Assessment of Water Quality in the Upper Brantas River Using Macrozoobenthos as Bioindicators

This research was conducted from April 2023 to May 2023 in the transition season from the rainy season to the dry season. The sampling location was determined in the upstream area of the Brantas River, which includes Batu City and Blitar Regency (Figure 1).

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Figure 1. Map of sampling locations at Batu and Blitar

2.1 Materials

Equipments and materials used in this study include a hand net (diameter 43 cm) with netting 0.5 mm, Secchi disk, DO meter, pH pen, thermometer, bottle sample 1 L and 50 mL, plastic clip, microscope stereo, magnifying glass, pinset, petridish, ruler, pipet, coolbox, GPS, Macrozoobenthos samples, water, formalin 4%, alcohol 70%, identification guidebook.

2.2 Sample collection

Sampling was carried out in the upstream area of the Brantas River; two stations were chosen: Station 1 in Batu City and Station 2 in Blitar Regency. Based on topographical considerations of environmental conditions, there are 5 points at each station to collect samples. Macrozoobentos sampling was carried out at two stations, each region consisting of 5 points. Sampling is carried out at each point every 2 weeks.

The first point at the first station, Batu, is at the Kekep River, the second one is at the Brantas Tulungrejo River, the third point is at the Lanang River, and fourth point is at the Sidomulyo River, and the last point at Station 1 is at the Pendem River. The first point in Station 2, Blitar Regency, is the Telaga Rambut Monte River as the first point, then the second one at the Bantaran area, the river in the Sanggrahan area as the third point, and the Jalan Tangkis Lahar Gn. Kelud, as well as the fourth point and the fifth one, is the Lekso River.

2.3 Pearson correlation

Correlation analysis was carried out between the diversity of macrozoobenthos and the physical and chemical parameters of water. The data normality test was carried out first using the Shapiro-Wilk test because the number of samples was only <50. If the significance value was >0.05, the data was normally distributed and tested with Pearson Correlations, while if the significance value was <0.05, the data was abnormally distributed and tested with Spearman's rho. The following is the table of coefficient intervals in Table 1.

Table 1. Level of relationship, interval of correlation coefficient

Coefficient Interval	Relationship Level
0 - 0.199	Very Low
0.20 -0.39	Low
0.40 - 0.59	Currently
0.60 - 0.79	Strong
0.80 - 1	Very Strong

Macrozoobenthos sampling was carried out at two stations, each area consisting of 5 points. Macrozoobenthos sampling was carried out by kicking and jabbing techniques. The kicking technique was carried out in shallow rivers, the net was placed in front of the person holding the net with the mouth of the net facing the direction of where the water flow come from, then the substrate was stirred and kicked with the person’s feet in front of the net for 1 minute or 10 meters long with rotating feet motion. This technique is done to stimulate animals or benthos hiding at the bottom of the river to get out and drift into the net. The jabbing technique can be carried out on the banks of shallow and deep rivers by placing a net at the bottom of the riverbank, then moving the net forward towards the source of the water flow for 10 meters. The substrate (sediment and gravel) that enters the net is sorted, then cleaned in a plastic bowl. The macrozoobenthos attached to the substrate were taken as samples. The sorted macrozoobenthos samples were transferred into a plastic sample bag, which had been labeled based on station points, and then given 4% formalin solution to preserve the macrozoobenthos for identification.

Water sampling and measurement were carried out in the same place as macrozoobenthos sampling. Parameter measurements were carried out in situ and ex-situ. Parameters examined in situ were temperature with a thermometer, pH with a pH meter, and DO (Dissolved Oxygen) using a DO meter. Furthermore, 1.5 liters of water samples were taken at each location for ex-situ testing, namely for BOD (Biochemical Oxygen Demand), COD (Chemical Oxygen Demand), and TSS (Total Suspended Solids) parameters.

Sampling of base substrate sediment was carried out in the same place as macrozoobenthos and water quality sampling. Sediment samples were tested ex-situ in the laboratory. Sediment samples were stratified to obtain data on sediment grain size. After that, the results are used to determine the type of substrate based on Shepard's triangle.

2.4 Data analysis

Collected macrozoobenthos and then analyzed for its abundance and diversity. Macrozoobenthos abundance is analyzed with Shannon-Wiener’s:

$D=\frac{N i}{N} \times 100 \%$        (1)

where,

D = Abundance

Ni = Number of individuals of a species

N = Total number of individuals found

The diversity of macrozoobenthos was also analyzed with Shannon-Wiener’s:

$H^{\prime}=-\sum_{l=1}^S P i \ln P i$          (2)

where,

H' = diversity index

Pi = the number of individuals of each species

S = number of types

Ni = the number of the i-th type

N = Total number of individuals found

If the diversity index shows a value of more than 3, then the level of diversity is high; if the value is between 1-3, then the level of diversity is moderate, and if the value is less than 1, then the level of diversity is low. The diversity index value can be used to determine the level of pollution, waters with macrozoobenthos diversity value that is more than 3 is categorized as not polluted, diversity value ranging 2-3 is categorized as lightly polluted, diversity value ranging 1-2 Is categorized moderately polluted, and diversity value less than 1 is categorized as heavily polluted [8].

