem damage. The principal environmental and public health dimensions of the global freshwater quality problem are highlighted below.
Five million people die annually from water-borne diseases, Ecosystem dysfunction and loss of biodiversity, contamination of marine ecosystems from land-based activities, contamination of groundwater resources and global contamination by persistent organic pollutants.
2.3. Agricultural impacts on water quality
Despite the availability of water sources, it is of utmost importance that the community needs to have access to the water sources. Not only the access, but also the quality of irrigation water matters. Abundant availability and access to irrigation water with quality being poor rather proves detrimental to the soil health and its environment. The results in Table 1 showed that the proportion of respondents who opined the access to tube well irrigation water as good was marginally more in fresh water village (88.89%) than the sewage water villages (83.33%).Whereas, the accessibility of sewage water 86.67 per cent of the farmers in sewage water villages reported as good access.
While, a majority of the farmers (63.33%) responded that the quality of the sewage water they used for irrigation was poor and only 36.67 per cent farmers responded as average. It might be due to various factors such as the color of the water, the debris that it deposits on to the farmlands, the harmful chemicals that it delivers, etc. The quality of tube well water that they used for irrigation in sewage water villages was contaminated. This may be due to high load of nutrients in sewage water. Across the villages surveyed, water for irrigation is available throughout the year except the sewage water, which is available in lesser quantity for few months due to reduced flow in sewage canal during summer.
The findings of the present study were in agreement with similar findings made with respect to traces of NO3N (upto 2.8mg l-1), Pb (up too.35mg l-1) and Mn (up to 0.23mg l-1) was observed in well waters nearthe disposal point thus indicating initiation of ground water contamination by (Yadav et al. 2001).
2.4. Environmental Impact of Irrigation
The environmental impacts of irrigation relate to the changes in quantity and quality of soil and water as a result of irrigation and the effects on natural and social conditions in river basins and downstream of an irrigation scheme. The impacts stem from the altered hydrological conditions caused by the installation and operation of the irrigation scheme.
2.4.1. Direct effects
The first direct impact is on output. Irrigation enhances farm output and thus, with prices remaining constant, raises farm incomes. Output levels may increase for any of at least three reasons. Firstly, irrigation boosts yield by mitigating crop loss due to unpredictable, unreliable or inadequate rainwater supply. Secondly, irrigation permits the possibility of multiple-cropping and a boost in total output. Thirdly, irrigation enables a greater area of land to be used for crops in times where rain-fed production is not possible or insignificant. Consequently, irrigation is expected to increase output and income levels (Lipton et. al, 2003).
The second major impact of irrigation is in the employment generated both on and off the farm, offering entitlement or purchasing power for the poor. For landless laborers, increased cropping intensity has the maximum impact on employment. Irrigation means extra work in more days of the year.
The employment impact is felt not only in irrigated areas but also in rain-fed areas. Sometimes, landless workers in rain-fed villages migrate long distances to take advantage of employment opportunities in the irrigated areas (Barker et al, 2000). According to (Lipton et al. 2003), there are two sources of extra demand for labor created by irrigation projects. Firstly, irrigation projects need labor for construction and on-going maintenance of canals, wells etc. This is expected to be a vital sector of employment for the poor, particularly the landless rural poor or rural households with extra labor or seasonal excess labor. Secondly, higher farm outputs as a result of irrigation will stimulate more demand for farm labor. Thus, rural poverty could be reduced by the increased employment opportunities associated with the adoption of irrigation schemes. The third direct effect on poverty is by means of food prices. If irrigation boosts the level of output, then this may result in lower prices of foods (Lipton et. al, 2003). Lower food prices have reduced vulnerability associated with distribution of food and its access among poor and marginal communities (Bhattarai et al, 2002). Therefore, both rural net purchasers and urban consumers will gain from cheaper food prices. Thus, a fall in the staple price as a result of more outputs from irrigated plots is expected to be poverty reducing.
