Influence of catastrophic climatic events and human waste on Vibrio distribution in the Karnaphuli estuary, Bangladesh

Abstract

Vibrios are bacteria of marine and estuarine origin that can cause human diseases, such as cholera, and also affect aquatic organisms. The impact of storm-driven changes in salinity and suspended particulate matter (SPM) on cultivable Vibrio counts (CVC) and distribution in Karnaphuli estuary, Bangladesh, was compared before and after a strong cyclone in mid May 2007 and after a monsoon landslide a month later. CVC were higher (approximately 10(3) colony forming units-cfu/ml) at estuary's mouth (salinity 20-15 parts per thousand, ppt) and steeply declined landwards. CVC and their proportion of total aerobic bacteria were highest after the cyclone and also increased after the landslide, likely due to higher SPM loads. The cyclone did not significantly change previous fecal coliform abundance, contrasting with the ten times increase after the landslide. Sewage input enhanced CVC near the point sources. CVC and salinity correlated highly significantly at salinities <10 ppt; however, at higher values dispersion increased, probably due to the effect of sediment resuspension on CVC. Cyclone or heavy rainfall-mediated turbidity changes jointly with salinity gradients can significantly influence abundance and distribution of estuarine vibrios. Extended salt intrusion and higher turbidities in tropical estuaries by stronger and more frequent storms and deforestation-derived erosion could favor Vibrio growth, with increasing risks for aquatic resources and human health in the coastal zone.