Abstract: The present research comprises an investigation of the vegetation analysis, a quantitative assessment of the soil and water characteristics and an evaluation of the relationship between the major identified vegetation groups and the environmental attributes of the canals, drains and their wet shorelines at four governorates in North East Nile Delta, namely: Damietta, El Dakahlya, El Sharkia and Al Qaliopia. Vegetation, soil and water were sampled in 65 representative stands. The floristic categories, life span and life-forms of the recorded species were described. The soil and water characteristics were determined for each stand. The vegetation analysis was carried out using the multivariate techniques. The classification (TWINSPAN) and ordination (DCA) techniques of the stands led to recognition of four vegetation groups: group A codominated by Veronica anagallis-aquatica, Potulaca oleracea and Cynodon dactylon, group B codominated by Rumex dentatus, Phragmites australis and Cynodon dactylon, group C codominated by Phragmites australis and Echinochloa stagnina and group D codominated by Phragmites australis and Bolboschoenus glaucus. Canonical Correspondence Analysis (CCA) was applied to detect the main environmental factors influencing the vegetation groups. The electrical conductivity, calcium, sodium, potassium, magnesium, total nitrogen, chlorides and bicarbonates are the most effective environmental variables, which showed significant correlations with the first and second ordination axes. Accordingly, these soil and water variables seem to be the major ecological factors control the distribution of vegetation in the study area.
INTRODUCTION
The irrigation and drainage systems of the Egyptian cultivated land comprise approximately 47000 km of waterways (El-Sherbeny, 2003). The canals and drains are infested with most types of aquatic weeds. The increasing spread of aquatic weeds was attributed to the deep penetration of sun-light in water, decrease of water fluctuations and less disturbed habitat was created, increasing fertilization of farm land and pesticides application lead to eutrophication of canals and drains, excess of algal growth leading to deoxygenation of water and increasing pollution from industrial centers and human activities along canals and drains cause environmental physico-chemical alteration (Seiki et al., 1991; Edwin, 1996; Khedr and El-Demerdash, 1997; Wang et al., 1997). The problems created by these plants are many such as, constituting a health hazard by providing mosquitoes larvae with an ideal breeding place, causing oxygen depletion, obstructing drainage and flow of water in irrigation canals, decreasing phytoplankton production, polluting water supplies, increasing sedimentation by trapping silt particles and causing loss of water through evapotranspiration (Idso, 1981; Zahran et al., 1998). Aquatic plants have received great attention, not only for the magnitude of problems caused by them in the management of water resources, but also for promise they hold as a new source, for such diverse uses as animal feed, compost, paper, fiber, bioenergy and above all the possibility of using them as biofilter for improving water quality and removing heavy metals (Pieterse and Murphy, 1990; Sajwan and Ornes, 1997; Rice et al., 1997; Samecka-Cyerman and Kempers, 2001; El-Sherbeny, 2003). Various ecological studies have been concerned with aquatic and canal banks weeds in the Nile Delta as example Shaltout and El-Sheikh (1991) and Shaltout et al. (1994) gave information about the vegetation of some canals and drains along Cairo-Alexandria agriculture road. Also, they evaluated the behavior of some common species distributed along canals and drains in the middle of Nile Delta. Shalaby (1995) recorded the flora of canals banks at Kafr El-Sheikh governorate. The vegetation analysis of canals, drains and lacks of northern part of Nile Delta region was studied by Al-Sodany (1998). To evaluate the relationship between the vegetation components of canals, drains and shorelines in Northeast Nile Delta and their environmental conditions, the multivariate techniques (classification and ordination) have been used.
