Study area
The study was carried out at Ipogun village, Ifedore local government Area of Ondo State, Nigeria. Ipogun (7° 18′ 53″ North 5° 04′ 48″ East) is a rural village adjacent Ilara-Mokin in Ondo State, Nigeria with an estimated population of about 6000. It is about 14 km from Akure the state capital of Ondo State. The climate in Ipogun is tropical with wet and dry seasons. The wet season (March–October) is characterized by heavy rains with occasional flooding of river banks and a dry season (November–February) distinguished by increased temperature, very little or no rainfall and consequently, the river dries up with a few stagnant pockets of water along its course. The inhabitants of the village are largely engaged in farming. The primary source of water supply for agricultural and domestic activities is the ‘Aponmu’ river, flowing through the village. The study was carried out at River Aponmu.
Study sites
Three study sites (Alaasin, Idi, and Aponmu) were selected along the course of River Aponmu (Fig. 1). The study sites were chosen based on the surrounding vegetation type and different human activities around the water bodies. The study sites are all part of River Aponmu but given different names by the people of the sites.
Alaasin stream
Alaasin stream (7° 19′ 2″ N 5° 4′ 23″ E) is a flowing stream that passes through cocoa, plantain, and banana farms. The stream is characterized by rocky beds; boulders can be seen at some part of the bank of the stream, while the bottom substrate is mainly silt. It is a permanent stream, though the water level reduces greatly during dry season but does not dry up completely. Other vegetation at the site includes grasses and shrubs. The cocoa trees, plantain plantation, and oil palm trees form shade at some part of the site. Human activities carried out at the site include washing of motorcycles, clothes, and farming.
Idi stream
Idi stream (7° 18′ 14″ N 5° 4′ 42″ E) is a slow-flowing water body and shallow, especially across major footpaths leading to Cocoa farms. “Idi” is a native name given to the area by the people living there. The surrounding of the stream is characterized by the presence of crop trees (e.g. cocoa trees and palm trees) and some shrubs. The site is shaded by Cocoa trees and a few other trees. The stream bed is made up of boulders, sand-loam soil, and rocks. The water is clear and sometimes dries up during dry season. The stream is influenced by regular cutting of surrounding vegetation and exhaust fumes from passing automobiles.
River Aponmu
River Aponmu (7° 17′ 44″ N 5° 4′ 49″ E) is an open river which allows direct penetration of sunlight. The river bed is made up of sand-loam soil, boulders, and stone. The water is moderately clear and slow-flowing. The major types of vegetation around the river are grasses and shrubs. Human activities here include regular cutting of riparian vegetation, construction work, and laundry. Other activities at the site include cassava processing mill. Some patches of human excrement can be seen in some parts of the site.
Sample collection
The research was carried out from January 2020 to December 2020 (with the exception of April 2020 due to the strict lockdown enforced as a measure against the spread of COVID-19 pandemic). The sampling period comprises of 4 months of dry season and 7 months of wet season. All samples were collected once a month between the hours of 9:00 a.m. and 2:00 p.m.
Sampling, identification, and preservation of Odonate specimens
Only adult specimens were sampled under favorable weather condition between the hours of 9:00 a.m. and 2:00 p.m. The adults were sampled using a large white sweep net with an orifice of 72 cm. The length of the net was long enough to be able to fold close so that the specimen(s) caught would not escape when flipping the rim over the net. When a dragonfly or damselfly was seen flying around, the net was swung from behind to capture it. Specimens that were difficult to identify at the field were taken to the laboratory for proper identification using standard identification manual: Dijkstra and Clausnitzer (2014). The specimens were also identified with Odonata pictures on the African Dragonfly and Damselfly Database (ADDO). The specimens collected were placed inside well-labeled white triangular envelopes at the site. The wings were carefully folded at the back to prevent it from getting rumpled. Male and female caught in tandem were kept in the same envelope. All specimens collected were soaked in acetone for minimum of 12 h to preserve it and retain the beautiful pigment coloration of the specimens. The samples were then removed from acetone and air-dried by placing them on tissue paper on the work table in the laboratory. The dried specimens were thereafter placed again in white rectangular envelope and placed in a well-labeled white box for future references.
Water sampling and analysis (physicochemical parameters)
Collection of water samples and measurement of some physicochemical parameters were done concurrently for 11 months. Water samples were collected using 1 L plastic bottles from the three study sites for analysis. Before collection of the water, the bottles were thoroughly rinsed with the stream water to be collected and the one for analysis was later collected inside the bottle. The sample bottles were labeled to indicate the site, name of the site, water type, date collected, and sample source. Sampling was done by lowering pre-cleaned plastic bottles into the water at accessible points. The plastic bottles were lowered to a depth of about 30 cm and allowed to overflow before withdrawing. A total of 33 water samples were analyzed throughout the sampling period. Some water parameters were measured in situ. They include Ambient and Water temperature (°C), pH, Total dissolved solid (mg/L), Dissolved oxygen (mg/L), Electrical conductivity (µS/cm) using HANNA multimeters. Water Turbidity (NTU) was also determined using turbidity meter (WGZ-B, China). Biochemical oxygen demand (BOD) was determined using Winkler’s method, nitrate and phosphate were determined in the laboratory using the HACH DR 2000 direct reading spectrophotometer, method 8039 and 8048 respectively. The HACH nitraVer 5 powder pillow reagents were added to 25 ml of water sample against deionized water at a wavelength of 500 nm for nitrate while The HACH phosVer 3, phosphate powder pillow reagent was added to 25 ml of the water sample against deionized water at a wavelength of 890 nm for phosphate.
Statistical analysis
All data collected from the three study sites for the 11 months period were accumulated and analyzed statistically using inferential and descriptive statistics. Data on physicochemical parameters were subjected to one-way analysis of variance (ANOVA) (p < 0.05), and were significant difference existed, means were separated using the Tukey’s test. ANOVA was done using SPSS 23.0 software package. Pearson correlation analysis was done to determine the relationship between physicochemical parameters and Odonata. Data on taxonomic composition and diversity of Odonata species at the three study sites (Alaasin, Idi, and River Aponmu) in Ipogun were subjected to diversity indices such as Shannon-Weiner (H′), Simpson 1-D, Margalef, Evenness (E) and Equitability using Paleontologist Statistical Software package (PAST) version 3.0. All the graphs were plotted using Microsoft Excel 2016.