Effects of hydraulic dredging on mudflats at Bahía Blanca estuary

PIZANI, N.V.; PARODI, E.R; CUADRADO, D.

Bahía Blanca

Congreso; ECSA 44; 2008

Estuarine Coastal Science Association

The use of water injection dredging (WID) is increasing in Argentinean waterways. This kind of dredging consists on jets of water injected under low pressure directly into bottom sediment creating a turbulent water-sediment mixture that’s flows under the influence of gravity. WID and the discharge of dredged sediments directly to the access channel of Rosales harbor has been proposed at Bahía Blanca Estuary.  The present study identified the response of microphytobenthos on mudflats owing to WID activities with an increment in the energy (wind and waves). Results indicated a high impact on environmental conditions. In the adjacent mudflats to the channel was a decrease in microalgae density, as well as a change in it composition immediately after dredging. This was related with the consequent decrease in chlorophyll a content and colloidal carbohydrates. The particle size of the sediment also showed variations, obtaining an increase in the surface sediment as well as the rate of accumulation. A month after dredging ended, the mudflats are recovered biologically and sedimentation rate decreases. It concludes that, while the sediments lost cohesiveness because reduced microbial activities, increases in the amount of sediment transported indicated that the erosive processes could be very important. Due to the importance of biological processes in the cohesiveness of the sediments, we conclude that the observation of microphytobenthos communities can be used as an indicator of the recovery of the tidal flats. In addition, the management of these environments should consider carefully the effects of multiple stressors and their interactions on microphytobenthos.