Introduction

The Texas Gulf Coast has some of the most abundant and diverse wetlands in the world. Unfortunately, very few of the more than 5 million people who live on or near the coast have any idea what kind of wetlands are near them and why they are important. Many people may actually know more about rainforests in the Amazon than they do about wetlands in their own backyards! The rainforests are important because they are part of the worlds "lungs" - they filter the air. But our coastal wetlands are just as important because they are part of the earth's "kidneys" - they filter the water! This book introduces readers to Texas' coastal wetlands by introducing the types of wetlands found here, explaining their importance, and describing where they are found.

Wetland education is a step toward wetland preservation. (Texas Parks and Wildlife)

This book is not intended as a comprehensive technical work, but rather a general introduction that will give the reader a better sense of Texas' coastal wetlands. Most of the guide is devoted to the section on regional wetland sites. This section should be useful to educators and others who would like to plan a visit to a regional wetland site. Many site descriptions include internet addresses that provide more detailed information. Additional references are provided on References/Suggested Reading.

This guide describes wetlands found on the Gulf Coastal Plain, a low, flat plain more than 360 miles long and 50 to 100 miles wide that borders the Gulf of Mexico (see map on Major Wetland Types). The area corresponds geologically to the Lissie and Beaumont Geological Formations, deposited during the Pleistocene Epoch starting about 1 million years ago, and the younger Holocene Epoch Formations (no older than 10,000 years), which include sediments adjacent to the coastline and on river floodplains and the Coastal Sand Sheet of South Texas.

< Back to Top

Coastal Wetlands: What Are They and Why Should We Care?

Wetlands Definition

Simply put, wetlands are "in-between" areas that have something of both dry uplands and open water environments: they are neither "land" nor "water" - they are a transition zone, which is what makes them so interesting. Wetlands have both upland and aquatic characteristics, and, thus, they often have a richer flora and fauna than other environments.

The high water line on these tupelo trees is an indication of the hydrology of this swamp - deep water for two to three months each year. (Texas Parks and Wildlife)

In practice, wetlands are hard to define, precisely because they are transition zones. It is important to recognize that an area does not have to be wet all year long to be considered a wetland - as few as two or three consecutive weeks of wetness a year is all it takes! The hydrology of a wetland (how much water it gets and how long it stays there) is the most important factor that determines its character. Because oxygen does not move very fast in water, water saturation very quickly results in a soil condition known as anaerobiosis, which refers to very low oxygen content. A lack of oxygen kills most plants, and hydrophytic or ` is the only kind of vegetation that can survive in these conditions. The reeds and rushes that are common in many wetlands can survive because they have hollow stems that allow them to push oxygen down into the saturated root zone. Other wetland plants have developed different strategies for surviving in the anaerobic environment. Waterlogged soils develop particular kinds of color patterns that make them recognizable as wetland or hydric soils. Hydric soils are typically gray and may have reddish stains along root channels. Wetland scientists use wetland hydrology, hydrophytic vegetation, and hydric soils to help them determine whether a given area is a wetland and the kind of wetland it is. We will examine each of these characteristics when we describe each of the major wetland types that occur on the Texas coastal plain.

< Back to Top

Why Are Wetlands Important?

There are many different kinds of wetlands and they all perform ecological functions, and produce certain goods and services that are valuable to humans. The most important functions wetlands perform on the Texas Gulf Coast are:

Pontederia cordata: pickerelweed

Hydric soils frequently have reddish stains along the plant root channels. (John Jacob)

	Water Quality: Wetlands are one of nature's most efficient water filters. Wetland plants and soils clean the water before it goes into groundwater or into rivers.
	Nurseries: Coastal near-shore wetlands serve as important nurseries for fish, crab, and other shellfish. The total economic impact of commercial fishing at the wholesale level is more than $400 million annually, employing about 30,000 coastal residents, all dependent on the wetlands! The total economic impact of saltwater sport fishing in Texas is almost $2 billion annually, employing about 25,000 coastal residents.
	Wildlife Habitat: Our coastal plain wetlands are home to many different kinds of animals. Birds from all over North America use Texas coastal habitats during migration and many species spend the winter on the coast.
	Flood buffers: Wetlands reduce the severity of floods by acting as natural detention areas. Destruction of many wetlands has made downstream flooding much worse.
	Erosion control: Nearshore wetlands act as buffers to reduce shoreline erosion and stabilize banks.
	Recreation: In addition to fishing, hunting and bird-watching are also economically important. Wildlife watching is the fastest growing segment of the tourism industry. In 1996, 3.8 million U.S. residents spent $1.2 billion watching wildlife in Texas.

< Back to Top

Wetlands Protection

It is illegal to drain or fill a wetland without a permit from the U.S. Army Corps of Engineers. The entire Texas coast is under the jurisdiction of the Corps' Galveston District Office. Before a permit can be granted, the requestor must show that the project has considered all viable alternatives and minimized impacts as much as possible. Any wetland loss must be compensated for by constructing new wetlands or by restoring or enhancing existing wetlands. The Corps of Engineers considers all public comments before granting a permit. Knowledgeable comments about local wetlands are particularly valuable. The Regulatory Branch can be contacted at (409) 766-3930 for those who wish to be added to the permit mailing list.

