The effects of freshwater flow and salinity on turbidity and dissolved oxygen in a shallow Macrotidal estuary: A case study of Portsmouth Harbour

Portsmouth Harbour was used to investigate the effects of fresh water flow and water physio-chemical properties such as salinity on turbidity and dissolved oxygen within industrialised Macrotidal estuaries. Nine sites were selected within the harbour for field sampling and data collection based on their contrasting hydrodynamic environment and accessibility from land. Sediment, water samples and water physio-chemical data were collected from the harbour once every season over a period of two years. Fresh water flow directly affects turbidity as an increase in fresh water flow leads to a decrease in turbidity. Increasing fresh water flow also leads to seaward transport of Suspended particulate matter. There is no significant migration of the estuarine turbidity maxima zone within Portsmouth Harbour due to the general low fresh water flow (average yearly flow of 0.6 m(3)/s) for all seasons unlike other Macrotidal estuaries. The area of intertidal flats have low dissolved oxygen ranging from about 4.5 mg/L to 10.4 mg/L compared to other areas within the harbour which ranged from 6.5 mg/L to 12.5 mg/L. This is due to the substantial amount of sediment supplied by bed forms such as runnels on the intertidal flats into receiving waters. Based on these findings, there is need for a synchronised management system within these type of estuaries.