Water quality analysis of Sumurup River in Gunungkidul, Indonesia, using the water quality index

Sumurup River is one of the rivers in Gunungkidul, Indonesia, that continuously flows water throughout the year and traverses different land use types. Consequently, it receives numerous waste inputs. Given the limited water resources in the area, it is necessary to assess the water quality regularly. Moreover, this river was previously a drinking water supply, but it can now only be used for purposes with lower requirements, e.g., bathing and washing. The water quality was assessed using three scenarios with different number of parameters in the composite and two indices: the Indonesian Modification of Water Quality Index (INA-WQI) and the Weighted Arithmetic Water Quality Index (WA-WQI). Parameters observed were pH, DO, BOD, COD, NH3, NO3, total phosphate, TSS, TDS, and fecal coliform. Results showed that the safe limits of pH, BOD, COD, NH3, NO3, total phosphate, TSS, and fecal coliform for drinking water (Class I) were exceeded at several sampling points. In contrast, DO and TDS were below their maximum allowable concentrations at all points. WQI assessment produced varying index values categorized as fair to good (INA-WQI) or excellent to unsuitable for drinking (WA-WQI). Further, the different composite scenarios had a significant effect on WA-WQI but not on INA-WQI scores.


Introduction
Water is the most important aspect in sustaining human life [1]- [2].However, the use of water resources for domestic and non-domestic purposes is limited by quality and quantity.Potable water is often in short supply in different parts of the world, forcing local populations to consume polluted water [3].Drinking poor-quality water has more effect on the human body than exposure to contaminants from other sources [4].
Gunungkidul is a karst area where surface water is typically scarce [5].The physiography consists of Baturagung Mountains in the north, Gunungsewu Karst Area in the south, and Wonosari Basin that separates the two landscapes [6].The research area is located in the Wonosari Basin, which is a karst transition zone that is geologically dominated by porous limestones, as indicated by ponors in the lower reach of the Sumurup River.
In Gunungkidul, the Sumurup River flows through four kapanewon units (equivalent to an administrative district): Karangmojo, Semanu, Wonosari, and Paliyan.Most parts of the river flow through Wonosari, the capital district of Gunungkidul, which is a densely populated urban area with varied land uses.Like many other urban regions, Wonosari is experiencing rapid urbanization and industrialization, which are the most common leading causes of poor river water quality [7].Water Quality Index (WQI) is a statistical tool to measure water quality that combines and simplifies the values of several parameters into one score for better understanding [8].Many WQIs have been developed for numerous cases in different countries, including the Interim National Water Quality Standard (INQWS-DOE) in Malaysia, the Overall Index of Pollution (OIP) in India, and the Canadian Council of Ministers of the Environment-Water Quality Index (CCME-WQI) in Canada [9]- [11].In this research, the Indonesian Modification of Water Quality Index (INA-WQI) and Weighted Arithmetic Water Quality Index (WAWQI) were used to assess the water quality of the Sumurup River and determine its suitability for drinking purposes.

Data
This research used two types of data: primary data, namely water quality parameter values, and secondary data, including satellite imagery for land use data, thematic maps, and other supporting data to assist the analysis.Ten parameters were calculated for the water quality assessment.TDS and pH were measured directly in the field, while DO, BOD, COD, NH3, NO3 -, total phosphate, and fecal coliform were tested in the laboratory.

Figure 1. Map of the water sampling points for water quality assessment in Sumurup River
Surface water was sampled at six different points on the Sumurup River (Figure 1).These sampling points were determined by first dividing the river into five segmeponornts according to waste-generating land use types.For each land use segment, one sample of the river water was collected, except for the last one in the southernmost part of the research location.Here, two sampling points were selected for better representation because the last segment had a larger land area and a longer river section.Finally, to determine the water quality, the measured parameter values were compared against the water quality standards for drinking water issued by the provincial government of the Daerah Istimewa Yogyakarta (DIY) Province, i.e., Governor Regulation No. 20 of 2008.

