Estuary Research Biome Project

Spenser Geideman

Estuaries: Where the River Meets the Sea


Estuaries are found where freshwater meets saltwater. Usually this is around the mouth of a river. The water found in estuaries is considered "brackish," or partly salty. There are five main types of estuaries: Coastal Plain, Bar-Built, Delta System, Tectonic, and Fjord. Coastal plain and delta system estuaries are formed around rivers , with CP estuaries being a result of rising water levels and DS estuaries forming at river deltas. Bar-built estuaries are created when sandbars or barrier islands cut off an area from the rest of the ocean. Tectonic estuaries are usually created by earthquakes that form basins that fill up with water. Lastly, fjords are the result of advancing glaciers that cut out narrow valleys which are later flooded with saltwater.

Abiotic Factors

The abiotic factors of an estuary include precipitation, salinity, water depth, temperature, sunlight, water and sediment.

Biotic Factos

The biotic factors of an estuary can include phytoplankton, mangroves, seagrass, and rushes as the producers and zooplankton, fish, birds, shellfish, snails, crabs, and marine worms as consumers.

Organisms that live in estuaries have developed unique adaptations to help them survive. The mangrove tree, for example, have developed the ability to survive in brackish waters by using filters in their roots to remove salt from the water they take in. Blue crabs have also adapted to life in estuaries by releasing their offspring into ocean water to develop before returning to estuaries and either moving upstream as males or downstream as females.

Food Chain

A food chain that can be found in an estuary is with phytoplankton, zooplankton, shellfish, and birds. The primary producer is the phytoplankton. The primary consumer is the zooplankton, with the secondary consumer being the shellfish, and the tertiary consumer as birds.

Food Web

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Why They are Important

Estuaries are extremely important breeding grounds for animal species. They act as filters for water entering the ocean, and are buffer zones that stabilize shorelines and inland areas from flooding.

How Have Humans Impacted Them?

1. Humans, as a result of population growth , agricultural activities, waste water treatment, urban runoff, and burning of fossil fuels, have dramatically increased the amount of nutrient flow into estuaries far beyond the natural levels. This leads to eutrophication, which will eventually cause hypoxia. This hypoxia causes the organisms living in the estuaries, like fish and submerged grasses, to die off. These submerged grasses act as habitats for nursery fisheries due to their poor water clarity, and losing them ends up in the loss of these fisheries as well.

2. Another way humans have impacted estuaries is through large-scale conversion of estuaries with draining, filling, damming, or dredging. This results in the loss of estuarine habitats.

3. Pollution is another impact humans have had on estuary biomes. Historically, estuaries have been considered areas to discard wastes. Pollutants like chemicals, heavy metals, and pathogens have severely degraded the water quality of the estuary and harmed the delicate and commercially important fish and shellfish that live in estuarine areas.


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