The water hyacinth (Eichhornia crassipes solms) in the Nile system, Egypt

Aquatic Botany, 1 (1975) 243--252 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

THE WATER HYACINTH (EICHHORNIA CRASSIPES SOLMS) IN THE NILE SYSTEM, EGYPT

K.H. BATANOUNY and A.M. EL-FIKY

Department of Botany, Faculty of Science, University of Cairo, Giza (Egypt) (Received December 5th, 1974)

ABSTRACT Batanouny, K.H. and EI-Fiky, A.M., 1975. The water hyacinth (Eichhornia crassipes Solms) in the Nile system, Egypt. Aquat. Bot., 1: 243--252.

Eichhornia crassipes was recorded in Egypt in the last decade of the 19th century, but it did not reach the plague proportions exhibited in the Nile Delta until recent times. The construction of a series of river control schemes caused several ecological changes in the Nile system, which encouraged the growth and spread of Eichhornia in almost all the aquatic habitats in the Nile system. The present study shows clearly the fast growth of Eichhornia in the Egyptian Nile system. A plantlet with 450 cm 2 basal area, 40 g fresh weight and 7.4 leaves, attained a basal area of 1.0827 m 2, fresh weight of 1.244 k g a n d had 208 leaves after 50 days in a drainage ditch (from September 6th to October 26th, 1973). During that period, a plant would produce about 43 new offsets on the average. The consequences would be disastrous if an Eichhornia plant reaches the open water reservoir of Lake Nasser. Such a plant, after 200 days during the growing season, would produce 3,418,800 new offsets with an area of 14,928 m 2. In winter, the plant growth is very slow and even death and decomposition of some parts of the plant occur.

INTRODUCTION

The water hyacinth (Eichhornia crassipes Solms) has become a serious menace in many countries of the world. It has spread from the American tropics and assumed a largely pan-tropical distribution (Robertson and Ba Thein, 1932; Simpson, 1932; Jepson, 1933; Bose, 1945; Parham, 1947; Bouriquet, 1949; T~ickholm and Drar, 1950; Vaas and Sachlan, 1949; Meadly, 1953; Robyns, 1956; Bates and Phipps, 1958; Mendonca, 1958; Gay, 1958, 1960 a and b; Allsopp, 1960; Chadwick and Obeid, 1966; Bock, 1969; Holm et al., 1969). The rapid growth of water hyacinth infestations is often spectacular and the problems it creates are many (cf Timmer and Weldon, 1967; Little, 1969). This paper presents a study undertaken of the growth of Eichhornia under field conditions in the Nile Delta, Egypt.

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THE NILE SYSTEM IN EGYPT

The Nile traverses the entire length of the country, bringing large volumes of water and suspended matter. Willcocks (1904) estimated the discharge regime of the river Nile at the turn of this century as follows: of the mean discharge of 3,400 m3/sec which passed Aswan, 400 m3/sec were utilized in the irrigation of 2,320,000 acres (ca 928,000 ha) in Upper Egypt, while 540 m3/sec were discharged into the Mediterranean. Ball (1939) estimated the quantity of suspended matter annually carried past Wadi Halfa to be 110 million tons; some 16 million tons was taken from the river by canals and pumps in Upper Egypt; a further 36 million tons subsides onto the river bed between Aswan and Cairo and is transported as part of the bottom load, and the remaining 58 million tons remained in suspension in the river at its passage past Cairo. The main trunk of the river divides 20 km north of Cairo into two branches (each about 240 km long), which debouche into the Mediterranean. The Nile water is led by a network of irrigation canals over the broad alluvial delta. The northern part of the delta is occupied by four shallow lakes. Due to the seasonal character of the Ethiopean rainfall from which the Nile derives its summer (flood) supplies, the volume, level and characteristics of water vary greatly through the year. The Nile system has been subject to a series of large-scale schemes of river control (barrages, dams, irrigation canals) and land use, especially during last 150 years. Recently, after the construction of the High Dam at Aswan to conserve water for irrigation, the man-made Lake Nasser will cover 5,736 km 2 (survey datum 182 m). Apart from the obvious consequences of changing a water course into a lake, there are many ecological repercussions of damming the river (cf Kassas, 1972). The likelihood of Eichhornia crassipes invasion of the lake, together with other water weeds, is alarming. The effects of damming on downstream reaches are more marked. THE A D V E N T OF EICHHORNIA TO THE NILE

