Species diversity of Odonata as a bioindicator of water pollution in the Batang Harau watershed, Tanah Datar District, West Sumatra

The Batang Harau River was located in Nagari Paninjauan, X Koto District, Tanah Datar Regency, West Sumatra. The local community uses this river as a water source to carry out various daily activities, such as the irrigation of rice fields; household activities, and household waste disposal. The research aimed to analyze the comparison of dragonfly species diversity as a bioindicator for pollution in several habitat types (natural, rice fields, and settlements). The observations were made by exploring and walking along the river in the morning (9 am – 12 am) and evening (3 pm - 5 pm). The Visual Encounter Survey (VES) method was modified using a 20 m x 10 m plot, and all dragonflies found in this area were collected using an insect net. The data obtained were analyzed using the ShannonWienner diversity index, the Margalef species richness index, and Simpson’s dominance index. A total of 280 individuals, 12 species from 7 families, were collected in this study site. Most Odonata species were found in natural areas, followed by rice fields and settlements. The environmental conditions have affected the diversity of Odonata. The odonates can be used as bioindicators of the aquatic environment, especially in the suborder Zygoptera, which is dominantly found in natural habitats.


Introduction
A river is an open body of water that flows and receives input from all waste from various human activities in the surrounding area's residential, agricultural, and industrial areas [1].Rivers are aquatic ecosystems that play an important role in the hydrological cycle and function as water catchments for the surrounding area.As an ecosystem, rivers have various biotic and abiotic components that interact with each other to form a functional network [2].Environmental quality is considered good if the interaction between the biotic and abiotic components is balanced [3].
Insects have the potential to be used as bioindicators of water pollution, one of which is the dragonfly (Odonata).Odonata is an aquatic insect closely related to environmental quality because it is susceptible to environmental changes and can be used as an indicator of ecological balance.The presence of Odonata can be used to determine clean water quality, thereby influencing its abundance.When the conditions of a habitat change, Odonata also show changes in diversity and distribution [4].It also depends on its tolerance to environmental changes, so it has the potential to live in such environments or habitats [5].Water quality greatly determines the survival of river biota and humans using water directly.Macroinvertebrates, such as dragonflies, can be used as indicators of water quality [6].
The main habitats of dragonflies are aquatic habitats such as lakes, reservoirs, ponds, rivers, and rice fields.Several types of dragonflies have specific habitats determined by habitat type, strong water currents, canopy cover, and vegetation conditions [7].It is because several species of dragonfly are susceptible to their environment.Several types of dragonflies are sensitive to environmental changes, namely the Ceonagridae and Platycnemididae families in the Zygoptera suborder and the Aeshnidae family in the Anisoptera suborder.Species in these families indicate it, found only in natural vegetation types [8].Therefore, dragonflies of this family can be used as bioindicators of water pollution.
The Batang Harau Watershed is located in Nagari Paninjauan, X Koto District, Tanah Datar Regency, West Sumatra.This area's topography is on Mount Merapi's slopes at an altitude of 800 to 970 meters above sea level.This area has a 2500-3000 mm/year rainfall with temperatures between 17 and 26°C [9].Nagari Paninjauan has several river basins flowing from Mount Merapi to Mount Singgalang.One of this area's most important river flows is the Batang Harau Watershed.
The local community uses the Batang Harau watershed as a water source for daily activities, such as irrigating rice fields, as a water source for household activities, and as a waste disposal site.With these activities, it is suspected that pollution has occurred due to insecticides and household waste in the Batang Harau River Basin.The pollution level in this watershed has not been studied in detail.However, this study will compare the diversity of dragonfly species among three habitats as a bioindicator for pollution (natural, rice fields, and residential) in the Batang Harau watershed.
The method used in this research is the Visual Encounter Survey (VES) Method.Observations were carried out by exploring and following the river flow during a predetermined period, namely, in the morning from 07.00 WIB to 09.00 WIB and the afternoon from 15.00 WIB to 17.00 WIB.The Visual Encounter Survey (VES) method was modified using a 20m x 10m plot.Dragonflies seen in the transect area were photographed with a camera and then identified based on several related books and article sources.The environmental parameters of every observation at the research location were measured.Environmental parameters include Environmental Temperature, Dissolved oxygen levels, and Water pH.