MATERIALS AND METHODS
Sixty-five sampling stands were selected to cover the irrigation and drainage canals in the study area (Fig. 1). The sampling processes of the plants, soil and water have been carried out during the year 2005-2006. In each stand, the plant species were recorded in five plots (25 m2 each). The identification and nomenclature of the plants were following Tackholm (1974) and Boulos (1999-2005). The description and classification of life forms were according to Raunkiaer (1937). The soil samples were collected at a depth of 0-20 cm then dried, thoroughly mixed and passed through a 2 mm sieve to be ready for physical and chemical analyses. Soil texture was determined using sieve method for coarse soil and Bouyoucous hydrometer for the heavy soil samples. Moisture content, porosity and water holding capacity were determined according to Piper (1947). Organic carbon was determined using Walkly and Black rapid titration method (Black, 1979). Calcium carbonate was determined as described by Jackson (1962). Soil salinity (EC) and soil reaction (pH) were estimated in 1:5 soil-water extract using the conductivity and pH meters, respectively. Chloride was determined by titration against N/35.5 AgNO3. Sulphate was estimated gravimetrically using 5% barium chloride. Carbonate and bicarbonate were determined using 0.1 N HCl. The cations Na+, K+, Ca++, Mg++ were estimated using flame photometer as described by Allen et al. (1974).
The chemical characteristics of the water samples were determined according to the methods previously applied in the soil analysis.
Two trends of multivariate analysis were applied, namely; classification
and ordination. The classification technique applied here was the two-way
indicator species analysis TWINSPAN-a fortran program (Hill, 1979; Gauch,
1982). While ordination techniques applied were the Detrended Correspondence
Analysis (DCA) and the Canonical Correspondence Analysis (CCA) using CANOCO-a
fortran program (Ter Braak, 1987, 1988). The relationships between vegetation
gradients and environmental variables can be indicated on the ordination
diagram produced by Canonical Correspondence Analysis (CCA biplot), on
which points represent species and arrows represent environmental variables.
The angle between an arrow and each axis is a reflection of its degree
of correlation with the axis. The statistical treatments applied were
according to Snedecor and Cochran (1967) and Nie et al. (1975).
| Fig. 1: | Location map showing the selected stands (●) of the different governorates (*) in the study area |
RESULTS
Floristic composition and features: The vegetation analysis
of the selected stands revealed that, the total number of hydrophytic
and canal bank species was 116 (Table 1). The recorded
species in the different governorates were 71 in Damietta, 49 in El Dakahlyia,
44 in El Sharkia and 62 in Al Qaliopia. These species could be classified
into three major groups according to their duration (life span): 67 perennials
(57.76%), 5 biennials (4.31%) and 44 annuals (37.93%). Out of the perennials,
sixteen species have wide ecological amplitude; they have been recorded
in the four governorates. The five biennials have been recorded only in
Damietta, El Sharkia and Al Qaliopia. Among the annuals, seven species
have been found in all governorates and two species in three governorates.
Concerning the life-forms Table 1 show that the recorded
species are grouped under five types: therophytes (48 species = 41.38%),
cryptophytes comprising geophytes, helophytes and hydrophytes collectively
(38 species = 32.76%), hemicryptophytes (14 species = 12.07%), chamaeophytes
(10 species = 8.62%) and phanerophytes (6 species = 5.17%).
| Table 1: | Floristic composition and distribution of the plant life in the study area |
Ph = Phanerophytes, Ch = Chamaeophytes, H = Hemicryptophytes,
G = Geophytes, He = Helophytes, Hy = Hydrophytes, Th = Therophytes,
COSM = Cosmopolitan, PAN = Pantropical, PAL = Palaeotropical, NEO
= Neotropical, ME = Mediterranean, ER-SR = Euro-Siberian, SA-SI =
Saharo-Sindian, IR-TR = Irano-Turanian, S-Z = Sudano-Zambezian, Nat.
= Naturalized, Cult. = Cultivated, Dam. = Damietta, Dak. = El-Dakahlyia,
Sha. = El-Sharkia, Qua. = Al-Qualiopia, P = Presence and P% = Presence
percentage |
|
| Table 2: | The principal floristic categories of the families in the study area |
Floristic analysis: The recorded plant species (116) in the study
area are belonging to 90 genera and related to 39 families (Table
2). Gramineae (26 species), Compositae (14 species) and Chenopodianceae
(10 species) are represented collectively by 50 species or about 43.1%
of the total number of the recorded species. Cyperaceae (7 species), Polygonaceae
(6 species), Amaranthaceae (5 species), Euphorbiaceae and Leguminosae
(4 species each) and Convolvulaceae (3 species) comprise 25%. The remaining
families (30) are either represented by two or one species. Floristically,
Table 2 reveals that the most common floristic elements
of Gramineae are: Pantropical (9 species), Cosmopolitan and Palaeotropical
(4 species each) and Pluriregional (3 species). In compositae, the most
common chorotypes are: Pluriregional (4 species) and Neotropical (3 species).
