Estuarine Geography


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Source: www.geosense.net

Source: www.geosense.net

Introduction

Geography is the study of the physical features of the Earth’s surface and the feature’s relative location. Geographic Information Systems (GIS) can be used to map the Earth’s surface and provide tools for managers. GIS based maps can provide us with a better understand of the dynamics between physical components like hydrology, sediments, climate and biology that make up a coastal environment and how it changes over time.

Geomorphic Type

Source: www.oregon.gov

Source: www.oregon.gov

Its coastal location, tidal influence, and the mixing of fresh and saltwater define an estuary. Within this broad definition, estuaries can be characterized based upon geomorphic types. Geomorphic means the estuaries are classified based on their surface and configuration. Below are the main geomorphic estuary types and a picture of each. 

        Major bay estuaries

Major bays are classically characterized as bar-built estuaries that have direct river inflow. Bar-built estuaries form when sand builds up along the coastline forming sandbars. The sandbars create buffers from the water behind them and the sea. Sand bars and peninsulas, reducing the interaction of the estuarine water and ocean tides, often protect estuarine waters. Therefore wind is frequently the most important most mixing tools for fresh and salt water. Major bay estuaries are the most dominant along Texas’ coast in the Gulf of Mexico.

        Lagoon estuaries

Lagoons in the Gulf of Mexico are locally referred to as minor bays. Lagoons are also characterized by bar built estuaries but they lack direct river flow inflow and receive freshwater by ungagged runoff or as an indirect source via circulation from adjacent bays (Montagna et al. 2013). Circulation from adjacent bays, or inter-bay connections, is enhanced along Texas’ coast in the Gulf of Mexico by the Gulf Intracoastal Waterway. The Gulf Intracoastal Waterway extends from Mexico to Florida with predominant southeasterly winds that drive the currents within the lagoons towards the northeast. Ungauged runoff is freshwater flows from areas are not monitored by USGS storm gages and include flows downstream of storm gages to the point where the stream meets the estuary.

 

        River-dominated estuaries

River-dominated estuaries are drowned river valley ecosystems that drain directly into the sea rather than into a bay (Palmer et al. 2011). River-dominated estuaries are low-lying areas that have been inundated by sea-level rise. Inundation occurs when the adjacent water body due to the rise of the water body level submerges the previously dry land during a storm or sea level rise.

Source:  www.googleearth.com

Source: www.googleearth.com

Habitat Types 

Within an estuary, there are many habitat types. The habitat type can be determined using elevation, water regime, and soil and vegetation type. Knowing the types and locations of habitats within an estuary is important when creating ecosystem-based management plans. Habitat types are important for understanding the dynamics of the estuary. The vegetation present can provide information including the soil type and salinity levels based on the plants salinity tolerance.

Vegetative survey. Source: www.tmerr.org

Vegetative survey. Source: www.tmerr.org

        Estuarine System Features

The estuarine system features include tidal habitats and adjacent tidal wetlands enclosed or partially enclosed by the estuarine boundaries whose organisms are capable of life in aquatic or semi-aquatic conditions. Tidal habitats are defined as areas where the substrate is exposed to tidal action and it also includes the shorelines that experience high and low tides (Cowardin et al. 1979). Estuaries are protected by strong ocean current by bar-built estuaries and peninsulas. Typical estuarine plants and organisms are mangroves, oyster, crabs, fish, and shrimp. Classification of Wetlands and Deepwater Habitats of the United States (Cowardin et al. 1979), describes characteristic features of an estuary as shown below.

Distinguishing features and examples of habitats in the Estuarine System. EHWS = extreme high water of spring tides; ELWS = extreme low water of spring tides. Source: Cowardin et al. 1979.

Distinguishing features and examples of habitats in the Estuarine System. EHWS = extreme high water of spring tides; ELWS = extreme low water of spring tides. Source: Cowardin et al. 1979.

Habitat Type References

The classes represent the habitat types. The above information as well as the dominant vegetation for estuarine habitats including unconsolidated bottom, aquatic bed, reef, unconsolidated shore, and emergent wetlands can be found online at:

http://www.npwrc.usgs.gov/resource/wetlands/classwet/table2.htm

For a complete list of vegetation, refer to the 2012 National Wetlands Plant List that can be found at the U.S. Fish and Wildlife Services’ website:

http://www.fws.gov/wetlands/
        Mapping Estuarine Habitats

There is a tool provided by the U.S. Fish and Wildlife Service called the Wetland Mapper that provides printable maps of habitat types for the United States (USFW b). The habitats are delineated by colors and given specific codes representing  the Wetlands and Deepwater Habitats Classification Hierarchy, which shows the relationship of wetland systems. The Wetland Code Interpreter allows you to input a code and get information on that habitat type including system type (e.g.-estuary), possible plant life, and water regime.

Source: U.S. Fish and WIldlife National Wetlands Inventory

If information is not provided for the estuary that you’ve identified, a great resource for mapping is the, Data Collection Requirements and Procedures for Mapping Wetland, Deepwater and Related Habitats of the United States.

Mapping Estuarine Habitat Resources:

For Wetland Mapper, refer to:

http://www.fws.gov/wetlands/Data/Mapper.html

For Wetlands and Deepwater Habitats Classification Hierarchy, The Wetland Code Interpreter, and Data Collection Requirements and Procedures for Mapping Wetland, Deepwater and Related Habitats of the United States, refer to USFWS:

http://www.fws.gov/wetlands/Data/Wetland-Codes.html

Gulf Ecological Management Sites Program

The Gulf Ecological Management Sites Program (GEMS) features an interactive viewing map for GEMS sites along the coast of the five US Gulf of Mexico states including Texas, Louisiana, Mississippi, Alabama, and Florida. GEMS is managed by the Gulf of Mexico Foundation in partnership with the EPA Gulf of Mexico Program and the five US Gulf States. The map viewer gives information a particular GEMS. It also gives you the ability to import layers from the web or on file onto different basemaps. For example, if you were looking at Guadalupe Delta Wildlife Management Area in Calhoun, Texas, you could select Terrain with Labels as your Basemap and discover that the Guadeloupe River runs through the area (shown in caption below). You could even add a population layer to see the size of the community in the surrounding area.

Guadeloupe Delta Wildlife Management Area. Source: www.gulfmex.org

GEM Resource:

Gulf of Mexico Foundation


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