Impact of Hindiya Dam on Rotifera Community of Euphrates River on the Northern of Babil Governorate, Iraq

This study was the first of its kind on the Hindiya Dam, which is considered one of the important dams in Euphrates River. Five sites were chosen on the north of Babil Governorate in order to know the rotifers biodiversity features and the impact of the Hindiya Dam on it's during the 2019. Site2(S2) was located near the dam to reflect the rotifers diversity of this site, whereas , S1 was located at the upstream of the dam as a control site, and S3, S4 and S5 were located down the dam. Rotifers showed higher density average at Hindiya Dam site compared with sites downstream the dam which was 9164 Ind./m 3 , whereas density average at the site downstream the dam was 5540 Ind./m 3 , site (downstream the dam ) decreased clearly compared with the dam site. It was showing the relative abundance index of rotifers: Keratella cochlearis was with the highest percentages followed by Rotaria neplunia , Syncheta oblonga and K. valga at the sites of study area. The study confirmed that the dam reservoir was the source of pelagic rotifers for the outflowing river which led to increase species numbers about 104 species of rotifers. The average values of species richness index of rotifers declined from 1.64 at Hindiya Dam site to 1.58 at site below the dam. Euphrates River rotifers were considered generally from moderate richness to disturbed during 2019 in study area. Site 3(downstream the dam) had the lowest similarity values with site 5 which was 47.5% in rotifers group. Whereas, the highest Jaccard similarity index percentage was between sites 1 with 4 which reached to 76.2%. The Shanon- Weiner index of rotifers reported average values at the dam site 1.7 and 1.8 bit/Ind. at site below the dam. Also, the average values uniformity index of rotifers increased from 0.6 at Hindiya Dam site to 0.7 at site downstream the dam. Euphrates River rotifers were considered generally as little diversified because of index value was ranged from 1 to 2 during 2019 in study area. According to uniformity index values, Euphrates River rotifers were considered generally from unbalanced to moderate balanced in study area. The constant species of rotifers showed that constant species were 8 at the dam site. While, it decreased to 7 constant species at site (downstream the dam). It was concluded that Hindiya Dam had a great effect on the spatial composition of the rotifers community related to the change in the hydrological conditions from current water in site1 to limnetic basins in site 2 (the dam reservoir) then again to current water at site 3, 4 and 5 downstream the dam. ISSN: 0067-2904


Introduction
Dams were built for a variety of reasons, including water supply, sediment control, agriculture, and around 48% for other purposes [1]. These sediment-control and irrigation dams, such as Hindiya Dam, are smaller than reservoir dams. [2].
The impacts of dam are either direct or indirect on river ecosystems by altering the structure of aquatic habitats and fluctuating flow pattern for river, loss biodiversity, population displacement, and ecosystem services [3], water discharge, sedimentation, and changes of water quality are the important factors in changing of ecological conditions in river ecosystems [4]. The zooplankton (Rotifera, Cladocera, Copepoda) reacts in various ways to different types of environmental stresses, so it is increasingly used in aquatic environments as a bioindicator [5] , as well as having a high sensitivity and reaction to environmental variation [6]. Therewith several local studies are dealing with a zooplankton group to indicative of environmental stress, such as [7][8][9][10][11][12][13][14][15][16][17][18] while this study considered as the first of its kind due to it included the study of the impact of Hindiya Dam on Euphrates rotifers assemblage, in Babil Governorate. Which we can include it's the main objectives by investigating these impact on Euphrates rotifers biodiversity and identification.

Material and Methods Study area Description
Hindiya Dam is situated on the Euphrates River in the south of Musayyib City in the north Babil Governorate, Iraq. The Dam length is 250 m and has 36 dams spillways, 5m wide of each one. It was designed for treating sediment matter of the one of two major branches of the Euphrates in this area called Hilla River.
We choose five sites for collection of study samples on Euphrates River near Hindiya Dam ( Figure-

Sample Collection
Samples were collected monthly from January to December 2019 at depth 0.5m with a volume of 40 L . Forty liters of water were filtered through net with mesh size 55 µ by using a graduated bucket (10 L). Rotifers were captured in a vial at the net bottom, and then it can be put the sample water into a bottle (500ml) for counting after concentrating to 10 ml. [19]. The biological material (Rotifers ) was preserved in 4% formalin [20].

