Natural Resources
Conservation Service

Ecological site TX150B01X730

Sandy Bay Bottom

Last updated: 6/13/2025
Accessed: 10/19/2025

Home / Esd catalog / MLRA 150B / Ecological site TX150B01X730

USC

Metric

General information

Provisional. A provisional ecological site description has undergone quality control and quality assurance review. It contains a working state and transition model and enough information to identify the ecological site.

MLRA notes

Major Land Resource Area (MLRA): 150B–Gulf Coast Saline Prairies

MLRA 150B is in the West Gulf Coastal Plain Section of the Coastal Plain Province of the Atlantic Plain and entirely in Texas. It makes up about 3,420 square miles. It is characterized by nearly level to gently sloping coastal lowland plains dissected by rivers and streams that flow toward the gulf. Barrier islands and coastal beaches are included. The lowest parts of the area are covered by high tides, and the rest are periodically covered by storm tides. Parts of the area have been worked by wind, and the sandy areas have gently undulating to irregular topography because of low mounds or dunes. Broad, shallow flood plains are along streams flowing into the bays. Elevation generally ranges from sea level to about 10 feet, but it is as much as 25 feet on some of the dunes. Local relief is mainly less than 3 feet. The towns of Groves, Texas City, Galveston, Lake Jackson, and Freeport are in the northern half of this area. The towns of South Padre Island, Loyola Beach, Corpus Christi, and Port Lavaca are in the southern half. Interstate 37 terminates in Corpus Christi, and Interstate 45 terminates in Galveston.

Classification relationships

USDA-Natural Resources Conservation Service, 2006.
-Major Land Resource Area (MLRA) 150B

Ecological site concept

The Sandy Bay Bottoms are continuously inundated by saline water on flood-tidal delta flats and washover-fan flats of lagoons. They were formed from sandy lagoonal deposits and sometimes include dredge spoils. Greater water clarity and shallow depths provide favorable conditions for subaquatic vegetation. The presence and type of vegetation within these sandy sites are dictated by soil and water characteristics, specifically disturbance, salinity, and turbidity.

Associated sites

TX150B01X732	Turbid Bay Bottom This site has higher turbidity and limited vegetation coverage.

TX150B01X732

Turbid Bay Bottom

This site has higher turbidity and limited vegetation coverage.

Similar sites

TX150B01X732	Turbid Bay Bottom This site has higher turbidity and limited vegetation coverage.
R150BY728TX	Subaqueous Grassflat This site has higher salinity and turbidity with a more southern geographic location.

TX150B01X732

Turbid Bay Bottom

This site has higher turbidity and limited vegetation coverage.

R150BY728TX

Subaqueous Grassflat

This site has higher salinity and turbidity with a more southern geographic location.

Table 1. Dominant plant species

Tree	Not specified
Shrub	Not specified
Herbaceous	(1) Ruppia maritima

Legacy ID

R150BY730TX

Download full description

Physiographic features

The sites are found on dredge-deposit shoals, flood-tidal flats, washover-fan flats, and slopes of lagoons on the coastal plain. This nearly level site's elevation ranges from -6 to 0 feet. These soils are permanently inundated and range in water depth from 0 to 6.6 feet (0 to 2.0 meters).

Table 2. Representative physiographic features

Landforms	(1) Lagoon > Flood-tidal delta flat (2) Lagoon > Washover-fan flat
Flooding duration	Very long (more than 30 days)
Flooding frequency	Very frequent
Slope	1%
Water table depth	80 in
Aspect	Aspect is not a significant factor

Climatic features

The climate is predominately maritime, controlled by the warm and very moist air masses from the gulf. The climate along the upper coast of the barrier islands is subtropical subhumid and the climate on the lower coast of Padre Island is subtropical semiarid (due to high evaporation rates that exceed precipitation).

Almost constant sea breezes moderate the summer heat along the coast. Winters are generally warm and are occasionally interrupted by incursions of cool air from the north. Spring is mild and damaging wind and rain may occur during spring and summer months. Tropical cyclones or hurricanes can occur with wind speeds of greater than 74 miles per hour and have the potential to cause flooding from torrential rainstorms. Despite the threat of tropical storms, the storms are rare.

Throughout the year, the prevailing winds are from the southeast to south-southeast. The average annual representative precipitation is 36 to 46 inches in this area. Rainfall typically peaks during the spring, summer, and fall months, yet is generally uniform through out the year. The average annual air temperature is 69 to 71 degrees Fahrenheit.

