First data on the diversity and structure of aquatic communities in the peri-urban river « Blondai » at Anyama (South; Ivory Coast)

 Corresponding author: Roland Kouakou DJENE Copyright © 2025 Author(s) retain the copyright of this article. This article is published under the terms of the Creative Commons Attribution License 4.0. First data on the diversity and structure of aquatic communities in the peri-urban river « Blondai » at Anyama (South; Ivory Coast) Roland Kouakou DJENE *, Jean-Renaud ALLOUKO, Issouf El Hadj KAMAGATE and Yves Kotchi BONY Department of Biodiversity and Sustainable Ecosystem Management, Faculty Environment, Jean Lorougnon Guede University of Daloa, Côte d'Ivoire. GSC Biological and Pharmaceutical Sciences, 2025, 32(03), 059–073 Publication history: Received on 22 July 2025; revised on 1 September 2025; accepted on 4 September 2025 Article DOI: https://doi.org/10.30574/gscbps.2025.32.3.0342 Abstract The aim of this study was to characterise the diversity and structure of aquatic communities in the « Blondai » River (Anyama) with a view to assessing its ecological status. Three representative points (upstream, middle and downstream) were set up for sampling. The physico-chemical parameters of the water were measured in situ and in the laboratory. Macroinvertebrates were collected using a Van Veen bucket and a dip net, while plankton was collected by filtering 30 litres of water using a plankton net. Macrophytes were inventoried by direct observation on the banks, and fish by experimental fishing and ethno-zoological surveys. Biological diversity was analysed using the Shannon-Weaver index, Piélou equitability index and canonical correspondence analysis. The water in the « Blondai » river is acidic, poorly mineralised and moderately oxygenated. The taxonomic inventory identified twenty-three species of phytoplankton (18 families, 14 orders), eight species of zooplankton (2 families, 2 orders), twenty-one species of macrophytes (14 families, 14 orders), twelve species of macroinvertebrates (11 families, 9 orders) and four species of fish (3 families, 3 orders). The order Cichliformes has proved to be the most diverse among fish. Chlorococcales, Euglenophytes and Euglenides dominate phytoplankton, Poales macrophytes, while Diptera (Chironomidae), Coleoptera and Basommatophores dominate macroinvertebrates. The Shannon index showed low to moderate diversity, reflecting an unbalanced community structure. The CCA revealed significant relationships between organisms and several physico-chemical variables: pH, total nitrogen and dissolved matter influence zooplankton; BOD₅, COD and temperature condition the distribution of macroinvertebrates; turbidity and dissolved oxygen determine that of macrophytes; and total phosphorus and conductivity structure phytoplankton communities. No significant correlation was observed for fish. Keywords: Macoinvertebrates; River « Blondai »; Phytoplankton; Zooplankton; Fish; Macrophytes 1. Introduction Freshwater, one of the rarest and least equitably distributed natural resources, is essential to life, not only for human populations, but also for the vast majority of living species [1]. The « Blondai » river, located on the outskirts of the town of Anyama, is a typical West African peri-urban aquatic ecosystem, highly exposed to anthropogenic pressures. Its catchment area is subject to increasing urbanisation, marked by the construction of road infrastructure, the extension of residential areas and the development of agricultural activities. These dynamics lead to a gradual deterioration in the quality of aquatic habitats and an alteration in the river's ecological functions ([2]; [3]). In this context, peri-urban aquatic ecosystems, despite playing a crucial role in maintaining local biodiversity, regulating hydrology and providing ecosystem services, are among the most vulnerable and least studied. Yet aquatic biodiversity is a sensitive and integrating indicator of the ecological status of environments, because living organisms respond directly to variations in physico-chemical parameters and environmental disturbances ([4] ; [5]). Assessing the structure and diversity of the biological communities in the River « Blondai » is therefore essential if an objective and scientifically robust ecological GSC Biological and Pharmaceutical Sciences, 2025, 32(03), 059–073 60 diagnosis is to be made. Not only does it enable us to assess the extent of the impact of human activities (organic and chemical pollution, destruction of habitats, changes in hydrological flows), it also provides a reference base for the implementation of biomonitoring tools ([6]; ([7]). The aim of this study is therefore twofold: (i) to contribute to an understanding of ecological dynamics in a peri-urban environment subject to multiple pressures, and (ii) to provide the scientific information needed to guide local strategies for managing and preserving water resources and associated biodiversity. 