3.1.Composition of odonates.
The result showed that there are 280 individuals, 12 species from 7 Odonata families in the Batang Harau river basin (DAS).6 types belong to the suborder Zygoptera, family Lestidae, Calopterygidae, Chlorocypidae, Euphaidae, Coenagrionidae, and three types belong to the suborder Anisoptera, family Corduliidae, Libellulidae.The highest number of Odonata species was found in natural habitats, followed by rice fields and residential habitats (Table 1).

3.2.Index.
The Odonata diversity index value in natural habitats is 1.62 in the medium category, in rice fields habitats with a value of 0.92, and 0.85 in disturbed habitats, each classified as low.The Odonata dominance index value in natural habitat is 0.24.In rice field habitat, it is 0.47; in disturbed habitat, it is 0.49, each classified as moderate.The Odonata species richness index value in natural habitat is 1346 (2024) 012026 IOP Publishing doi:10.1088/1755-1315/1346/1/0120263 1.67, in rice field habitat, it is 0.84, and in disturbed habitat, it is 0.77, meaning that Odonata species richness in these three areas is relatively high, with the highest value in natural habitat (Table 2).

3.3.Abiotic factor.
The abiotic factors measured included temperature, air humidity, dissolved oxygen levels, and water pH, showing slight differences at each observation location.Comparison of abiotic factors that are visible in the three types of habitat are dissolved oxygen levels (Table 3) Odonata can live in various habitats, such as rice fields, rivers, mangroves, and rural and urban areas with water sources to support their lives.This study used three types of habitat to compare the diversity of dragonfly species in the three habitats: natural habitat (forest), rice field habitat, and disturbed habitat (residential).
Various types of trees dominate forest habitats.Other vegetation found in natural habitats includes shrubs, herbs, bamboo, bushes, and various weeds with relatively moist soil physical conditions.The minimal disturbance by humans in natural habitats impacts the number of odonatan species found.Rice plants, bush vegetation, and grass dominate the rice field habitat.Other vegetation in this habitat are bananas, sugar cane, jackfruit, taro, and coconut.Buildings dominate residential habitats.Some vegetation is grass, bananas, grasses, and coconuts growing around the river.Dragonflies are more commonly found in natural habitats, followed by rice field habitats and residential habitats.It is shown by the high number of species and individuals of dragonflies in natural habitats compared to other habitats.
In natural habitats, there are nine species of dragonflies found, and 4 of them are only found in natural habitats such as Heliocypha fenestrata, Vestalis luctuosa, Neurobasis sinensis, and Euphaea variegata.The Euphaea variegata species dominate the natural habitat, namely 34 individuals.Euphaea variegata is perched on rocks and flying low above the water surface.Euphaidae-like places with quite bright light intensity always perch on protruding rocks or fallen twigs or branches.Males are territorial, preferring to perch in bright places on twigs and rocks.They often attract females with strikingly colored wings and defend territories near flowing water.Females are usually found in shady forest areas, perching on tree branches to hunt prey.Euphaea variegata is rarely around water except to lay eggs or mate.In this study, Euphaea variegata was found around river flows.Male Euphaea variegata was more commonly found than female Euphaea variegata.The same thing was found in research [10], where male Euphaea variegata were often found around river flows with low light intensity.The second species that is often found in this habitat is Vestalis luctuosa.Vestalis luctuosa was found flying alongside the Euphaea variegata species at the observation location.According to Aswari [11], the flight activity of Vestalis luctuosa is often seen with other types of dragonflies, such as Euphaea variegata and Rhinocypha fenestrata; this is due to the similarity in the type of food and habitat required.Calopterygidae needle flies like aquatic habitats in the form of ditches or rivers with slow to fast currents, which flow in protected areas or forests at an altitude of up to 2000 meters above sea level [12].In observations, Vestalis luctuosa was found on the banks of the Bearus River under the canopy and in irrigation canals around the river at 932 meters above sea level.Research conducted by Aswari [11] found Vestalis luctuosa at an altitude of 1500 meters above sea level, namely in the forest area of Mount Kendeng.The natural habitat in this study has many canopied plants and is far from human activity.Habitat variations such as rocky rapids and secondary forests with various vegetation support the diversity of Odonata species at the research location.Other species, such as Heliocypha fenestrata and Neurobasis sinensis, are only found in natural habitats.From research conducted by Ma'rufah [13], male and female Heliocypha fenestrata prefer habitats far from busy populations and lush vegetation.They were found perched on rocks and grass on the river bank in the observation area.The Neurobasis sinensis dragonfly prefers to perch in open places around rivers exposed to hot sun.Adult male and female Neurobasis sinensis are only found along river banks and rarely move away from water [12].
Pantala flavescens, namely 71 individuals, dominate the rice field habitat, and the second is Orthetrum sabina, with 34 individuals.The high number of individual Odonata in rice fields indicates that the environmental factors around the rice fields support the life of Odonata [14].Pantala flavences are most commonly found in rice field habitats.This species likes open water areas with calm water surfaces.The maximum number of this species is seen flying during the day, and some hovering around rice fields in the afternoon [15].At the observation location, Pantala flavences were often found in the afternoon, mostly perched on grass, embankments, and weeds around rice fields.
In disturbed habitats (residential areas), the Orthetrum sabina species dominate.This species is found in all three habitat types; this type of dragonfly has a wide distribution range.This species is a fierce predator that often preys on planthoppers, aphids, butterflies, bees, and even other types of IOP Publishing doi:10.1088/1755-1315/1346/1/0120266 dragonflies.They can live in poor water environments and solitary lives [16].In rice fields and disturbed habitats (residential areas), there are rivers with various human activities that cause the river to be polluted.The vegetation in both habitats is only covered by weeds along the river, rice fields, and surrounding bushes.