Methods
This study employed two types of water quality index (WQI): the Indonesian Modification for Water Quality Index (INA-WQI) and the Weighted Arithmetic Water Quality Index (WA-WQI).Three scenarios of water quality assessment with different numbers of parameters were used.Each index was calculated with ten, seven, and five parameters, with the composite shown in Table 1.Quality Index (NFS-WQI) that uses the sub-index and weight score of each parameter to determine the composite index [12].In this research, parameter weights and sub-index curves were determined according to the expert judgment on the level of significance of each parameter in shaping the overall water quality, which was obtained from Ratnaningsih et al. [13] that surveyed a panel of 98 experts in the field of hydrology.The INA-WQI value was calculated using Equation 1 below: where Wi is the weight of parameter i and Ii is the sub-index value of parameter i.The derived index value was then classified into one of the water quality classes in Table 2.
The three composite scenarios, where the index incorporated five, seven, or ten parameters, changed the weight of each parameter.The weight was thus modified using Equation 2 below: where Wi(modified) is the modified weight of parameter i based on the composite scenario, Wi(initial) is the initial or original weight of parameter i, Σx is the initial total weight value of the used parameters, Σy is the initial total weight value of the unused parameters.Weighted Arithmetic Water Quality Index (WA-WQI) WA-WQI combines numerous parameters to assess water quality and describe the condition of a water body for drinking purposes [14].This index was calculated using Equation 3 below [15]: where Qi denotes the quality rating scale for parameter i (Equation 4), Vi is the measured value of parameter i, V0 is the ideal value of parameter i in pure water (V0 = 0, except for pH = 7 and DO = 8 mg/L), Si is the recommended value (standard) of parameter i. Wi is a dimensionless factor representing the weight of a parameter, expressed as (Equation 5below): and K, a proportional constant (Equation 6), The WA-WQI score was then classified according to provisions in Table 3.