Tackholm and Drar (1950) report that the plant was introduced to Egypt during the reign of Khedive Tawfiq (1879--1892) by a certain Mr Birdwood who was at that time Director of E1-Giza and EI-Gezira domains. Percheron (1903) mentioned the cultivation of Eichhornia crassipes in the ponds of public gardens at that time, warned against the dangers of the spread of this water pest in Egyptian canals and drew attention to the serious troubles of Americans in clearing their waterways of this plant. Thirty years later, Simpson (1932) writes "In Egypt the plant is near Cairo, Alexandria, Damanhour, Damietta and near Bilbis to Lake Manzala where it is a serious pest in Bahr EI-Baqar drain system. There is also a stretch of it at the mouth of Bahr Hadus. It is found in fresh and brackish water but is killed

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by sea water. I have no other record for the plant in Egypt, from the above distribution it seems fairly clear that the plant has spread from cultivation in towns." He (1932) also reports " A t the present time the water hyacinth is so localized in Egypt that it can be dealt effectively by manual labour supported by strictly inforced legislation. Every year delay makes this less possible on account of large areas becoming contaminated." This has become the present situation. It is very rare to find a water habitat in Egypt, particularly in the delta, n o t menaced b y Eichhornia crassipes. Floating islands of the weed are c o m m o n in the Nile at Cairo, particularly during summer months. These floating mats drift northward with the current, and accumulate in the northern reaches of the Nile and completely cover the water surface, especially in the Damietta branch which is closed by an earthen dam. In the Sudan, the first report of the weed in the White Nile was in 1958 {Gay, 1958, 1960 a, b; Gay and Berry, 1959). The origin of the infestation is uncertain. The plant invaded many parts of the Nile system in the Sudan (cf Faris, 1972). Quoting the words of Obeid and Tag-El-Seed (1973) shows h o w serious the present situation in the Sudanese Nile system is: "In the period April to October vast amounts of water hyacinth plants drift north toward the Jebel Auliya Dam where they accumulate, completely covering the water surface for a considerable distance. Wind and current action during that period continuously compress them into a thick carpet that people may walk on them." GROWTH OF EICHHORNIA

UNDER FIELD CONDITIONS

METHODS

The experiments were carried out from September 6th to October 26th, 1973 and from December 18th, 1973 to February 5th, 1974 in a 4-m wide drainage ditch in Giza, some 4 km west of the University of Cairo. The water depth in the ditch, the total soluble salts, dissolved oxygen concentration and the pH value showed wide fluctuations during the experimental periods. These, almost rhythmic, fluctuations depend on the irrigation system adopted in the land crossed by the ditch. The ditch receives its water from the fields which are irrigated by minor canals, in which water is high for 5 days, then low for 10 days. The water depth ranged from 45 to 85 cm in the first experiment and from 25 to 100 cm in the second experiment. An area of 4 × 30 m was cleared from vegetation in the ditch. Plantlets of Eichhornia crassipes growing in the same ditch were used in the experiments. In each experiment 200 plantlets of almost uniform size and weight were used. Plantlets were weighed and the number of leaves and the basal area as calculated from diameter measurements of the plantlets were estimated. On average, each plantlet had a fresh weight of a b o u t 60 g and had 7.4 leaves with a basal area of 600 cm: in summer, and a b o u t 116 g, 8.5 leaves with basal area o f 850 cm 2 in winter experiment. After tagging the plantlets, they were placed in the cleared area. The water c o n t e n t and dry weight were determined in comparable samples.