Table 3. Representative climatic features

Frost-free period (characteristic range)
Freeze-free period (characteristic range)
Precipitation total (characteristic range)	36-46 in
Frost-free period (actual range)
Freeze-free period (actual range)
Precipitation total (actual range)	35-50 in
Frost-free period (average)
Freeze-free period (average)
Precipitation total (average)	42 in

Characteristic range

Actual range

Bar

Line

Figure 1. Monthly precipitation range

Characteristic range

Actual range

Bar

Line

Figure 2. Monthly minimum temperature range

Characteristic range

Actual range

Bar

Line

Figure 3. Monthly maximum temperature range

Bar

Line

Figure 4. Monthly average minimum and maximum temperature

Figure 5. Annual precipitation pattern

Figure 6. Annual average temperature pattern

Climate stations used

(1) CORPUS CHRISTI NAS [USW00012926], Corpus Christi, TX
(2) GALVESTON [USW00012944], Galveston, TX
(3) GALVESTON SCHOLES FLD [USW00012923], Galveston, TX
(4) MATAGORDA NO 2 [USC00415659], Matagorda, TX
(5) PORT O'CONNOR [USC00417186], Port O Connor, TX

Influencing water features

These soils are continuously inundated and are located in gulf-side subtidal areas. Sites are polyhaline with typical water salinity ranges of 25 to 35 parts per thousand. Ambient water temperature follows the same pattern as air temperature, averaging 0.8 to 3.0 degrees Fahrenheit warmer. From 2018 to 2023, the monthly average annual water temperature from four nearby buoys was: 56.5, 58.5, 67.0, 72.0, 80.5, 85.8, 87.5, 88.0, 84.4, 76.0, 64.8, and 60.7 degrees Fahrenheit. Stations used include: LUIT2, EPTT2, GRRT2, and GTOT2 from NOAA's National Data Buoy Center.

Wetland description

Classification System: Cowardin
System: Estuarine
Subsystem: Subtidal
Class: Aquatic Beds

Soil features

The ecological site consists of very deep, subaqueous soils that formed in sandy lagoonal sediments and/or anthropogenic dredge deposits. Surface textures range from loamy fine sand to loam. Dredge spoils may have gravelly sandy clay loam textures. Soils are hyperthermic with some portions of the site containing dredge spoils. Dredge spoils are defined as unconsolidated, randomly mixed sediments composed of rock, soil, and/or shell materials extracted and deposited during dredging and dumping activities. Dredge spoils lie unconformably upon natural, undisturbed soil or regolith and can form anthropogenic landforms. Soil Series correlated to this site include: Basford (human-altered soil), Bastropbay, Hoeckers (human-altered soil), and Westbay.

Table 4. Representative soil features

Parent material	(1) Lagoonal deposits (2) Dredge spoils
Surface texture	(1) Loamy fine sand (2) Loam (3) Gravelly sandy clay loam
Drainage class	Subaqueous
Soil depth	80 in
Surface fragment cover <=3"	30%
Surface fragment cover >3"	Not specified
Calcium carbonate equivalent (0-80in)	5%
Clay content (0-80in)	10 – 20%
Electrical conductivity (0-80in)	5 – 30 mmhos/cm
Sodium adsorption ratio (0-80in)	12 – 60
Soil reaction (1:1 water) (0-80in)	6.6 – 9

Ecological dynamics

Interwoven through tidal flats, lagoons, estuaries, and bay bottoms adjacent to the barrier islands reside the Sandy Bay Bottom ecological sites. Protected from the harsh oceanside shorelines, these hyperthermic subaqueous bottoms contain predominately widgeongrass. Soils are continuously inundated, displaying iron and sulfate chemical reductions, indicating soils have decreased oxygen availability. Despite their fragile nature, subaqueous soils are nursery grounds for a variety of plants and animals. Subaqueous soils protect shorelines from storm impacts, sequester carbon, and filter water of pollutants. Sandy Bay Bottom sites may be affected by anthropogenic factors including dredging and coastal development, as well as natural forces such as hurricanes.

State and transition model

More interactive model formats are also available. View Interactive Models
Click on state and transition labels to scroll to the respective text

Ecosystem states

1. Submerged Seagrass Flat

2. Dredge Spoil

T1A	-	Increased turbidity, lowered salinity, vegetation burial, and alterations to bay bottom substrate.
R2A	-	Restoration of seagrass flats by improvements in soil and water quality to reestablish plant growth.

State 1 submodel, plant communities

1.1. Widgeongrass Flat

1.2. Bare Flat

1.1A	-	Tropical storm or other natural disturbance negatively changing conditions for submerged aquatic vegetation.
1.2A	-	As time allows sediments to settle and water conditions to improve, plants will recolonize the ecological site.

State 2 submodel, plant communities

2.1. Dredge Flat

State 1
Submerged Seagrass Flat

Submerged aquatic vegetation is a term for plants that grow completely underwater, except for brief exposures during low tides. Healthy vegetative communities are important to estuarine systems for erosion control and create vital habitat for a diversity of aquatic organisms.

Community 1.1
Widgeongrass Flat

The Sandy Bay Bottom ecological site is primarily composed of widgeongrass (Ruppia maritima). Widgeongrass can tolerate moderate to highly saline waters, yet does not bode well in highly turbid systems. Grass flats reduce turbidity in the water column and provide smaller organisms food and shelter.