Diversity of Odonata Types.
A total of 280 individuals, seven families, and 12 odonata species were obtained in this study.The type of Odonata with the highest number of individuals found is Pantala flavescens, with a total of 71 individuals in rice fields, and the species with the lowest number of individuals are Epophthalmia vittigera, Rhodothemis rufa and Orthetrum testaceum with a total of 1 individual each in natural habitats, and Tholymis tillarga one individual in rice field habitat.The species found in all three habitats (natural, rice fields, and disturbed) are Lestes praemorsus praemorsus and Orthetrum sabina.
The Libellulidae family has the largest number of individuals in this study.Dragonflies belonging to the Libellulidae have a higher abundance and distribution than other dragonflies.Generally found in residential areas or areas that have experienced pollution [10].Dragonflies of this family generally live solitary lives, such as Orthetrum testaceum, Orthetrum sabina, and Tholymis tillarga, with a wide distribution [17] and have a high level of tolerance to environmental changes, including polluted water conditions [18].In this study, the Libellulidae family, namely Orthetrum sabina, was found in three habitat types: natural habitat, rice field habitat, and disturbed habitat.However, this type is more commonly found in rice field habitats.The same results were also obtained in Virgiawan's [19] research.
The type with the second largest number of individuals is Euphaea variegata, with 39 individuals belonging to the Euphaidae family and only found in natural habitats.The type with the third highest number of individuals is Vestalis luctuosa in the Calopterygidae family, with 34 individuals.This family is only found in natural habitats at the observation location.The Calopterygidae family is found mainly in rocky rivers of secondary forests [10].They can live with other types of Zygoptera, such as Heliochypa angusta and Libellago lineata in the Chlorophydae family.The Trithemis festiva type in the Libellulidae family is also often found in natural habitat types [10].The Calopterygidae family likes places with light intensity that is not too high and temperatures below 28°C.The body temperature produced by dragonflies comes from exposure to environmental heat and will significantly influence their flight performance, increasing maneuverability, agility in catching prey, and mating success [20].
The diversity index of dragonflies in natural habitats is classified as moderate.The number of individual dragonflies found in this habitat was 117, the species with the most individuals found among the three types of research habitat.There are 4 species of odonata that are only found in natural habitats, such as Heliocypha fenestrata, Vestalis luctuosa, Neurobasis sinensis, and Euphaea variegata.The large number of species and individuals found in natural habitats make dragonflies in these places bioindicators of the aquatic environment.The lack of human activity is a supporting factor for the diversity of dragonflies in this habitat.
The number of species in a habitat influences the level of dragonfly dominance-the fewer species, the higher the dominance value, and vice versa [15].Simpson's dominance index category, 0.01 -0.30 is low, 0.31 -0.60 is medium, and 0.61 -1.0 is high [21].The natural habitat diversity index value at the observation location is classified as moderate, meaning that the conditions in the habitat are most suitable for the life of dragonflies.It is caused by several factors, namely human activity and environmental abiotic conditions such as temperature, pH, DO, and light intensity [19].