Correlation analysis was carried out between macrozoobenthos diversity and water physical and chemical parameters. The data normality test was carried out first using the Shapiro-Wilk test because the number of samples was only <50. If the significance value is > 0.05, then the data is normally distributed and tested with Pearson Correlation, whereas if the significance value is <0.05, then the data is not normally distributed and tested with Spearman's rho.

Diversity index (H') and abundance (D) are index studies that are often used to predict the condition of an aquatic environment and community stability based on biological components. The environmental condition of water is said to be good or stable if a high diversity index is obtained. If diversity is equal to zero (0), then the community will consist of a single species or species. The diversity value will be close to the maximum if all species are evenly distributed in the community [13, 14], so it can be concluded that the diversity index value is strongly influenced by the number of types of organisms; therefore, the abundance of each species is also analyzed.

Diversity of macrozoobenthos can provide information about water quality. At Station 1 (Batu), the diversity values ranged from 1.29 to 2.02; these values can be categorized as lightly and moderately polluted [13]. This is due to the evenly distributed abundance of macrozoobenthos, especially at point 1, which has the highest diversity value, so that it is included in the lightly polluted category. The highest abundance at that point was only 18.6% in the family Baetidae, while the lowest was 6.3% in the Gomphidae family. Baetidae is categorized as a macrozoobenthos that is tolerant to a lightly polluted environment, meanwhile Gomphidae is categorized as being tolerant to a very lightly polluted environment [15]. Baetidae is a species that is sensitive to pollutants such as insecticides [16]. As stated, Baetidae only live in clean water habitats [17].

Conditions of diversity and abundance are quite different at Station 2 (Blitar). Station 2 has diversity values ranging from 1.28 to 1.83. This difference is sufficient to categorize Station 2 in the moderately polluted category. The highest abundance value at Station 2 was found in the Thiaridae family of 62.4% which was found at point 5, which also had the lowest diversity value of all station points. The lowest abundance value at point 3 is in the Perlidae family, which has an abundance value of only 1.8%. However, at this value of abundance and diversity, the waters of Station 2 in the upstream of the Brantas River can still be categorized as moderately polluted. Thiaridae is an indicator species for high TSS [18]. Thiaridae is categorized as a macrozoobenthos that is tolerant to a moderately polluted environment, meanwhile Gomphidae is categorized as being tolerant to a very lightly polluted environment [15]. Thiaridae is a type of gastropod that is tolerant of contaminants. Macrozoobenthos such as Thiaridae, which are very abundant in waters, are influenced by agricultural waste in river water ecosystems and are tolerant to a high TSS value [19].

The results of the diversity and abundance of these macrozoobenthos were then compared with the physical and chemical parameters of water quality. The diversity results appear to be directly proportional to the TSS and BOD values. The TSS value appears to be outside the class II quality standard according to PP RI no. 22 of 2021 for almost all station points except for point 1, Station 1. Point 1 at Station 1 is also the only point that shows results of diversity values, which are categorized as lightly polluted. TSS can affect the composition of macrozoobenthos in an aquatic environment [20]. Waters with lower TSS values have higher diversity of macrozoobenthos.

BOD values at all station points show values that are outside the second-class quality standard according to PP RI No. 22 of 2021. This fact is thought to be directly proportional to the results of macrozoobenthos diversity, which still shows that the condition of these waters is polluted. In accordance with the results of diversity at point 1, Station 1, which shows moderate diversity values, is still in the lightly polluted category. Increased BOD in waters can be caused by the entry of organic and inorganic materials into the waters and can cause loss of macrozoobenthos, which are intolerant to these changes [21].

After obtaining these results, Pearson correlation was used to further understand the correlation between macrozoobenthos diversity and chemical and physical parameters of water. After we found that all the data obtained had a normal distribution, we could continue with the Pearson correlation test. In the first correlation test between macrozoobenthic diversity and temperature parameters, the results obtained were that there was no significant correlation (P > 0.05) between macrozoobenthic diversity and temperature. The results also show that the relationship between the two is low and opposite.

