The Affon River is one of the important rivers of the Ouémé River whose benthic diversity remained unknown. The present study aims to make the relationship between macroinvertebrates and physico-chemical parameters to access water quality of the Affon River. The measurement of physico-chemical parameters (temperature, pH, conductivity, transparency, depth and TDS, dissolved oxygen, ammonium, nitrite and phosphate) and the sampling of macroinvertebrates using a Surber net were carried out during floods in eight stations. A principal component analysis (PCA) and canonical correspondence analysis (CCA) were used. The indices of Shannon, Piélou, Simpson, Hilsenhoff, EPT and EPT/Chironomidae were used to assess the level of water pollution. The study identified 9755 macroinvertebrates divided into 4 classes, 14 orders and 49 families. Pollution-sensitive families (14 families) that are organic pollution indicators, as well as pollution-tolerant families (Chironomidae, Limnaeidae, Bithynidae, Physidae) were captured. Chironomidae were the most predominant and abundant family (FO = 100%). The predominance of Chironomidae coupled with the rarity of the Ephemeroptera, Trichoptera and Plecoptera would reflect the poor quality of the Affon River waters. The principal components analysis yielded groups of associations: The first group of stations Taneka 2 and 3 characterized by high values of ammonium and phosphate; and low values of conductivity and TDS; the second group of Tanéka 1 and Kolokondé 1 stations with low values of pH, transparency, ammonium and phosphates; and the third group of stations Kolokondé 2, Kpébouko1, Kpébouko 2 and Affon marked by high values of conductivity, TDS, transparency, depth and temperature. The canonical correspondence analysis revealed a strong positive correlation between Nemouridae and ammonium as well as between Perlidae, Taeniopterygidae, Ephemeridae, Heptageniidae, Isonychiidae, Elmidae and phosphate. This study is a crucial step for any management and monitoring of this river.
Agricultural intensification is the major cause of degradation of aquatic ecosystems in rural areas [
The Affon River is located on the right bank and in the classified forest of Upper Ouémé. This river is one of the tributaries of the Ouémé River. It has a length of 152 km and a catchment area of 4320 km2. The river is located in the Sudano-Guinean zone and is under the influence of the tropical climate characterized by the succession in the year of a single rainy season from April to October and a single dry season from November to March, marked by the preponderance of the harmattan. On the Affon River, 08 stations were selected after prospecting. They were chosen based on the sustainability of the water, the altitude, accessibility in all seasons, the depth and speed of the water [
At each station, the measurements of physical parameters (temperature, depth, transparency, TDS, conductivity, pH, oxygen) were carried out in situ very early in the morning between 08:00 and 12:00, before the sampling of macroinvertebrates to avoid any disturbance of the environment. Water temperature, TDS and conductivity were determined using a portable conductivity meter (HANNA HI 99300). The pH was measured with a portable pH meter (HANNA HI 98107). A Secchi disk with a graduated rope is used to measure the transparency of the water and depth of the stations. Water samples were made at each station in 500 ml plastic bottles decontaminated and stored in a cooler containing ice for transport to the laboratory for analysis of the dissolved substances. The dissolved elements concentration’s determination of the water samples was carried out in the Laboratory of Hygiene, Sanitation, Ecotoxicology and Environmental Health (HECOTES) using a spectrophotometer DR 6000. The chemical parameters such as ammonium, nitrite and phosphate were respectively measured by the Nessler method [
Stations | Codes | Geographic coordinates | Altitude | Pollution sources |
---|---|---|---|---|
Tanéka-Koko1 | Tan1 | N: 09˚51'21" E: 01˚32'34" | 484 m | Artisanal extraction of gold |
Tanéka-Koko2 | Tan2 | N: 09˚53'89" E: 01˚47'48" | 429 m | Laundry, dishes, artisanal extraction of gold |
