Assessment of pollution status and spatialtemporal distribution of physico-chemical parameters using the STORET index and GIS methods in Lake Laut Tawar, Aceh, Indonesia

Lake Laut Tawar (LLT) is the largest freshwater lake in the Aceh Province, and its water quality is affected by the influx of waste and pollution. The objective of this study was to assess the water quality of LLT, which is significantly affected by anthropogenic activity. Water samples were collected at nine sampling points within the lake during both the dry and wet seasons. Twelve physico-chemical parameters were analyzed: water transparency, temperature, total dissolved solids, total suspended solids, pH, dissolved oxygen, biochemical oxygen demand, chemical oxygen demand, nitrate, total phosphorus, nitrite, and ammonia. The parameters were estimated using the Indonesian National Standard Protocol (SNI 6989.57-2008). Water pollution status was determined using the Storage and Retrieval (STORET) method based on the US EPA grading system. Water quality distribution maps were used to obtain a detailed understanding of the distribution patterns of physico-chemical parameters of the lake. Spatiotemporal distribution maps were created using ArcGIS software, employing inverse distanceweighted (IDW) interpolation of the mean values of physico-chemical parameters across all hydrological seasons. Temporal changes in physico-chemical parameters indicate better water quality during the dry season. The spatiotemporal distribution map revealed that discharge from residential areas, fish farming in floating net cages, and conversion of rice fields were the primary sources of water pollution in the study area. The water quality status of LLT, at the studied sampling locations, falls under the category of severe pollution (STORET index -56) according to class I water quality standards, and in the moderate pollution category (STORET index -28 and -20) according to class II and III water quality standards. The results from the evaluations of water quality and IDW analysis helped identify key areas requiring control in LLT, highlighting the need for better lake management.