Abstract: The present study provides quantitative analysis of the vegetation and spatial variations of environmental factors controlling the abundance and distribution of vegetation in canal and drain banks in the Nile Delta region of Egypt. Five vegetation groups have been recognized: group A codominated by Arundo donax and Polygonum equisetiforme, group B codominated by Rumex dentatus and Polypogon monspeliensis, group C dominated by Eichhornia crassipes, group D codominated by Phragmites australis and Echinochloa stagnina and group E dominated by Typha domingensis. The total number of weeds recorded in the study area is 113 species belonging to 36 families. Therophytes (48.67%) and geophytes (14.16%) are the most frequent life-forms. The major chorotypes in the study area are Mediterranean (42.48%), Cosmpolitan (19.47%), Pantropical (13.27%) and Palaeotropical (12.39%). The relationships between the vegetation gradients and edaphic factors showed that, potassium and sodium cations, potassium adsorption ratio, chlorides, sodium cation adsorption ratio, pH value and water-holding capacity are the main controlling edaphic factors.
INTRODUCTION
The Egyptian cultivated lands are almost irrigated permanently by the river Nile through a huge network of canals and drains. The total length of both water systems exceeds 47000 km >31000 km of canals and >16000 km of drains (Khattab and El-Gharably, 1982, 1984). Most of these canals and drains were dug in the last 150 years (Hurst, 1952).
El-Gharably et al. (1982) attributed the increasing spread of aquatic weeds in the irrigation and drainage canals of the Nile Delta to some other ecological factors e.g. increasing pollution from agricultural practices, industrial centers and human activity along canals and drains. The factors that control the species composition and richness of the vegetation along the banks of rivers and other water bodies are still poorly understood (Nilsson et al., 1989).
From the ecological point of view, the study of the vegetation of the aquatic ecosystems and particularly that of irrigation and drain canal banks have received the attention of many authors in the Nile Delta region for examples, the vegetation analysis and species diversity along the irrigation canals and drains in the Nile Delta have been studied by Shaltout et al. (1994). The shoreline vegetation of El-Salam canal (Egypt) has been studied by Serag and Khedr (1996). The analysis of vegetation types of the canals and drains in Damietta Province has been studied by Mashaly et al. (2001). Mashaly et al. (2003) also studied the ecology of water hyacinth community type in the River Nile system in Egypt. Zahran and Willis (2003) gave a full description about the plant life in the River Nile in Egypt. Abu Ziada et al. (2008) reported an ecological study on the aquatic vegetation in North East Nile Delta of Egypt.
The objective of the present study is to describe the floristic composition and plant communities of the irrigation and drainage canal habitat in the Nile Delta region. Soil-vegetation relations will be also evaluated.
MATERIALS AND METHODS
The study area: The Nile Delta starts at Cairo, where the Nile pursues a northwesterly direction for about 20 km and then divides into two branches, the western branch (239 km in length) debouches into the Mediterranean at Rosetta, the Eastern branch (Damietta branch) which is about 245 km in length and three effluents namely: Riah-El-Tawfiki, El-Monoufi and El-Behari (Said, 1981). The area chosen for the present study is located in the Northern part of the Nile Delta region of Egypt which covers the North and middle limits of four Governorates namely, El-Dakahlia, Damietta, Kafr-El-Sheikh and El-Behira. The total average of these Governorates is about 17922 km2 and inhabited by about 11.361 million population (survey organization of Egypt, personal communication). Eight localities were selected to represent most of the plant life in the irrigation and canal bank habitat in this region.
| Fig. 1: | Map of the Nile Delta region showing different location (sites)
as indicated by ( |
The selected localities are: El-Mansoura, Talkha, Dekernus, Sherbin, Bilqas, Kafr-Saad, Farskour and El-Hamoul (Fig. 1).