Ecological Indices
The following Ecological Indices were accountable: Relative Abundance Index (Ra) was calculated depending on the formula used by Odum [21]. The Species Richness Index (D) was calculated monthly according formula for Margalefe [22]. Jaccard Presence -Community was calculated according to the formula of Jaccard [23]. Shannon -Weiner Diversity Index (H) of rotifers communities were calculated monthly by using the formula of Shannon and Weiner [24]. The Species Uniformity Index (E) was measured by the formula of Neves et al. [25]. Uniformity is in appearance if value of index is higher than 0.5 according to Pielou [26]. Constancy Index (S) was calculated according the equation used by Seraphim et al. [27].

Results and Discussion
It was shown that the rotifers density values of Hindiya Dam site were 1743 Ind./m 3 to 26220 Ind./m 3 , the lowest values were in September, whereas the highest values were in December. For sites downstream the dam, the numbers of rotifers decreased in site 3 compared with site the dam, then increased in sites 4   As for spatial variation, site 5 had high density may due to it had favorable conditions for rotifers growth such as higher value percentage oxygen saturated [28], and the presence of macrophytes [29].
Whereas, the density values in site 3 (below the dam) decreased compared with the dam site. This could be either due to the effect of the dam as a barrier which caused a reduction in rotifers densities compared with the dam site [30]. Or the low water quality in site 3 compared with the dam site which effect negatively on rotifer density [31].
A number of studies have found that rotifers density values in site (below the dam) decreased compared with the dam site such Portinho et al. [32] pointed out that rotifers density on the Paraná River site downstream was less than the Itaipu Reservoir in Brazil. Likewise, Zhao et al . [30] when they compared dam effect on the Ying River which is tributary of the Huaihe River in China.
In view of all that has been mentioned so far from our findings and the previous agreed studies, it was proved that the dam affected on rotifers densities, especially on site 3 downstream the dam compared with the dam may due to the effect of the dam as a barrier which decreased rotifers densities .Or due to the lower quality in site 3 as explained above.
The relative abundance index of rotifers which indicated that Keratella cochlearis with highest species percentages followed by Rotaria neplunia, Syncheta oblonga, K. valga, Trichocerca bicristata, Polyarthra dolicoptera, Euchlanis deltata then Polyarthra vulgaris at all sites of the study area Figure- 4 and  Sabri et al. [33] recorded pelagic rotifers taxa through study of Samarra Dam on Tigris River , which contributed to river plankton was influenced by many factors such as the seasonal pattern of lentic plankton, reservoir levels and outflow characteristics in the impoundment. Czerniawski and Kowalska-Góralska [34] when they studied the effects the impoundments of carp ponds on zooplankton in Poland. They referred to the domination of pelagic rotifers (e.g., Keratella cochlearis ,Rotaria neplunia, Syncheta oblonga, K. valga ,Trichocerca bicristata, Polyarthra dolicoptera, Euchlanis deltata and polyarthra vulgaris ) as shown in this study results at all sites because of sites of dams on Barycz River considered a suitable place for drifting pelagic rotifers to proliferate, and reproduce in rivers.
Czerniawski et al. [35] point out the abundance of most the benthic rotifers which correlated positively with the current velocity. However, abundance of some benthic Rotifers, such as Euchlanis sp and other taxa , in contrast pelagic rotifers, was negatively correlated with the current velocity, and they were most abundant in the dam site than sites downstream the dam. In view of all that has been mentioned so far from our findings and the previous agreed studies, it was proved that the dam affected on relative abundance of a mentioned rotifers species may be the reservoirs, even with short water retention times, led to high presence of pelagic rotifers in rivers because the dams sites considered suitable place for drifting pelagic rotifers to proliferate, and reproduce in sites of rivers downstream the dam [34] as explained above. Lepadella depressa   As for spatial variations, site 3 (below the dam) had lower richness values for rotifers compared with the dam site. This might be related to the effect of current velocity on chlorophyll a content and physicochemical conditions. The rotifers densities and richness clearly correlated with the concentration of chlorophyll a, which is associated with better nutritional conditions for filter-feeding rotifers that is more frequently occurred in lentic waters [36].
However, site 5 had the highest values of richness index for rotifers. This could be owing to the more diversity of washed out rotifers from other habitats in this site compared with other sites [37]. Or