Abiotic Factor.
There are several influencing factors when collecting research data, such as vegetation in each habitat and differences in weather.The weather in the morning tends to be sunny and cloudy, while in the afternoon, it is cloudy; data collection was carried out during the rainy season.
Dissolved oxygen levels in the three habitats are classified as high, with respective values of 8.54 in the natural habitat, 7.61 in the rice field habitat, and 7.84 in the disturbed habitat (residential).Based on Government Regulation Number 82 of 2001 concerning Water Quality Management and In water pollution control, it is emphasized that the minimum DO level that must be present in water is >2 mg/lt.High water content in waters can be caused by photosynthesis and air absorption [22].According to Sastrawijaya, [23] dissolved oxygen (DO) content influences the amount and type of macrobenthos in waters.It aligns with the research results: the natural habitat has the highest DO value and number of individuals and species found among the three habitats.The higher the dissolved oxygen level, the greater the amount of macrobenthos.The DO value in the natural habitat has the highest number and the largest DO value among the three observation sites, namely 117 individuals with a DO value of 8.54 mg/lt.The highest DO levels are in natural habitats because this habitat has dense vegetation and is covered by canopy plants.The minimal level of pollution also causes high DO values in this area.River flow conditions also affect DO levels in the water.Waters with fast currents have high dissolved oxygen content.In contrast, rivers with slow currents have lower dissolved oxygen levels, which is caused by the large amount of organic material deposited at the bottom of the water [19].
The temperature obtained in this study was around 26-28°C, which is the optimal temperature for dragonfly life.Differences in temperature at the observation location will affect the dragonfly population.An increase in temperature will affect the dissolved oxygen levels in it.The hotter the water temperature, the less dissolved oxygen levels in the water [24].
The degree of acidity (pH) value at the three observation locations was 7 in the natural habitat, 6.9 in the rice field habitat, and 7.4 in the disturbed habitat (settlements).Most aquatic biota are sensitive to changes in pH and prefer a pH of around 7 to 8.5 [25].Based on the research results, the pH levels in the three places were still within the tolerance limits of dragonflies.The highest pH value in disturbed habitat (combatment area) was 7.4.Abiotic factors at each observation location can be seen in Table 3.
Based on the results of research in the Batang Harau Watershed (DAS), data analysis shows that biotic factors in natural habitats support odonata life activities, as indicated by the high diversity index and richness index of dragonfly species found in this habitat.Several types of dragonflies are found in natural habitats and are not found in other habitats, such as Heliochypa fenestrata, Vestalis luctuosa, Neurobasis sinensis, and Euphaea variegata.This species can only live under certain conditions that support its life.Another supporting abiotic factor is the high levels of dissolved oxygen in natural habitats, which support the life of aquatic biota such as dragonflies.

Conclusion
Based on the research conducted, the following conclusions were drawn.The diversity and abundance of dragonfly species are correlated with water pollution levels, dissolved oxygen levels, and habitat types.Orthetrum sabina is more commonly found in areas with higher pollution and Euphaea variegata in cleaner waters.So, can be concluded that certain Odonata species are identified as indicator species for pollution levels, dissolved oxygen levels, and different habitat types.The presence or absence of dragonfly species provides an overview of the health of the aquatic ecosystem in the Batang Harau watershed.

Table 2 .
Biodiversity index of Odonates in Batang Harau river