B. Mixing of Fresh & Seawater
• freshwater mixes with seawater to create brackishwater
(0.5-35 ppt salt)
• salinity gradientsform from mouth (ocean) to back (river)
— many species have a limited range of salinities they can tolerate
— salinity gradients change over time: depending on weather
(rainfall) and tidal flushing
– seasonality: wet season in Mediterranean climates is low
salinity season
– tides: high tide pushes saltwater in
• requires toleranceto variable salinity (euryhalinespecies)
— limits diversity of organisms in estuaries
—sets patterns of distribution within estuaries