Impact of freshwater inflow on bacterial abundance and activity in the estuarine system Ria de Aveiro

• Freshwater inflow into an estuarine system influences the dynamics of bacteria and their activity.
• Local hydrodynamic was simulated and related with microbiological parameters.
• Freshwater regime leads to distinct patterns of bacterial abundance and activity.
• Freshwater inputs contribute to increase the number of particle-attached bacteria.
• The activity of estuarine bacteria is controlled by nitrogen concentration.

The influence of freshwater flow on bacterial communities in the estuarine system Ria de Aveiro (Portugal) was investigated at two sites differently impacted by river inputs, representative of the marine and brackish water zones of the estuary. Sampling events were clustered based on hydrological features. The hydrodynamic was simulated with a Lagrangian model and related to microbiological parameters. Estuarine bacteria responded to different freshwater regimes developing distinct patterns of abundance and activity at the marine and brackish water zones. A circulation pattern induced by high river inflow produced vertical stratification in the marine zone, promoting a seaward flux of bacterioplankton, and stimulating the import of riverine phytoplankton and particle-attached bacteria to the brackish water zone. Advective transport and resuspension processes contributed to a 3-times increase in abundance of particle-attached bacteria during intense freshwater inputs. Additionally, bacterial activity in the estuary was controlled by inorganic nitrogen, responding to different freshwater inputs, which, in association with different prevailing sources of organic substrates induced significant changes in bacterial production. The dynamic and main controlling factors of bacterial communities are clearly impacted by freshwater inputs. Therefore, significant changes in the recycling of nutrients by microbial activities can be expected from alterations in freshwater inputs either related to global climate change or regional hydrological regimes.

Conceptual model of the effect of freshwater inputs on bacterial biomass production (BBP) in the estuarine system Ria de Aveiro. The present study indicates that the different inorganic nitrogen concentration, resulting from the different seasonal freshwater inputs and prevailing organic sources in the estuarine system produces an inhibition or stimulation of bacteria biomass production. DOC – dissolved organic matter; PP – primary production; DIN – dissolved inorganic nitrogen; ⊕ – stimulation; ⊗ – inhibition;Figure optionsDownload high-quality image (110 K)Download as PowerPoint slide