2. Materials and Methods 2.1. Sampling site Table 1 Summary table of sampling station characteristics Code ES1 ES2 ES3 Types of ecosystems River River River Situation Upstream Median price Downstream Latitude 382804.00 m O 382055.00 m O 381925.00 m O Longitude 609863.00 m N 609933.00 m N 609847.00 m N Appearance of the water Slightly cloudy Claire Claire Substrate Sandy Sandy Sandy Flow speed 0.10 m/s 0.15 m/s 0.20 m/s Depth (cm) 56 cm 55,5 cm 55 cm Canopy 15% 0% 5% Right bank Chinese bamboo (Bambusa vulgaris) and macrophytes Chinese bamboo (Bambusa vulgaris) and macrophytes Chinese bamboo (Bambusa vulgaris) and macrophytes) Left Bank Chinese bamboo (Bambusa vulgaris) and macrophytes Chinese bamboo (Bambusa vulgaris) and macrophytes Chinese bamboo (Bambusa vulgaris) and macrophytes Figure 1 Presentation of the sampling stations GSC Biological and Pharmaceutical Sciences, 2025, 32(03), 059–073 61 This spot study was carried out in the « Blondai » river located in the town of Anyama in the south of Côte d'Ivoire. The study area lies between latitudes 380,500 m N and 383,000 m N and longitudes 609,300 m W and 610,000 m W (UTM, zone 30N, WGS84) (Figure 1). This study was carried out from 20 to 25 March 2023 at three (03) sampling stations coded ES1, ES2 and ES3 located respectively upstream, midstream and downstream of the river « Blondai ». These points were selected on the basis of the durability of the water, their accessibility and the human activities to which they were subject. Table 1 below shows the characteristics of the various sampling stations 2.2. Methods 2.2.1. Analysis of physico-chemical parameters Physicochemical parameters were measured in the field and in the laboratory. Temperature, dissolved oxygen content, pH, electrical conductivity and turbidity were measured in situ using an AZOTA multimeter. Water transparency and depth were assessed by fully immersing a Secchi disc attached to a rope until it reached a level below the river bottom. Water samples were also taken at various stations along the river in 500 ml polyethylene bottles. They were transported to the ENVAL laboratory in coolers containing ice packs, where they were kept refrigerated at 5°C before being analysed. These water samples were used to measure total nitrogen (N), total phosphorus, BOD5, COD and dissolved solids according to the standard protocols of the Association Française de Normalisation [8]. 2.2.2. Plankton sampling Sampling of planktonic organisms at each of the stations selected on the « Blondai » river consisted of taking 30 litres of water using three (3) buckets of 10 litres each. This quantity of water was taken and filtered using a plankton net with a mesh size of 20 µm. The filtrate was then collected in 125-millilitre pillboxes containing 70% ethanol. In the laboratory, the plankton were observed directly with an optical microscope between slide and coverslip, after sedimentation of the samples. Phytoplankton organisms were identified using the identification guides in [9], [10] and [11]. Zooplankton organisms were identified using the works in [12]. Counting was carried out using an inverted microscope. Samples were homogenised by hand and poured into 10-millilitre sedimentation tanks in a single operation. In the case of media with a high concentration of particles (epiphytic solution), dilutions of epiphytic samples were made. A pipette with removable one-millilitre tips was used for this purpose. One millilitre of the sample was introduced into a 10-millilitre sedimentation chamber, which was then topped up with 10 millilitres of distilled water using a wash bottle. The solution in the tank was left to settle for 8 hours. Observations were then made at 40x magnification. The count was carried out by transect (diameters). Several fields were visited, enabling at least 400 planktonic objects to be counted [13]. Plankton density (D) is given by the following formula Where: N = number of organisms per mL; n. ind = number of individuals counted; V = sedimented volume (mL); R = count ratio; 0.112 mm = strip width; 13 = chamber radius; nb dia = number of diameters counted; F = dilution factors. When samples are diluted, the dilution factor is 10, when samples are not diluted, the dilution factor is 1. 