Estuaries

• what are estuaries?

  transient zones between rivers and the sea with intermediate levels of salinity
• what are estuaries characterised by?

  high nutrients, low species diversity, but the highest biomass of all aquatic habitats
• what is tidal range?

  the height difference between maximum (spring tide) and minimum (neap tide)
• why are estuaries complex and dynamic habitats?

  there are lots of daily fluctuations in abiotic factors such as water depth, salinity and temperature
• what are the daily fluctuations in abiotic factors seen in estuaries driven by?

  tidal movement of water
• what do organisms need to deal with salinity changes?

  good osmoregulation
• is freshwater more or less dense than seawater?

  less
• why is fresh water less dense than sea water?

  it is warmer and less saline
• does freshwater sit on top of or below seawater?

  on top
• what does the mixing of fresh water and sea water in estuaries result in?

  a salinity gradient
• what type of sediment is seen on the ocean side of estuaries?

  clay
• what type of sediment is seen on the river side of estuaries?

  sand
• does sand or clay settle quicker?

  sand
• what is turbidity like at the river side?

  it can hold more sediment so is more turbid
• what is turbidity like at the sea side?

  much clearer
• what is estuary production dominated by?

  periphyton
• why is estuary production dominated by periphyton?

  the turbid water limits the light for photoplankton, while the sediments exposed by low tide get plenty of sunlight