Ecological resources for conservation and developn1ent in Wadi Allaqi, Egypt*

Transcription

1 Botanical Journal rifthe Linnean Sociery (1992), 108: With 2 figures Ecological resources for conservation and developn1ent in Wadi Allaqi, Egypt* I. D. PULFORD, K. ]. MURPHY, G. DICKINSON AND]. A. BRIGGS University of Glasgow, Glasgow GJ2 BQQ AND I. SPRINGUEL Assiut University, Aswan, Egypt PULFORD, I. D., MURPHY, K.J., DICKINSON, G., BRIGGS,]. A. & SPRINGUEL, 1., Ecological resources for conservation and development in Wadi Allaqi, Egypt. The creation of Lake Nasser behind the Aswan High Dam on the River Nile has brought about significant environmental changes in Upper Egypt. A multidisciplinary project was started in 1987 to assess the environmental changes associated with periodic inundation in desert ecosystems. The data presented here provide a baseline for studies aimed at assessing the potential for, and ecological impacts of, sustainable development in the target area, and may act as a blueprint for wider-scale development. Soil, water, vegetation, animal and human resources are being monitored. There has been a major increase in plant communities dominated by riverain species, at the expense of the original desert wadi vegetation. The water has attracted human settlement, with some people now living in the wadi. The inherent high fertility of the soil has allowed them to grow a range of crops in small plots, using a system of shifting cultivation dictated by the lake water level. While this degree of development may be sustainable, larger-scale development of the fragile wadi ecosystem demands a full assessment of appropriate management techniques. ADDITIONAL KEY WORDS:-Desert ecosystems - River Nile- soils. CONTENTS Introduction. The Wadi Allaqi Region Soil resources. Vegetation resources Human resources and agriculture Challenges for development Conclusions Acknowledgements References INTRODUCTION The Wadi Allaqi Project is a joint venture between the Faculties of Science at the Universities of Glasgow and As wan. It is both inter-institutional and interdisciplinary, and is concerned with the broad theme of agro-ecological * Paper presented to the First Annual Regional Meeting of the Linnean Society, Reading, September /92/ II $03.00/ The Linnean Society of London

2 132 I. D. PULFORD ET AL. development potential in an arid environment influenced by groundwater infiltration. Wadi Allaqi was chosen as the study area for three main reasons. Firstly, it is the largest wadi in the Eastern Desert of Egypt and has experienced considerable ecological change since the completion of the Aswan High Dam in The subsequent inundation of the Nile valley created Lake Nasser and resulted in the introduction of surface water into the wadi. Seepage from the lake has also caused changes in groundwater distribution. The second reason for choosing to study Wadi Allaqi has been the building of an asphalt road from Aswan to facilitate the transport of marble and granite, both of which are mined in the area. This road has made the wadi more accessible, with journey times from Aswan now of the order of 4 hours as opposed to 10 hours previously, and so economic development pressures are more likely to increase. The third reason for the project is concerned with the Egyptian government's desire to increase internal food production. Egypt's population is currently over 50 million and growing at about 3% per annum. The present cost of imported food is c. US$3 billion per year, so any increase in internal food production would have important implications for the national balance of payments deficit. As only about 3% of Egypt's land is currently cultivatable, and that is mainly in the Nile valley and delta, the shorelands of Lake Nasser offer a new and hitherto largely undeveloped resource. Because of its remoteness, and lack of need for development until now, little is known about the ecological resources of the area and their response to development. This paper outlines the nature of the changes in Wadi Allaqi over recent years and presents some initial findings concerning the ecological resources. These processes are complicated by the influx of people into the wadi, who are themselves an important aspect of this change. THE WADI ALLAQI REGION Wadi Allaqi is located in the Eastern Desert of Egypt, between longitudes E and latitudes N, about 180 km south of Aswan (Fig. 1). It is the major structural feature of the Eastern Desert, aligned in a north-west to south-east direction approximately on the juction of basement complex rocks to the north-east and Nubian sandstone to the south-west. The wadi extends as far south as the Sudan border and is fed by a number of tributaries. Its upstream tributaries drain some of the mountains that form the natural division between the Eastern Desert and the Red Sea coastal land (Fig. 2). The climate in Allaqi is extremely harsh. The annual mean maximum temperatures range from 25 C in winter to 42 C in summer. No rainfall has been recorded in the lower part of the wadi for at least 10 years, but severe storms which occur occasionally in the Red Sea Hills can result in water flow down the wadi. The last recorded storm event was in September 1988 and resulted in a flow of surface water occurring along the full length of Wadi Allaqi for a period of a few hours. A major change in the ecology of this area has resulted from the building of the Aswan High Dam and the creation of Lake Nasser (White, 1988). As the water built up behind the dam, the mean level of Lake Nasser rose annually throughout the 1970s, reaching a maximum of 179 m above sea level in 1978.

