Study location

The location of the study was Saguling Reservoir, which is located upstream of the Citarum watershed in West Java Province, Indonesia. Saguling is part of the Citarum Cascade Reservoir, which also comprises the Cirata and Jatiluhur Reservoirs. Saguling is located on the upper Citarum River and acts as a trap for pollutants discharged into the river and around the residential areas of Bandung. The main purpose of the Saguling establishment is to generate electricity. The location is illustrated in Figure 2.

Figure 2.

Location of Saguling and Citarum watershed.

Saguling has been heavily polluted, particularly by domestic sewage and industrial waste. Most of the contaminants in Saguling (such as organic matter, nutrients, and heavy metals) come from Bandung, the reason why Saguling has been identified as a very trophic reservoir.⁶

Monitoring quality stations in Saguling Reservoir

The water quality in Saguling was monitored regularly every 3 months (in March, June, September, and December). There were 11 quality monitoring stations at different locations: Nanjung (the input), Batujajar, Muara Cipatik, Muara Ciminyak, Cimerang, Cihaur, Muara Cijere, Muara Cijambu, Muara Cihaur, Turbine Intake, and Tailrace. A total of 44 water quality parameters were monitored, which consist of physical and chemical parameters. The main study locations were Nanjung Station, Muara Ciminyak Station, and Turbine Intake Station, as shown in Figure 3.

Figure 3.

Locations of monitoring quality stations at the Saguling Reservoir.

The water quality data were used to determine the trophic status, especially the total phosphorus, total nitrogen (ammonia and nitrate), and water clarity. Data were regularly obtained 4 times a year for 16 years (1999-2013). The overall water quality was determined by comparing the data with the criteria from Ministerial Regulation (Permen) of the Environment Number 28 of 2009 on the Water Pollution Load Capacity of Lakes or Reservoirs. The chlorophyll a parameter was also considered but it was not measured from the reservoir and instead calculated as follows⁷:

Determination of wet, normal, and dry years with a Markov model

A Markov model was used to determine wet, normal, and dry years by dividing them into 3 classes according to the water discharge that entered the reservoir. Based on the water division, a stochastic matrix can be created for each month to divide the historical data into 3 classes. The stages of the process are as follows.⁸

Class division

The second phase was the classification of water discharge levels. A first-order process was investigated for 3 classes. The amount of discharge was divided as follows:

1. Dry discharge (represented by 0);

2. Normal discharge (represented by 1);

3. Wet discharge (represented by 2).

Class intervals for each class divisions were obtained by dividing the probability curve of the distribution of the selected population into 3 equal parts at 0.333, 0.667, and 1, as shown in Figure 4. The range value of each class was the middle value of each one at 0333, 0.667, and 1 in the probability curve. The probability of each of the data was determined using the Weibull method as follows:

where P(Xm) is the probability of a set of values that are expected during the observation period, N is the number of observations of variate X, and m is the rate of events.

Figure 4.

Class divisions based on the probability in the Markov model.

Fertility level of Saguling Reservoir water

The trophic status is determined from 4 parameters: total phosphorus, total nitrogen, water clarity, and chlorophyll a. The trophic status of the reservoir was determined by comparison with the criteria shown in Table 1.

Table 1.

Trophic status criteria for a lake or reservoir.⁹

The data in Table 2 show average of the parameters from 11 monitoring posts in 15 years (1999-2013). The data indicated that the reservoir is in a hypertrophic state. Thus, the water in the reservoir has a high level of organic matter contamination, which can cause algal blooms.

Table 2.

Trophic status data of Saguling Reservoir.

Table 3 indicates the trophic status of 3 monitoring posts, representing the upstream reservoir areas with the Nanjung Post, the middle of the reservoir with the Muara Ciminyak Post, and the downstream area of the reservoir at the Turbine Intake Post. The parameters showed fluctuations every year during the study period. The transparency, total phosphorus, and chlorophyll a parameters appeared to be in a fixed hypertrophic range from year to year at all 3 stations. However, the total nitrogen showed varying ranges. The overall average for all 4 parameters was consistent with the hypertrophic status. This indicates that the reservoir is heavily polluted by a very high nutrient content. The government actually has some plans and strategies to solve the problems in Saguling Reservoir. Hence, we suggest government with all stakeholders to work together to implement those immediately because Saguling Reservoir’s condition is critical.

