Environmental impact of mud volcano inputs on the anthropogenically altered Porong River and Madura Strait coastal waters, Java, Indonesia

Increasing human modifications of the coastal zone are endangering the integrity of coastal ecosystems. This is of particular importance in SE Asia where large parts of the population live in the coastal zone and are economically dependent on its resources. The region is also affected by a high frequency of extreme natural events like storms, earthquakes and volcanic eruptions. The eruption of a mud volcano, nicknamed “Lusi”, near the city of Sidoarjo in eastern Java, Indonesia, on May 29, 2006 represents such an event. One of the measures to minimize the potential detrimental effects to the environment and the local population was to channelise part of the mud into the nearby Porong River, the major distributary of the Brantas River, which is affected by intensive land use and hydrological alterations in a densely populated catchment. Here we report for the first time on the effects of the mud volcano on the aquatic environment. The “Lusi” input more than doubled the suspended matter and particulate organic carbon load of the river. Moreover, we found decomposition of the additional organic matter worsening oxygen depletion in the river and adjacent coastal waters that can severely affect the well-being of aquatic organisms. We conclude that the mud volcano input adds to the adverse effects of human activities in the river catchment on the ecology and biogeochemistry of the estuary and Madura Strait coastal waters.