An estuary is a partially enclosed, coarse water body where freshwater from rivers and streams mixes with salt water from the ocean. Salt marshes and mangrove forests are two habitats associated with estuaries. Estuaries filter pollutants and excess sediment, and they stabilize shorelines and protect coastal areas, inland habitats and human communities from floods and storm surges from hurricanes.
Climate changes, rising sea levels, drought and ocean acidification threaten to degrade estuaries.
Rising sea levels will move ocean and estuarine shorelines by inundating lowlands, displacing wetlands and altering the tidal range in rivers and bays.
Increased frequency and intensity of rainfall can lead to greater stormwater runoff, erosion and sedimentation. Greater nutrient, pollution or sediment introduction in an estuary can threaten estuarine ecosystem function.
Conversely, it can also affect the salinity of coastal waters. Estuaries require a natural balance of freshwater and saltwater. Droughts reduce fresh water input into tidal rivers and bays, which raises salinity in estuaries and enables salt water to mix farther upstream. The increase of salinity in brackish water environments can threaten to degrade ecosystem health. The intrusion of saltwater in groundwater also requires additional risks for coastal water infrastructure.
The rising concentration of carbon dioxide, and subsequent absorption in the ocean, leads to marine waters becoming more acidic. Increased acidity of ocean and coastal waters can be reduced to a certain extent and are more likely to be used as shellfish. Ocean acidification in combination with other stresses can lead to greater coral reef die-off and threatening aquatic life, threatening the success of coastal estuary programs. For more on ocean acidification see the U.S. Environmental Protection Agency's Ocean Acidity webpage .