An irrigation scheme draws water from groundwater, rivers, lakes or overland flow, and distributes it over an area Hydrological, or direct, effects of doing this (Catherine Pringle et al. 2000). Include reduction in downstream river flow, increased evaporation in the irrigated area, and increased level in the water table as groundwater recharge in the area is increased and flow increased in the irrigated area. Likewise, irrigation has immediate effects on the provision of moisture to the atmosphere, inducing atmospheric instabilities and increasing downwind rainfall, (M. H. Lo and J. S. Famiglietti, 2002) or in other cases modifies the atmospheric circulation, delivering rain to different downwind areas.
According to (O. A. Tuinenburg et. al. 2012) Increases or decreases in irrigation are a key area of concern in precipitation shed studies that examine how significant modifications to the delivery of evaporation to the atmosphere can alter downwind rainfall.
2.4.2. Indirect effects
There are a number of irrigation induced linkages that affect the economy of rural households. Bhattarai et al 2002) analyzed linkage effects such as forward linkages (in farm output market), backward linkages [in farm factors market] and adjustments for the shadow prices of the factors and products in the economy [feedback effects from foreign exchange rates]. (Lipton et al. 2003) argued that access to irrigation also has second round impacts through output, employment and prices on poverty. In the longer run with a dynamic general equilibrium scenario and farm outputs, irrigated land in general initiate farmers to adopt fertilizers, pesticides, improved seeds and other agricultural factors of production. This also has a positive effect in poverty reduction.
Indirect effects are those that have consequences that take longer to develop and may also be longer-lasting. The indirect effects of irrigation include the following: Water logging, Soil salination, Ecological damage, and Socio-economic impacts. The indirect effects of water logging and soil salination occur directly on the land being irrigated. According to (Velasco and Josefa 2005) the ecological and socio-economic consequences take longer to happen but can be more far-reaching. Some irrigation schemes use water wells for irrigation. As a result, the overall water level decreases. This may cause water mining, land/soil subsidence, and, along the coast, saltwater intrusion. Irrigated land area worldwide occupies about 16% of the total agricultural area and the crop yield of irrigated land is roughly 40% of the total yield. As suggest that (Bruce Sundquist, 2007) In other words, irrigated land produces 2.5 times more product than non-irrigated land. This article will discuss some of the environmental and socioeconomic impacts of irrigation.
2.4.3. Increased Groundwater Recharge, Water Logging, Soil Salinity
Increased groundwater recharge stems from the unavoidable deep percolation losses occurring in the irrigation scheme. The lower irrigation efficiency is results with the higher the losses. Although fairly high irrigation efficiencies of 70% or more (i.e. losses of 30% or less) can occur with sophisticated techniques like sprinkler irrigation and drip irrigation, or by well managed surface irrigation, in practice the losses are commonly in the order of 40% to 60%. This may cause the following issues:
v Rising water tables
- Increased storage of groundwater that may be used for irrigation, municipal, household and drinking water by pumping from wells
- Water logging and drainage problems in villages, agricultural lands, and along roads - with mostly negative consequences.
- The increased level of the water table can lead to reduced agricultural production.
- Shallow water tables - a sign that the aquifer is unable to cope with the groundwater recharge stemming from the deep percolation losses
- Where water tables are shallow, the irrigation applications are reduced. As a result, the soil is no longer leached and soil salinity problems develop
- Stagnant water tables at the soil surface are known to increase the incidence of water-borne diseases like malaria, filariasis, yellow fever, dengue, and schistosomiasis (Bilharzias’) in many areas.
- Health costs, appraisals of health impacts and mitigation measures are rarely part of irrigation projects, if at all.
- To mitigate the adverse effects of shallow water tables and soil salinization, some form of water table control, soil salinity control, drainage and drainage system is needed as drainage water moves through the soil profile it may dissolve nutrients (either fertilizer-based or naturally occurring) such as nitrates, leading to a buildup of those nutrients in the ground-water aquifer.
