Hydrosphere 8 th NC/WCPSS

An estuary is formed when two bodies of water and their habitats meet. For example, when a river empties into the ocean. Off the coast of NC, the Pamilico Sound is one of the largest estuaries in the US. They are very special because their waters are brackish. This means the water is a mixture of freshwater from the river and ocean water. This mixture lowers the overall salinity content (typically less than 35 ppm). Estuaries are some of the most productive ecosystems in the world because many animals rely on it for food, places to nest, and breed. Humans also rely on estuaries for food, fun, and jobs!

They are a transition between two very different environments. The daily tides (usually 2 high and 2 low tides each day) have a big impact on these environments, but depends greatly on its location, depth, winds, shape of the coastline, and anything that may restrict water flow. Because estuaries are partially enclosed by land, it is protected from the full impact of the ocean waves, winds and storms. No two estuaries are the same! They are classified by scientists by their geology and how the salt and fresh water mix in them.

Estuaries are home to lots of different organisms: salmon, herring, horseshoe crabs, bass, and ducks to name just a few. These organisms come here to live, feed, nest and reproduce. They provide an estimated 75% of commercial fish and a larger percentage of the recreational fish catch for the US. Estuaries also are visited by millions of people every year to swim, boat, watch birds and other wildlife, and fish.

As the water enters from the river and ocean, the marsh grasses and peat filter out pollutants like herbicides, pesticides, heavy metals, excess sediments and nutrients, storing them in the sand. Oysters will eat some of these bad things, collecting the contamination inside their bodies. Bacteria also eat the organic matter and release carbon dioxide, hydrogen sulfide, and methane into the atmosphere. Because of the excess nutrients coming from the watersheds and drainage basins, it creates a highly fertile area to make it the “nursery of the sea.”

They are considered a buffer zone, stabilizing the shoreline and protecting the coast, inland habitats, and human communities from flooding and storm surges from hurricanes. They also protect rivers, streams, and coasts from excess erosion by wind, water, and ice. Sand bars buffer the impact of waves, and plants and shellfish beds anchor the shore against the tides. Swamps and marshes are the first to be impacted by high winds, soak up heavy rains and storm surges, and release extra water slowly into rivers and groundwater areas.

Trunk estuaries Run perpendicular to the coast, in line with the rivers that feed them Example: Neuse River estuary Tributary estuaries Flow into trunk estuaries Back barrier estuaries Lie parallel to the coast, between the mainland shore and the barrier islands This is what the Pamilico Sound estuary is considered.

The Pamilico Estuary is the largest estuary in NC. Water that drains here are the Chowan, Roanoke, Pasquotank, Pamilico, and Neuse rivers to name a few. These rivers deposit sediments high in nutrients, which will settle on the sand and mud of the bottom of the estuary. It is less than 30 feet deep, so sunlight can reach the bottom which allows plants to grow.

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Changes to the land: As the land is developed for human use, it will change the flow of water through this ecosystem. Roads made of asphalt and concrete deflect water so that it runs off with all the contaminants directly into the rivers, estuaries, and sea. Wetlands were used for logging and farming before laws and restrictions were in place. Nearly half of the NC wetlands were destroyed before the laws went into place.

Dredging allows large boats to pass through or dock closer to shore. Dredging is when the bottom of the water is scraped and made deeper. This causes damage to plants, oyster beds, and stirs up sediments that clouds the water. When the water is cloudy, fish cannot breath properly and may take in contaminants, and predators cannot see their prey to eat. It can actually have the reverse affect on the water, where sediment deposition is increased and dredging has to continually occur. Global warming is causing sea levels to rise as well as hurricanes which causes a lot more erosion than can be handled.

Increase in nutrients can have a negative affect. Sewage treatment plants, septic systems, polluted air, and fertilizers deposit nutrients like nitrogen and phosphorus into rivers which make it into estuaries. These high levels of nutrients can increase the amount of algae at such a rate that the algae will block sunlight from reaching through the water, killing off other plants. When alive, the algae produces a lot of oxygen as a result of photosynthesis, but once it dies off and decomposes, it consumes the oxygen which will suffocate and kill off fish and other organisms needing oxygen to survive.

Sewage plants, septic tanks and run off from farms into rivers carry fecal matter from humans and animals to the estuarine system. This brings bacteria, viruses, and parasites that transmit diseases to this ecosystem. Toxins can also cause an overgrowth of plants, removing too much oxygen from the environment, which kills fish and other organisms through suffocation. This can also happen when the salt and freshwater are not appropriately mixed together: salt water sinks and freshwater floats. Bottom dwellers begin to live in very salty conditions, which has less oxygen and causes them to suffocate. Dead organisms increases the amount of bacteria, which further decreases the amount of oxygen in the water.

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