In the correlation test between the second parameter between macrozoobenthos diversity, and DO, the results showed that there was a significant correlation between macrozoobenthos diversity and DO (P <0.05). In addition, the results show that the relationship between DO and macrozoobenthos diversity is very strong. There are other parameters that show the same conclusion as DO, namely BOD, COD, and TSS, all three of which showed significant correlation results and very strong and contradictory relationships with macrozoobenthos diversity. Meaning the higher the diversity value, the lower the value of the water parameters will be. Meanwhile, the pH parameter also shows a significant correlation with macrozoobenthos diversity, but only has a strong correlation with the in-line relationship.

Waters that show a reduction in DO will cause the BOD value to increase, because the BOD value increases, the COD value also increases. The increased COD value is also caused by the entry of organic and inorganic materials into the water, and causes the loss or reduction of macrozoobenthos, which are intolerant to these changes [20]. TSS can affect the penetration of light into the waters, and can affect DO in the waters, and sedimentation in the waters, and where macrozoobenthos are located, so that they can affect their abundance and diversity [22]. In aquaculture, if the BOD and COD values increase in waters, it can result in anoxia in fish or a lack of oxygen, as well as high TSS values, which affect DO values.

Still water pond cultivation is a type of cultivation that is mostly carried out in the cultivation activities carried out around the upstream area of the Brantas River, reaching 14,000 cultivators. Cultivation at both stations, namely Batu and Blitar, is famous for cultivating goldfish, and this commodity has become a superior product [23]. The highest aquaculture production in Batu City is in tilapia, which will reach a production volume of 29,814 tons in 2021, while the volume of tilapia production in Blitar will reach 411,500 tons in 2021. Therefore, these two commodities are included in the commodities most frequently cultivated in the region. around the headwaters of the Brantas River.

The cultivation of still water ponds for carp is regulated by SNI 01-6131-1999, while for tilapia it is regulated by SNI 7550-2009. In the SNI for goldfish cultivation in still water ponds, the optimal temperature for cultivating is 25℃, while in the SNI for tilapia, it ranges from 25-32℃. The temperature of the waters of the Brantas River is slightly below the SNI quality standard, which is in the range of 20.3-23.7℃. This is thought to be caused by the upstream area of the Brantas River, which is generally located in mountainous areas that have a cooler climate than the lowlands.

The pH parameter for carp and tilapia culture in still water ponds is 6.5-8.6, while the PP RI no. 22 of 2021 for class 2 water quality standards, the quality standards for the pH parameter are 6-9. There are slight differences between the three quality standards, but the pH measurement results obtained in the upstream area of the Brantas River ranged from 7.7 to 8.6, so they are still included in the three quality standards.

The DO parameter for goldfish farming in still water ponds is more than 5 mg/L, while for Tilapia, the optimal level is more than 3 mg/L, and in PP RI No. 22 of 2021 for class 2 water quality standards, the quality standard for the DO parameter is more than 4 mg/L. There are slight differences between the three quality standards, but DO measurements obtained in the upstream area of the Brantas River ranged from 7.7 to 8.6, which are still included in the three quality standards.

After obtaining the data results, a Pearson correlation was performed between the diversity of macrozoobenthos and the chemical and physical parameters of water. Since it was found that all the data had a normal distribution, the Pearson correlation test was continued. In the first correlation test, which is the correlation test between the diversity of macrozoobenthos and the temperature parameter, the result obtained was that there was no significant correlation (P > 0.05) between the diversity of macrozoobenthos and temperature. The results also indicate that the relationship between the two is weak and inverse. In the correlation test between the second parameter, namely the correlation between macrozoobenthic diversity and DO, the results showed that there is a significant correlation between macrozoobenthic diversity and DO (P < 0.05). Furthermore, the results indicate that the relationship between DO and macrozoobenthic diversity is very strong, with opposing characteristics. There are other parameters that show the same conclusion as the DO parameter, namely BOD, COD, and TSS, all of which indicate significant correlation results and very strong and opposing relationships with macrozoobenthic diversity. The pH parameter also shows a significant correlation with macrozoobenthic diversity, but only has a strong relationship that is direct.

The results of the diversity and abundance of macrozoobenthos in the upstream area of the Brantas River show that the upstream waters of the Brantas River are categorized as lightly and moderately polluted. The same results were found in the Citarum Hulu River Basin (DAS), indicating that the macrozoobenthos bioindicator shows levels of pollution ranging from light to heavy [24]. When compared with class II quality standards, PP RI No. 22 of 2021 is thought to be closely related to TSS and BOD. One of the most important cultivation commodities in the upstream of the Brantas River is carp and tilapia, so that the results of water quality obtained in the upstream area of the Brantas River are also compared with SNI 01-6131-1999 concerning carp cultivation in still water ponds and SNI 7550-200 regarding the cultivation of tilapia in still water ponds. The results obtained were that the temperature parameter was slightly below the quality standards of SNI 01-6131-1999 and SNI 7550-200, but other parameters, such as DO and pH, were still sufficient for cultivation in the upstream area of the Brantas River.