The diversity of aquatic insects surrounding the gold mining areas of central sulawesi and their relation with mercury levels and water quality

Human activities may influence the diversity of aquatic insects in rivers. This study aims to assess the diversity of aquatic insects and their relation with mercury levels and water quality along rivers located near the gold mine in Poboya, Central Sulawesi. The insects were collected at six locations based on human activity levels. At each site, the mercury level of water was measured using atomic absorption spectrophotometry (AAS). In addition, water temperature, acidity, dissolved oxygen, and total dissolved solids were determined. The study recorded 23 species of aquatic insects belonging to 7 orders and 14 families. Mercury levels in the rivers did not exceed the threshold except at two sites and did not affect aquatic insects’ diversity. The diversity of aquatic insects, however, tends to decrease downstream. The diversity of aquatic insects, particularly the Ephemeroptera, Plecoptera, and Trichoptera orders, tended to be higher at the higher dissolved oxygen sites.

. Map of the study area.

INTRODUCTION
One of Indonesia's local gold mines is located in Poboya, about 7 km east of Palu, the capital city of Central Sulawesi. Poboya is a village with hilly topography and mountain slopes and is traversed by the Poboya watershed with moderate rainfall of 1,500 mm/year (Ruslan & Khairuddin 2010). Initially, this area was a shallot farming area. However, since the discovery of gold deposits around 2009, this area has been transformed into an illegal community gold mining. Since then, the farmers in this area have changed their professions as traditional gold miners. Currently, traditional gold mining activities have decreased and been replaced by a company called PT Citra Palu Minerals (CPM).
During the traditional gold mining in Poboya, they used mercury in amalgamation and disposing of waste containing mercury directly into the water stream. Subsequently, it causes mercury pollution in the river (Purnawan et al. 2013). Poboya gold mine is a concern because it is a buffer zone for the city of Palu and used to be a source of clean water for Palu residents. Human activities in exploiting natural resources along streams or around rivers can harm the environment because they can affect the water's physical, chemical, and biological conditions (Edegbene et al. 2015). Mercury contamination of river water impacts the diversity, abundance, and distribution of aquatic insects.
Research on the diversity of aquatic insects has been widely studied. However, studies on the effects of gold mining activities on aquatic insect diversity are rarely reported. This study is vital since aquatic insects are one of the components that determine the stability of aquatic ecosystems (Rasdi et al. 2012) as predators, decomposers, energy sources for other predators in the food chain (Takhelmayum & Gupta 2015), as well as bio-indicators of water quality (Chakona et al. 2009;Ferianto 2012;Prommi & Payakka 2015). This study aims to determine the composition, distribution, and abundance of aquatic insects in the river around the Poboya gold mine.

Study sites
The research was carried out along the Pondo River which flows near the Poboya gold mine, Palu, Central Sulawesi, Indonesia and subsequently passes through the Poboya urban village and Palu city from the east (Figure 1). During small-scale traditional gold mining in Poboya, the river was a waste disposal site from the gold amalgamation process. Now that illegal mining no longer occurs except at site 1 (Table 1), the river is used for the daily needs of local people and surrounding agriculture. Water samples were collected at six sites located (Table 1 and Figure 1).

Measurement of mercury levels and water quality
Measurement of water mercury levels was carried out in the laboratory of Balai Besar Industri Hasil Perkebunan (BBIHP) Makassar with SNI 6989 78.2011 by using atomic absorption spectrophotometry (AAS). Water temperature, water acidity, dissolved oxygen, and total dissolved solids were measured using a water checker (HORIBA-U-50 Series).

Aquatic insect sampling and identification
Aquatic insects were collected from the stream near the gold mining areas from September 2017 until Mei 2018. They were collected three times following Subramanian & Sivaramakrishnan (2007a). The insects were sampled using a 25 cm × 40 cm Surber sampler equipped with a collecting net. The Surber net was placed in the middle of the river facing the direction of the water current, then sediment and rock in the area of the plot are dredged into the Surber. All insects in the Surber net were taken using a brush and tweezers and then put into a microtube containing 70% alcohol. All samples of aquatic insects obtained were taken to the laboratory for identification by using available aquatic insect identification keys (Subramanian & Sivaramakrishnan 2007b). Unidentified samples were recorded at the morphospecies level.

Data analysis
The Shannon-Wiener index and canonical correspondence analyses (CCA) were used to measure the diversity of aquatic insects and its relationship with mercury levels and water quality, respectively (Hammer et al. 2001).

Diversity of aquatic insects around the Poboya gold mine
The study recorded 23 species of aquatic insects belonging to 7 orders and 14 families. The highest species number and diversity were recorded at site 1 and, moving downstream from site 1 to site 6, both tended to decrease. The composition and abundance of aquatic insects at each site are quite different (Table 2). Ephemeroptera Order is a group that has the largest number of species (8 species) which is included in 3 families, where the Batidae Family dominates with five species. Two of them were found at all sites, while five other species were only found at sites 1 through 5. Plecoptera Order was recorded at site 1. Trichoptera order had five species and was found scattered at stations 1, 2, and 3. Odonata larvae were also found in this study, although the numbers were relatively small. Hemiptera orders were also collected and dominate by Rhagovelia sp. The Diptera species were found at stations 4-6, but not collected at stations 1-3.

