3.1 Water Quality Data of the Saguling Reservoir during Dry, Normal, and Wet Years
Table 4 shows the average water quality data for the Saguling Reservoir at several monitoring locations during normal years. At 11 monitoring locations, water temperatures were generally in normal conditions, which was around 26oC to 27oC. The concentration of dissolved residue or TDS at 11 monitoring locations remained below the quality standards for surface water quality Class I (surface water which is used for drinking water purposes) based on Government Regulations Number 82 of 2001.
The highest TDS concentration was found at the Cihaur location and was 308.2 mg L-1, while the lowest TDS concentration was measured at the Muara Ciminyak location. For turbidity parameters, the highest concentration was a water sample from the Nanjung location, which was 196.3 NTU, while in 10 other locations, the turbidity concentration was below 100 NTU. The lowest turbidity concentration was measured at the Tailrace location. pH condition at the monitoring location was generally normal, in the range of 7-8. However, at the monitoring location of Muara Cijambu and Tailrace, the water conditions were alkaline, having a pH of more than 10. Alkaline conditions in water can be affected by various factors and can be an indicator of polluted waters. Other information in Table 4 includes water samples from 11 monitored locations, nitrate parameters in all locations remain under the clean water quality standards (Class I in Government Regulation Number 82 of 2011). For phosphate parameters, water samples at the Cimerang location have exceeded the Class III of water quality standards based on Government Regulation Number 82 of 2001 which is a maximum of 1 mg L-1. For DO parameters, overall from 11 monitoring locations it was shown that the concentration of DO in water samples was very small, which was in the range of 0 - 1.5. Besides, for the Fecal coli parameter, monitoring of 11 locations shows that the water quality of these locations is still under the Class III of water quality standards. By reviewing 9 test parameters, the water quality from the Najung site was found to have a worse quality compared to other locations for turbidity, nitrate, DO, BOD, and fecal coli.
Table 5 shows the average water quality data of the Saguling Reservoir at several monitoring locations during a dry year. At 11 monitoring locations, water temperatures were generally at normal conditions, which are around 260C to 270C, and slightly lower at the Cimerang location, which was 25oC. The concentration of dissolved residue or TDS at 11 monitoring locations was still under the quality standards for surface water quality Class I (surface water which is used for drinking water purposes) based on Government Regulations Number 82 of 2001.
The highest TDS concentration was found at the Cihaur location (330.5 mg L-1), while the lowest TDS concentration was at the Muara Ciminyak location. When compared with TDS data during normal years, TDS concentrations during dry years tend to be greater. For the turbidity parameter, the highest concentration was found in water samples from the Nanjung location, which was 220.9 NTU, while in the other 10 locations, the turbidity concentration was below 60 NTU. The lowest turbidity concentration was measured at the Tailrace location. Water pH at the monitoring location was generally normal, in the range of 7-8. But at the monitoring location, intake water was determined to be alkaline with a pH of more than 11. Other information that can be gathered from Table 5 is that nitrate measurements from all 11 locations are still under clean water quality standards (Class I in Government Regulation Number 82 of 2001). For the phosphate parameter, water samples from 11 locations are also still under the Class III of water quality standards based on Government Regulation Number 82 of 2011, which is a maximum of 1 mg L-1. The concentration of DO in water samples from all 11 locations was determined to be very small, in the range of 0 - 1.2 mg L-1. Fecal coli measurements from 11 locations did no deviate from Class III of water quality standards. Bolstad and Swank [14] concluded that transportation of coliforms in water can occur mainly through land or direct input by warm-blooded animals (e.g. livestock). By reviewing 9 test parameters, water quality from the Najung site was found to have worse quality compared to other locations with regards to turbidity, nitrate, phosphate, DO, BOD, and Fecal coli. Overall data regarding water quality during dry years shows that concentrations are higher than water concentrations for various parameters during normal years.
Table 6 shows the average water quality data of the Saguling Reservoir at several monitoring locations during the wet year. At 11 locations, water temperature was generally in normal, and around 25oC to 27oC, slightly lower than the water temperature during normal and dry years. The highest TDS concentration was found at the Cihaur location (299.1 mg L-1), while the lowest TDS concentration was found at the Muara Ciminyak location.