Sixty stands have been chosen to cover all physiographic variations in the irrigation and drainage canal habitat. The stands were distributed as follows: the banks of irrigation canals (11 stands), drainage canals (10 stands), Damietta and Rosetta branches of the River Nile (9 stands) and open water bodies including canals (8 stands), drains (8 stands), branches of the River Nile (10 stands) and lakes (4 stands). The present study was carried out during 2003-2005.
Seasonal records of the weed flora have been carried out during regular visits. The description and classification of life forms are according to Raunkiaer (1934). The classification, identification, nomenclature and floristic categories are according to Tutin et al. (1964-1980), Zohary (1972, 1975), Feinbrun-Dothan (1978-1986) and Boulos (1999-2005). The density and phytomass of each species have been estimated in each selected stands according to Shukla and Chandel (1989) and Mueller-Dombois and Ellenberg (1974), respectively. The relative values of density and phytomass are calculated for each plant species and summed up to give an estimate of its importance value (IV) in each stand which is out of 200.
Soil samples are collected from each stand which is representing profile at a depth of 0-50 cm. The soil texture is determined using drying sieve method for the coarse soil, while the heavy textured soil samples are determined by the Bouyoucous hydrometer method (Piper, 1947). The moisture content and water-holding capacity are determined according to Piper (1947). The calcium carbonate is determined by titration against 1 N NaOH (Jackson, 1962). The oxidizable organic carbon is determined using Wakely and Black rapid titration method as mentioned by Piper (1947). For preparation of soil solution, add 500 mL. of distilled water to 100 g of air dry soil. Electrical-pH meter (Model Lutron pH 206) digital analyzer with glass electrode is used to determine the soil reaction (Jackson, 1962). Electrical conductivity is measured using YSI Incorporated Model 33 conductivity meter (Jackson, 1962). Estimation of chlorides is carried out by titration method using N/35.5 silver nitrate (Jackson, 1962). Sulphate content is estimated gravimetrically using barium chloride solution (Piper, 1947). Carbonates and bicarbonates are determined by titration method using 0.1 N HCl (Pierce et al., 1958). Determination of Na+, K+, Ca++ and Mg++ in the soil solution is carried out using flame photometer (Allen et al., 1974). The Sodium Adsorption Ratio (SAR) and Potassium Adsorption Ratio (PAR) are calculated according to McKell and Goodin (1984).
Water samples are collected from the studied water bodies including canals, drains, lakes and branches of the River Nile located in the four Governorates for analysis. Organic carbon, pH, electrical conductivity, chlorides, sulphates, carbonates, bicarbonates and extractable cations (Na+, K+, Ca++ and Mg++) are analyzed by the same methods previously described in the soil analysis. On the other hand, the total phosphorus is determined by digestion and followed by direct stannous chloride method (APHA, 1985). The total nitrogen is determined in the water samples using the micro kjeldahl method (Allen et al., 1974).
The classification technique applied here is the Two Way Indicator Species Analysis (TWINSPAN), while the ordination technique is the Detrended Correspondence Analysis (DCA) (Hill, 1979a, b; Ter Braak, 1988). All statistical treatments applied here are according to Snedecor and Cochran (1968).
RESULTS
The total number of flowering plants in the study area is 113 belonging to 93 genera and related to 36 families. Table 1 shows that, Gramineae comprises 27 species (23.89%), Compositae 15 species (13.27%), Chenopodiaceae 10 species (8.85%), Cyperaceae, Leguminosae and Polygonaceae, 6 species each (5.31%). These are the major families contributing about 61.94% of the total recorded species. The recorded species include 51 annuals (45.13%), 5 biennials (4.42%) and 57 perennials (50.44%). According to the life-form spectra, the recorded species are mainly therophytes (48.67%) and geophytes (14.16%) and partly helophytes (11.50%), hemicryptophytes (9.73%), hydrophytes (8.85%), chamaephytes (5.31%) and nanophanerophytes (1.77%).