2.5. Soil Properties
The accumulation of salts in soils can lead to irreversible damage to soil structure is essential for irrigation and crop production. Effects are most extreme in clay soils where the presence of sodium can bring about soil structural collapse. This makes growing conditions very poor, makes soils very difficult to work and prevents reclamation by leaching using standard techniques. Gypsum in the irrigation water or mixed into the soil before irrigation is a practice that is used to reduce the sodium content of sodic soils. In certain areas, in particular in tropical coastal swamps, acid sulphate soils may be a problem. The danger of potential soil acidification needs to be considered. The transfer from rain fed to irrigated crop production, or intensification of existing irrigated crop production requires a higher level of nutrient availability in the soil profile. If this aspect is not given adequate attention, the irrigation efficiency remains low. High water losses through the profile will result and useful cat ions may be washed out from the soil complex. A general lowering of pH may result in a decrease of the plants capability to take up nutrients. The decrease of pH may also result in an increased availability/release of heavy metals in the soil profile. Rectifying soil acidification problems can be very costly. For similar reasons the content of organic material in the soil may decrease. Such decrease leads to a degradation of soil structure and to a general decrease of soil fertility.
2.5.1. Saline ground water
An increase in the salinity of the groundwater is often associated with water logging. An appropriate and well-maintained drainage network will moderate against such effects. Saline groundwater can be particularly critical in coastal regions. Drainage may not be required initially but it should allow for if there is insufficient natural drainage. Areas with a flat topography or with water tables that have a low hydraulic gradient are at risk from salinization as are areas with soils of a low permeability, which are difficult to leach. Groundwater drains, pipe (tile) drains or deep ditches, carry out the dual task of controlling the water table and through leaching, counteracting the buildup of salts in the soil profile. Normally water applied in excess of the crop water requirement and soluble salts were carrying away in the drainage water although in some areas leaching can achieved during the rainy season. An increase in solute concentration from the applied irrigation water to the drain water cannot be prevented. Typically, salt concentrations in drainage water are 2 to 10 times higher than in irrigation water, (Hotes and Pearson 2004). Good irrigation management can reduce the quantity of drainage water though this will tend to have the effect of making the quality worse. Reducing salt inputs is one way of improving drain water quality. The safe disposal of salts is of prime importance, either to the sea (using dedicated channels if river quality is threatened) or to designated areas such as evaporation ponds where the negative impacts can be contained. Leaching typically requires an extra10-20% of water.
2.5.2. Saline intrusion
The location of the boundary between fresh and salt water at the coast line is a function of the hydraulic potential of the fresh water. A lowered water table will result in the boundary moving inland as the pressure reduces. Large numbers of people may be affected by a reduction in the quality of their drinking supplies when fresh water is replaced by salty water.
Table1. Chemical composition of water used for irrigation of the three sites.
Abbildung in dieser Leseprobe nicht enthalten
Source (Mohamed Seid and Tessema Genanew 2013)
Moreover, people may be forced to turn to sources of water whose collection and use have important health risks. The plant life in the area may also change as only salt tolerant species survive. The environmental effects can be irreversible as reversing the movement of a salt water wedge is usually both difficult and very expensive. Changes to the flow regime may alter the salinity of the estuary. This is likely to have a major impact on the local ecology: a highly productive habitat which is often sensitive to salinity levels.