Al-Bahathy and Nashaat
Iraqi Journal of Science, 2021, Vol. 62, No. 9, pp: 2872-2886 3992 with higher water quality for aquatic life compared with other sites which had a positive effect on rotifers richness [31; 38].
If richness value was ( ≥ 5). It would be classified as perfect. If it was from 3 to 5 classified as moderate and if index value was (≤ 2 ) classified as distributed [39]. So, Euphrates River rotifers was considered generally from distributed to moderate richness during 2019 in study area.
Overall, these local and global studies highlighted on decline of rotifers richness values in site below the dam compared with the dam site such as Sabri et al. [33] when they examined the effect of Samarra Dam on rotifers during the low water discharge period in River Tigris. As well as, Zhao et al. [30] when they studied the Ying River which is tributary of the Huaihe River in China.
In view of all that has been mentioned so far from our findings and the previous agreed studies it was proved that the dam affected on rotifers richness especially on site 3 (downstream the dam) which was lower compared with the dam. This might be related to the effect of current velocity on chlorophyll a content and physicochemical conditions. The rotifers densities and richness clearly correlated with the concentration of chlorophyll a, which is associated with best nutritional conditions for filter-feeding rotifers which is more frequently occurred in lentic waters [36] as explained above.
Table-1 showed that 104 species of rotifers occurred at 2019 . The genus Brachionus included 17 species, Monostyla included 11 species, Trichocerca included 10 species, Lecan included 9 species and Keratella included 7 species, Lepadella included 5 species Cephalodella included 4 species as well as other genus occurred with more than one species.
In general, Figure-6 showed that the higher Jaccard similarity index value was noted between sites 1 with 4 could be attributed to values of physical chemical characteristics of Euphrates River at these sites .
While, site 5 with site 4 was less similarity value compared with other sites may be related with water quality of site5 which had the higher quality compared with site4 and other sites. In view of all that has been mentioned so far from our findings and the previous agreed studies it was proved that the dam was affected by decrease similarity value on site 3 which became more polluted site compared with other sites.
Regarding to Shannon Weiner diversity values of rotifers at site 1 (upstream the dam) declined which ranged from 1.  The spatial variation for rotifers showed that Hindiya Dame site had the lower Shannon index values of rotifers. Although it had high richness at the dam site but it was found that it had less evenness as consequence rotifers had less diversity which considered the major group of zooplankton in the study area. This could be either due to their diversity in the reservoir zone were declined by internal processes, such as predators or food whereas rotifers were dominated in the river particularly in the channelized zone [40]. Or owing to the slower water current in reservoirs provide less diversity of rotifers compared with the streams and rivers. This phenomenon is caused by the washout of numerous benthic taxa by higher velocity flow from macrophytes or the substrate, and by the water retention time, which is too short and hinders the development of dominant planktonic forms [35].
If Shannon Index value was more than 4 bit/Ind. It would be classified as most highly diversified. If it was from 3 to 4 bit/Ind. classified as highly diversified and if index value was from 2 to 3 bit/Ind. classified as moderately diversified. If index value was from 1 to 2 classified as little diversified and if index value was less than 1 bit/Ind. classified as very poor [38]. So, Euphrates River was considered generally little diversified during 2019 in study area.
A number of studies have found that Shannon index values declined in the dam site compared with site (below the dam) for example Al-Shamy [41] who discussed effect of Kut Dam site on zooplankton. Similarly, Czerniawski & Sługocki [29] when recorded an increment of Shannon's index values with a higher current velocity ˃0.1 m s/L. While, Shannon's index values were reduced with a less water current velocity ˂0.1 m s/L, when discussed man-made ditch in the Drawa catchment (Poland) which are similar with influence of artificial dams. As well as, Czerniawski et al. [28] when studied Barycz River and its tributaries which are outlets of carp ponds (in Poland).
In view of all that has been mentioned so far from our findings and the previous agreed studies it was proved that the dam affected on Shannon index values of rotifers especially on the dam site which caused decline of Shannon index values in this site. This could be either due to rotifers diversity in the reservoir zone were declined by internal processes, such as predators or food whereas rotifers were dominated in the river particularly in the channelized zone [40]. Or owing to the slower water current in reservoirs provide less diversity of rotifers compared with the streams and rivers. This phenomenon is caused by the washout of numerous benthic taxa by higher water current from macrophytes or the substrate, and by the water retention time, which is too short would to hinder the development of dominant planktonic forms [35]as explained above.
The results in Figure-8 showed uniformity index values of rotifers at site 1 (upstream the dam) which ranged from 0.46 to 0.94, the lower value was in December, whereas the higher value was in January. The values of Hindiya Dam site declined which ranged from 0.31 to 0.84 that was recorded in October and July, respectively. The values of this index on rotifers at sites (downstream the dam)

