1. Introduction

     There are over 751,000 known insect species, which is about 75 percent of all known animal species on Earth.  Some of them are living in water ecosystem as benthic macroinvertebrates and they can be used for water quality monitoring ⁽¹⁾. Despite the fact that most insects live in inland water; for instance, (swamps, ponds, lakes, springs, rivers and streams) these are referred to as water insects ⁽²⁾. Approximately 3% of all insect species have water phases in some inland water biotopes; insects can account for more than 95% of the complete macroinvertebrates population ⁽³⁾. Biosocial methods have recently been replaced or compensated for physical and chemical factors in evaluate water qualities ⁽⁴⁾. Furthermore, ⁽⁵⁾ concluded that the role of biota is usually the last point of water degradation and contamination and are therefore significant indicators of a healthy ecosystem. The biodiversity is the variety of living forms in a certain area and represented by the number of existing species. It is indicated that anthropogenic contamination and environmental stress will reduce the biological productivity of the wetland communities which will led to changes in their communities, reduction of their optimal nutritional activities, reduction in the richness and abundance of the endogenous species ⁽⁶⁾. However, highlighted five major impacts affecting on biodiversity in water general: (I) the fluctuation of the water levels; (II) The overexploitation; (III) water contamination; (IV) destruction of the habitat; (V) and the effect of the invasive species ⁽⁷⁾. Biodiversity implies the organisms that reside in a region, plus the ecological factors that are essential to maintain them, but also the relationship between these two factors that can be translated into the water system's capacity to support different forms of living organisms ⁽⁸⁾. The use of aquatic insects as biological indicators is supported by the fact that they are usually stable in time and place; thus, appearing the variations of the ecosystem had gone through ⁽⁹⁾. Aquatic insects are used to evaluate the “healthy status” of a stream, and also determined water quality by characterized by finding sensitive as well as tolerance organisms ⁽¹⁰⁾. In various researches, aquatic insects were used to assess the biological-ecological integrity of the lotic water environment. They estimated the biological integrity and to validate the Index of Biological Integrity based on macroinvertebrate assemblages in rivers ^{(11 and 12)}. Conditions of aquatic ecosystems can be evaluated to assess the degradation of freshwater ecosystems, hence the current work has been completed to estimate the aquatic insects’ diversity in relation to physical and chemical characteristics of Shekh Turab stream in Erbil province.

2. Materials and Methods

2.1. Study Site

     Erbil is the capital city of Kurdistan and is situated in northeastern Iraq (figure 1A). It is bordered to the north-east and south-east the Upper and Lower Zabs. It is located between longitudinal 43º 58ˉ to 44º 03ˉ E and from latitude 36º 09ˉ to 36º 14ˉ N (13). Climate in the region is regarded a broad daily and annual temperature variation. The climate of the area is nearer to the sort of Iran-Turan. The average annual precipitation exceed 1000mm ⁽¹⁴⁾. Shekh Turab stream located about 20 km from the east of Erbil city, Kurdistan Regional of Iraq. The stream is mainly used for irrigation and drinking purposes. The riparian areas are occupied by residence and therefore it is exposed to domestic waste and agricultural runoff.  The locations of the sampling sites are shown in figure 1B.

 Figure 1: A- Map of Erbil province within Iraq, B- Map of studied sites within Erbil province (Shekh Turab Stream) ⁽³⁴⁾

2.2. Sample Collection and Analyses

     Five sites were homogenously distributed in the studied Shekh Turab stream. Water samples were taken in July and November 2017, when the responses of the systems to nutrient enrichments were more significant and growth and decay rates of macrobenthic species were at the highest ⁽³⁵⁾. From upper stream (site 1) to downstream, each site was located 7 km from each other except site 4 was located 6 km from site 3. Temperature measured using alcohol thermometer, pH, EC (μS.cm-1) and total dissolved solids was directly measured with portable equipment (pH-EC-TDS meter, HI 9812, Hanna instrument), dissolved oxygen (mg.l^-1), BOD5 (mg.l^-1), alkalinity (mg CaCO3.l^-1), HCO3 (mg.l^-1), total hardness (mgCaCO3.l^-1), calcium (mg Ca2+.l^-1), magnesium (mg Mg2+.l^-1), nitrate (mg NO3-N.l^-1), chloride (mg.l^-1), sodium (mg.l^-1), potassium (mg.l^-1) and sulfate (mg SO4.l^-1) were estimated according to ⁽¹⁵⁾.  Aquatic macroinvertebrate insect samples were collected at each site by gathering the rocks using Surber sampler ⁽¹⁶⁾. The benthic invertebrate has been separated for the primary taxonomic group, and conserved in 4% formalin vials ⁽¹⁷⁾. Most samples were taxonomically identified at the generic level and some participants at the species level through the taxonomic key of ^{(18, 19 and 20)}. The Tukey HSD multiple comparison test was used for the significant differences of means of physio-chemical variables between sites (one-way ANOVA; P < 0.05).  Pearson correlation coefficient analysis was performed to find out the relation between physio-chemical parameters versus taxonomic levels of diversity of aquatic insects. The aim was to find the strength of association between the two sets of variables ⁽³⁶⁾. All statistical analyses were carried out using SPSS (version 19) and using a significant level of 0.05.