Table 3.

Trophic status parameters (transparency, total phosphorus, total nitrogen, and chlorophyll a).

Figure 5 shows that Nanjung Post had the highest total P, total N, and chlorophyll a compared with the Muara Ciminyak Post and Turbine Intake Post. Nanjung Post shows that the highest pollution occurs upstream of the reservoir, which receives pollution from the upper Citarum watershed, as shown in Figure 6. The watershed is dominated by industrial activities from 542 companies, as well as domestic waste from the population of ±8.6 million people, 79.8 hectares of rice fields, livestock, and other activities.¹⁰

Figure 5.

Trophic status of Nanjung, Muara Ciminyak, and Turbine Intake Posts.

Figure 6.

Comparison of N-Total Concentration and P-Total Concentration of Nanjung, Muara Ciminyak, and Muara Intake in 1999-2013.

The Muara Ciminyak Post represents the mid-reservoir area, which is widely used as a location for floating net cages. This increases the concentration of reservoir nutrients. Fish waste and fish feed residues containing phosphorus and nitrogen stimulate the growth of phytoplankton or algae and increase aquatic productivity. An increase in air temperature, sunlight warming, and strong wind can stir the water levels of the lake. This causes the current to rise from the bottom of the lake and lift up the settling water mass. The water mass carries toxic compounds from the bottom of the lake and causes the oxygen content in the body of water to decrease. The low oxygen level can lead to the sudden death of fish.

Some of the impacts of eutrophic conditions are reduction in water clarity, anoxic hypolymnetic zones, the occurrence of aquatic plants problems, the survival of only fish that can live in warm water, and dominance of blue-green algae. Around 10% of the phosphorus that causes eutrophication comes from natural processes in the water environment itself (background source), whereas 7% comes from industry, 11% from detergents, 17% from agricultural fertilizers, 23% from human waste, and 32% from livestock waste, which is the largest source. These percentages show the enormous extent that populations and the diverse activities of modern societies contribute to the release of phosphorus to the aquatic environment.¹¹

The water fertility of the Saguling Reservoir is greatly influenced by the high phosphorus content. Some studies have illustrated how phosphorus is an important element that causes eutrophication. Its presence contributes to the growth of algae, a phenomenon that was first discovered in 1968.¹² Another compound that also affects the fertility of the water is nitrogen. The usage of nitrogen fertilizer in the upper Citarum watershed continues to increase from year to year. The nitrogen component is highly soluble and easily migrates in the soil, and plants are less able to absorb all of the nitrogen fertilizers.

Division of Saguling Reservoir according to climate (1999-2013)

The research period (1999-2013) was divided into dry, normal, and wet years using a discrete Markov method. The class divisions were performed for Nanjung, Muara Ciminyak, and Turbine Intake Stations. The results are shown in Table 4.

Table 4.

Determination of dry, normal, wet years according to discrete Markov method.

Analysis of trophic status based on dry, normal, and wet years

The trophic status of Saguling Reservoir which was analyzed based on dry, normal, and wet years is shown in Table 5. The overall averages indicate a hypertrophic status. However, in dry years, the highest concentrations of total P, total N, and chlorophyll a occur in the upper reservoir. This indicates that the concentration of pollutants is higher in dry years, including total P and total N. In wet years, the 3 parameters appear to have the greatest concentration downstream of the reservoir due to the accumulation of pollutants in this area. Pollutants more rapidly flow downstream in wet years. In normal years, total P and total N are high in the middle of the reservoir due to the use of floating cage nets that dominate in the area.

Table 5.

Trophic status of Saguling Reservoir in dry, normal, and wet years.