The abundant floristic elements in Chenopodiaceae are Pluriregional (4
species) and Cosmopolitan (3 species). In Cyperaceae, Polygonaceae and
Leguminosae, The common element is Palaeotropical (3 species each). Other
families comprise different types of floristic elements, which are represented
by a few numbers of species. The floristic analysis of the study area
as shown in Table 2 reveals that 41 species (35.34%)
are Mediterranean taxa. They are either pluriregional (25 species), Biregional
(14 species) or monoregional (2 species). Also, 63 species of the recorded
plants are either Cosmoplitan (17.24%), Pantropical and palaeotropical
(16.38% each) or Neotropical (4.31%). The other floristic categories are
poorly represented.
| Fig. 2: | Two Way Indicator Species Analysis (TWINSPAN) dendrogram of the 65 sampled stands based on the importance values of the 116 species |
Vegetation analysis
Classification of stands: The application of TWINSPAN classification
led to the recognition of four vegetation groups (Fig. 2).
The vegetational composition of these groups is presented in Table
3. Group A comprises 8 stands codominated by Veronica anagallis-aquatica,
Portulaca oleracea and Cynodon dactylon. The important species
in this group include Sonchus oleraceous (indicator species), Cyperus
rotundus and Amaranthus lividus. Group B comprises 19 stands
codominated by Rumex dentantus, which also identified as indicator
species, Phragmites australis and Cynodon dactylon. The
important species in this group comprise Malva parviflora, Sonchus
oleraceus, Echhornia crassipes and Echinochloa stangnina.
Other indicator species are Plantago major, Chenopodium
album and Bidens pilosa. Group C includes 33 stands codominated
by Pharagmites australis and Echinochloa stagnina. The most
common species in this group are: Myriophyllum spicatum, Cynodon
dactylon, Cyperus alopecuroides, Nymphaea lotus (indicator
species), Ludwigia stolonifera and Ipomoea carnea. Group
D includes 5 stands codominated by Phragmites australis and
Bolboschoenus glaucus. The most important species are Paspalidium
geminatum, Cynanchum acutum, Leptochloa fusca, Panicum
repens and Atriplex portulacoides. No indicator species have
been identified in this group.
| Table 3: | Mean value and coefficient of variation (value between
brackets) of the importance values of indicator and preferential plants
in the different vegetation groups resulting from TWINSPAN classification
in the study area |
Ordination of stands: The ordination of the surveyed stands given by Detrended Correspondence Analysis (DCA) is shown in Fig. 3. It is obvious that, the vegetation groups obtained by TWINSPAN classification are distinguishable and having a clear pattern of segregation on the ordination planes. Group A is separated at the right side of the DCA diagram, while group B is separated at the middle position of the DCA diagram. On the other hand, Group C is segregated at the lower left side. And Group D at the upper left side of the DCA diagram.
Variations in soil variables: The soil variables of the four groups
of stands which derived from TWINSPAN classification are shown in Table
4, it is notable that most of the soil variables showed a little variation
between the different groups of stands. The soils of the four groups have
coarse sandy texture with sand fraction more than 80%. The fine fractions
(silt and clay) were relatively high in group B than in the other groups.