2.2.3. Sampling macrophytes The inventory of macrophytes on each of the banks of the selected sections (Upstream, Midstream and Downstream) of the « Blondai » river in the Anyama area consisted of all-round sampling. The specimens encountered were photographed and counted. Identification was carried out using the identification books and keys in [14], [15] and [16]. 2.2.4. Sampling, sorting, observation and analysis of macroinvertebrates Macroinvertebrates were sampled using a stainless steel Van Veen bucket for sediment organisms and a dip net for submerged macroinvertebrates. For the benthos, a sediment sample corresponding to a total surface area of 0.15 m2 was taken at each station. For submerged organisms, a haze net (250 μm mesh) was used using the SASS (South African Scoring System) method [17]. Samples were collected for 3 minutes by submerging the net and dragging it through the water column over an area of 1 m² (2 m * 0.5 m). The collected organisms were fixed with 70% ethanol in labelled jars and transported to the laboratory. In the laboratory, each sample, previously preserved in alcohol, was rinsed with tap water. The samples were then sieved and the individuals collected sorted using a binocular magnifying glass to separate the fauna from the debris and sedimentary particles. The organisms collected were counted, photographed and identified to the lowest possible taxonomic level using the appropriate determination keys ([18] ; [19]) and preserved in 70% ethanol. GSC Biological and Pharmaceutical Sciences, 2025, 32(03), 059–073 62 2.2.5. Ichthyofauna sampling The inventory of fish in the « Blondai » river in the Anyama area was carried out using two techniques, experimental fishing and ethno-zoological surveys of resource persons in the sacred parts of this river. Experimental fishing was carried out using two (2) landings nets. The ethno-zoological surveys consisted of the identification of fish images by the guardians of the sacred parts of the river. The specimens collected were identified at the specific level using the keys proposed by [20]. 2.2.6. Data analysis method Method of Diversity Analysis Taxonomic richness, taxonomic group abundances, Shannon diversity indices and Piélou equitability indices were determined to analyse the biological diversity of communities. • Taxonomic richness, highlighted the total number of species encountered at the various sampling stations [21]. • Abundance of taxonomic groups was used to determine the structure and distribution of macroinvertebrate communities in the river Blondai. It represents the ratio of the number of individuals of taxon (i) present to the total number of individuals [21]. It varies in space and time. Relative abundance is expressed as follows: 𝑃𝑖 =𝑛𝑖/𝑁 where Pi is the relative abundance of species (i), ni is the number of individuals of species (i) and N is the total number of individuals. • The Shannon-Weaver diversity index was used to measure specific diversity within macroinvertebrate communities. It is based on the number of species and the regularity of their distribution. H' = - Σ p i log 2 pi where pi represents the relative abundance of species i in the sample (p i = n i /N). H' fluctuates between 0 and log S. A high Shannon index corresponds to favourable environmental conditions allowing many species to establish themselves. Generally, the value of H' is between 0.5 (very low diversity) and 4.5 or 5 (most diverse communities). • Piélou equitability, has been used to evaluate the degree of homogeneity in the distribution of macroinvertebrate taxa, independently of their species richness. [22]. 𝐽 = 𝐻 𝑙𝑜𝑔2 (𝑆) Where H is the Shannon diversity index for a sample and S is its species richness. Equitability varies from 0 to 1. 