EVALUATING RIVER WATER POLLUTION IN A COASTAL CITY IN JAVA, INDONESIA, THROUGH SATELLITE TIME SERIES ANALYSIS OF CHLOROPHYLL-A AND TOTAL SUSPENDED MATTER

Pekalongan, Indonesia is a coastal City in Central Java greatly impacted by environmental issues from land use change and industrial activity. Being one of the national batik industrial centers of Indonesia, this city faces a growing issue with wastewater disposal in coastal waters of Java Sea. As the batik industry within Pekalongan continues to expand, the abundance of untreated wastewater carrying heavy metals from the batik dyeing process entering the waterways has increased. In addition, agricultural activities (rice fields, fishponds) introduce organic pollutants to waterways through runoff and land subsidence resulting in increased flooding of agricultural plots. To investigate the impact of land use change and the contribution of growing industries on urban river water pollution, multiple image time series were constructed from different satellite sensors (MODIS, Landsat 8/9, Sentinel-3) at varying resolutions and time scales. The remotely sensed aquatic parameters of chlorophyll-a and total suspended matter concentrations were used as proxies for agricultural and industrial pollution respectively. Chlorophyll-a is a parameter used to detect phytoplankton within the water column, which are typically in greater abundance when there is excess nutrient runoff from agricultural lands, suggesting pollution from agricultural sources. Total suspended matter is a parameter used to detect solid particles suspended in the water column, which can be used to detect heavy metal pollution known to be introduced to urban waterways from batik industries. The methodology consists of 1) monitoring chlorophyll-a and total suspended matter concentrations along the coastal waters where Pekalongan’s three urban rivers discharge into the sea, and 2) use the proximity of batik industries and agricultural land to each river to determine the likely contributor of pollution per each river. In monitoring and characterizing the water quality of river discharge based on the time and location of peaks in concentrations of each parameter, the goal is to identify potential sources of pollution to inform decision making on human intervention in the form of water treatment.