Riffle areas have a high O 2 content because of the churning. They serve as catch basins for organic materials and produce the CO 2 used by the producers in the next riffle. Bogs depend heavily on precipitation to supply nutrients, so they usually are low in mineral salts and are acidic. Salt Water Salt concentration is a limiting factor for organisms which live in salt water. While open sea contains about 35 ppt of salt, estuary areas contain much less, and the concentration is more variable.
Water pressure increases with depth.
The photic zone is the epilimnion, and photosynthesis occurs here. The mesopelagic zone is the metalimnion, which has a thermocline, and not much seasonal variation in temperature. Organisms in an estuary must adjust to variable salt concentrations. All rights reserved.