A study of spatial land use analysis to understand red tide phenomenon in Lampung Bay, Indonesia

In this paper, we present a spatial land cover classification and hydrologic characteristics analysis to understand red tide occurrence in Lampung Bay, Indonesia, by using high resolution satellite images (WorldView-3) and digital elevation (DEM) data. Red tide causes damage to ecosystems, fisheries resources and even recreational facilities, which also cause economic loss. Lampung Bay is one of the areas that is seriously damaged by red tides. A very large red tide was first found in Lampung Bay in 2012. Since then red tides have continuously occurred in Lampung Bay and were associated with mass mortalities of maricultured fish. In 2010 there were approximately 150 mariculture facilities, yet, in 2018 only 26 remain. The very first large red tide in 2012 was reportedly occurred due to port digging activity. However, after the port digging has ended, the red tide after 2012 was triggered by another factor. We suspect that the trigger of red tide is fertilizer runoff. From spatial analysis and ground truth we found out that there are plenty of slope farmlands in our target area. We also learned that the agricultural land is located next to water streams. At the same time, farmers tend to use excessive amounts of fertilizer. The flow direction and flow accumulation analysis resulted that when it rains the water flows passing through agricultural land to water stream and ends in the sea. The water possibly bring fertilizer causing algae to grow rapidly and causing red tide.