MONITORING THE RESTORATION OF THE BAHIA GRANDE (LOWER LAGUNA MADRE): CONNECTING THE ECOSYSTEM TO THE GEOLOGY

After approximately 70 years of anthropogenic impact on this tidal wetland, the U.S. Fish and Wildlife Service has begun restoration efforts on approximately 11,000 acres of the Bahia Grande Estuary (Lower Laguna Madre, TX). Construction of the Brownsville Ship Channel during the 1930’s severed the natural water flow into Bahia Grande, leaving behind an arid salt flat. Dust from the Bahia Grande caused travel and health problems in the local community. The area has functioned recently as an ephemeral pond filled with rainwater from tropical systems. The restoration involves dredging channels to reconnect the Bahia Grande estuary with the Lower Laguna Madre system. This study is the preliminary study in a long-term monitoring program in the Bahia Grande Estuary system.

Past - The paleoecological record for the area is a baseline to evaluate the recovery of the ecosystem. Sediment and fossil distribution in the estuary system provide the key to evaluating the anthropogenic impact on this ecosystem by establishing the pre-anthropogenic communities. Foraminifera provide a paleo-ecological record because they have well-preserved hard-parts.

Present - The ephemeral ponds are part of an ecosystem that has jump-started the recovery of the system. The rainfilled ponds are brackish (14-17 ppt) because the salts from the sediments have dissolved. Sediments cloud the water because the water is between 15 to 85 cm in most of Bahia Grande with some areas as deep as 200 cm. The communities of flora and fauna in the ephemeral ponds are filling the available niches. Blue crabs, shrimp, several species of marine fish, bivalves, gastropods have been recovered in sediment cores and seines. Many species of birds have moved into the wetlands.

Future – The reconnection of the ecosystem with Laguna Madre and the Gulf of Mexico will provide a nursery for birds, fish, invertebrates. The shoreline and sub-aquatic flora will stabilize the sediments in the estuary thus clearing the water and limiting the erosion. Sedimentation in the basin will impact the flora and faunal communities. Continued monitoring of the geology of the wetlands will provide insight into the recovery and health of the wetlands. The restored wetlands will be a nursery for fish and invertebrates for the western Gulf of Mexico. Continued monitoring will establish the success of the restoration efforts.