Water Quality Status by Parameter
The total dissolved solids (TDS) measured in the field were between 130 and 442 mg/L (Figure 1), which are safe for drinking because the upper limit of TDS for class I water is 1000 mg/L.The lowest TDS of 130 mg/L was detected at the first sampling point in the upper reach, SM 1, which was 130 mg/L.Then, it rose substantially to 443 mg/L at SM 2 and was more or less stable until the last sampling point downstream.High TDS at several points can be attributed to land utilization in their vicinity, including effluents from domestic and industrial activities in highly populated areas [16].
The total suspended solids (TSS) tested in the laboratory varied from 6 to 19.6 mg/L (Figure 2).Among the six sampling points, TSS was the highest (19.6 mg/L) at SM 1 and the lowest (6 mg/L) at SM 5.In these concentrations, the allowable limit of TSS for class I water, which is 0 mg/L, was exceeded.TSS is a measure of silt and sand suspended in a body of water as soil erosion products [17].TSS was detected at high concentrations because the river water samples were collected during the rainy season.
The pH values measured in the river ranged from 7.8 to 9.2 (Figure 4), with a significant fluctuation between the six sampling points.pH was the highest (9.2) at SM 1 and then dropped to 7.9 at SM 2. Between SM 2 and SM 4, pH remained stable before increasing to 8.5 at SM 5.The water quality standards for this parameter recommend a range of 6 to 8.5, meaning that the upper limit was exceeded at three sampling points.Carbonate rocks in the Kepek Formation cause high pH values at SM 1, 5, and 6.Carbonate compounds in limestones increase water pH [18].Dissolved oxygen (DO) was identified at different levels across the sampling points, from the lowest (6 mg/L) at SM 2 to the highest (8.2 mg/L) at SM 1 and 5 (Figure 5).Per the regulated standard, drinking water should have a minimum of 6 mg/L of DO.Based on this parameter, water at the six sampling points is suitable for drinking.SM 1 and 5 are located in areas with less intensive anthropogenic activities than other points; hence, it is natural that both have more oxygen dissolved in the water.In contrast, low DO at SM 2 can be linked to its position in a river section that passes through an urban area and thus receives various waste inputs.The primary source of DO in freshwater is photosynthesis by aquatic plants and phytoplankton [19].Discharging waste into rivers creates an unfavorable environment for their growth, inhibiting photosynthesis and oxygen production in the water.Laboratory analysis showed varying concentrations of COD and BOD.COD was found in the range of 5.06-15.2mg/L (Figure 6).Per Governor Regulation No. 20 of 2008, the maximum allowable concentration for COD is 10 mg/L.Therefore, high COD levels at SM 1 (15.1 mg/L) and SM 6 (10.1 mg/L) were above the standard.COD measures the amount of oxygen needed to oxidize organic matter (i.e., pollutants).This means that the higher the COD level, the more the organic matter in the water that consumes oxygen [20].Meanwhile, BOD varied from 0.42 to 2.84 mg/L (Figure 7).The upper limit of BOD for drinking water, 2 mg/L, was exceeded at two sampling points: SM 4 (2.02 mg/L) and SM 6 (2.84 mg/L).BOD showed a decreasing trend from the upper reach to the middle before increasing substantially downstream.With more organic matter and different kinds of effluents introduced into the water, the amount of oxygen needed for their decomposition or biological oxidation increases, resulting in high BOD levels [20].Laboratory tests detected ammonia (NH3) in the Sumurup River between <0.01 and 0.66 mg/L (Figure 8).High NH3 contents were spotted at SM 2 (0.41 mg/L) and SM 3 (0.66 mg/L).However, only SM 3 exceeded the permissible limit of NH3 for class I purposes, 0.5 mg/L.The high NH3 at this point can be attributed to its location in the production area of the tofu industry.Effluents from tofu production increase the presence of NH3 in the receiving body of water [21].
The six water samples of the Sumurup River contained different levels of total phosphate (Figure 9).Results showed an increasing trend in phosphate from the upper to the middle reach before decreasing downstream.The highest level of 0.66 mg/L was observed at SM 3 (Figure 9), which receives phosphate-containing effluents from many tofu industries in the area [22] and domestic activities, specifically the use of detergents from washing [23].There are densely populated settlements between SM 1 and SM 4, from which wastewater from the laundry is disposed of directly into the river, increasing the phosphate content in the receiving body.Nitrate (NO3 -) contents of the six river water samples were constantly high in the range of 34.1-48.2mg/L (Figure 10) from the river's upper to lower reach.In these concentrations, the upper limit of NO3 - in class I water, 10 mg/L, was exceeded at all sampling points.The primary source of NO3 -is runoff from agricultural areas that apply organic or chemical fertilizers [24].The high NO3 -levels can be associated with plantations along the river.Most of the local crops do not require much water, such as CGRPT plants (coarse grains, pulses, roots, and tubers).
Laboratory test results showed a decreasing trend in fecal coliform concentration from the river's upper to lower reach.Water samples at SM 1, 2, and 3 contained 1100 MPN/100 ml of fecal coliforms, exceeding the permissible presence for these organisms in drinking water, 100 MPN/100 ml.However, these readings might be higher because the maximum concentration detectable in the laboratory is 1100 MPN/100 mL.Fecal coliform bacteria originate in the feces of humans and other mammal [25].Based on observations in the field, SM 1-3 are located in densely populated areas where sewage is disposed of directly into the river instead of flowing into a sanitation system for further treatment.In contrast, SM 4-6 showed lower fecal coliform concentrations, which corresponds to the decrease in the number of settlements downstream.

Segment 1
The main river in segment I is 4.9 km, passing through a land area of 1,366 ha.The majority of this catchment is used for dryland farming and small settlement clusters.Even though this river is seasonal, only a few parts were inundated, and there was no flowing surface water during sampling in the rainy season.WQI assessment showed that the segment had varying index values depending on the composite scenario: from 74.3 to 78.8 with the INA-WQI method and from 68.7 to 281.6 with WA-WQI (Table 4).INA-WQI produced fairly consistent values that indicated fair water quality at the first sampling point, SM 1, for each scenario.In contrast, WA-WQI values were significantly different between the scenarios.Scenarios 1 and 3 categorized the water sample at this point into the lowest class, unsuitable for drinking water, while scenario 1 indicated poor water quality.