2.5.3. Water and salt balances in an irrigated soil
Irrigation water quality can have a profound impact on crop production. All irrigation water contains dissolved mineral salt, but the concentration and composition of the dissolved salts vary depending on the source of the irrigation water. Relatively surface water contains less, whereas ground water or waste water has higher salt level. An understanding of the quality of water used for irrigation and its potential negative impacts on crop growth is essential to avoid problems and to optimize production. The key factors to avoid the process of secondary soil salinization can be easily identified if water and salt balances in the root zone of an irrigated soil and the saturated zone below the water table are considered. The components of these balances can be identified in the scheme of the water cycle in an irrigated soil. The water balance in the root zone of an irrigated soil in a given time interval is the following equation,
Abbildung in dieser Leseprobe nicht enthalten
Where;
I = effective amount of irrigation water infiltrated (mm)
P = amount of effective precipitation (mm)
G = capillary rise from the water table (mm)
ETc = actual crop evapotranspiration (mm)
R = deep percolation (mm)
∆W = variation of water stored in the root zone (mm)
2.5.4. Sources and causes of salinity
The main sources and/or causes of salinity are shallow groundwater tables and natural saline seeps. Poor drainage and lack of appropriate irrigation water management is also known to facilitate secondary salinization (Abebe et al. 2015). Improperly planned irrigation projects not supported by improved irrigation and drainage management technologies had invited serious degradation causing salinity and sodicity problems in the Awash basin which accounts for about one-third of total irrigated area of the country (Dubale et al. 2002; Ruffeis et al. 2007). This high salinity problem is also related to uncontrolled irrigation practice and lack of knowledge on crop water requirements and water management leading to increased saline groundwater level or capillary rise (Ayenew 2007). Discharge to the groundwater by surplus irrigation water has caused a rise in the water table (0.5 m/year) in middle Awash irrigated field and problems with secondary salinity in surface and sub- surface soil horizons (Taddese et al. 2003). Another source of salinity for rivers and other sources of irrigation water is attributed to salts of marine origin. During the rainy season, water quality of River Wabishebele for irrigation deteriorates as a result of very high flooding which dissolves soluble salts from loose marine origin along its course (Taddese 2001). Climate is also a key factor in the salinization process. The high temperature of the Middle Awash (annual average 26.7°C) and low annual rainfall (500 mm) and the high free evaporation of water have aggravated the salinization process (Ayenew 2007; Bekele 2005).
2.5.5. Consequences of salinity
Salt affected soils are characterized with excess concentrations of calcium (Ca+), sodium (Na+)and chloride (Cl-) which are easily soluble (Bekele 2005). This has an adverse effect on seedling growth of several crops, by creating an osmotic potential in the rhizosphere of the plant which inhibits the absorption of water or creates toxic effect due to Na+ and Cl- to the roots and the whole crop (Abraha and Yohannes 2013; Singh, 2015). Osmotic potential is the potential of water molecules to move from a high solutes concentrated solution to a less solutes concentrated solution across a semi permeable membrane. When salt affected soils are intensively cultivated without proper caution for the gradual accumulation of salts and soluble substances, it may result in severe land degradation. Poor irrigation water management and operation coupled with the absence of drainage system can cause groundwater rise (water logging), salinization and considerable losses in crop yields, which ultimately led to abandonment of substantial irrigable areas. The problems of salinity and water logging persist in many regions where farmers apply excessive irrigation water, and where farmers and irrigation departments fail to invest inadequate drainage solutions (Wichelns and Qadir 2015). For example, soil salinity has caused abandonment of banana plantation in Amibara, cotton plantation in Melka Sedi and nearly 30ha of farmland in Metahara sugar plantation due to a progressive rise of groundwater because of over irrigation (Abegaz 1996; Ayenew 2007; Abebe et al. 2015). According to (Asfaw and Itanna 2009) also indicates that of the entire Abaya State farm, 30% has already been salt affected. With the high tendency of the country to introduce and implement large-scale irrigation agriculture to meet the demands of the ever-increasing human population by elevating productivity and the absence of efficient ways of irrigation water management and well-designed drainage ditches, salt build up is an inevitable problem which is expected to be severe in the years to come (Asfaw and Itanna 2009; Behailu and Haile 2002; Geressu and Gezaghegne 2008).It is also stated in (Wichelns and Qadir 2015) that salinity and water logging will continue to impact agriculture in arid and semi-arid areas for the foreseeable future. Yet we can beg into reduce the degree to which salinity and water logging impair productivity and reduce crop yieldsby designing and implementing effective regional solutions (Wichelen and Qadir 2015).
3. Summary, Conclusion and Recommendation
3.1. Summary and Conclusion
Wherever we manage rivers and groundwater there is a relationship between the amount of water available and the quality of the water. For example, when water is taken from a river for irrigation, it can increase the concentration of salinity downstream, as well as the amount of salt in the landscape. Improving water efficiency will address many of the causes of irrigation, dry land and urban salinity. To reduce water usage in irrigation areas will require improvements in irrigation infrastructure and irrigation technology, as well as better matching of crops such as rice to suitable soil types. In dry land areas, water use efficiency means managing vegetation and land use to reduce recharge to the groundwater system. This includes management of remnant vegetation, re-vegetation and use of appropriate agricultural practices. In urban areas, water use efficiency means changing the way we water our lawns and gardens, including changing the amount of water we apply and when, what and how we water.