2.3. Statistical method The Shapiro-Wilk normality test was used to test the normality of the various data. The Kruskal-Wallis test was used to compare the various parameters measured at different sampling stations. Canonical Correspondence Analysis (CCA) was performed using Past 3.4 software [23] to match the biotic and abiotic data obtained during sampling. All statistical analyses were carried out using Past 3.14 software. 3. Result 3.1. Spatial variations in the river's physico-chemical parameters Temperature values ranged from 27.13±1°C (station ES1) to 32.7±0.81°C (station ES3). For pH, the minimum and maximum values observed in the river are 5.06±0.20 (ES3) and 5.83±0.72 (ES1) respectively. Conductivity values in the river ranged from 53.73±0.64 µS/cm (ES1) to 75.16±1.04 µS/cm (ES2). Spatial variation in dissolved oxygen in the river ranged from 3.66±0.5 mg/L (ES2) to 7.53±0.47 mg/L (ES1). The total nitrogen value varies between 0.53±0.04 mg/L (station ES3) and 1.08±0.07 mg/L (station ES1). Spatial variation in turbidity at the river stations ranged from 18.93±0.92 NTU (ES2) to 41.06±0.92NTU (ES1). The minimum and maximum BOD5 values observed at the river stations are 14±1mg/L (ES2) and 22±1 mg/L (ES3) respectively. COD concentrations measured at the river stations ranged from 51.86±0.50 mg/L (ES1) to 80.59±0.53mg/L (ES3). Total phosphorus values varied between 0.03±0.00 mg/L (stations ES1) and 0.12±0.01mg/L (station ES2). Dissolved solids concentrations at the river stations varied GSC Biological and Pharmaceutical Sciences, 2025, 32(03), 059–073 63 between 14±0.5 mg/L (ES2) and 14.5±0.5 mg/L (ES1). Variations in all the parameters measured in the river were not significant at the stations studied (Kruskal-Wallis test, p-value > 0.05). Table 2 Spatial variation in the river's physical-chemical parameters Stations ES1 ES2 ES3 Temperature (°C) 27.13±1 30.83±0,15 32.7±0.81 pH 5.83±0.72 5.2±0,2 5.06±0.20 Conductivity (µS/cm) 53.73± 0.64 75.16±1,04 70.33±0.58 DBO5 (mg/L) 14.5±0,5 14±1 22±1 Total nitrogen (mg/L) 1.08±0.07 0.81±0,05 0.53±0.04 COD (mg/L) 51.86±0.50 52.51±0.5 80.59±0.53 Dissolved oxygen (mg/L) 7.53±0.47 3.66±0.5 7.16±0.37 Total phosphorus (mg/L) 0.03±0.00 0.12±0.01 0.04±0.00 Turbidity (NTU) 41.06±0.92 18.93±0.92 25.8±0.72 Dissolved Substances (mg/L) 14.5±0.5 14±0.5 14±1 3.2. Taxonomic composition of aquatic organisms in the river 3.2.1. Plankton The specific compositions of phytoplankton and zooplankton in the river Blondai are shown in the table below. Sampling revealed the presence of 23 species of phytoplankton in 18 families and 14 orders. The most diverse orders were Chlorococcales, followed by Euglenophytes and Euglenides with 05 species, 04 species and 03 species respectively. The other orders are less rich, with 01 species each. Navicula sp. and Eugleuna polymorpha are the species most commonly found in the area. As regards zooplankton, 08 species belonging to 5 families and 04 orders were encountered. Mesocyclops leuckarti is the most common species. Table 3 Taxonomic composition of plankton in the « Blondai » river Orders Families Species Upstream Median Downstream Phytoplankton Chlorollales Oocystistaceae Oocystis solitaria (Wittrock. 1879) - - + Desmidiales Closteriaceae Closterium dianae (Ehrenberg ex Raifs. 1848) + - - Euglenides Phacaceae Lepocinclis ovum (Ehrenberg) Lemmerm. 1901 - - + Lepocinclis oxyuris (B.Marin & Melkonian 2003) - - + Phacidae Phacus sp. (Dujardin. 1841) - + + Euglenophytes Eugleunaceae Eugleuna polymorpha (Dangeard. 1901) + + + Eugleuna spirogyra (Ehrimberg. 1878) - + - Strombomonas sp. (Guiry. 2025) + - + GSC Biological and Pharmaceutical Sciences, 2025, 32(03), 059–073 64 Trachelomonas sp. (Ehrenberg. 1833) - + + Naviculineae Naviculaceae Navicula sp. (Bory de Saint-Vincent. 1822) + + + Pseudanabaenale s Pseudanabaenacea e Pseudanabaena catenata (Lauterborn 1915) + - - Pseudanabaenale s Pseudanabaenacea e Pseudanabaena mucicola (Schwabe. 1964) + - - Ulotrichales Ulotrichaceae Ulothrix sp. (Thuret. 1863) - - + Peridiniales Peridiniaceae Peridinium sp. (Ehrenberg.1828). - - + Chlorococcales Hydrodictyaceae Pediastrum duplex (Meyen. 1829) - - + Microcystaceae Microcystis elachista (West. 1894) - - + Scenedesmaceae Actinastrum hantzschii (Lagerh.1882) + - - Scenedesmus sp. (Meyen. 1829) - + - Aphanothecaceae Aphanothece sp. (Nägeli. 1849) - - + Synechococcales Merismopediaceae Aphanocapsa sp. (West. 1894) + + - Aulacoseirales Aulacoseiraceae Aulacoseira ambigua (Simonsen. 1979) - - + Licmophorales Ulnariaceae Ulnaria ulna (Compère. 