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247 At the termination of each 5-day interval, 10 plants were examined for weight, number of leaves, new offsets, inflorescences and the basal area. Plants were dried at 85°C till constant weight to obtain the dry weight. Water depth was determined at 5-day intervals and water samples were collected for analysis. The total of soluble salts, dissolved oxygen concentration and the pH value have been determined. The mean daily air temperatures during the experimental periods, which lasted 50 days in each experiment, were obtained from the nearest Meteorological station (Giza). RESULTS

Experiment 1 Water hyacinth plants showed notable growth during the first experiment (September and October), Fig.1. The increase was 3,010% of the original fresh weight after 50 days. In other words, an individual with a fresh weight of 100 g will attain a fresh weight of 3.110 kg after 50 days under field conditions in months representing the end of the growing season of the plant. The data illustrated in Fig.1 reveal a gradual increase in the fresh weight during the first 20 days of the experiment, followed by a sharp increase in the fresh weight till the end of the experiment. It should be noted that the percentage increase per day was not uniform throughout the experiment; it varied from 31 to 130 per day. This is probably related to variations in water characteristics and air temperature during the experimental period. Large increases in fresh weight were associated with episodes when the total soluble salts were low. Dissolved oxygen concentration reached the zero level for a period of 5 days during the experiment. However, this did not show obvious effects on the plant growth. Increase in basal area of the plants showed almost the same trend as the fresh weight during the first 35 days, and in the following 5 days the basal area did not show further increase, was followed by low growth during the last 10 days of the experiment. The crowdedness of the plants in the area already cleared is probably the main reason for the decrease in growth rate of the basal area of the plants. The widely separated plantlets placed in the cleared area (4 × 30 m} covered the whole area completely within 30 days, although 10 individuals were removed every 5 days. This means that the rest of plants (150 plants) covered an area of 120 m 2 in 20 days. Despite the low percentage increase of the basal area of the plant in the last 15 days, there is a considerable increase in fresh weight and number of leaves. The growth of the plants is mainly vertically. The increase in the number of leaves per individual (the plantlet with its offsets) shows almost the same trend as that of the fresh weight and basal area during the first half of the experimental period. During the first 5-day interval of the second half of the study period, the plant showed little increase in the

248 number of leaves: the considerable increase in the fresh weight and basal area was due to increase in leaf area and not in number of leaves. During the period with low production of new leaves {25--30 days after the start of the experiment) the plant produced inflorescences. After that period the plants produced a fresh crop of new leaves. Increase in the number of leaves was not uniform throughout the experimental period. On the average, a plant with 7.4 leaves produced 208 leaves by the end of the experiment. The number of newly produced offsets showed a continuous rise during the experiment {Fig.2). The rate of increase was gradual in the first half of the experimental period, while in the rest of the experiment the increase was sharp. One plantlet produced about 43 new offsets having 208 leaves during the experiment. The original dry weight was calculated for ten plantlets comparable to those used in the experiment. The data illustrated in Fig.2 represent the average dry weight for ten individuals taken at 5-day intervals. The rate of increase in the dry weight production is considerable. A plantlet with a dry weight of 7.6 g attained an average dry weight of 235.2 g in the 50-day period of the experiment.

Experiment 2 The winter experiment was carried out from December 12th, 1973 to February 5th, 1974 in the same locality. The data illustrated in Figs 1 and 2 show that the winter growth of water hyacinth is low. Death and decomposition of some parts of the plants are obvious from the decrease in the various parameters of growth during the experiment. The percentage increase in fresh weight by the end of the experiment was only 28.5%. The rate of growth was not uniform throughout the experimental period. The increase in fresh weight as a percentage of the original weight ranges from 0.5 to 12.5 per day. However, the highest percentage increase is less than half the lowest recorded in the first experiment. The fresh weight values were almost constant during the first 25 days of the experimental period, then exhibited fluctuating values till the end of the experiment. The measured water characteristics showed little fluctuation during the winter experiment. During the major part of the experimental period, the air temperature fluctuated between 10 and 15°C, while in the autumn (September October) experiment, it ranged from 20 to 30°C. It is interesting to note that the basal area of the individual plants showed wide fluctuations during winter. The basal area decreased, sometimes as much as 30%. Such a decrease may be ascribed to the death and decomposition of some parts of the plant body. The production of new leaves is accompanied by the death of older leaves, hence the number of leaves showed wide fluctuations during the experiment. In this experiment, the increase in the number of leaves does not mean an

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increase in the basal area. This may be explained by the fact that the newly produced leaves in winter have small areas, while the decomposing old leaves have relatively large areas. So, the fluctuations in the number of leaves do not coincide with those of the basal area. The production of new offsets during winter is very limited. Formation of new offsets is often replacement of old ones. By the end of the winter experiment, the number per individual reached 1.2 as compared with 43 in the first experiment (Fig.2). Dry matter production in winter is very low and the plant may lose some of its dry weight (Fig.2). A plantlet with a dry weight of 10.2 g (calculated as average of ten plant.s) showed slight changes during the experiment, reaching 13.1 g after 50 days. DISCUSSION

