A Study of Benthic Macroinvertebrate Community in the Lower Part of Greater Zab River Near Guwer Subdistrict

In this study, the analysis of 48 qualitative macroinvertebrate samples were taken from four sites in the lower reach of Greater Zab river near Guwer subdistrictErbil from May 2008April 2009. Sixteen taxa belong to Ephemeroptera, Diptera, Plecoptera, Hemiptera, in addition to one taxa belong to class Arachnides were identified. Site 1 is characterized by more identified taxa (12 taxa) than the other sites. Most abundant taxa were Tanypus spp. during studied period which followed by Hydrachna spp., with highest F index percentage reached to 75% and 58.3% respectively. According to Sorenson index, sites 2 and 3 were the most similar sites with values reached to 75%.


INTRODUCTION
During the last decades, benthic macroinvertebrates had been the most commonly used group for the assessment of anthropogenic impacts on the quality of surface water (Skoulikidis et al., 2009).Many stream and river assessment methods based on macroinvertebrates which have been developed worldwide and they are the preferred means of assessing aquatic quality (Arimoro and Ikomi, 2009).
Spatial variation in lotic macroinvertebrate community structure due to a combination of intrinsic biotic community interactions, environmental conditions and historical factors (Murphy and Davy-Bowker, 2005).Aquatic insects which are important elements in the ecological dynamics of lotic environment are playing an important role in the cycle of materials and introphic transfers (Hynes, 1970).The communities of aquatic insects are affected by several factors related to water quality, stream morphology and food availability and quality (Bispo et al., 2006 ;Ifigenia et al., 2006).
Many researches had been done during the last three decades concerning aquatic insects in Iraq.Most studies concentrated on Tigris River and their tributaries in northern and a central part of Iraq: (Hussain et al., 1984;Salih et al., 1986 ;Salih et al., 1990).They are made survey of microfauna, macrofauna and zoobenthos in Tigris River at Mosul city.Whereas, (Mohammad, 1980;Al-Mukhtar et al., 1986 ;Saadalla, 1998) studied the impacts of anthropogenic stress on abundance and distribution of benthic invertebrate in Diyala River.Preliminary water quality reports on the Greater Zab River were made by (Al-Nimma, 1982;Aziz, 1997;Aziz, 2006 ;Lak, 2007) dealt with ecological aspects.While, (Ali, 2006) described microinvertebrate, macroinvertebrate abundance, diversity, ecological variables on communities structure.
The goal of the present paper is to investigate and describe the macroinvertebrate community structure in unperturbed lower reach of Greater Zab River.

MATERIALS AND METHODS
Greater Zab River is one of the main Tigris River tributaries.It passes through mountains and valley areas and many branches discharged to it.The total length within Iraqi land reached to 171 Km.The substrate of the studied portion of the river consist of large stones and pubbles.
Monthly, macroinvertebrate samples were collected at 4 sites from lower stretch of Greater Zab River, from May 2008 to April 2009 (Figure 1).Benthic organisms were collected using a handnet (mesh < 0.3 mm), fixed 5% formalin in the field and preserved with 70% ethanol in the laboratory.Taxonomic identification of most samples was made to the generic level and some members to the species level through the taxonomic key of (Edmonson, 1959;Quigley, 1977;Macan, 1979;Tachet et al., 1984;Hynes, 1977;Bouchard, 2004).
The frequency of benthic occurrence species were calculated by using the F index which described by (Muniz and Venturini, 2001): F= Pa/P *100, where: Pa= is the number of sites where the species are occurred and P is the total number of sites.Using this formula the species were classified in: Constant species (F > 50%), Common (10 < F < 49%) and Rarely species (F < 10%).
Sorenson similarity (Hamayoan et al., 2003) was used to compare the sampling locations and to determine which one was similar in taxa composition.S = 2J/ (a+b) *100, where: J= number of species occurred in both sites.a= number of species occurred in (a) site, b= number of species occurred in (b) site.

RESULT AND DISCUSSION
Altogether, 17 taxa are belonging to 12 families were identified from quantitative samples.Among them 9 taxa belong to Ephemeroptera were represented by 4 families, 4 taxa to Diptera represented by 4 families, 2 taxa to Plecoptera and one taxa for Hemiptera and class Arachnides.
Baetidae and Ecdyonuridae were the most common families which accounted for 17.6% of the total taxa collected for each one.Although the number of species were identified in all sites: Isonychia spp., Tanypus spp.and Hydrachna spp.(Table 1).Site 1 is characterized by more identified taxa (12 species) compared with other sites which are contributed by only 7 species for each one.It may be due to less anthropogenic impacts in site 1 rather than other site downstream it (Shekha, 2008).Some of description and measurement of taxa are summarized as follows: Baetis rhodani (Pictet, 1844): Body tapered.top of femora with long and short pointed spines.Small pointed spines on tibiae, base on antennae and edge of gills.Length 12-15 mm.( Plate 1, A, B, C, D).
Prosopistoma spp.: Body flattened dorsoventrally.A shell covers the chest and part of the abdomen, leaves only the last abdominal segments, gills invisible cachese completely under the shells.Eyes dorsal compounds significantly.(Plate 2, E, G).Amphinemura spp.: Dark brown color.Long bristle present about two-thirds along length of each femur region of legs.Length up to 6 mm.Gills 4, cervical, with 5 or more branches each).(Plate 3, A, B, C).
Tanypus spp.: Antennae retractile, usually elongated, prolegs long, stilt-like, anterior pair with a common base.Ventral pair of anal gills attached to base of prolegs, remote from anus.Three pairs of anal gills.(Plate 3, D).
Tendipes tentans : Thoracic respiratory organ a tuft of numerous filaments.(Plate 3, E).Simulium spp.: Head with a pair of prominent mouth brushes.Hooked false leg on thorax.Abdomen ends in an attachment organ of radial rows of strong hooks.Length 10 mm.(Plate 3, F, G).
The larva of Chironomidae (Tanypus spp.) were the most dominant species which presenting in all sites during studied period with frequent percentage (F %) 66.6, 41.6, 75, 66.6% respectively (Tables 2, 3, 4, 5).These are represented as constant species (Muniz and Venturini, 2001).(Al-Mukhtar et al., 1986 ;Saadalla, 1998) have found that Chironomide larva represents higher than 50% of benthic fauna in Diyala river.Chironomidae are broadly distributed worldwide and frequently which are the most abundant insects in many freshwater ecosystems (Callisto et al., 2002 ;Garcia and Suarez, 2007).Furthermore, their quick generation turnover and rapid growth guarantee are an availability of biomass to aquatic ecosystem dynamics (Marques et al., 1999).On the other hand, Hydrachna sp. was the second abundant species in all sites with F index 16.6, 33.3, 58.3, 33.3% respectively. Ali (2006) recorded Hydrachna spp. in Khabat site in Greater Zab River during July and August.Isonychia spp. was identified in all sites.It is regarded as common species in sites 2 and 3 and as rare species in sites 1 and 4. Ali (2006) found same species in Greater Zab River.

Table 1 :
List of macroinvertebrates recorded during studied period.

Table 2 :
Monthly recorded of macroinvertebrates in site 1, with their constant index percentage.

Table 3 :
Monthly recorded of macroinvertebrates in site 2, with their constant index percentage.

Table 4 :
Monthly recorded of macroinvertebrates in site 3, with their constant index percentage.

Table 5 :
Monthly recorded of macroinvertebrates in site 4, with their constant index percentage.