2.3. Biological indices

a- Species Richness: Species richness is a measure of the amount of species contained in a sample. This specific measure of species richness is known as D, the index of the Menhinick ⁽²¹⁾.

D=S/ √¯N

Where S is equal to the amount of distinct species in the sample, and where N is equal to the complete amount of individual sample organisms.

b- Species diversity: Species diversity differs from species richness by taking into consideration both the number of species current and species dominance or evenness in relation to each other. Shannon index was calculated as a measure of species diversity, H. ⁽²²⁾.

𝑯 = ∑ (𝑷𝒊) /ln𝑷𝒊/

Where: Pi is the proportion of the total number of individuals in the population that are in species “i”.

c- Simpson dominance index: Simson’s Index is regarded as a dominance index because it weighs towards the most prevalent species ' abundance

Ds=∑^s_i=10 (ni(ni-1)/N(N-1))

Where: ni is the number of species and N complete amount of species in the ith species ⁽²³⁾.

3. Results and Discussions

      All the variables studied includes water temperature, air temperature, pH, EC, total dissolved solid, dissolved oxygen, BOD5, alkalinity, HCO3, total hardness, calcium, magnesium, nitrate, chloride, sodium, potassium and sulfate shows significant at different sites in the two different months (Table 1 and 2). Air and water temperatures varied between 12.40 Cº to 35.45Cº and 7.20 Cº to 26.30 Cº respectively. The pH values ranged from 7.89 to 8.38, this implies water samples are almost sub-alkaline in nature. The present results indicate a comparative coincidence with pH values of surface water which lie within the range of 6.5 to 8.5 ⁽²⁴⁾. The values of Electrical Conductivity varied between 977 to 1198 µs/cm. The values of total dissolved solid (TDS) changed from 624 to 766 mg/l respectively. In drinking water, the most desirable limit for TDS is 500 mg/l according to WHO standard and all samples go beyond this limit ⁽²⁴⁾.

Table 3: Aquatic insects that recorded in Shekh Turab stream in July and November, 2017.

Table 4: Pearson correlation coefficient between water parameters, (Shannon index and Taxa richness).

* Correlation is significant at the 0.05 level (two-tailed).

In the Shekh Turab water there were several variables responsible for more aquatic ecosystems, including water temperature, EC, TDS, DO, alkalinity, hardness and other ions. Periphyton development in relation to geology and velocity parameters was investigated in New Zealand ⁽³¹⁾. The nature of the underlying substratum of Shekh Turab stream is another one, too important factors affects the variety water insects. Species variety ranged from 0.365 to 0.755 bits/ind according to the Shannon-Weiner index. The highest diversity value recorded at site 2 whereas the minimum diversity calculated at site 4 (Table 5).

Table 5: Diversity and other indices of aquatic insects in the study stations of Shekh Turab stream.

In general, sites diversities 1, 2, 3 and 5 were greater; this can be ascribed to greater human activity at site 1 sewage disposal containing more water nutrients and other ions used as food from phytoplankton cells and aquatic insects dominated at this site.  Organically enhanced environments have a reduced diversity, with some dominant species, according to ⁽³²⁾. Meanwhile, ⁽³³⁾ wrote that, in many instances, diversity at intermediate polluted locations is greater than at clean locations. Menhinick's richness index disclosed the largest richness calculated in site 1 and the lowest in locations 3 and 5, which likely linked to the amount of taxa recognized in each site for the region studied. Taxa dominance in this study ranged from 0.284 at site 4 to 0.582 at site 5.

4. Conclusion

     From the results throughout this study, a total of 3 families representing 2 orders were recorded in this survey. Caenis macrura and Caenis meosta were present in the large amount of individuals at all sampling sites. This indicates the richness and diverse group of aquatic insects in the study area. It reinforces to the fact that the habitat quality is most suitable for insects to breed and multiply under the natural ecosystem. Furthermore, the river’s environmental factors had directly and/or indirectly affected aquatic insect assemblages, showing that aquatic insects were useful indicators of water quality in the Shekh Turab Stream. All sampling stations in the study came out as moderately polluted by indication of diversity index.

Conflict of interest

None.