The highest mean value of water holding capacity was attained in group
A (56.13%). However, the lowest mean value in group D (47.24%). The mean
values of soil pore spaces are obviously comparable at all groups. The
percentages of calcium carbonate content are high in groups D and B as
compared with the A and C groups. Organic carbon contents are obviously
comparable in all groups. The pH values indicate that the soil reaction
is slightly alkaline in all groups. It is clear that, the mean values
of electrical conductivity, chloride, bicarbonate, total nitrogen content
and concentration of extractable cations: Na+, K+,
Ca++ and Mg++ are obviously high in group D and
low in group A. The phosphate and total phosphorus contents are highly
represented in group B.
| Table 4: | Mean value and standard error (±) of the different soil variables in the stands representing the different vegetation groups obtained by TWINSPAN classification in the study area |
| Fig. 3: | Detrended Correspondence Analysis (DCA) ordination of the 65 stands |
Variation in water variables: Table 5 shows
the means of water variables of the four vegetation groups. It is obvious
that the water reaction is weakly alkaline with pH values ranged between
7.98 in group B and 8.68 in group D. Also, it has been found that the
highest mean values of electrical conductivity, dissolved oxygen, chlorides,
sulphates, total nitrogen, organic carbon, sodium, potassium, calcium
and magnesium are attained in group D. On the other hand, the most mean
values of the previous variables are attained in group B except organic
carbon, chloride, total nitrogen, calcium and magnesium in group A. The
total phosphorous in water reached the highest concentration in group
C and the lowest concentration in group B.
| Table 5: | Mean value and standard error (±) of the different water variables in the stands representing the different vegetation groups obtained by TWINSPAN classification in the study area |
| Fig. 4: | Canonical Correspondence Analysis (CCA) ordination diagram with
hydrosoil variables represented by arrows. The indicator and preferential
species are abbreviated to the first three letters of each of the
genus and species |
Relation between vegetation and environment: The correlation between
vegetation and environment is indicated on the ordination diagram produced
by Canonical Correspondence Analysis (CCA) of the biplot of species-environment
as shown in Fig. 4 and 5 for the soil
and water, respectively. It is notable that, electrical conductivity,
the percentages of calcium, sodium, potassium, magnesium, total nitrogen,
chlorides, bicarbonates, calcium carbonates, sulphate, organic carbon,
sand, clay and silt are effective soil variables which show relatively
high significant correlations with the first and second axis of CCA ordination
diagram. The codominant species of the most identified groups, Veronica
anagllis-aquatica and Rumex dentatus as well as the important
species Cyperus rotundus, Amaranthus lividus, Malva parviflora,
Chenopodium album, Myriophullum spicatum (indicator species)
and Eichhornia crassipes are separated at the upper right side
of CCA biplot diagram. These species showed a close relationship with
sodium, total nitrogen, bicarbonate, calcium carbonate, organic carbon
and porosity. While the codominant species Bolboschoenus glaucus
as well as the indicator species Plantago major, Bidens pilosa
and Ipomoea carnea are segregated at the lower right side of
the CCA-bipilot diagram. These species exhibit a clear relationship with
electrical conductivity, calcium, potassium, magnesium, chlorides and
sulphates. Cynodon dactylon as a codominant species in group A
and B and as an important species in group C and Echinochloa stagnina
as a codominant species in group C and as an important species in
group B are separated at the upper left side of the CCA-biplot diagram.
These species showed a clear relationship with silt and water holding
capacity. Cyperus alopecuroides as an important species in group
C is separated at the lower side of the CCA-biplot diagram and showed
a distinct relationship with soil reaction.
| Fig. 5: | Canonical Correspondence Analysis (CCA) ordination diagram with
water variables represented by arrows. The indicator and preferential
species are abbreviated to the first three letters of each of the
genus and species |
It is obvious that, electrical conductivity, potassium, sodium, bicarbonate, chlorides, magnesium, total nitrogen, sulphates, calcium, pH, carbonate and dissolved oxygen are the most important water variables which exhibited a relatively high significant correlation with the first and second axes of the CCA-biplot diagram (Fig. 5). The codominant Veronica anagallis-aquatica of group A and Rumex dentatus of group B, the important species Amaranthus lividus of group A, Malva parviflora and Echhornia crassipes of group B, Myriophyllum spicatum and Nymphaea lotus of group C, Paspalidium geminatum, Cynanchum acutum and Atriplex portulacoides of group D, also the indicator species Chenopodium album of group B are collectively segregated at the upper right side of the CCA-biplot diagram. These species show a close relation with the high contents of K+, Na+, HCO3–, Cl–, Mg2+, total N and Ca2+. However, Portulaca oleracea, Phragmites australis and Bolboschoenus glaucus are in groups A, B, C and D, respectively. And the indicator species Sonchus oleraceus in group A, Plantago major and Bidens pilosa in group B and Ipomoea carnea in group C are separated at the lower right side of CCA-biplot and showed a distinct relationship with EC, SO4– –, pH, dissolved O2 and CO3– –. On the other hand, a few species: Cynodon dactylon, Solanum nigrum, Echinochloa stagnina and Sorghum virgatum are obviously segregated at the upper left side, while Cyperus alopecuroides alone in the lower left side.