In some cases, additional water is needed to manage salinity. In areas such as wetlands, as river salinity increases, the amount of water (duration and flow) needed to maintain that wetland health will also have to increase to avoid over-concentration of salt. Under irrigation, salty water soaks though the soil and concentrates in the root zone, eventually preventing plant growth. One option is to pump water out from the ground water to lower the water table. You can then ‘over-water’ to move the salt below the root zone.
As we can see, the relationship between water quality and quantity is complex. The NSW Government’s water reform process is integrating the management of water quality and quantity, so that the two can be managed more effectively.
Engineering solutions involve physically stopping the ground water table rising and/or salt from entering our rivers via pumps, for example. Where conditions are suitable and their impacts on the environment are minimal, they are cost-effective in quickly and significantly reducing salinity.
Engineering solutions can be helpful in cases where other salinity management actions may actually increase the problem in the short term. For example, if we plant trees, in the short term we may see a reduction in the amount of surface water running into the river. This may lead to higher salinity concentrations. In the longer term, the trees will soak up more water, so there is less saline groundwater entering the river, leading to a net reduction in salinity. We may use engineering solutions such as salt interception schemes in these situations to offset these undesirable short-term impacts. Engineering solutions can also be low cost and on a smaller scale than salt interception schemes. For example, during a storm, the first ‘flush’ of water running off salt-affected land is usually highly saline. Land managers might use structures such as small dams to hold this first flush of saline water, preventing large salt loads running into rivers. However, engineering solutions are ultimately a means of treating the symptoms of salinity, rather than its causes. Disposing of the intercepted salt can result in significant financial and environmental costs (although it can also present opportunities to benefit from the products of the salt).
Where salt affects the landscape and cannot economically be removed, there are still options available to use the land productively. These options can involve use of more salt-tolerant crops and pastures, re-vegetation for wood products and possibly carbon credits, and development of new business opportunities such as aquaculture in salinized water. Of those at risk, not all are threatened to the same extent. Some landscapes are more saline than others or can potentially cause more salinity than others. Scientists can analyze the natural features of a landscape to assess whether it is likely to be affected by salinity, or whether it is likely to cause salinity. To do this, they look at characteristics of the area such as geology, groundwater and soils and at changing features of the landscape such as its vegetation cover, changes in land use and long-term climate cycles. The Department of Land and Water Conservation’s scientists, in partnership with other scientists, will look at how salt is stored and mobilized in the landscape and the pathways that it follows. Modeling, together with an understanding of land use impacts, will help communities to decide what levels of salt they are prepared to live within hazard landscapes. Catchment Management Boards, on behalf of communities, land managers, conservation interests and governments, will overlay social and economic considerations onto the biophysical salinity information.
3.2. Recommendation
Despite the presence of vast areas of salt-affected phases with the high possibility of the expansion of the same in the country, research and development endeavor to alleviate the problem of salinity and sodicity have been still minimal in Ethiopia. As result, the extent of salt affected is not known, the cause are not studied to the desired level and documented, economic implication of the problem is not brought to attention of all concerned to make timely and appropriate action, and there is no autonomous institution to make inventory of the natural resource we have, assess the extent of degradation taking place every year (Kidane et al., 2006).
Regarding irrigation schemes and quality of irrigation water as well a drainage facility; there are no force full binding rules and regulations that enforce designers and owners to practice to incorporate. Also after implementation monitoring is also very essential for preventing salinity problem from happing or expanding.
Even though there are trials to control regulate fertilizer application and utilization, in some areas still there are problems. This is creating problem groundwater pollution in addition to salinity.
4. REFERENCE
Ababa, Ethiopia, 27-29 November 2007. In: Conference Proceedings,. International Water Management Institute.
