Environmental Issues Facing the Laguna Madre, Mexico and USA25.5N 97.7W
Visible south of the bend in the coastline is the Laguna Madre, located on a coastal plain of the Gulf of Mexico. It is the largest hyper-saline coastal wetland in North America and one of seven in the whole world. It harbours a wealth and diversity of species and ecosystems, due to the fact that the lagoon is located between two biogeographical regions, the Nearctic and the Neotropical regions, with the influence of the Carolinian and the Caribbean marine provinces giving rise to various types of soil, climate and rainfall regimes and relative humidity.
The most important human impacts on this region over the past 30 years have been: water diversion and flood-control projects, brushland clearing, pollution, continued dredging, and pressures from population growth. The lower Laguna Madre, for instance, has lost about 60 square miles of seagrass cover due to reduced water clarity since the 1960s. Extensive agriculture has fragmented and reduced the areas of native terrestrial ecosystems. In addition, the large number of people now living in “colonias” without sewage treatment contributes to the contamination of ground and surface waters and poses a human health problem. This is worsened by untreated wastewater from Mexican municipalities released into the Rio Grande.
Global warming will compound these human pressures on Laguna Madre, in some cases improving, in others cases worsening the situation. For example, if future climate change brings a prolonged and more intense wet season in this region, the reliability of rainfall and soil moisture could improve. In wet periods, the land can retain rainfall and runoff, so wildlife and native plants increase their productivity, and the lagoon’s salinity is moderated.
If rainfall decreases in the future, however, a relatively small reduction in moisture could lead to increased desertification. Moreover, all types of coastal wetlands in Texas would decline with less freshwater delivery to the estuaries, thus worsening wetland losses already occurring. Over the long term, such coastal wetland losses would diminish estuarine-dependent fisheries.
Warmer winters are especially important from an ecological point of view. A northward shift of the freeze line would bring dramatic effects to the Coastal Bend and upper Laguna Madre, allowing southerly plant and animal communities to expand northward and, due to fewer disturbances from frost, mature and develop different ecosystems over time (click here for more information).