3 ECOLOGICAL RESOURCES IN WADI ALLAQI 133 MEDITERRANEAN SEA EGYPT r Lake NASSER I SUDAN I Figure I. Project location. This is only 1 m short of the planned maximum permissible level of 180 m, above which water is lost from the lake by a spillway into the desert. From this high point in 1978, the mean level of the lake showed a long-term decline, reaching a low of 151 m above sea level in Since then, high rainfall in the source areas of the Nile has resulted in the mean level of the lake rising to 16 7 m in 1989, and to almost 170 m by February Superimposed on these longterm fluctuations in mean lake level, there is also a well-defined pattern of annual variation. Within each year, the lake level tends to peak in November and be at its lowest in July. The difference between these two extremes is typically 5-6 m.

4 134 I. D. PULFORD ET AL. Jebel Um Noqo Qorn el"" Teis Tort el Bibon ' Tropic of Cancer Kilometres t N Figure 2. Allaqi Region, Upper Egypt. In essence, the creation of Lake Nasser has resulted in a finger of water advancing some 80 km along Wadi Allaqi from the line of the pre-inundation Nile channel, into what had previously been an almost completely waterless, arid part of Egypt. However, this body of water is not static, so both its presence and its movement had significant effects on the area. Because of the shallow gradient of the wadi, the fluctuations of water level in the lake result in significant lateral movement of water along the wadi. The annual variation causes the shoreline to move by a few kilometres, while the long-term

5 ECOLOGICAL RESOURCES IN WADI ALLAQI 135 fluctuations have resulted in changes of the order of tens of kilometres. These changes have had major effects on the soil and vegetation within the wadi, and have provided a source of water to allow the local people to grow crops on a limited scale. SOIL RESOURCES The soils of Wadi Allaqi are primarily alluvial in origin, with some aeolian deposits. Visual examination of a soil profile in the wall of a dry well to a depth of c. 4.5 m clearly showed the distinct layering of the soil caused by successive depositions. As a result of the arid conditions, there has been very little action by soil forming factors other than physical weathering. Some degree of particle size sorting is brought about by the periodic surface water flows. This is particularly seen as fans of silt and clay sized material deposited on the downstream side of the larger plants in the wadi. Overall, however, this process is not likely to be of major importance. Much more significant are two effects of lake water inundation. Flooding has resulted in the spreading oflacustrine deposits, mainly silts, on the surface of much of the downstream part of the wadi. Although these deposits vary in thickness depending on the period and frequency of inundation, they provide a fertile material which may be a basis for agriculture. The second effect of flooding is the formation of an anaerobic zone in the upper part of the profile, which may have important effects on the availability of some nutrients, especially trace metals (see below). A survey of soils in the downstream part of the wadi has been undertaken in conjunction with the vegetation survey, and the results are summarized in Table 1. The range in ph found here is similar to that measured by Kassas & Girgis ( 1970) in their study in Allaqi prior to inundation (ph ), and to that of Ali (1987), who studied the effects of inundation on the soils and vegetation of the downstream part of the wadi, (ph ). Both studies showed that the TABLE l. Summary of data from survey of the soil in Wadi Allaqi Soil property ph Conductivity Loss on ignition Exch. Ca* Exch. Mg Exch. K Exch. Na Oxalate-Fet Oxalate-Mn Oxalate-Cu Oxalate-Zn Range of values umhos cm % 0.13-I.B% ppm ppm ppm ppm ppm ppm ppm *Exchangeable ions extracted by 0.5 M ammonium acetate, ph 7.0. toxide bound elements extracted with oxalic acidammonium oxalate buffer ph 3.3.