Abebe TF, Alamirew T, Abegaz F (2015). Appraisal and mapping of soil salinity problem inAmibara irrigation farms, Middle Awash basin, Ethiopia International Journal of Innovation and Scientific Research 13:298-314
Abegaz F (1995, 1996). Effect of subsurface drainage system on ground-water table, soil salinity and crop yield in Melka Sadi pilot drainage scheme. In: Proceedings of the Conference of the Agronomy and Crop Physiology Society of Ethiopia, Addis Abeba (Ethiopia).
Abegaz F, Tadese G (1996). Reclamation of salt affected soils in the Middle Awash region
Abraha B, Yohannes G (2013). The role of seed priming in improving seedling growth of maize
Adamson, D. and A. Loch (2014). ‘Possible negative feedbacks from “gold-plating” Irrigation and agricultural water management
Asegid., F. Messele and B. Mohamed. 2006. Report of the national task force on irrigation affected soils and for sustainable utilization.
Awulachew SB, Yilma A, Loulseged D, Loiskandl W, Ayana M, Alamirew T, (2007). Water Resources and Irrigation Development in Ethiopia. Colombo, Sri Lanka: International Asamenew G, Beyene H, Haile A, Negatu W, (1993). Technology validation and transfer.
Asamenew G, Jutzi S, Tedla A, McIntire J, Haque I, Stares J (1988) Economic evaluation of improved Vertisol drainage for food crop production in the Ethiopian highlands Management of Vertisols in Sub-Saharan Africa:263-283.
Asfaw KG, Itanna F (2009) Screening some tef [Eragrostis tef (Zucc.) Trotter] accessions/varieties for salt tolerance during germination and seedling stage Momona Ethiopian Journal of Science 1.
Awulachew SB, Erkossa T, Namara R (2010) Irrigation potential in Ethiopia: Constraints and opportunities for enhancing the system Unpublished Report to the Bill and Melinda Gates Foundation.
Awulachew SB, Loulseged M, Yilma A.D (2008) Impact of irrigation on poverty and environment in Ethiopia: draft proceedings of the symposium and exhibition, Addis
Awulachew, S. B., Yilma, A. D.,Loulseged, M., Loiskandl, W., Ayana, M., Alamirew, T.,(2007). Water Resources and Irrigation Development in Ethiopia. Colombo, Sri Lanka: International Water Management Institute. 78p. (Working Paper 123).
Ayenew T (2007) Water management problems in the Ethiopian rift: Challenges for development Journal of African Earth Sciences 48:222-236.
Ayers, R.S., Westcot, D.W. 1985. Water quality for agriculture. FAO Irrigation and
Behailu M, Haile M (2002) Water harvesting in northern Ethiopia: Environmental, health and socio-economic impacts Integrated water and land management research and capacity building priorities for Ethiopia: pp 1-85.
Bekele G (2005). The Nature and properties of salt affected soils in middle Awash Valley of Ethiopia Journal of Soil Science 8:23-30 water management.
Bouma, J. A., Hegde, S. S. and Lasage, R. (2016). ‘Assessing the returns to water harvesting : A meta-analysis’, Agricultural Water Management. Elsevier B.V., 163, pp. 100–109.
Bruce Sundquist, 2007. Irrigation overview. The earth's carrying capacity, Some related reviews and analysis. On line. Archived from the original on 2012-02-17. 6. World Wildlife Fund.
California State Water Resources Control Board, (SWRCB, 2016). A Compilation of Water Quality Goals, 17th Edition.
Donma, S., Nagano T., and Watanabe, T., 2004: Irrigation system and improvement in the Lower Seyhan pub.3.
El Wakeel A, Astatke A (1996). Intensification of agriculture on vertisols to minimize land degradation in parts of the Ethiopian highlands Land Degradation & Development Water Management Institute. PP.78.
Erkossa T, Gizaw A, Stahr K (2004). Land preparation methods efficiency on the highland Vertisols of Ethiopia Irrigation and Drainage 53:69-7
FAO (2002), ‘World agriculture: towards 2015/2030’, Rome: Food and Agriculture Organization of the United Nations.