Tanéka-Koko3 | Tan3 | N: 09˚52'40" E: 01˚30'80" | 415 m | Laundry, dishes, artisanal extraction of gold |
Kolokondé1 | Kol1 | N: 09˚53'94" E: 01˚47'44" | 410 m | Agricultural waste, washing of motorcycles and Laundry |
Kolokondé2 | Kol2 | N: 09˚57'17" E: 01˚51'43" | 369 m | Household waste, agricultural waste, washing of motorcycles and Laundry |
Kpebouco1 | Kpe1 | N: 09˚57'15" E: 01˚51'43" | 365 m | Agricultural, household and livestock wastes |
Kpebouco2 | Kpe2 | N: 09˚56'58" E: 01˚50'54" | 363 m | Laundry, household and livestock waste |
Affon | Aff | N: 09˚57'46" E: 01˚51'78" | 348 m | Watering cattle, washing of motorcycles and laundry |
The benthic macroinvertebrates were sampled at the 08 stations. They were taken by using a Surber sampler with a 500-µm mesh. This material was placed on the bottom of the river, the opening of the net facing the watercourse and the substrate is scraped a few centimeters with the hand. Twelve samples with a unit area of 1/20 m2 were done per station: (08) eight on the dominant habitats and (04) on the marginal habitats as recommended by the standard IBGN and already used in the North of Benin by Abahi et al. (2018) [
In the laboratory, the captured macroinvertebrates were rinsed in order to rid them of the formalin and then they were sorted station by station under a binocular dissecting microscope. After the sorting, we grouped them according to their classes up to their families apart from oligochaetes, nemathelminths, hydracarians, hydrozoans, sponges, bryozoans and nemerteans that are kept aside such as Abahi et al. (2018) [
The identified fauna data allowed us to calculate the following metrics and indices:
Taxonomic richness (S) = number of taxa present in each station
Abundance (N) = number of individuals from a taxonomic group in each station
Relative abundance (Nr) = ratio as a percentage of the number of taxon individuals in a station to the total number of individuals of all species of all stations.
Frequency of family observation (FO) = (Fi × 100)/Ft. In such, Fi = number of stations containing the family and Ft = total number of stations studied. Three families were thus distinguished as Abahi et al. (2018) [
Shannon diversity index (H) = − £ p i ⋅ log 2 p i , with pi meaning the relative abundance of the i species in the sample. The Shannon index is expressed in bits. It was determined by station. Shannon index values obtained were used to assess water quality. The Shannon index is subdivided into three classes of water quality: 2 ≤ H for clean water; 1 < H < 2 for moderately polluted water and H ≤ 1 for polluted water.
Piélou index (E) = H'/log2S with S standing for the total number of individuals.
Simpson index (D) = 1 − £ i = 1 S ( p i ) 2 with S standing for the total number of individuals and pi = meaning the relative abundance.
Family biotic index (Hilsenhoff index): To determine the water quality of the different stations, the family biotic index developed by Hilsenhoff was used. It has been calculated as follows:
F B I = ∑ i F n i t i N
in which F is the family number, ni is the number of individuals, ti is the tolerance value of the family i and N is the total number of individuals. The tolerance values of the macroinvertebrate families come from Hilsenhoff (
The obtained data was processed using Excel 2010 software and R3.4.4 software [
A canonical correspondence analysis (CCA) was performed to correlate physico-chemical parameters and macroinvertebrate densities (
Value of FBI | Water quality | Degree of organic pollution |
---|---|---|
0.00 à 3.75 | Excellent | Without organic pollution |
3.76 à 4.25 | Very good | Slight organic pollution |
4.26 à 5.00 | Good | Probable organic pollution |
5.01 à 5.75 | Average | Substantially organic pollution |
5.76 à 6.50 | Rather bad | Substantial organic pollution |
6.51 à 7.25 | Bad | Very substantial organic pollution |
7.26 à 10.00 | Very bad | Serious organic pollution |
Spatial variation of the Shannon biodiversity index (H')
Spatial variation of Piélou and Simpson’s equitability indices
The spatial variations of Piélou and Simpson’s equitability indices are presented in
Spatial variation of the EPT and EPT/Chironomidae indices
Stations | Value of Shannon (H’) | Water quality |
---|---|---|
Tan1 | 1.48 | Moderately polluted |