Segment 2
Segment 2 is a densely populated urban area with several centers of economic activities that potentially contribute to river pollution, such as markets and hospitals.The main river in this segment is 3.4 km long, traversing a land area of 1,221 ha.WQI assessment with three composite scenarios showed index values ranging from 77.7 to 80.9 with the INA-WQI method and 101.5 to 216 with WA-WQI (Table 5).
INA-WQI produced fairly consistent values that indicated good to fair water quality at SM 2 for each scenario.In contrast, despite the substantial difference, the WA-WQI values were all higher than 100.This means the water sample at this point is unfit for drinking purposes.7).On the contrary, WA-WQI assessments produced substantially different index values: 68.8 (poor water quality) with scenario 2 but much higher ones, 267.6 and 125.9 (unfit for drinking purposes), with scenarios 1 and 3.  9), suggesting fair to good water quality.On the contrary, the measured WA-WQI values were more varied for the three scenarios.With scenario 2, the index value indicated poor water quality, while the values calculated with scenarios 1 and 3 suggested that the water was unfit for drinking.The use of two different methods in this study generates different index values.INA-WQI incorporates parameters with a known weight, while WA-WQI calculates the weight based on the measured parameter values.As a result, the latter have substantially different parameter weights, which contrasts the less varying parameter weights used in the former.In addition, the different composite scenarios affect the weight of each parameter more significantly on WA-WQI than INA-WQI.The resulting INA-WQI values are relatively unchanged despite the variation in the number of parameters used in the calculation.

Conclusion
The parameter values of the water quality of Sumurup River have exceeded the upper limits for class I purposes set by the government of the Daerah Istimewa Yogyakarta (DIY) Province in Governor Regulation No. 20 of 2008.TSS, fecal coliform, and nitrate are higher than the safe limit for drinking purposes at all the sampling points.Only DO and TDS are found in their recommended levels.Water Quality Index (WQI) assessment with INA-WQI and WA-WQI methods resulted in different index 1313 (2024) 012011 IOP Publishing doi:10.1088/1755-1315/1313/1/01201110 values.Generally, the further downstream, the better the index value and the water quality.In addition, the different numbers of parameters used in the composite scenario for each WQI calculation influences the resulting index values.While the INA-WQI values tend to remain the same for all scenarios, the WA-WQI values differ significantly.

6 Figure 6 .Figure 7 .
Figure 6.COD levels at all sampling points in the Sumurup River COD Figure 7. BOD levels at all sampling points in the Sumurup River COD

Table 1 .
Three scenarios of WQI assessment with different number of parameters in the composite

Table 2 .
Water quality classifications for the INA-WQI method

Table 3 .
Water quality classifications for the WA-WQI method

Table 4 .
Water Quality Index values at the first sampling point, SM 1

Table 5 .
Segment 3 is the production area of many tofu industries.The main river has a length of about 1.2 km and an area of 56 ha, which is the narrowest among the five segments.The index values calculated with INA-WQI varied from 73.2 to 83.1 (Table6), suggesting fair to good water quality.Meanwhile, the WA-WQI values were in the range of 111.9-392.8.WA-WQI assessment with scenario 1 at SM 3 yielded the highest index value of all sampling points and composite scenarios in the Sumurup River.Water Quality Index values at point SM 2

Table 6 .
Water Quality Index values at point SM 3 In segment 4, the main river has a length of 3.2 km and an area of 835 ha.Settlements with moderate density dominate the land use in this segment.The INA-WQI values were stable between 82.6 and 86.7 across the three scenarios (Table

Table 7 .
Water Quality Index values at point SM 4 Segment 5 is dominantly covered by forests and used for dryland farming.It has the largest area compared to the others, namely 1,366 ha.Similarly, the main river in this segment is also the longest, which is about 7.2 km.For these reasons, water samples were collected at two points: SM 5 and SM 6.At SM 5, the INA-WQI values ranged from 81.9 to 85.3 (Table8), indicating good water quality.WA-WQI calculations showed index values varying from 50.1 with scenario 2 (good water quality) to 115.5 and 128.5 with scenarios 1 and 3 (unfit for drinking purposes).WQI analysis at the last sampling point on the Sumurup River, SM 6, showed INA-WQI values of 79.1 to 82.7 (Table

Table 8 .
Water Quality Index values at point SM 5

Table 9 .
Water Quality Index values at point SM 6