6 136 I. D. PULFORD ET AL. dominant water soluble anion was bicarbonate, hence the alkaline reaction of the soils. Kassas & Girgis ( 1970) found significant levels of sulphate only in association with Tamarix communities, which is a plant known to accumulate salts. Similarly, Ali (1987) found high concentrations of water soluble sulphate in the 0-3 em layer, which may reflect both accumulation in Tamarix litter and deposition in lacustrine deposts. Generally, the amounts of water soluble nitrates and chlorides are low. The soluble salt content of the soil is highly variable (see range in Table 1), but overall the soil is not saline. However, in view of the low degree of leaching salt accumulation is a factor which must be considered, if irrigation-based cropping systems are used. Current studies are underway to assess the salinity of well water and lake water, both of which appear to be low. The concentrations of exchangeable cations (Table 1) would seem to be satisfactory. Little is known at present about the nitrogen and phosphorus supply. Values of loss on ignition are generally low, except in the limited areas where plant litter has accumulated on the surface. Kassas & Girgis ( 1970) reported a range of % for loss on ignition in surface layers. The low amounts of organic material entering the soil, and the likely rapid oxidation rate of organic material due to the high temperatures, would suggest that there will be little capacity to store nitrogen and phosphorus in organic forms. Phosphorus availability will be controlled by the solubility of calcium phosphates. Extraction studies have shown that the amounts of plant-available trace elements will be low. This is probably a reflection of the high ph, the poor holding ability, the low overall concentrations and the low degree of chemical weathering of the soil. Use of acid oxalate, an extractant which removes oxides and associated trace metals, has indicated significant amounts of iron and manganese oxides, both of which are known to adsorb and occlude elements such as zinc and copper. Such a reservoir may be sufficient to supply essential trace elements to crops. This is particularly so in view of the redox changes brought about in the surface layers of the soil by inundation. Examination of soil pits in transects away from the current lake shoreline has shown the presence of a black layer immediately below the surface, which thins and eventually disappears with distance from the edge of the water. This layer is rich in sulphide, which will immobilize metals such as zinc and copper, which will be released on subsequent oxidation. Visual evidence suggests that oxidation results in a surface layer rich in iron oxide, and so the trace metals may be held in an available form. The texture of the soil is generally very sandy, although this can vary locally. Kassas & Girgis ( 1970) found that in the original wadi soils, silt plus clay content (material < mm) was usually less than 5%, with only occasional samples showing values as high as 20%. On the other hand, Ali (1987) found that the silt plus clay contents of soils which had been inundated could be as high as 70%. This fine material was usually present only in the 0-3 em layer, suggesting that it was lacustrine in origin. Visual evidence from the current study has indicated a surface layer in recently flooded areas up to c. 10 em in depth. In general, the soils of Wadi Allaqi appear to be fertile and capable of supporting crop production (see section on human activity). What is not clear at present is their ability to provide nutrients over the long term; in particular, the supply of nitrogen and phosphorus. The limiting factor to food production will be a supply of water. Use of lake water would seem to be unsuitable as