Tan2 | 1.31 | Moderately polluted |
Tan3 | 1.07 | Moderately polluted |
Kol1 | 0.96 | Polluted |
Kol2 | 0.55 | Polluted |
Kpe1 | 1.74 | Moderately polluted |
Kpe2 | 0.55 | Polluted |
Aff | 1.46 | Very polluted |
Stations | Tan1 | Tan2 | Tan3 | Kol1 | Kol2 | Kpe1 | Kpe2 | Aff | p |
---|---|---|---|---|---|---|---|---|---|
Index of Pielou | 0.43 | 0.63 | 0.59 | 0.33 | 0.19 | 0.58 | 0.18 | 0.49 | 0.01 |
Index of Simpson | 0.59 | 0.62 | 0.55 | 0.4 | 0.22 | 0.73 | 0.2 | 0.62 | 0.001 |
Stations | ||||||||
---|---|---|---|---|---|---|---|---|
Descriptors | Tan1 | Tan2 | Tan3 | Kol1 | Kol2 | Kpe1 | Kpe2 | Aff |
Taxonomic richness | 30 | 8 | 6 | 19 | 19 | 20 | 20 | 20 |
EPT Richness | 8 | 1 | 2 | 4 | 4 | 10 | 3 | 3 |
Total abundance | 2652 | 98 | 43 | 756 | 2940 | 468 | 1459 | 1339 |
EPT abundance | 447 | 23 | 2 | 13 | 228 | 253 | 17 | 320 |
Chironomidae abundance | 1645 | 55 | 12 | 577 | 2594 | 169 | 1306 | 780 |
% EPT | 16.9 | 23.5 | 4.7 | 1.7 | 7.8 | 54.1 | 1.2 | 23.9 |
% Chironomidae | 62.0 | 56.1 | 27.9 | 76.3 | 88.2 | 36.1 | 89.5 | 58.3 |
EPT/Chironomidae | 0.3 | 0.4 | 0.2 | 0.0 | 0.1 | 1.5 | 0.0 | 0.4 |
of the EPT index reflect the deterioration of the water quality of the Affon River. Regarding the percentage of Chironomidae, it is higher than 55% on all stations except Tanéka 3 and Kpébouco 1 stations. In addition, the values of the EPT/C index of the different stations are generally low and close to zero. These results indicate that the waters of the different stations are of poor ecological quality and reveal the environmental stress suffered by the Affon River.
Family Biotic Index (Hilsenhoff Index)
(FBI) calculated for the Affon River is 7.14. This high value of the family biotic index indicates that the water of this river is of poor quality and that it presents a very substantial organic pollution.
The calculated Shannon-Weaver index is less than 2 indicating that the waters of the stations have qualities varying between moderately polluted, polluted and very polluted. These results also reflect a lower biological diversity in the studied stations. The values of the Shannon diversity index recorded are lower than the values obtained by Foto et al. (2013) [
The study has identified in the Affon River 9755 macroinvertebrates divided into 49 families. The observed taxonomic abundance is very low compared with the one reported by Agblonon Houelome et al. (2017) [
The present study inventoried 9755 macroinvertebrate individuals belonging to four classes, fourteen orders and forty-nine families. Insects were the most dominant with 97.40% of the total richness. Taxonomic richness and abundance tend to follow an altitudinal gradient. The analysis of the indices reveals an undiversified population and the environmental stress that this river undergoes. The strong positive correlations observed between Nemouridae and ammonium on the one hand and between Perlidae, Taeniopterygidae, Ephemeridae, Heptageniidae, isonychiidae, Elmidae and phosphate show the invulnerability of these families, which are mostly pollution-sensitive families, at the doses of phosphate and ammonium measured in this study. Nevertheless, certain protection and recovery measures must be taken to preserve and improve the ecological status of the Affon River waters. It involves the implementation of a sustainable river management plan, the promotion of organic farming, the awareness of the population on the importance of water and its quality. In addition, a long-term investigation based on biomonitoring and a sustainable management program are recommended to conserve the biodiversity of this river.
We thank the people of our sampling places for their participation in the study. Special thanks go to the team of the Laboratory of Hygiene, Sanitary, Ecotoxicology and Environmental health (HECOTES) and the team of the Laboratory of Ecology, Health and Animal Production (LESPA).
The authors declare that they have no conflict of interest.
Gouissi, F.M., Samon, O., Abahi, K.S., Adje, D.D., Tchaou, C.M., Orou Piami, Z., Okoya, J.G.A. and Gnohossou, M.P. (2019) Relationship between Macroinvertebrates and Physico-Chemical Parameters to Access Water Quality of the Affon River in Bénin. Advances in Entomology, 7, 92-104. https://doi.org/10.4236/ae.2019.74008