< Back to Top

Major Threats to Wetlands

Human activity has been the major threat to wetlands. Agriculture, industrial development, and urban and suburban sprawl have caused the greatest losses of freshwater wetlands. Agriculture is no longer expanding on the Gulf Coast, and very little of the current loss can be attributed to it. In fact, riceland agriculture, because of the flooding that goes with it, provides some additional wetland habitat not otherwise available. The biggest current source of loss for freshwater coastal wetlands is from urban sprawl. Land subsidence caused by the mining of oil, gas and groundwater has been the primary source of saltwater wetland loss. Subsidence causes the land surface to drop, which can then become flooded if the surface is already very near to sea level. Subsidence-induced flooding has drowned many wetlands, especially in and around large coastal cities such as Houston.

Estuarine wetlands are dependent upon freshwater inflow from rivers. In some estuaries, such as Corpus Christi Bay, there is not enough freshwater inflow to maintain maximum estuarine productivity. The Nueces River, which once flowed down through the marshes of the Nueces River Delta, has been diminished and rerouted and no longer provides much freshwater inflow to the deltaic wetlands.

< Back to Top

How Our Wetlands Came To Be

The Role of Water, Wind and Time

To understand the present pattern of wetlands we must go back about 60 to 100 million years ago, when the edge of the continent was about where Dallas, Austin, and San Antonio are now. The entire region that would become the Texas coastal plain was then at the bottom of the newly opening Gulf of Mexico. Since then, the Gulf has been continuously filling in with sediment carried by rivers. These layers of gravel, sand, silt and clay may be up to 40,000 feet thick, and have extended the edge of the continent some 250 miles into the Gulf. This process of sediment deposition continues today as Texas rivers add their sediment loads (the portion that is not trapped in man-made reservoirs) to their bays or directly to the Gulf. The Texas mainland shore, coastal plain, beaches, barrier islands and peninsulas, river deltas, and bays and estuaries are all products of the processes of erosion and deposition of water-borne (alluvial) sediments.

Bird's eye view of the Upper Gulf Coast of Texas. The Flat lying Beaumont and Lissie Geological Formations, laid down during past ice ages, are the location of Prairie potholes and marshes and coastal flatwood wetlands. (Redrawn from Doering, 1935)

The building of the Coastal Plain through sedimentary deposition has taken place against a backdrop of rising and falling sea levels, and what we see on the surface today is the result of the last two million years (the Ice Ages of the Pleistocene Epoch). The younger the sediments are, the easier it is to see the remains of the depositional processes. For example, many of the freshwater wetlands on the Gulf Coast today have formed in old sediment-filled channels that once formed the deltas and floodplains of ancient rivers. The channel remnants consist of oxbow lakes, cutoff channels, and, in the lower Rio Grande valley, resacas.

At the height of the last Ice Age, about 18,000 years ago, sea level was 300 to 400 feet lower than it is today and the shoreline was at least 50 miles farther out in the Gulf. During this period the coastal rivers cut deep valleys into the coastal plain sediments, which flooded and filled with sediment once the climate warmed and sea level rose as a result of the melting glaciers. Most of our fringing salt marsh wetlands have formed in the bays and estuaries that resulted from the flooding and filling of these river valleys.

Sea level rise also resulted in the formation of large sand bars along the coastline that developed into barrier islands, with Galveston Island and Padre Island among the most well known. As these islands have built seaward, a series of swales have been left behind the building sand ridges. These depressional swales are the location of prominent freshwater wetlands on these islands. Tidal fringe wetlands occur on the back or bay side of the islands.

Wind action has modified almost all of the wetland features, more so the older the landscape. Pimple mounds or small dunes, for example, are found in almost all undisturbed prairie potholes. But wind action has been the dominant landscape shaping force in the semi-arid area of the coastal plain known as the Coastal Sand Sheet. Here, coastal winds are constantly reshaping this dune-dominated landscape. Wetlands are found in the swales between the dunes, much in the same way as on the barrier islands. These wetlands often depend upon high groundwater levels.

< Back to Top

The Role of Climate

The average rainfall drops from 55 inches at Port Arthur in Jefferson County to less than 29 inches along most of the lower coast

Rainfall changes drastically from one end of the Texas Coast to the other. Average annual rainfall drops from 55 inches at Port Arthur in Jefferson County to less than 29 inches along most of the lower coast. The humid upper coast supports well-vegetated wetlands dominated by grasses and other temperate-climate plants.

In contrast, the lower coast becomes increasingly subtropical and more arid toward the Rio Grande. This climate does not support the lush wetland vegetation typical of the upper coast. The relatively sparsely vegetated sands of the lower coast are more susceptible to wind erosion, and dunes dominate many of the landscapes.

Rainfall amount also dictates how many wetlands occur in an area and where they are found. The upper coast, for example, has abundant wetlands. Almost any flat surface in the Beaumont area has slow-enough drainage to qualify as a wetland. This means that it is actually hard to find a natural area in this zone that does not have some kind of wetland characteristics. In contrast, wetlands on the lower coast are much less abundant and are confined to very distinct depressions.

Less rainfall results in less freshwater inflow supplied by rivers to the bays and estuaries. From Sabine Lake to Corpus Christi Bay, major rivers supply freshwater to the bays. The upper and lower Laguna Madre, on the other hand, has no major sources of freshwater inflow due to low rainfall and the absence of major drainages between the Nueces River and the Rio Grande. The lack of freshwater, combined with high evaporation rates and restricted Gulf inlets, normally keeps the Laguna saltier than seawater. Barren or sparsely vegetated tidal flats are typical of the wetlands fringing the Laguna, in contrast to the rather lush marshes of the upper coast estuaries.

< Back to Top

Definicion Humedales (Word Doc) - 861 KB

Home | Introduction | Wetland Types | Wetland Sites to Visit | References | Appendix | Contact | Links