Sabine: The Salinity Medley

The Sabine Lake ecosystem, located in southeast Texas, is quite unique on the Texas coast due to the existence of its saltwater and freshwater influences. This ecosystem includes the Neches and Sabine rivers, Sabine Lake and adjacent marshes, Sabine-Neches Canal and Port Arthur Canal, and Sabine Pass which connects the system to the Gulf of Mexico. Fluctuating tides, coming in from the Gulf, bring in higher salinities, while freshwater flows into the system from the Sabine and Neches Rivers. Such changing hydrological conditions makes this ecosystem extremely dynamic while providing suitable habitat for both saltwater and freshwater organisms.

One of the largest ecosystems in the state, Sabine Lake encompasses approximately 240,000 acres of marsh habitat that surrounds a 100 square-mile lake. Sabine is among eight estuarine ecosystems in Texas, but is the only system that includes swamp habitats. In fact, the name Sabine comes from the Spanish word Sabinas meaning cypress, in reference to the extensive growth of cypress trees along the lower Sabine River, which the Spanish called Ro de Sabinas. Sabine Lake supports a large amount of surrounding habitat that consists of 34,002 acres of marshland, 238,951acres of coastal wetlands, and has a drainage area of 24,710,538 acres. Sabine Lake is shared between Louisiana and Texas, and is regarded as part of the Chenier Coastal Plain Ecosystem.

Sabine Lake receives the largest amount of freshwater inflow on the Texas coast, usually about 13.0 million acre-feet per year (graph). The lake requires approximately 9.6 million acre-feet of freshwater a year in order to maintain its unique habitat that is suitable for the vast amount of organisms that call the area home. The Sabine Lake system receives the highest precipitation in Texas, averaging about 60 inches per year and experiences little evaporation, only about 44 inches per year.

The salinity in the lake is heavily influenced by the tides. The tide ranges from an estimated 3.3 feet to 1.0 foot for offshore from Sabine Pass, and 1.3 feet to 0.7 feet for the Beaumont and Orange areas. This variance is largely due to the lakes shallower flow. The offshore tide loses about half of its amplitude at Mesquite Point, and a little over half again at the Rainbow Bridge. Overall, the average salinity of the lake is about 11 parts per thousand (ppt).

Aside from natural flows, the Sabine system is also heavily influenced by human activity. The Intracoastal Waterway, dug in the 1930s, bisects the system and channels large amounts of saltwater through the area. Man-made levees also redirect the natural flow of water.

During an internship with Texas Parks and Wildlife Department Coastal Fisheries Division, I was able to see the fruits of such a dynamic ecosystem. Sabines fluctuating salinity truly creates a medley of flora and fauna, and this was made evident in many samples collected during the past summer months. While collecting bag seine samples on June 4, 2012, a largemouth bass (Micropterus salmoides) , a freshwater species, measuring 2.75 inches was collected in the same bag seine sample that also caught a Scovell's Pipefish (Syngnathus scovelli) , an estuarine species, measuring 3.3 inches, and a crevalle jack (Caranx hippos), a marine species, that measured 1.6 inches. Other, more common species such as Atlantic croaker (Microponias undulatus), pinfish (Lagodon rhomboides), and sand seatrout (Cynoscion arenarius) were also collected in this particular bag seine. The water in which these samples were collected had a temperature of 28.9C, a dissolved oxygen content of 5.6 parts per million (ppm), and a salinity of 2.8 ppt.

On May 30, 2012, a bighead searobin (Prionotus tribulus) measuring out to a whopping 11.5 inches was collected in Keith Lake in a gill net. This species is usually found in shallow Gulf waters. This bighead searobin was collected in water with a temperature of 31.0C, a dissolved oxygen content of 6.4 ppm, and a salinity of 10.5 ppt. Similarly, on June 12, 2012, a 3.7 inch Gulf stone crab (Menippe adina), typically an offshore species, was collected inshore with a gill net. The hydrological conditions consisted of a temperature of 31.0C, a dissolved oxygen content of 5.1 ppm, and a salinity of 22.0 ppm.

Aside from a diversity of wildlife found in Sabine, there is also a wide range of aquatic vegetation. Incoming tides carry in large amounts of sargassum (Sargassum fluitans and Sargassum natans) during the summer months. Also considerable amounts of invasive Water hyacinth (Eichhornia crassipes) and Sylvinia (Silvinia minima) were noticed in the Sabine Lake area shortly after a substantial rainfall in June 2012.

The Sabine Lake system provides a habitat suitable for a multitude of flora and fauna. Its distinctive layout and locale enable this estuarine ecosystem to be very productive and incredibly dynamic. The influxes of saltwater and freshwater truly bring out the uniqueness of this medley of a system.