7 ECOLOGICAL RESOURCES IN WADI ALLAQI 137 movement of the shoreline precludes the establishment of permanent irrigation systems. There is much greater potential for using shallow groundwater which has collected due to seepage from the lake. At present, this allows cultivation close to the shore, where there is water 1-2 m below the surface. Clearly, this system is also vulnerable to shifts in the shoreline. Some initial studies have indicated some deeper groundwater which may be a result of seepage, and which may allow cultivation further from the lake if wells can be dug. The clear danger of establishing an agricultural system based on utilization of shallow groundwater is the pollution of the water, which will be recycled, by use of fertilizers and by leaching of salts through the light textured soil. There is also a danger of contamination of the lake by over-development of agricultural production. VEGETATION RESOURCES Kassas & Girgis (1970) described the vegetation of Wadi Allaqi prior to the creation of Lake Nasser, and concluded that the extremly arid climate was the major ecological factor limiting plant growth. They suggested that plant species required one of the following attributes in order to survive: I. Perennial plants that have deeply seated roots and that can survive throughout a series of rainless years. 2. Perennial plants with the capacity of storing water m their tissues (succulents). 3. Perennial plants that may accommodate the span of their life in accordance with the volume of moisture that is available after rain. 4. Ephemerals that appear only in rainy years. Of particular interest was their observation that Tamarix nilotica (Ehrenb.) Bunge (a riverain species) occurred in the upstream part of wadis in this region, but only on silt terraces where the groundwater was fairly close to the surface. In general, they described typically desert vegetation. As noted above, the creation of Lake Nasser resulted in the introduction of water into Wadi Allaqi at some considerable distance from the original Nile channel. This has had a significant effect on the plant ecology of the area. A survey of vegetation in the downstream part of the wadi was undertaken during the period of falling water level (Springuel, Ali & Murphy, 1989). A total of 26 stands was surveyed on a longitudinal transect for c. 25 km along the wadi, starting from the water's edge. This area was inundated at least once during the period between 1978, when the lake was at its highest level, and Within each stand, the vegetation was sampled using a random quadrat technique. Quadrat size and number of samples taken were varied as appropriate to the type and structure of the vegetation present in the stand. The vegetation showed a clear pattern of zonation with increasing distance from the lake shore, with five zones being distinguishable:,(one I. Closest to the lake shore, in an area completely inundated between , and periodically inundated during The soil was wet, with pools of water in depressions and the groundwater only em below the surface. The vegetation was dominated by annual species particularly Glinus lotoides L. Many plants were present as seedlings and young plants, which were

8 138 I. D. PULFORD ET AL. easily destroyed by the fluctuating water level, often before completing their life cycle. Zone II. A transitional zone, showing a gradually reducing history of complete or partial inundation with increasing distance from the shoreline. The groundwater varied up to 4 m below the surface. Dominant species were Glinus lotoides and the shrub Tamarix nilotica, with T. nilotica becoming predominant with increasing distance from the lake. Zone III. An area completely inundated between 1976 and early 1981, but completely exposed during Groundwater was 4-6 m below the surface. Vegetation was almost exclusively Tamarix nilotica, forming large thickets, particularly in the middle of the zone. Zone IV. Located km from the lake shore, this area was completely inundated for only 3 years ( ), and was fully exposed from 1983 to Groundwater was 6-7 m below the surface. This zone appeared to mark a vegetation transition: Pulicaria crispa (Forsskal) Bentham & Hooker Fil. ( = Francoeuria crispa (Forsskal) Cass., see Tackholm, 1974) here became codominant with T. nilotica, forming an open shrub community. Zone V. The final vegetation zone distinguished along the transect, located km from the lake, with groundwater at least 7 m below the surface. This area was inundated for only one year, 1978, when the lake was at its highest level. The vegetation was dominated by Pulicaria crispa, forming large bushes up to 2 m high and 4 m across. Individual bushes were widely spaced, to form an open shrub vegetation, in which a few large shrubs of T. nilotica were also present. The total cover of vegetation in was low at both ends of the transect, and generally higher in the middle. In Zones III and IV cover regularly reached 80-90%, mainly T. nilotica. Where P. crispa stands began to become prominent in Zone IV there was a marked decline in total cover, corresponding to the smaller size of individual Pulicaria plants compared both with the Tamarix and the older Pulicaria plants found higher up the wadi. Both Tamarix and Pulicaria showed a steady increase in height along the transect, corresponding to the time available for colonization and growth since the last submergence. The range of Tamarix height was greatest in the middle of the transect, where both mature and young plants were present. In Zones I and II only small seedlings and saplings of Tamarix were present, while from Zone III onward only mature plants were found. Pulicaria crispa is a plant characteristic of the runnels in desert wadis, where water from the infrequent storm events runs off. Its presence in abundance appears to mark the maximum extent of flooding in Wadi Allaqi. In general, a succession of communities can be distinguished in Wadi Allaqi extending away from the shoreline of Lake Nasser. The main influence of the lake has been to transform the ecology of the lower wadi by stimulating the development of plant communities dominated by riverain species, showing mesophytic characteristics, at the expense of the more xerophytic desert vegetation. HUMAN RESOURCES AND AGRICULTURE A further consequence of the introduction of water into Wadi Allaqi has been to increase settlement in the area. People have been attracted by the supply of