FAO (2011). ‘The state of the world’s land and water resources for food and agriculture (SOLAW) – managing systems at risk’, London: Food and Agriculture Organization of the United Nations, Rome and Earth scan.
FAO (2012), ‘Irrigation water requirement and water withdrawal by country’, London: Food and Agriculture
Gadissa T, Chemeda D (2009). Effects of drip irrigation levels and planting methods on yield and yield components of green pepper (Capsicum annuum, L.) in Bako, Ethiopia Agricultural Water Management 96:1673-1678
Gebrehiwot KA, Gebrewahid MG (2016). The Need for Agricultural Water Management in SubSaharan Africa Journal of Water Resource and Protection 8:835
Geressu K, and Gezaghegne M, (2008). Response of some lowland growing sorghum (Sorghum bicolor L. Moench) accessions to salt stress during germination and seedling growth African Journal of Agricultural Research 3:044-048.
Haile GG, Kasa AK (2015). Irrigation in Ethiopia: A review Academia Journal of Agricultural Research 3:264-269 doi:10.15413/ajar.2015.0141.
Hawando T (1994). Desertification in Ethiopian highlands. Norwegian Church Aid, Addis Ababa.
Hordofa T, Menkir M, Bekele S, Erkossa T (2008). Irrigation and Rain-fed Crop Production System in Ethiopia. In: Impact of Irrigation on Poverty and Environment in Ethiopia.
John Oswald, Sarah Harris, (2016). Biological and Environmental Hazards, Risks, and Disasters.
KidaneGiyorgis, F. Abebe., G. Hiluf., A. Fantaw., C. Wondimagegne., A. Hibistu., A. Organization of the United Nations, available at: http://www.fao.org/nr/water/aquastat/water_use_agr/ index.stm assessment of salt affected soil.
Kinfe H(1999). Impact of climate change on the water resources of Awash River Basin, Ethiopia. Climate. Res. 12: 91-96.
Kume, T., AKÇA, E., Nagano, T., Donma, S., Serdem, M., Kapur, S., and Watanabe, T., 2006: An analysis of spatial variability of soil salinity in an irrigated area-southern Turkey, Water and Land Management for Sustainable Irrigated Agriculture,
O. A. Tuinenburg e, 2012. The fate of evaporated water from the Ganges basin, Journal of Geophysical Research: Atmospheres, Volume 117, Issue D1, 16 January
P. W. Keys et al., Analyzing precipitationsheds to understand the vulnerability of rainfall dependent regions.
SUAREZ, D.L. Impact of Agricultural Practices on Groundwater Salinity, Agric., Ecosystems and Environment https://www.ars.usda.gov/SP2U/20360500/pdf_pubs/ Revised
Richards, L.A. (Ed.), 1994. Diagnosis and improvement of saline and alkali soils. USDA Agricultural Handbook No. 60, Washington, 160 pp.
Tadesse G, Bekele E(1996). Saline and Saline Sodic soils of the Middle Awash Valley Ethiopia. In: Teshome Yizengaw, Eyasu Mokonnen, and Mintesinot Bahilu.
Taddese G (2001) Land degradation: a challenge to Ethiopia Environmental management 27:815-824
Taddese G, Sonder K, Peden D (2003) The water of the Awash River Basin a future challenge to Ethiopia International Livestock Research Institute, Addis Ababa
Teshome A 2012 Agriculture, growth and poverty reduction in Ethiopia: policy processes around the new PRSP (PASDEP). In: a paper for the Future Agricultures Consortium Workshop,
Tessema G (2011). Management of Salt Affected Soils. Soil Analysis for Soil Salinity and Fertility Status. VDM Publishing House Ltd.Verlag Dr.Muller GmbH and Co.KG. Germany. pp. 84.
Westcot, D.W., 1998. Reuse and disposal of higher salinity subsurface drainage water: a review. Agricultural Water Management. 14,483.