When compared to TDS data during normal and dry years, TDS concentrations during wet years tend to be smaller than water quality data from dry years and are not much different than measurements during normal years. The highest concentration of turbidity was in the water sample from the Nanjung location of 193.6 NTU, while in the other 10 locations the turbidity concentration was below 65 NTU. The lowest turbidity concentration was at the Muara Cihaur location. Water pH was generally normal, and in the range of 6-8. Other information that can be gathered from Table 6 is that nitrate measurements from all locations were determined to be in accordance with clean water quality standards. Phosphate measurements from all 11 locations were also still under the Class III of water quality standards based on Government Regulation Number 82 of of 2001, which is a maximum of 1 mg L-1. The concentration of DO in water samples from all locations was very small, in the range of 1-3 ppm, slightly better than the quality of DO during normal and dry years. The Fecal coli measurements were still under the Class III of water quality standards based on Government Regulation Number 82 of of 2001. By reviewing 9 test parameters, water quality from the Nanjung site was found to have worse quality compared to the other locations for turbidity, nitrate, phosphate, BOD, and Fecal coli parameters. Overall water quality data during the wet year reveals lower concentrations of water for various parameters during the dry year and not much of a difference in the water concentrations during the normal year.
3.2 NSFWQI Values of Saguling Reservoir during Dry, Normal, and Wet Years
In this part, the NSFWQI value will be discussed spatially for each monitoring location, and temporally, which is based on the conditions during the dry year and the wet year.
Figure 2(b) shows the results of the NSFWQI water quality in the Saguling Reservoir during the dry year period where the distribution of monitoring points is shown in Figure 2(a). The NSFWQI values obtained were then compared to Table 2 on the NSFWQI water quality ratings. The Saguling Reservoir during dry years shows that at the Nanjung monitoring point the water quality at fair water quality category with an index score of 45. This is also seen at the monitoring points of Batujajar and Cihaur with index scores of 49 and 46, respectively. While in Cimerang, Cihaur Estuary, Cipatik Estuary, Ciminyak Estuary, Cijere Estuary, Cijambu Estuary, Intake, and Tailrace, the water quality ratings are medium or average. Index scores are as follows: Cimerang- 51, Cihaur Estuary- 53, Cipatik Estuary- 56, Ciminyak Estuary- 55, Cijere Estuary- 54, Cijambu Estuary- 57, Intake- 59, and Tailrace- 61. The highest index score at 11 monitored locations during the dry season was at the Tailrace location. The lowest index score was at the Nanjung location.
Figure 3(b) shows the results of NSFWQI water quality in the Saguling Reservoir during the normal season period where the distribution of monitoring points is shown Figure 3(a). The NSFWQI values obtained were then compared to Table 2 regarding NSFWQI water quality ratings. The value of NSFWQI Saguling Reservoir during dry years shows that all monitoring points have a medium or average water quality. Index scores obtained at each monitoring point are as follows: Nanjung - 43, Batujajar, Cimerang and Intake have scores of 60, Cihaur - 58, Cihaur and Ciminyak Estuaries have scores of 57, Cipatik Estuary, Cijambu Estuary, and Tailrace have scores of 59, and Cijere Estuary- 56. The highest index score at 11 monitored locations during the normal season was found at the Batujajar and Cimerang locations, while the lowest index score was measured at the Nanjung location.
3.3 Correlation Matrix of Water Quality and NSFWQI Values of the Saguling Reservoir during Dry, Normal, and Wet Years
From Table 7, 8 and 9, it can be seen that the strongest and most significant correlation between parameter concentration and WQI score is the turbidity concentration and Fecal coli. This indicates that these parameters make a major contribution to the WQI value or water quality data at the Saguling Reservoir location, whether it is a dry, normal, or wet year. Using these two parameters (obtained from the correlation matrix), the calculation of NSFWQI can be cost-effective and save time and energy, which are fundamental aspects of an effective monitoring program in water quality determination [15].
3.4 Nitrate Concentration Distribution using IDW (Inverse Distance Weighted)
With regard to the NSFWQl values above, the highest NSFWQl value for dry, normal, and wet conditions is measured in the Nanjung post, which is a post located in the most upstream area before entering the Saguling Reservoir. This may be caused by the upstream river basin conditions of the Saguling Reservoir, which are dominated by pollution sources that include agricultural, domestic, and industrial activities. In order to prove that the pollution is concentrated in the Saguling Reservoir inlet, the nitrate concentration distribution was analyzed using the Inverse Distance Weighten Method.
IDW (Inverse Distance Weighted) method is a simple deterministic method performed by considering the points in the vicinity. The assumption of this method is that the interpolation value will be more similar to near sample data than to more distant data. Weights will change linearly according to the distance to the sample data. This weight will not be affected by the location of the sample data. IDW assumes each point size has a local effect that decreases with distance. The points that are closer to the estimated location are given greater weight than those located further away, so they are called inverse distance weighted. The general equation of Inverse Distance Weighted is shown below:
See equation 3 in the supplementary files.
