Short-term Local Phytoplankton Response to Dredging Effects on a Subtropical Large Lowland River

Abstract

This study evaluates the short-term local impact of dredging on phytoplankton assemblages on the Baradero River (Argentina). Samples were taken during winter and early spring in eight sampling points over five months: five points near the dredging area and three points near the disposal. Samples were collected during dredging (three months) and two months after dredging (recovery). Environmental variables, including nutrients, were recorded, and phytoplankton was analyzed using the Phytoplankton Reynolds Functional Groups classification. Phytoplankton groups were organisms adapted to high nutrients and lotic environments. No significant differences were found between the dredging and disposal sites during dredging, but variations in RFG biovolume (not diversity) emerged during recovery in both sampling points (dredging and disposal area) respect to dredging phase. No effect on diversity patterns were found. Changes observed in biovolume during the recovery phase were attributed to reduced water flow rather than dredging itself since changes were observed throughout the whole study area. This study challenges the often-assumed negative impacts of dredging and highlights the resilience of phytoplankton communities under specific environmental conditions, contributing to a better understanding of when and where dredging is least harmful. Such knowledge is essential for minimizing ecological disruption and safeguarding aquatic ecosystem services.