DISCUSSION
The present study reveals that the eastern section of the Nile Dalta, which comprises Damietta, El Dakahlyia, El Sharkia and Al Qaliopia governorates, is rich in its flora on specific generic and families levels. The total number of macrohydrophytes of the irrigations and drainage canals and weeds of its shores is 116 species belonging to ninety genera grouped under thirty-nine families. Graminae, Compositae, Chenopodiaceae, Cyperaceae, Polygonaceae, Amaranthaceae, Euphorbiaceae, Leguminosae and Convolvulaceae constitute the major part of its floristic composition. The cause of interspecific association are varied, but are usually related to similar response of species to the environmental variables. The degree of water availability and the sandy texture of the soil activated the therophytes to maintain predominance over other life forms. Cryptophytes are the second active life form. This could be emphasized through consideration of both its growth habit and the nature of the soil of its habitat. This trend is similar to spectra reported by Mashaly (1987). From the floristic point of view, about 35.34% of the total number of the recorded species are Mediterranean taxa. The other floristic elements are Cosmopolitan, Palaeotropical, Pantropical, Neotropical, Irano-Turanian, Saharo-Sindian, Euro-Seberian and Sudano-Zambesion are represented by varying number of species, reflection their different capability to penetrate the region. Similar investigations have been described by El Ameir (2005). The application of TWINSPAN technique has proved useful in classifying stands, on objective basis, into four vegetational groups, although these groups are not absolutely distinct because the member of some groups are linked together by having one of the dominant species in common. The recognized vegetational groups named after their codominant species as follows: Veronica anagallis-aquatica, Portulaca oleracea and Cynodon dactylon (group A), Rumex dentatus, Phragmites australis and Cynodon dactylon (group B), Phragmites australis and Echinochloa stagnina (group C), Phragmites australis and Bolboschoenus glaucus (group D). Comparable groups have been described in the Nile Delta by El-Sheikh (1989), Al-Sodany (1992), Khedr and El Demerdash (1997) and Mashaly et al. (2001). The CCA-biplot ordination diagrams indicated that the effective soil and water variables which significantly correlated with the abundance and distribution of vegetation groups in the study area are numerous such as Salinity (EC), soil fractions (sand, silt and clay), pH value, soil fertility (organic carbon, phosphorus and nitrogen contents), dissolved oxygen, calcium carbonate, soluble anions (chlorides and sulphates) and extractable cations (sodium, potassium, calcium and magnesium). Several studies confirmed this trend such as those of El-Shiekh (1989) and Shaltout and El-Sheikh (1991). Veronica anagallis-aquatica as codominant in group A and Rumex dentatus as codominant in group B showed a close relationship with sodium, bicarbonate, total nitrogen, calcium carbonate, organic carbon and porosity. However, Cynodon dactylon as codominant in group A and B and Echinochloa stagnina as codominant in group C exhibited a close relationship with silt and water holding capacity. Phragmites australis as codominant in groups B, C and D, Bolboschoenus glaucus as codominant in group D and Portulaca oleracea as codominant in group A showed a close relationship with electrical conductivity, sulphates, pH value, chlorides, dissolved oxygen. It may be concluded that the most important soil variables which correlated with the distribution and abundance of the aquatic and canal banks weeds in the Nile Delta are: soil salinity (EC), sodium, calcium, potassium, chloride, soil fertility (organic carbon, nitrogen and phosphorus contents) and fine fraction (clay). The most important water variables are salinity, potassium, sodium, bicarbonate, chloride, nitrogen content and pH.