Al-Bahathy and Nashaat
Iraqi Journal of Science, 2021, Vol. 62, No. 9, pp: 2872-2886 3994 raised compared with the dam site which ranged from 0.46 to 1. The lowest values were at site 4 in December, whereas the higher value was at the same site in January. The spatial variation for rotifers showed that Hindiya Dam site had lower uniformity index values of rotifers compared with other sites. This could be due to the slower water current in reservoirs provides less evenness with more taxa dominance of rotifers compared with the streams and rivers [35].
If uniformity index value was (0.8-≥0.9), it would be classified as highly balanced. If it was from 0.6 to 0.7 classified as moderate balanced and if index value was (≤ 0.5) classified as unbalanced or under stress [39]. So, Euphrates River zooplankton was considered generally from moderate balanced to highly balanced during 2019 in study area.
Together, these local and global studies found that uniformity index values for rotifers were lower in the dam site compared with the site (below the dam) for example Al Shamy [41] when discussed effect of Al-Kut dam on zooplankton. Similarly, Czerniawski et al. [35] when studied beaver impoundments on lowland streams (Poland).
In view of all that has been mentioned so far from our findings and the previous agreed studies it was proved that the dam affected on uniformity index values of rotifers especially in Hindiya Dam site which caused decrease Uniformity Index values of rotifers in this site owing to the slower water current in reservoirs provide more taxa dominance of rotifers compared to the streams and rivers [29], as explained above.
The constant species were 9 at site 1 (upstream the dam). While, it dropped to 7 constant species at site 3 (below the dam), whereas appeared 8 constant species at site 4 and finally the number of constant species increased to 12 constant species after removal the effect of Hindiya Dam on site 5. While, the constant species of the Hindiya Dam represented by 8 constant species (Table-1).
The spatial variation of constant species of rotifers showed that site 5 was more constant species compared with other sites might be related with its water quality which had higher quality resulted from the far distance from pollution city sources.
While, site 4 had less constant species compared with other sites could be related to the poor water quality as a consequence to the exposure to discharge of city sewage effluents in the river [31].
Our findings agreed with Zhou et al. [42] referred to the increment of occurrence and abundance positively of some pelagic rotifer species (e.g., Keratella cochlearis, Rotaria neplunia, Syncheta oblonga, K. valga, Trichocerca bicristata, polyarthra dolicoptera and polyarthra vulgaris ) in the reservoir of the number of dams built on the river. The existence of small reservoirs, even with a short water retention times, lead to more presence of these species in rivers, and lead to drift them from the upstream impoundments, especially with existence of several upstream reservoirs as ( Haditha Dam, Ramadi Barrage, Fallujah Barrage) that would influence abundance of pelagic rotifers in Hindiya Dam sites.
Similarly, Czerniawski and Kowalska-Góralska [34] found that the dam reservoir provide a place for drifting pelagic rotifers to proliferate in the dam site and sites (downstream the dam) owing to the ability to colonize new habitats by reproduce through cyclical parthenogenesis, short life span, production the resting eggs that are easily transferred as well as, the small size.
In view of all that has been mentioned so far from our findings and the previous agreed studies it was proved that the dam affected on occurrence and constancy of most rotifers species. This could be due to the reservoirs, even with short water retention times, led to high presence of pelagic rotifers (e.g., Keratella cochlearis, Rotaria neplunia, Syncheta oblonga, Trichocerca bicristata, polyarthra dolicoptera). Also, reservoirs provide a place for drifting pelagic rotifers and to proliferate in sites downstream the dam [34].