Though the water hyacinth has been present in Egypt since the 1890's, it did not reach the plague proportion exhibited in the Nile Delta until recent times. Since the construction of a series of river-control schemes, the Nile system has been subject to several ecological changes: silt-free water running

250 downstream and the consequent excessive use of fertilizers to compensate for the lack of silt, changes of the chemical character of irrigation and drainage water, permanent presence of water in canals and drains all the year round, low current velocity in the Nile, and stopping the water flow to the Mediterranean. These factors seem to have encouraged the growth and spread of Eichhornia crassipes. The most serious potential problem is the invasion of the Aswan Dam Reservoir by the water hyacinth. Kassas {1972) reports that invasion of the reservoir by water weeds will sooner or later follow the phase of filling the reservoir. In this situation, one must consider the high air temperature favourable for plant growth in this area during the major part of the year. Gay (1960 a) states that Eichhornia crassipes is not completely held by the Jebel Auliya Dam on the White Nile, for during storms plants are blown over the top and they can pass down fish ladders and pass with steamers through the lock. The way is open for its passage to Upper Egypt. The present study showed clearly the very fast growth of E. crassipes in the Egyptian Nile system even at the end of the growing season, which extends from the end of March to October. Westlake (1963) reviewed the literature concerned with productivity in uncontrolled environments and showed that the productivity potential of E. crassipes is tremendous. This species appears to be among the most productive of photosynthetic organisms (Westlake, 1963; Yount, 1964; Bock, 1969). An important character of water hyacinth as a colonizing species is due to its rapid rate of vegetative reproduction by means of offsets. Owing to the brittleness of the stolons connecting the offsets to their plant, they are easily broken and the offsets are set free: potential colonizers. Bock (1969) observed that the water hyacinth plants grew fastest under the warmest temperature regime (27.6°C); the growth decreased by lowering the temperature. She concluded that this is not surprising since the plants are native to the lowland American tropics. The results obtained from the present study reveal that the air temperature that prevailed during the two experiments controls the productivity of the water hyacinth: However, the water characteristics have their influence on the growth of the plant as is evident from fluctuations in the growth rates due to changes in the water characteristics. In the present investigation, a plantlet (average of 10) with 450 cm ~ basal area, 40 g fresh weight and 7.4 leaves attained a basal area of 1.082 m 2, fresh weight of 1.244 kg and had 208 leaves after 50 days {from September 6th to October 26th, 1973). During this period, a plant would produce an average of 43 new offsets. The two experiments show that pJants do not grow at a constant rate. Measurements were made at short intervals for sufficiently long periods and the collected data furnish a sound measure of growth rate fluctuations over a growing season. We do not assume that the plants are increasing in basal area and number of offsets at a geometrically constant rate for a period of

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200 days which represent the main growing period of the plant (the growing season may extend from March to October). There is good evidence to assume that the newly produced offsets will exhibit growth rates equal to the original (parent) plant after 50 days of their being set free from the parent plant. Based upon this assumption, the 43 offsets (1.0827 m 2) produced by a single plantlet after 50 days will produce (at the same rate) 1849 offsets (ca 26 m 2) in the subsequent 50 days. Again these offsets will produce after 50 days 79,507 new offsets (622 m:) which in turn produce 3,418,800 new offsets (14,928 m:) by the end of the following 50 days period, i.e. 200 days from the start. It is evident that water hyacinth shows tremendous growth rates in the Egyptian Nile system. This is truly alarming. Sculthorpe {1971) writes "In a suitable habitat during active growth plants can double their number every 2 weeks, the floating mat extending by as much 0.5 to 0.75 m per month. Penfound and Earle (1948) calculated that at this rate of multiplication ten individuals would have produced 655,360 plants, equivalent to a solid acre, during one growing season which in Louisiana extends from at least March 15th to about November 15th. ACKNOWLEDGEMENT

The authors wish to express their deep gratitude to Professor M. Kassas for reading the manuscript, and for valuable suggestions.

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