Wheeler, S., H. Bjornlund, M. Shanahan and A. Zuo (2008), ‘Price elasticity of allocations: water demand in the Goulburn–Murray Irrigation District of Victoria, Australia’, Australian Journal of Agricultural ResourceEconomic s, 52, 37–55. (Zea mays L.) under salt stress at field conditions Agricultural Sciences 4:666 7:57-
Wichelns D, Qadir M (2015) Achieving sustainable irrigation requires effective management of salts, soil salinity, and shallow groundwater Agricultural Water Management.
Frequently asked questions
What is the document about?
The document is a language preview, similar to an academic paper that provides an overview of a study, possibly an environmental impact assessment related to irrigation. It includes an abstract, introduction, literature review, summary/conclusion/recommendation, and references.
What is the central theme?
The core theme revolves around the environmental impacts of irrigation, particularly large-scale irrigation projects, and their effects on soil quality, water quality, hydrology, and ecosystems. It focuses on the challenges of balancing increased agricultural productivity with the potential for land degradation, especially soil salinity.
What are the key issues discussed?
Key issues include:
- The role of irrigation in food security and livelihood improvement.
- Water scarcity and its impact on agriculture.
- The mechanism of salt accumulation in soils due to irrigation.
- The impact of irrigation water quality on soil properties and crop production.
- Environmental impacts of irrigation such as water logging, soil salinization, and ecological damage.
- Groundwater recharge, water logging, and soil salinity as consequences of irrigation practices.
What is the problem statement?
The problem statement highlights the issue of salt accumulation in the root zone, preventing water uptake by plants and reducing crop yields. This is exacerbated by low-quality irrigation water, leading to salinity hazards in soils and water.
What are some potential solutions mentioned?
Possible solutions include:
- Improving irrigation infrastructure and technology to increase water use efficiency.
- Matching crops to suitable soil types.
- Managing vegetation and land use to reduce groundwater recharge in dryland areas.
- Implementing water table control and drainage systems to mitigate the effects of shallow water tables and soil salinization.
- Using salt-tolerant crops and pastures in affected areas.
What are some key keywords highlighted?
The abstract highlights the following keywords: Impact of irrigation, Soil salinity, Freshwater, Agriculture
What does the literature review cover?
The literature review examines the mechanisms of salt accumulation, the importance of water quality in agricultural production, and the direct and indirect environmental effects of irrigation.
What are the direct effects of irrigation?
Direct effects of irrigation include increasing farm output, generating employment (both on and off-farm), and potentially lowering food prices.
What are the indirect effects of irrigation?
Indirect effects of irrigation include water logging, soil salination, ecological damage, and socio-economic impacts.
What is the significance of groundwater recharge in irrigation schemes?
Increased groundwater recharge, resulting from irrigation, can lead to rising water tables, water logging, and drainage problems. It can also cause shallow water tables, leading to reduced agricultural production and soil salinity.
How does soil quality get affected?
Irrigation can lead to soil structural damage due to the accumulation of salts, particularly sodium. It can also decrease soil fertility and organic material content.
What is saline intrusion?
Saline intrusion occurs when the boundary between fresh and salt water moves inland due to a lowered water table, often caused by over-extraction for irrigation, leading to the contamination of drinking water supplies.
What are the components of the water balance in an irrigated soil?
The components include effective irrigation water infiltrated, effective precipitation, capillary rise from the water table, actual crop evapotranspiration, deep percolation, and the variation of water stored in the root zone.
What causes salinity?
The causes of salinity include shallow groundwater tables, natural saline seeps, poor drainage, and improper irrigation water management. Climate also plays a role.
What are the consequences of salinity?
Salinity negatively affects seedling growth by creating an osmotic potential and inhibiting water absorption. It can also lead to land degradation and abandonment of irrigable areas.
What are the main recommendation?
The document recommends implementing binding rules for irrigation schemes, monitor implementation and regulating fertilizer application and utilization
- Arbeit zitieren
- Bayisa Muleta (Autor:in), 2021, Impact of Irrigation Water Use on Groundwater Environment and Soil Salinity in Ethiopia, München, GRIN Verlag, https://www.hausarbeiten.de/document/1007758
