Shorelines attached to the land are the main areas of sedimentation, commonly with extensive tidal flats. Tidal currents move through breaks in the barrier islands depositing sediment with both ebb and flood tides. High sed rates, very nutrient rich, lots of bioturbation. Coarser sediments are washed in during storms and are commonly wave rippled. Tidal channels commonly cut into lagoonal deposits as the location of concentrated flow migrates back and forth.
Lagoons have extremely variable water chemistry depending on climate.
If the climate is dry and a river does not flow into it, they tend to be evaporitic and hypersaline. The types of organisms living in the lagoon is a good indicator of local climate. As sea level rises relative to the land, they shift one way, and vice versa. Estuaries are a special end member of lagoons. They are river mouths that have been drowned by relative sea level rise and contain a mix of fresh and salt water.