Diversity Measurement Indices of Diatom Communities in the Tigris River within Wasit Province , Iraq

The study was conducted to measure diatom species diversity in the lotic ecosystem across the Wasit Province for 12 months. The quantitative study of diatoms (phytoplankton) was investigated in the Tigris river. The density of algae was ranged from 60989 cell×10 3 /l to 112780.82 cell×10 3 /l in the five sites. These algae were belonging to 39 genera. The richness index values ranged from 1.53 at site 5 in January 2016 to 6.34 at site 1 and June2015. Shannon-Weiner diversity index (H ́) was 2.33 in February 2016 and 3.72 in June 2015 both values at site 3, whereas Evenness index was 0.54 at site 5 in March2016 and 0.98 at site 1 in both August2015 and May2016. The lack of homogeneity of the appearance of species indicates the dominance of a few species with high densities, which is an indicator of the existence of environmental pressure. All studied indices showed that the Tigris River quality is suitable for the living aquatic life or may be slightly affected by the pollutants.


Introduction:
The freshwater aquatic systems are the important sources the life of most aquatic organisms in inland water environment (1).The alteration in water quality and biodiversity in the lotic ecosystems caused by pollution, these alterations were lead to change the living strategy of organism and only the tolerant species were remains in this environment (2).Some algae such as diatom group use due to their ability to tolerate the cleaning in the enivronment (3,4).Due to their life characterized such as rapid reproduction and short generation times these organisms considered as a good bioindicators and an alarm agent in aquatic ecosystems and their ability to respond to the alteration in the environment (5,6).Hassan and Shaawiat (7) used phytoplankton as bio-indicators in Euphrates river, their study found 11 diatomic algae sensitive and 7 species tolerant to pollution species.Hassan and Shaawiat (8) applied 15 indices to evaluate the water quality of the Euphrates River.

Materials and Methods:
The Tigris River within the Wasit Province was selected for application diversity indices.Monthly sampling was taken from five sites along the Tigris River during the period from June 2015 to May 2016, 2014 (Fig. 1).The selected sites for this study were about 180 km from Baghdad city in the Wasit Province.This area is characterized by different an agricultural activity and to control the water discharge in this area a big dam constructed (Kut dam) for irrigation and power production purpose (9).For this study, five sites were selected along the river in this region (Figure1, Table 1).The algal samples were preserved by Lugolʼs iodine solution, and concentrated nitric acid and the methods were used to clarify diatom frustule (10,11).The following references were used to identify the algae (12,13,14,15,16,17).Richness index was calculated according to Stiling (18), and the value of Shannon and Weaver and Evenness indices were calculated as follows (19).

Results and Discussions:
The total number of algae ranged from (5082.41 cells × 10 3 /l at site5 to 9395.88 cells × 10 3 /l at site1.The centric diatom ranged (590.38 -2045.52)cell × 10 3 /l at the sites3 and 1, respectively.The pinnate diatom recorded the lowest value (4255.35cell × 10 3 /l) at site5, and the highest rate (7350.36 cells × 10 3 /l) at site1 (Table 2).The total number of species and genera were ranged 159-179 and 38-39, rspectively (Table 2).The results in the present study showed the total number of diatoms is higher than that recorded by Al-Janabi (20).The increase in the total number of phytoplankton recorded in the present study on the Tigris River may be due to increased nutrient concentrations in these sites where they are exposed to additions of agricultural land and household waste from residential areas near the river (21,22).The low number recorded may be due to the lack of nutrient concentrations due to the reduction in water levels and the increase in flow velocity in the river, which prevents the growth of phytoplankton well as it moves quickly to areas other than is suitable for its growth and reproduction (23), and may be due to the lack of light permeability due to increase the turbidity from the speed of flow in the river, which works to move the bottom sediments and return to the water column, which is the turbidity caused lack of sufficient light access to the phytoplankton spread in the water column (24).Also the increase and decrease in the numbers of diatoms may also be attributed to the disruption of water levels in the river (25), which may lead to the re-attachment of some benthic species in the water column (26).The relationship between river drainage and living mass is inversed (27).
The richness index ranged from 1.53 at site5 in January 2016 to 6.34 at site1 in June2015 (Table3).Significant temporal and spatial differences (P≤0.05) were noticed.When comparing these values with the standard values, the higher the values indicate the high diversity of diatoms in the Tigris River, indicating that the diversity in the Tigris River is high, may be due to variation in the values of the index to increase algae during the period Study or lack of pollution and lack of grazing by zooplankton for algae (28).Species abundance is the number of taxonomic units diagnosed and represents diversity within the sample.This indicator is defined as the absolute number of taxonomic units in a biomass at a location within the water surface.This indicator uses a key to other measurements, which consists of taxonomic units classified to the species level, so that the abundance of species reflects the diversity of water groupings (29).
The Shannon diversity index (H´) varied between the lowest value (2.33) at site 3 in February 2016 and the highest value (3.72) at site3 in June2015 (Table 3).A significant differences (P≤0.05) of noticed among seasons and sites.
The results revealed that the Shannon index values were more than 1.These results indicated a high diversity in the study area and the nondominance of certain types of phytoplankton, while the few values (less than1) indicate the dominance of certain species of phytoplankton on the appropriateness of environmental conditions from physical and chemical factors in the study sites that assist in the growth and diversity (30).
The results showed species similarity among sites.The differences recorded for the species in the sites may be due to the nature of the site, in the nature of the land in which the river passes and the residential areas and the specifications of the site itself in terms of the presence of curvature and the presence of some drainages in which it flows (31).The spread of aquatic plants has been helped, to the adherence algae on these plants, as well as nutrients and other factors.(32).The water of the Tigris River in the present study, based on this index, it is found that water quality ranges from moderate polluted to clean water.
The Evenness index values ranged from 0.54 at site5 in March2016 to 0.98 at site1in August2015 and May2016 (Table 3).The significant differences were noticed among seasons and sites (P≤0.05).Higher values of the species of Evenness index in the river indicate that there is no stress or environmental pressure on the diatomic species in the rivers, where the values exceeded 0.5 in most seasons and months of the study so that the species are homogeneous in appearance (33).This is agreed with Green (34).Green (34) revealed that the lack of homogeneity of some algae existence indicated the dominancy of a few species with high densities and these considered an indicator of the existence of environmental pressure.
The difference in values may be due to the index of diatoms adhered to the runoff system that can cause a change in the depth and geology of the river's surface and surface, and may be due to the dominance of a particular species over other species (34).Different in the result values between sites and months to the nature of conditions that may be appropriate or inappropriate for the presence of diatoms (35).

Figure 1 .
Figure 1.Map of study areas (Used Arc-GIS Map program)