| Table 1: | Floristic composition of the plant species of the irrigation and drainage canal habitat |
| A: Life-span, B: Life-Form, C:Floristic category, Ann.: Annual, Th: Therophytes, COSM: Cosmopolitan, Bi.: Biennial, Ch: Chamaephytes, PAN: Pantropical, Per.: Perennial, H: Hemicryptophytes, PAL: Palaeotropical, He: Helophytes, NEO: Neotropical, G: Geophytes, ME: Mediterranean, Hy: Hydrophytes, ER-SR: Euro-Siberian, Nph: Nanophanerophytes, SA-SI: Sahro-Sindian, P: Parasites, IR-TR: Irnao-Turanian, S-Z: Sudano-Zambezian, AUS: Australian, CULT: Cultivated | |
The floristic analysis of the study area revealed that, the Mediterranean elements (Mono, Bi or Pluriregional) include 48 taxa (42.48%), Cosmopolitan 22 species (19.74%), Pantropical 15 species (13.27%), Palaeotropical 14 species (12.39%) and Neotropical 5 species (4.42%). These floristic elements represent the major chorotypes in the study area. The other floristic elements are poorly represented.
The application of TWINSPAN classification on the importance value (out of 200) of 99 plant species recorded in 60 sampled stands representing irrigation and drainage canal habitat indicated to distinction of 5 vegetation groups (Fig. 2) and the vegetational composition of these groups are presented in Table 2. Group A is codominated by Arundo donax (IV = 19.53) and Polygonum equisetiforme (IV = 17.23). The most important species are Cynodon dactylon (IV = 14.39), Persicaria salicifolia (IV = 14.32), Paspalum distichum (IV = 12.55) and Paspalidium geminatum (11.47). Group B is codomianted by Rumex dentatus (IV = 25.33) and Polypogon monspeliensis (IV = 16.01). The other important species in this group are Stellaria pallida which is identified as indicator species with moderate IV = 11.75 and Chenopodium murale (IV = 11.03). Group C is dominated by Eichhornia crassipes which attained the highest mean importance value (IV = 57.44) and it is also considered as indicator species. The most common species are Echinochloa stagnina (IV = 26.82), Phragmites australis (IV = 21.68) and Lemna gibba (IV = 17.88). Group D is codominated by the indicator species Phragmites australis (IV = 31.24) and the abundant species Echinochloa stagnina (IV = 25.54). The most important species in this group are Persicaria salicifolia (IV = 15.19), Bassia indica (IV = 14.14) and Polygonum equisetiforme (IV = 11.83). Group E is dominated by the indicator species Typha domingensis (IV = 90.71). The most common species in this group are Lemna gibba (IV = 54.47), Bolboschoenus glaucus (IV = 26.33), Cyperus laevigatus (IV = 20.58) and Schoenoplectus litoralis (IV = 11.73).
| Table 2: | Mean value and coefficient of variation (between brackets) of the importance values (out of 200) of the recorded species in the different vegetation groups resulting from the TWINSPAN classification of the sampled stands in the irrigation and drainage canal habitat |
| Fig. 2: | Two Way Indicator Species Analysis (TWINSPAN) dendrogram of 60 sampled stands based on the importance values of 99 plant species of the irrigation and drainage canal habitat. The indicator species are abbreviated by the first three letters of genus and species, respectively |
| Table 3: | Mean value and standard error of the different soil variables in the sampled stands representing the different vegetation groups obtained by TWINSPAN classification of the irrigation and drainage canal habitat |
| W.H.C.: Water-holding capacity, T.N.: Total nitrogen, SAR: Sodium adsorption ratio, EC: Electrical conductivity, T.P.: Total phosphorus, PAR: Potassium adsorption ratio | |
| Fig. 3: | Detrended Correspondence Analysis A) ordination diagram of 60 sampled stands of (DC the irrigation and drainage canal habitat |
The ordination diagram of the sampled stands in irrigation and drainage canal habitat is shown in Fig. 3. It is obvious that, group A and B are superimposed and segregated at the right side of the diagram. While group C and E are separated at the left side. However, group D is separated at the middle part of the DCA diagram.