2001) - - + Gymnodiniales Brachidiniaceae Karenia sp. - - + Zooplankton Cyclopoides Cyclopidae Mesocyclops leuckarti (Claus. 1857) + + + Ploimidaes Brachionidae Brachionus urceolaris (Müller.1773) - - + Brachionus sp. (Daday. 1883) - + - Brachionus plicatilis (Müller. 1786) + - - Diplostraca Daphniidae Ceriodaphnia affinis - - + Ceriodaphnia dubia (Richard. 1894) - - + Chydoridae Camptocercus sp. (Baird. 1843) + - - Hexarthridae Flosculariaceae Hexarthra intermedia (Wiszniewski. 1929) - + - + = present; - = absent 3.2.2. Macrophytes The specific compositions of macrophytes in the river ‘Blondai’ are shown in Table 4. The macrophyte inventory yielded 21 species belonging to 14 families and 14 orders. The most diverse order was the Poales (05 species, i.e. 24% of species). However, the Arales, Asparagales, Fabales, Filicales, Gleicheniales, Juncales, Malpighiales, Polypodiales, Solanales and Theales are the least diverse orders, with 01 species, or 05% of the total number of species. The upstream part of the river is the richest in species (10 species). However, the middle section is the least diverse (06 species). Ludwigia octovalvis and Synedrella nodiflora are the most common species found in all three parts of the river (upstream, midstream and downstream). All other species are less common in the area. GSC Biological and Pharmaceutical Sciences, 2025, 32(03), 059–073 65 Table 4 Taxonomic composition of macrophytes in the « Blondai » river ES1 ES2 ES3 Orders Families Species Upstream Median Downstream Arales Araceae Cyrtosperma merkusii (Hassk. Schott, 1857) + - - Asparagales Liliaceae Dracaena fragrans (Ker Gawl. 1808) + - - Asterales Asteraceae Struchium sparganophorum (Kuntze. 1891) + - - Synedrella nodiflora (Gaertner.1791) + - + Commelinales Commelinaceae Palisota bracteosa - - + Palisota sp. + - - Fabales Fabaceae Vigna radiata (Wilczek.1954) + - - Filicales Woodsiaceae Gymnocarpium dryopteris (Newman. 1851) - - + Gleicheniales Gleicheniaceae Gleichenella pectinata (Ching. 1940) - - + Juncales Juncaceae Luzula sylvatica (Gaudin. 1811) + - - Malpighiales Euphorbiaceae Alchornea cordifolia (Müll.Arg.. 1865) - - + Myrtales Onagraceae Ludwigia decurrens (walter.1788) - + - Ludwigia octovalvis (Raven. 1962) - + + Poales Poaceae Sorghum arundinaceum (Stapf. 1917) - + - Oplismenus compositus (Beauv.1812) + - - Paspalum dilatatum (Poir. 1804) - - + Pennisetum pedicellatum (Trin. 1832) - + - Sorghum halepense (Pers. 1805) - + - Polypodiales Thelypteridaceae Thelypteris palustris (Schott. 1834) + - - Solanales Convolvulaceae Ipomoea aquatica (Forssk. 1775) - + - Theales Cluciaceae Hypericum calycinum + - - Total = 14 14 21 10 6 7 + = present; - = absent 3.2.3. Macroinvertebrates The taxonomic compositions of aquatic macroinvertebrates in the ‘Blondai’ river are shown in Table 5. Sampling revealed the presence of 12 species divided into 11 families and 9 orders. The most diverse orders were Basommatophora, Coleoptera and Diptera, with 02 species each, or 17% of the species richness. The other orders are less rich, with 01 species each, or 08% of species. The downstream part of the river is the richest in species (10 species). However, the middle and upstream sections are the least diverse, with 02 species each. Grenitis sp. and Polypedilum abyssiniae are the species most frequently encountered in the three sections (upstream, midstream and downstream). All the other species were seen less frequently in the river. GSC Biological and Pharmaceutical Sciences, 2025, 32(03), 059–073 66 Table 5 Taxonomic composition of macroinvertebrates in the « Blondai » river Upstream Median Downstream Orders Families Species ES1 ES2 ES3 Rhynchobdellides Erpobdellidae Barbrania sp. - - + Archaeogastropods Neritidae Clithon sp. - - + Basommatophora Physidae Aplexa marmorata - + - Planorbidae Afrogyrus rodrignezensis - - + Littorinimorphs Hydrobiidae Tomichia differens - - + Sorbeoconchs Thiaridae Melanoides tuberculata - - + Coleoptera Gyrinidae Dineutus sp. - - + Hydrophilidae Grenitis sp. + - + Diptera Chironomidae Polypedilum laterale - + - Polypedilum abyssiniae + - + Hemiptera Belostomatidae Diplonychus sp. - - + Odonata Libellulidae Zygonyx torrida - - + 9 11 12 2 2 10 + = present; - = absent 3.2.4. Fish Table 6 shows the specific composition of fish in the ‘Blondai’ river. A total of 04 species of fish were inventoried, divided