Fluctuations in carbon levels in Surabaya river are linked to changes in river discharge. By analyzing water samples, researchers found that during low discharge, there is a higher amount of Total Inorganic Carbon (TIC) and Total Organic Carbon (TOC), while high discharge leads to lower levels of TIC and TOC. This indicates a dilution of carbon during rainy seasons and accumulation during dry seasons. Inorganic carbon (TIC) is the main form of carbon transport in the river, with a significant amount coming from carbonate rocks in the Brantas basin.