Teacher Guide
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Nueces River Delta
The Nueces River Delta is a semi-enclosed body of water where the Atascosa, Frio and Nueces rivers meet the Gulf of Mexico. This area, containing a mix of fresh and salt water, is referred to as a “brackish water system.”

The Nueces River Delta is an estuary. It offers a variety of habitats to the different species that have adapted to the wide range of salinity as the freshwater meets the salty ocean. Other kinds of estuaries include coastal marshes, natural reefs, open bays, tidal flats, sea grass meadows, gulf beaches and barrier islands. Each provides a unique ecological area for organisms that have adapted to conditions found in these systems.

At the Nueces River Delta, water from three rivers and groundwater contribute to the inflow of fresh water. Here, as in other estuaries, the difference in the densities between the fresh water and salt water cause the salt water to flow upstream along the bottom of the delta and the fresh water to flow downstream along the surface, producing a layered effect. Some of the saltwater mixes with the freshwater the area where the bodies of water combine. This area is called the interface.

The river carries not only water, but also sediments and nutrients to the delta. This provides the buildup of soils and nutrients at the mouth of the river. As the soil travels downstream, it is tumbled and eroded from large particles into smaller ones. As the water approaches the mouth of the river, the sediments are deposited to create new land masses. This new land is under continual change due to seasonal flooding that causes erosion and re-deposition. This physical weathering produces nutrient rich habitats for different species of organisms to find a niche at the point of deposition.

Estuaries, such as the Nueces River Delta, are unique ecosystems because they provide variety in physical and chemical conditions. Because of the varying degrees of salinity, estuaries provide several diverse habitats for a variety of organisms that have adapted to these unique factors of the ecosystem.