Below is the use of IDW to determine nitrate concentrations in the Saguling reservoir: See figure 5.
Figure 5 shows the distribution of nitrates during the wet year in the Saguling Reservoir. In the figure, it can be seen the different nitrate concentrations at 11 monitoring locations. At the monitoring point in Nanjung, the concentration of nitrate is shown in red and ranges between 3.24-3.75 mg L-1. Meanwhile, at the monitoring point in Batujajar, (shown in light green) has nitrate concentration values between 1.15-1.66 mg L-1. Whereas at other monitoring points that include Cihaur, Cimerang, Cihaur Estuary, Cipatik Estuary, Ciminyak Estuary, Cijere Estuary, Cijambu Estuary, Intake, and Tailrace (shown in dark green), nitrate concentration values range between 0.623-1.14 mg L-1. The highest value of nitrate concentration during the wet season is in the Nanjung locations, while the lowest value of nitrate concentration is found at Cihaur, Cimerang, Cihaur Estuary, Cipatik Estuary, Ciminyak Estuary, Cijere Estuary, Cijambu Estuary, Intake, and Tailrace. However, nitrate parameter water samples in 11 locations are still under the Class III of water quality standards based on Government Regulation Number 82 of 2001, which is a maximum of 20 mg L-1.
Nitrate concentrations of more than 0.2 mg L-1 can lead to eutrophication (enrichment) of waters and subsequently stimulate the growth of algae and aquatic plants rapidly (blooming). This is detrimental because it can affect the health and biodiversity of the local aquatic ecosystem. Naturally, the concentration of nitrate in natural waters is only a few mg L-1 and is one of the compounds that functions to stimulate the growth of marine biomass so that it directly controls the development of primary production. This function is closely related to the fertility of waters. James et al. [16] concluded that high nitrate concentration is affected by agricultural activities, aquaculture, industry and household waste or population waste.
Figure 6 shows the distribution of nitrates during a normal year in the Saguling Reservoir. In the figure, the different nitrate concentrations at each monitoring location can be seen. At the monitoring point in Nanjung, the concentration of nitrate is shown in red and the range value is 3.24-3.75 mg L-1. Meanwhile, at the monitoring point in Batujajar, nitrate concentration values between 2.74-3.02 mg L-1 are indicated in orange. Furthermore, at other monitoring points, namely Cihaur, Cimerang, Cihaur Estuary, (shown in neon) have nitrate concentration values between 2.17-2.45 mg L-1. At the monitoring point of Cipatik, Ciminyak and Cijere Estuaries, (shown in dark green) have nitrate concentration values between 1.59-1.88 mg L-1. Meanwhile Cijambu Estuary, Intake, and Tailrace (shown as light green) have nitrate concentrations in the range of 1.89 -2.16 mg L-1. The highest value of nitrate concentration during normal season is in Nanjung, while the lowest value of nitrate concentration is found at Cijambu, Intake, and Tailrace. However, nitrate parameter water samples in 11 locations are still under the Class III of water quality standards based on Government Regulation Number 82 of 2001, which is a maximum of 20 mg L-1.
Figure 7 shows the distribution of nitrates during the dry year in the Saguling Reservoir. In the figure, it can be seen that there are different nitrate concentrations at each monitoring location. At the monitoring point in Nanjung, the concentration of nitrate is shown as a red color and the range value is 3.24-3.75 mg L-1, while the monitoring point in Batujajar is shown as an orange color with nitrate concentration values between 2.74-3.02 mg L-1. Other monitoring points, namely Cihaur, Cimerang, Cihaur Estuary, are shown as a neon color with a nitrate concentration value of 2.17-2.45 mg L-1. The monitoring points of Cipatik, Ciminyak and Cijere Estuaries, are shown as a dark green color with nitrate concentration values between 1.59-1.88 mg L-1. Furthermore, Cijambu Estuary, Intake, and Tailrace are shown as a light green color with nitrate concentration values in the range 1.89 -2.16 mg L-1. The highest value of nitrate concentration during the dry season is in Nanjung, while the lowest value of nitrate concentration is shown at Cijambu, Intake, and Tailrace. However, nitrate measurements for all 11 locations are still under the Class III of water quality standards based on Government Regulation Number 82 of 2001, which is a maximum of 20 mg L-1.