The averages of the soil variables of the five vegetation groups representing irrigation and drainage canal habitat are presented in Table 3. It should be noticed that, the physical soil variables are almost comparable in all vegetation groups. The percentage of coarse fraction attained the highest mean average (95.31%) in group A and the lowest mean value (82.99%) in group D. The highest mean percentages of silt (7.00%) and clay (0.58%) are attained in group C and group B respectively. Group B showed the highest mean percentage (26.01%) of moisture content and the lowest mean percentage (43.82%) of water-holding capacity. While, the lowest mean percentage of moisture content is attained in group A (23.10%) and the highest mean percentage of water-holding capacity (53.67%) is attained in group C. The highest mean percentages of calcium carbonate (19.13%) and organic carbon (2.65%) are estimated in group B, while the lowest mean percentages (8.33%) and (0.25%) are attained in groups D and E, respectively. The soil reaction varied between pH = 7.74 (slightly alkaline) in group D to moderately alkaline (pH = 8.35) in group E. The electrical conductivity varied from 7.55 to 0.82 mmhos cm-1 in groups E and A, respectively. The soluble anions (chlorides and sulpahtes) are exhibited a marked variation in all groups. Chloride content attained the highest mean percentage (1.71%) in group E and the lowest mean value (0.04%) in group A. While, sulphate content attained the highest mean percentage (1.36%) in group D and the lowest mean average (0.23%) in group B. The carbonates and bicarbonates are very low in all groups of this habitat type. The highest mean values of the total nitrogen and the total phosphorus contents are estimated in group E (1.39 and 27.35 mg L-1, respectively), while the lowest mean average (0.2 and 3.39 mg L-1, respectively) are attained in group D.
| Table 4: | Pearson-moment correlation (r) between the different soil variables in the sampled stands surveyed of the irrigation and drainage canal habitat |
| Explanation: *Significant at p≤0.05, **Significant at p≤0.01, ***Significant at p≤0.01 | |
| Fig. 4: | Canonical Correspondence Analysis (CCA) ordination diagram of plant species in the irrigation and drainage canal habitat along the gradient of soil variables (arrows). The indicator and preferential species are indicated by three first letters of genus and species, respectively |
The monovalent cations: sodium and potassium attained their highest mean concentrations in group E (757.07 and 28.12 mg 100-1 g dry soil, respectively) and the lowest mean concentrations (43.47 and 2.49 mg 100-1 g dry soil, respectively) in group A. The highest mean concentrations of divalent cations: calcium and magnesium (5.72 and 66.09 mg 100-1 g dry soil, respectively) are estimated in groups C and E, while the lowest mean concentrations (17.82 and 11.46 mg 100-1 g dry soil, respectively) are attained in groups A and B. The mean values of sodium adsorption ratio ranged between 347.76 to 10.60 in group D and B, respectively. While, potassium adsorption ratio varied from 4.21 in group E to 0.68 in group B.
The correlation coefficient (r) between the different soil variables in the sampled stands of the irrigation and drainage canal habitat are shown in Table 4. All of the soil variables are significantly correlated with each other. The Canonical Correspondence Analysis (CCA) ordination of plant species recorded in the irrigation and drainage canal habitat is shown in Fig. 4. It is obvious that, potassium cation, potassium adsorption ratio, chlorides, sodium cation, sodium adsorption ratio, pH value and water-holding capacity are the main effective edaphic variables which exhibited a close distinct relationships with the first and second axes of the CCA diagram.
