Emerging Pollutions From Small-Scale Industries and Chlorophyll-a as a Eutrophication Indicator in Pekalongan Waters Using Hydrodynamic Modeling

Pekalongan City is a large batik industry center in Indonesia. The large number of industrial activities that produce organic waste form nitrate molecules that dissolve in water and support the growth of phytoplankton, with an increase in chlorophyll-a as an indicator. The organic waste from industries is carried in the river stream (Mrican River, Sengkarang River, Loji River, and Banger) to the sea and influences the fertility of the coastal area. This study aims to determine the content and analyze the distribution of nitrate and chlorophyll-a from 2021 to 2024 as indicators of eutrophication. In situ observations were conducted and analyzed using 2-dimensional hydrodynamic modeling. Hydrodynamic modeling was used to simulate the distribution pattern of nitrate and chlorophyll-a, considering the impact of water currents, tides, and pollutant sources. The results showed that high nitrate contents of 0.0073 mg/L, correlated with high chlorophyll-a contents of 0.0028 mg/L that were located in each river estuary. The correlation analysis showed that the two variables are highly correlated, with r = 0.8, showing that an increase in nitrate contents will likely increase chlorophyll-a. The high level of chlorophyll in the river estuary was categorized using Hagy et al. and defined as mesotrophic, CHL 0.005–0.10 mg/L.