9 ECOLOGICAL RESOURCES IN WADI ALLAQI 139 TABLE 2. Crops grown in cultivated plots ofwadi Allaqi, April 1989 Crop Water melon Okra Sorghum Beans Karkadeh (Hibiscus) Onions Mulakheer Helba Saba Khosa (Courgette) Tomatoes Lentils Gargirh Pesium Lupin Number of growers I water, the availability of fodder from dried aquatic weeds (notably species of Najas abundant in the shallow margins of Lake Nasser, Springuel & Murphy, 1989) and the grazing for camels afforded by Tamarix. Once settlement had started, the potential of the soil for cultivation was quickly recognized. A survey undertaken in April 1989 suggested a population in Wadi Allaqi of people, 80% of whom had settled in the wadi since inundation. These people were located in 50 houses in seven clusters ofbetween four and 14 houses. Five of these clusters were close to the then shoreline, and had associated with them small cultivated plots ranging in size from x 5-40 m. The total cultivated area was c m 2 Each plot was surrounded by a fence of Acacia and Tamarix branches, and occasionally old fishing nets, in order to protect the crops from grazing animals. One or more wells, depending on plot size, had been dug beside each plot to provide irrigation water. At this point the water was some 1-2 m below the surface. Irrigation was by bucket and rope, the water being poured into a pre-organized system of surface feeder channels. These methods have proved successful in producing a range of crops for household consumption, despite the lack of husbandry experience and the shortage of labour at critical times. Table 2 lists the crops being grown when the survey was undertaken in April In addition to these crops, maize and barley have also been seen growing at other times. The other main agricultural activity undertaken in Wadi Allaqi is livestock grazing. Camels constitute the most valuable form of livestock, while sheep and goats are kept for milk and meat. As the animal population increases, grazing pressure becomes more of a problem. In 1985, the leaders of the four family groups in the area agreed to divide the wadi floor up into 'zones of influence', in a so far successful attempt to avoid grazing and land disputes. However, the problem, is starting to build up again as herd sizes, especially of sheep and goats, are starting to increase. It is exacerbated by the passage of camel trains, or dabuka, through the wadi. Each dabuka typically comprises camels, and between 500 and 600 pass through Wadi Allaqi each year, a total of some camels. During the peak months of November to March there are clear

10 140 I. D. PULFORD ET AL. signs of heavy grazing pressure on the natural vegeta'tion along the routes taken by the dabuka through the wadi. CHALLENGES FOR DEVELOPMENT The ecology of Wadi Allaqi has clearly been affected by the creation of Lake Nasser and the consequent inundation of an area which had previously been arid desert. Exploitation of this on a small scale by the few inhabitants of the wadi has shown that there is potential for further development. This new ecosystem is extremely fragile, and any development will have to be carefully planned so that deleterious processes are avoided. While it seems likely that mining and fishing will be important activities in the future, it is the development of agriculture in the wadi which is the greatest cause of environmental concern. The major limiting factor to cultivated agriculture is a supply of water through the growing season. Currently, the local people are exploiting the shallow groundwater close to the lake shore which has been left following 'the dropping of the water level in the lake. Such a development is vulnerable to any significant movement of the lake. If the lake recedes, then the water supply may disappear. Indeed, plots with newly germinated crops have been abandoned for this reason, reflecting the lack of manpower to carry water from the lake. Alternatively, if the lake level rises plots may be flooded. So cultivation close to the shoreline would not be a suitable practice for long-term agricultural development. For similar reasons, the establishment of large irrigated areas further from the shore, but supplied with water piped from the lake would also not be successful. Attempts to do this have indeed already failed. Water sources of greater potential are to be found as deeper groundwater resulting either from lake seepage, believed to lie some metres below the surface, or from rainfall in the Red Sea Hills, which is found at much greater depths in the solid rock underlying the wadi deposits. The first of these two sources of water is believed to hold the greater potential for agricultural use. At present, not enough is known about the distribution of such water, particularly its extent above the 180 m contour. Agricultural development above this height would be safe from inundation, but may be limited by water supply. Long-term cultivation below 180 m would be vulnerable to flooding if the water level in the lake again approached its maximum. However, such areas appear at present to be attractive for development, with either the acceptance of occasional loss or protection by some type of engineering works. Data from the soil study, and the success of small scale cropping, have shown the fertility of the soil and its ability to support crop growth in the short term. Nothing is yet known about the long-term supply of plant nutrients by the soil. If, however, larger scale cultivated agriculture is to be practised in the wadi, there must be minimum reliance on inputs of artificial fertilizers and pesticides. The sandy texture of the soil will allow rapid leaching of such inputs, with consequent contamination of both the irrigation water supply, and potentially, the lake water. Attention is being given to the use of nitrogen fixing plants, and the potential of nitrogen fixing micro-organisms, as ways of improving soil fertility. Consideration is also being given to the use of mulches and composts, possibly using aquatic weeds harvested from the lake, and the role of soil fauna in their breakdown and incorporation into the soil.