DISCUSSION
The present study revealed that, the study area is rich in its floristic composition both in specific and generic levels. Thirty six families are represented by 113 species constitute the major part of the floristic composition of the study area. Gramineae, Compositae, Chenopodiaceae, Cyperaceae, Leguminosae and Polygonaceae are the most leading families. The percentage of life-span in the present study showed that, the predominance of life-span is related to perennial species (>50%). This agrees with the studies of Shaltout et al. (1994), Mashaly et al. (2001, 2003) and Abu Ziada et al. (2008). In accordance to Quezel (1978), the nature of the prevailing climate in the study area (semi-arid), the degree of water availability and the sandy texture of the soil activated therophytes (48.67%) to maintain predominance over the other life forms. Cryptophytes are the second active life form (14.16%) this could be emphasized through consideration of both its growth habit and the nature of the soil of its habitat. This study indicated the presence of a Mediterranean phytogeographical belt in Egypt and this belt represents a transitional sector between the Mediterranean and the Saharo-Sindian territories. This conclusion is based on the richness of the Mediterranean taxa (42.48%) in the study area, the bioclimatic features and the life-form spectrum. In contrary, this does not agree with Zohary (1975), who concluded that, there is a gap in the Mediterranean territory between southern Palestine and Libya in which the Saharo-Arabian belt closely approaches the Mediterranean coast.
From the phytosociological point of view, the vegetation of the irrigation and drainage canal habitat is classified by TWINSPAN classification into five groups. Each group comprises a number of stands and characterized by dominant and/or codominant species. Group A is codominated by Arundo donax and Polygonum equisetiforme, group B is codominated by Rumex dentatus and Polypogon monspeliensis, group C is dominated by Eichhornia crassipes, group D is codominated by Phragmites australis and Echinochloa stagnina and group E is dominated by Typha domingensis. Groups A, B and D may represent the vegetation types of the banks of irrigation canals and drains, while group C may represent the vegetation type of open water bodies (canals and drains) and group E may represent the vegetation type of open water of the Delta Northern lakes.
It is of interest to mention that, Simpson (1932) has classified the vegetation of irrigation channels in Egypt into five clases: aquatic, invading, bank retainers, weed controllers and sand controllers. In the Nile region (Nile Delta and Valley) of Egypt, Hassib (1951) has enumerated several unlisted plant associations (9 in uncultivated lands, 25 in marshlands, 12 in aquatic habitat and 8 halophytic communities). Some of these associations and communities are comparable to the vegetation groups recognized in the irrigation and drainage canals in the present study.
According to Braun-Blanquet’s (1932) floristic association system , the identified vegetation groups in the irrigation and drainage canal habitat can be categorized into three classes: Phragmitetea, Lemnetea and Ceratophylletea. The first class (Phragmitetea) occupies a wide moisture gradient extending from canal and drain bank zone and even the open water zone. This class include most of the plant communities in the ruderal habitats such as road sides, waste lands and abandoned fields in the Nile Delta. The second class (Lemnetea) represents the free floating hydrophitic vegetation and it is characterized by Lemna gibba and Eichhornia crassipes. The characteristic species which may be related to the second class include: Phragmites australis, Cynodon dactylon, Portulaca oleracea, Phyla nodiflora, Pluchea dioscorides, Imperata cylindrica, Mentha longifolia, Rumex dentatus, Echinochloa stagnina and Persicaria salicifolia. The third class (Ceratophylletea) occupies as Lemnetea, the litoral and open water zones. The characteristic species comprise Ceratophyllum demersum and Potamogeton crispus. In the present study, the associations of the vegetation groups recognized in the irrigation and drainage canal habitat may be similar to the associations described by Serag and Khedr (1996) and Mashaly et al. (2001, 2003) with respect to the macrophytic communities in the water bodies and along canal and drain banks in Nile Delta region.
In the present study, the application of Canonical Correspondence Analysis (CCA-biplot) indicated that, the most important soil variables correlated with the distribution of weed vegetation in the irrigation and drainage canal habitat are: potassium cation, potassium adsorption ratio, chlorides, sodium cation, sodium adsorption ratio, pH value and water holding capacity. A similar conclusion has been reported by Shaltout et al. (1994), Serag and Khedr (1996), Mashaly et al. (2001, 2003) and Abu Ziada et al. (2008).