Editing Estuary (section)

==Physiochemical variation==
The most important variable characteristics of estuary water are the concentration of dissolved oxygen, [[salinity]] and [[sediment]] load. There is extreme spatial variability in salinity, with a range of near-zero at the [[tidal limit]] of tributary rivers to 3.4% at the estuary mouth. At any one point, the salinity will vary considerably over time and seasons, making it a harsh environment for organisms. Sediment often settles in intertidal [[mudflats]] which are extremely difficult to colonize. No points of attachment exist for [[algae]], so vegetation based habitat is not established.{{clarify|date=June 2012}} Sediment can also clog feeding and respiratory structures of species, and special adaptations exist within mudflat species to cope with this problem. Lastly, [[dissolved oxygen]] variation can cause problems for life forms. Nutrient-rich sediment from human-made sources can promote primary production life cycles, perhaps leading to eventual decay removing the dissolved oxygen from the water; thus [[hypoxia (environmental)|hypoxic]] or [[Dead zone (ecology)|anoxic]] zones can develop.<ref>{{cite book |last=Kaiser |year=2005 |title=Marine Ecology. Processes, Systems and Impacts |location=New York |publisher=Oxford University Press |isbn=978-0199249756 |display-authors=etal}}</ref>