Relationship between mercury levels and water quality on the diversity of aquatic insects
The mercury levels and water quality at all sampling stations were varied (Table 3). Mercury concentration was around 0.0004-0.0008 ppm except at sites 2 and 5 which reached 0.0032 and 0.003 ppm, respectively. In general, this mercury level is still lower than the threshold level i.e. 0.001 ppm according to the regulations of The Ministry of Healthy Republic of Indonesia Number 82/2001. However, the mercury concentration at sites 2 and 5 exceeded the threshold levels. The multidimensional scaling analysis results using canonical correspondence analysis (CCA) showing that among variable measured, the presences aquatic insects particularly Ephemeroptera, Plecoptera, and Trichoptera (EPT) species was  highly correlated with the dissolved oxygen. While the presence of Chironomids was mainly related with the dissolved solid. Interestingly, mercury levels were not correlated with the diversity of aquatic insects (Figure 2).

DISCUSSION
The study found 23 species of aquatic insects in the river around the mining area in Poboya, Central Sulawesi. The insect diversity at all survey sites tended to decrease moving down river, except for the Diptera Order. Several studies have also reported a decrease in the diversity and abundance of aquatic insects at a distance closer to the river mouth (Candra et al. 2014;Leba et al. 2013;Maramis & Makal 2011). These results are thought to be related to habitat conditions at each location. The rocky and fast-flowing habitat at location 1 is an ideal place for aquatic insects to live. According to Voshell (2009), although aquatic insects can live and adapt to various aquatic habitats, in rocky and swift rivers, aquatic insects can be found with a high number of species and abundance. The nature of the sub-extracts on the riverbed, undisturbed habitat, and clean canopy are also breeding grounds for aquatic insects (Rasdi et al. 2012;Arimoro & Ikomi 2009).
Ephemeroptera was the most diverse and abundant order of aquatic insects recorded in this study, while Plecoptera was the minor group. At the global scale, there are 3000 species of Ephemeroptera, which belong to 400 genera and 42 families (Barber-James et al. 2008). In Turkey, for example, 14 families, 39 genera, 138 species, and five subspecies were reported (Girgin et al. 2010).
Ephemeroptera, Plecoptera, and Trichoptera, commonly abbreviated as EPT, are essential aquatic insect grouping that is very sensitive to changes in the aquatic environment. Therefore, EPT is often used as a bioindicator to study the habitat and water quality of aquatic ecosystems (Rosenberg & Resh 1993). The presence of EPT indicates a habitat has not been heavily polluted (Chun et al. 2017). These groups of insects prefer clear, unpolluted fast flowing streams and are sensitive to water pollution (Subramanian & Sivaramakrishnan 2007a).
In this study, mercury levels were much lower compared to those of previous studies. Purnawan et al. 2013 reported that the river around the Poboya gold mine was contaminated with mercury, exceeding the tolerance threshold, which was around 0.0103-0.183 mg/kg. The decrease in mercury levels in river water after a long time is because there is no gold processing activity that discharges the remaining tailings in the river and also because basically, the solubility of mercury in water is low (Adlim 2016) or in the aquatic environment, metal mercury quickly becomes a gaseous form (Amyot et al. 2005). According to Clever et al. (1985), the solubility of mercury in water is very small. For example, if 1 ton of mercury is thrown into fresh water, only 0.06 g is dissolved. Also, in fast-flowing water, the concentration of mercury is diluted. These features may explain what is happening in the waters of the Poboya River.
In contrast, if mercury enters seawater, it binds to chlorine in the seawater to form organic mercury HgCl bonds. As HgCl, mercury easily enters plankton and moves to other biotas, and accumulates in a food chain (Amyot et al. 2005). In water or sediment, mercury can also become methyl mercury compounds by bacterial activity. Methylmercury is particularly dangerous because it dissolves in fat to accumulate in organisms of various tropic levels. The higher the tropic level in the food chain, the higher the mercury content in the body (Carrasco et al. 2011).
The CCA analysis results showed no effect of the mercury content in the water on the presence of aquatic insects. This is probably related to the low content of the mercury at our study sites with levels that do not differ significantly among sites. However, some previous studies showed that mercury contamination in water due to smallscale community gold mining activities affects the abundance, species richness, and diversity of aquatic insects, especially Ephemeroptera, Plecoptera, and Trichoptera (Chula et al. 2013;Mudyazhezha & Kanhukamwe 2014).
Dissolved oxygen is also known as an environmental factor that influences the presence of EPT (CCA analysis results show that dissolved oxygen levels affect EPT insects). Aquatic insects can be used as an indicator of the quality of a water. Ephemeroptera, Plecoptera, and Trichoptera (EPT) are often found in clean waters and very sensitive to changes in water physics and chemistry (Chun et al. 2017). Apart from the metal content in water, several other environmental factors such as temperature, pH, dissolved oxygen, electrical conductivity, turbidity, sulfate, nitrate -nitrogen, orthophosphate, ammonia-nitrogen, and alkalinity in water also influence the presence of aquatic insects (Prommi et al. 2014). The presence and composition of aquatic macroinvertebrates can also be influenced by human anthropological activities (Malmqvist 2002;Heino 2013;Márquez-García et al. 2009) as these activities can damage the physical and/or chemical environment (Pallottini et al. 2015;Castro et al. 2018;Malmqvist 2002).

CONCLUSION
The study conducted at the river around the Poboya gold mine in Central Sulawesi found 23 species of aquatic insects belonging to 7 orders and 14 families. Ephemeroptera, totaling 32%, dominated the family numbers and abundance of aquatic insects and were recorded at all sites.
These studies also confirmed that mercury levels are still below the threshold and therefore have no relation with aquatic insects' diversity. The dissolved oxygen correlated with the presence and abundance of Ephemeroptera, Plecoptera, and Trichoptera while dissolved solids were associated with Chironomus.