Part 1 of Essay
When examining waters transition from fresh to salt as well as from salt to fresh one quickly finds the importance of estuaries. In terms of geology, present-day estuaries are young and ephemeral coastal features. Today's estuaries began to take their current form during the last interglacial period, when sea level rose ....

Part 2 of Essay
.... oceans. Because fresh water is lighter, or less dense, than salt water, unless the two are mixed by the tides or winds, the fresh water remains at the surface, resulting in a salinity gradient. Tides force seawater inland as a countercurrent and produce a saltwater wedge below the freshwater surface waters (Bellamy 62). Estuaries are always in a state of change and hardly ever in a steady state. The principal energy source are tides, causing estuarine mixing, but wind, wave motions, and river runoff can also ....