Community 1.2
Bare Flat

Seagrass beds on the Texas Gulf Coast can suffer degradation due to a variety of natural causes. Tropical storm impacts on seagrass beds are influenced by multiple factors, including storm recurrence, washover deposition, and the unique composition and environment of the plant community. The intensity of a hurricane plays a large role on the overall impact.

Pathway 1.1A
Community 1.1 to 1.2

Tropical storm or other natural disturbance negatively changing conditions for submerged aquatic vegetation.

Pathway 1.2A
Community 1.2 to 1.1

As time allows sediments to settle and water conditions to improve, plants will recolonize the ecological site.

State 2
Dredge Spoil

Dredge spoils are materials taken from the bed or banks of waters by using dredging equipment. Areas in the Gulf Intracoastal Waterway are periodically dredged to aid in marine navigation and transport.

Community 2.1
Dredge Flat

This plant community is in a dredge impacted state. Alterations to water and soil characteristics following dredging drive a change in plant community away from a submerged aquatic dominated plant community to a site with little to no vegetation coverage. The mass movement of subaqueous soils from dredging may decrease pH levels and increase turbidity causing cascading impacts across trophic levels. As light attenuation raises from increased suspended sediment, subaqueous vegetation no longer receives the required energy to survive and vegetation presence becomes sparse to none.

Transition T1A
State 1 to 2

The driver of this change is alterations to the bay bottom substrate. This occurs by the human-influenced activities of piling spoil after dredging channels.

Restoration pathway R2A
State 2 to 1

Significant improvements in soil and water quality are necessary to reestablish plant growth. Restoration of seagrass flats in areas affected by dredge spoils may necessitate human intervention.

Additional community tables

Supporting information

Inventory data references

The provisional concepts listed are based on observations from soil survey staff during the associated subaqueous soil mapping project, as well as, literature review and professional consensus. As more data is collected, the concepts will continue to be tested and refined.

Other references

Austin, A.N., J.P., Hansen, S. Donadi, and J.S. Eklof. 2016. Relationships between aquatic vegetation and water turbidity: A field survey across seasons and spatial scales. PLoS ONE 12:1-20

Cowardin, L.M. 1979. Classification of wetlands and deepwater habitats of the United States. U.S. Fish and Wildlife Service, U.S. Department of the Interior.

Erich, E., P.J. Drohan, L.R. Ellis, M.E. Collins, M. Payne, and D. Surabian. 2010. Subaqueous soils: Their genesis and importance in ecosystem management. Soil Use and Management 26:245-252.

Johnson, J.S., D.M. Cairns, and C. Houser. 2013. Coastal marsh vegetation assemblages of Galveston Bay: Insights for the east Texas Chenier Plain. Wetlands 33:861-870.

Lester, J., and L. Gonzalez. 2022. The state of the Bay: A characterization of the Galveston Bay ecosystem. Galveston Bay Estuary Program. http://gbep.tamug.edu

Pulich, W.M., and W.A. White. 1991. Decline of submerged vegetation in the Galveston Bay System: Chronology and Relationships to Physical Processes. Journal of Coastal Research 7:1125-1138.

Scheffer, M. 1999. The effect of aquatic vegetation on turbidity; how important are the filter feeders? Hydrobiologia 408/409:307-316.
Sheridan, P., G. McMahn, K. Hammerstrom, and W. Pulich Jr. 1998. Factors affecting restoration of Halodule wrightii to Galveston Bay, Texas. Restoration Ecology 6:144-158.

Stolt, M., J. Turenne, and M. Payne. Soil Survey Manual - Ch. 10. Subaqueous Soil Survey. United States Department of Agriculture, Natural Resources Conservation Service. https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/ref/?cid=nrcseprd1343022

U.S. Department of Agriculture, Natural Resources Conservation Service. 2016. National soil survey handbook, title 430-VI. Part 629—Glossary of landform and geologic terms.

U.S. Department of Agriculture, Natural Resources Conservation Service. 2022. Plant Fact Sheets. Retrieved from PLANTS Database: https://plants.usda.gov/java/

Contributors

Monica Polgar
Tyson Hart

Approval

Jamin Johanson, 6/13/2025

Rangeland health reference sheet

Interpreting Indicators of Rangeland Health is a qualitative assessment protocol used to determine ecosystem condition based on benchmark characteristics described in the Reference Sheet. A suite of 17 (or more) indicators are typically considered in an assessment. The ecological site(s) representative of an assessment location must be known prior to applying the protocol and must be verified based on soils and climate. Current plant community cannot be used to identify the ecological site.

Author(s)/participant(s)
Contact for lead author
Date	06/16/2025
Approved by	Jamin Johanson
Approval date
Composition (Indicators 10 and 12) based on	Annual Production