into 03 families and 03 orders. The most diverse order is the Cichliformes (02 species, i.e. 50% of the species collected). However, the least diverse are the Siluformes and Synbranchiformes with 01 species, or 25% each. The distribution of species richness shows that the upstream part of the river is the richest in species (04 species), while the middle and downstream parts are the least diverse (03 species each). Sarotherodon melanotheron and Mastacembelus nigromarginatus are the two species most frequently encountered in the three sections of the river (upstream, midstream and downstream). The least common are Hemichromis bimaculatus and Clarias anguillaris. Table 6 Taxonomic composition of fish in the « Blondai » river ES1 ES2 ES3 Orders Families Species Upstream Median Downstream Cichliformes Cichlidae Hemichromis bimaculatus (Gill. 1862) + - + Sarotherodon mélanotheron (Rûppell. 1852) + + + Siluriformes Clariidae Clarias anguillaris (Linnaeus. 1758) + + - Synbranchiform es Mastacembelid ae Mastacembelus nigromarginatus (Boulanger. 1898) + + + Total = 3 3 4 4 3 3 + = present; - = absent GSC Biological and Pharmaceutical Sciences, 2025, 32(03), 059–073 67 3.3. Diversity of aquatic communities in the « Blondai » river 3.3.1. Plankton Station ES3 recorded the highest taxonomic richness with 20 taxa, while the lowest taxonomic richness was recorded at station ES2 with 10 taxa. The highest value of the Shannon diversity index (1.51bits) was observed at station ES3, while the lowest value of this index (1.01bits) was recorded at station ES2. The maximum equitability value (0.96) was observed at station ES1, while the lowest index value (0.9206) was recorded at station ES2, located in the middle of the river. 3.3.2. Macrophytes Maximum abundance (37 individuals) was recorded at station ES1 located upstream in the river, while minimum abundance was observed at station ES2 (18 individuals) in the middle of the river. Station ES1 recorded the highest taxon richness with 10 taxa, while the lowest taxon richness was recorded at station ES2 with 6 taxa. Relative abundance varied between 34.52% (ES1) and 44.04% (ES1). The highest Shannon diversity index value (2.05bits) was observed at station ES1, while the lowest value (1.49bits) was recorded at station ES3. The maximum equitability value (0.89) was observed at station ES1, while the lowest index value (0.77) was recorded at station ES3, located downstream. 3.3.3. Macroinvertebrates Maximum abundance (46 individuals) was recorded at station ES3 downstream from the river, while minimum abundance was observed at station ES1 (2 individuals) upstream from the river. Station ES3 recorded the highest taxon richness with 10 taxa, while the lowest taxon richness was recorded at stations ES1 and ES2 with 2 taxa. Relative abundance varied between 3.85% (ES1) and 92% (ES3). The highest Shannon diversity index value (1.65bits) was observed at station ES3, while the lowest value (0.69bits) was recorded at stations ES1 and ES2. The Piélou equitability index shows a different pattern to the Shannon index. The maximum value of equitability (1) is observed at stations ES1 and ES2, while the lowest value of the index (0.72) is recorded at station ES3, located downstream of the river. 3.3.4. Fish Abundance (4 individuals) was similar at all sampling points. Station ES1 recorded the highest taxon richness with 4 taxa, while the lowest taxon richness was recorded at stations ES1 and ES2 with 3 taxa. Relative abundance was similar at all sampling points. The highest Shannon diversity index value (1.38bits) was observed at station ES1, while the lowest value (1.04bits) was recorded at stations ES1 and ES2. The Piélou equitability index shows a different pattern to the Shannon index. The maximum equitability value (1) was observed at station ES1, while the lowest index value (0.94) was recorded at stations ES2 and ES3, located respectively in the middle and downstream reaches of the river. Analysis of the indices using the Kruskal-Wallis test revealed no significant difference between the stations (p > 0.05). Table 7 Diversity of aquatic organisms in the « Blondai » river Upstream Median Downstream Organisms Diversity Index ES1 ES2 ES3 Plankton Taxonomic richness 11 10 20 Shannon index (H) 1.33 1.01 1.51 Equitability E 0.96 0.9206 0.9591 Macrophytes Taxonomic richness 10 6 7 Number of individuals 37 18 29