11 ECOLOGICAL RESOURCES IN WADI ALLAQI 141 Expansion of livestock agriculture is perhaps a more attractive possibility. Such an undertaking would require improvement of the grazing in the wadi, which is under pressure from the current numbers of animals, including those passing through the wadi in the dabuka. Both Tamarix and Acacia species are known to thrive in the wadi, and provide excellent food for livestock. Management of such plants, especially the supplying of water by irrigation in the early stages of their life cycle, could be a profitable development. There are in the wadi Acacia and Eucalyptus trees which were planted in 1989 and irrigated for 4 years. These trees are still surviving despite the lack of surface supplied water, presumably because their roots are exploiting one of the deeper sources of groundwater. In addition to grazing of shrubs and trees, fodder for livestock could also be produced in the wadi by a greater exploitation of harvested aquatic weeds and by the growing oflucerne. This last crop is a legume which would also help to improve soil fertility. Development of naturally occurring species would also assist two other economic activities; charcoal production and the harvesting of medicinal plants. Both of these activities are currently being undertaken by the inhabitants of the wadi on a small scale, and there is a ready market for these products in Aswan, although it has still to be established how elastic this demand is. CONCLUSIONS Wadi Allaqi would appear to offer scope for development in Upper Egypt, and may be only one of a number of such sites on the shores of Lake Nasser. These areas are attractive as they represent new lands away from the highly developed Nile Valley and Delta regions. The ecology of the wadi has shown a rapid and remarkable response to change over the last 20 years. Safeguards must be built in to any development to ensure that processes are not introduced which could initiate equally rapid, but deleterious, changes to the newly developed and still fragile ecosystem. ACKNOWLEDGEMENTS The authors gratefully acknowledge financial support for this study from The British Council and The United Nations Environment Programme. REFERENCES ALI, M. M. M., Studies on the shoreline vegetation of Aswan High Dam Lake (Lake Nasser) and impact of the lake on the desert. Unpublished M.Sc. Thesis of the Faculty of Science at Aswan, Assiut University. KASSAS, M. & GIRGIS, W. A., Plant life in the Nubian Desert east of the Nile, Egypt. Bulletin de l'egypte, 51: SPRINGUEL, I. & MURPHY, K. J., Plant ecology of Wadi Allaqi and Lake Nasser, I. Aquatic plants of Lake Nasser and associated waters in Egyptian Nubia. Allaqi Project Working Papers No. 4. Glasgow: University of Glasgow. SPRINGUEL, 1., ALI, M. M. M. & MURPHY, K. J., Plant ecology of Wadi Allaqi and Lake Nasser. 2. Preliminary vegetation survey of the downstream part ofwadi Allaqi. Allaqi Project Working Papers No.5. Glasgow: University of Glasgow. TACKHOLM, V., Students' Flora of Egypt. 2nd edition. Cairo: Cairo University. WHITE, G. F., The environmental effects of the High Dam at Aswan. Environment, 30: 4-11,