Application Of Story Method To Determine Lake Sentani Water Quality Status In Papua Province

ABSTRACT


Introduction
Lake Sentani is the largest lake in Papua, located on the slopes of the Cyclops Nature Reserve Mountains at an altitude of 85 meters above sea level, with water depths reaching 75 m (Suhartawan, Alfons, & Daawia, 2022).This lake was formed due to tectonic activity in the form of landslide dams and has an area of approximately 9,360 hectares with a length of 28 km and a width of 19 km.There are 12 rivers supporting Lake Sentani (inlet) and one discharge river (outlet).Apart from being the primary source of clean water and raw drinking water for coastal communities, Lake Sentani water is also used for industrial purposes, irrigation of plantation land, capture fisheries for fishermen, aquaculture with cages, and even as a means of water transportation (Asocadewi, Oktiawan, & Hadiwidodo, 2015).
In addition to the lake mentioned above, they use it as a garbage dump, and family waste, including human and animal feces, is thrown into Lake Sentani.So that Lake Sentani becomes the center of all community activities.Conditions like this certainly cause a decrease in lake water quality and are very dangerous to the health and sustainability of the lake water environment (Ashok Lumb, Halliwell, & Tribeni Sharma, 2006).
Water is a very important part of supporting the sustainability of life because life will not occur without water.The water needed for life, both flora and fauna, must be by its designation because if it is not appropriate, life will be disturbed (Akhtar et al., 2021).Likewise, the increasing population of residents who live on the shore of the lake and settlements that dispose of domestic waste that empties into Lake Sentani certainly negatively impact the environmental sustainability of Lake Sentani's waters.In addition, population growth also impacts the increasing need for clean water, conditions of which are increasingly scarce.In addition, (Yacub et al., 2022), the problem of poor urban sanitation management systems, industrial development, and the use of pesticides and chemical fertilizers are also causes of declining water quality.This condition is very concerning and requires serious attention from various parties, especially the Jayapura district/city government.
Evaluating water quality can be done in a conventional way, where laboratory test results are compared with the water quality standards applied, whether drinking water, clean water, or wastewater, but sequential and routine sampling is the main obstacle.Therefore, a quantitative method has been developed for calculating a single index, which is a combination of several values of water quality parameters (Saraswati, Sunyoto, Kironoto, & Hadisusanto, 2014) and is a popular method developed in Indonesia (State Minister of the Environment, 2003), namely the STORET method.The STORET method can be adjusted to the desired quality standards and applicable in each region.The use of the STORET method is also adjusted to the allocation of the water being tested; one of the requirements of the STORET method is to have quality data that describes the time series (Reza, 2021).
This study aims to examine the use of the STORET method to determine the status of Lake Sentani water quality by applying ten water quality parameters, namely: 1) temperature; 2) total dissolved solids (TDS); 3) total suspended solids (TSS); 4) degree of acidity (pH); 5) biochemical oxygen demand (BOD); 6) chemical oxygen demand (COD); 7) lead (Pb); 8) oils and fats; 9) total detergent; and 10) total coliform as a reference for comparison in conducting water quality analysis guided by PP Number 22 of 2021 concerning Environmental Management, annex VI part 2 concerning Lake Water Quality Standards and the like, annex VI part 2 concerning Lake Water Quality Standards and the like.With the knowledge of the status of Lake Sentani water quality, the Regency / City Government of Jayapura or Papua Province control strategy can be known so that the lake water functions optimally (Sumaji, 2017).

Data Collection
Data collection was carried out in-situ (on-site tests) and ex-situ (laboratory tests) on water samples at three research stations based on procedures by the Indonesian National Standard (SNI) for appropriate water quality parameters.Three parameters are tested initially.Namely, temperature, TDS, pH, and seven parameters are tested in the laboratory: TSS, BOD, COD, Pb, oils and fats, total detergents, and total coliforms (Nemerow, 1971).

Method STORET
Step-rare calculation of STORET index: 1. Collect data based on time series.

Figure 3 Chemical Oxygen Demand (COD)
Household waste containing organic matter and a large enough amount that empties into Lake Sentani is the cause of the high organic matter in the waste and is the leading cause of the high concentration of COD in Lake Sentani (Amin, 2014).

Figure 4 Lead (Pb)
Figure 4 shows that the Pb parameter at station 2 (Asei) in January and April was very high and exceeded the quality standard.This is due to the dense water transportation that operates.Dense transportation because Asei is a tourist area close to Kalkota Pier, the center of water transportation facilities on Lake Sentani.Waste use of transportation fuel resulted in high Pb content in Lake Sentani water in the Asei area (station 2) (Maufilda, 2015).

Figure 5 Oils and Fats
Oil and fats are classified as domestic waste that is difficult to destroy and decompose by microorganisms.This waste has a smaller density than water, so its existence floats above the water's surface and forms a small layer, and a small part dissolves in water (999).The picture above shows that at station 3 (outlet), the highest oil and fat content is caused by the smaller surface area of the water, causing the oil and fat layer on the surface of the water to get thicker and more soluble in water (Burhanuddin & Setyobudiarso, 2019).Unlike oils and fats, total detergents are readily soluble in water.Total detergent is domestic waste due to the use of detergent for households to clean household appliances and wash clothes.High detergent content in waters can decrease the diversity of aquatic biota and the death of fish species in the aquatic ecosystem.In addition, it will result in silting the lake for a long time (Karliansyah, 2016).
As with detergents, oils, and fats, the total coliform content at station 3 is so high that it exceeds the maximum quality standards limit.The high total coliform is caused by the disposal of human and animal fecal waste into the water of Lake Sentani.In addition, station 3 is the estuary of Lake Sentani, where people quite densely inhabit the coast, so activities at the mouth of the lake are getting denser (Irma Lusi & Annisa Salsabilla, 2020).In the same way, station 2 and station 3 are obtained : Skor STORET (st2) = -64 Skor STORET (st3) = -116 (Sari & Wijaya, 2019)

Conclusion
Lake Sentani, located on the slopes of the Cyclops Nature Reserve Mountains with an area of about 9,360 hectares and a depth of 75 meters, has a vital role as a source of clean water, raw water, as well as for industrial, irrigation, and fisheries purposes, but faces water quality problems such as high Total Suspended Solids (TSS) especially at station 3 which is the outlet of the lake, indicating the need for further management and monitoring actions to maintain the sustainability of the lake ecosystem.

Figure 6
Figure 6 Total Detergent