In honor of the official “First Day of Fall” on Saturday, September 22, let’s fall into seasonal changes in wetlands! When many people think of the transition from summer to autumn, the first thing that pops into their heads is leaves changing colors and seeing more sweaters and long pants. A less common thought is how wetlands change in the later months of the year. From species composition to hydrology, many wetlands undergo radical changes when summer turns into fall. Wetlands in coastal Louisiana are no exception.
For a start, seasonal changes can be observed with migratory species. Many species of birds and some fish and crustaceans use our swamps, estuaries, and other wetlands for breeding habitat in the summer months because of the abundance of food and warmth. On the other hand, some migratory birds like the famous Bald Eagle use the Mississippi River Delta as a wintering ground.  Blue Crabs, another species found in wetlands, mate around this time of year before going dormant for the winter.  Migratory birds are starting to migrate back to the southern hemisphere around this time to follow food resources.
Decreasing temperatures and humidity also cause plant communities to change. Wetlands experience loss of vegetation from wilting and freezes.  Black Mangrove distribution is limited by minimum winter temperatures. You can read more on mangroves and freezing here. Swamps and marshes lose much of their greenery with lower temperatures, which really decreases their water storage potential. Evapotranspiration, or water vapor leaving plants through their leaves, often decreases too, which means that water is not being cycled as quickly as at other times of the year.
Ecosystems in a stable state can weather the changes between seasons and bounce right back to full productivity in their peak season, but sometimes a large disturbance or even small, incremental changes over time can degrade habitat to the point of no return. Degraded wetlands provide less storm buffer, which is a crucial ecosystem service that protects us during hurricanes. It is in our best interests to preserve our wetlands through projects like CWPPRA because they are so critical and invaluable to us.
The recent cold weather in Louisiana may have been the end of the road for some plants as temperatures dipped into the teens and stayed below freezing for full days. The hibiscus in your garden may have survived because you gave it extra insulation, but what about marsh plants? Louisiana salt marshes are home to black mangroves (Avicennia germinans), but this represents the very northernmost part of their range. Of the three mangrove species found in the continental United States [red (Rhizophora mangle), black, and white (Laguncularia racemosa)], black mangroves are the most cold-hardy, but they are still sensitive to winter weather- they generally cannot establish above 28° N and S latitude because winters are too cold (a sliver of the Birdsfoot Delta is below 29° N, so we really are at their limit).
The three mangrove species are also different in their tolerances for other environmental conditions: red mangroves establish in the intertidal zone, while black and white mangroves are found at higher elevations, and white mangroves can colonize areas with little to no soil. In Florida where all three species occur, mangrove zones can be defined from the water extending inland and up in elevation .
Black mangroves are an important component of Louisiana salt marshes, providing habitat to a variety of species. The complex root systems trap and collect sediment, limiting erosion and maintaining land. Juvenile invertebrates and fish find shelter among the roots, while seabird chicks, such as brown pelicans and roseate spoonbills, are protected from high water events and predators up in the branches.
CWPPRA projects that nourish barrier islands and create new marsh habitat help maintain black mangrove populations by providing new land for the plants to colonize; in turn, the mangroves help the new land persist in the face of wind and wave energy.
Known to be one of the most easily recognizable species of waterfowl, the mallard duck is majestic, distinctive, and a wintering resident of the bayou state. The mallard is one of the most common ducks in the United States. With great variation between the two mallard genders, drake or male mallards have a bright yellow bill, prominent emerald green head, and white neck-ring, followed by a chestnut colored chest and dark colored rear. The hen or female mallards have a dark colored bill and are a mottled brown color with a dark brown stripe across the eye. Both drake and hen mallards have the characteristic violet-blue speculum with black and white borders. Mallard ducks are a migrating waterfowl species that can be found in Louisiana during winter. Among the dabbling ducks, mallards are one of the latest fall migrants with one of the most extended migration periods, lasting from late summer to early winter. During their migrant stay, mallards are found in agricultural fields, shallow marshes, oak-dominated forested wetlands, and coastal inlets with aquatic vegetation. Louisiana sits in the Mississippi Flyway, North America’s greatest and most heavily-used migration corridor. Louisiana’s coastal wetlands provide habitat for more than 5 million migratory waterfowl, approximately half of the wintering duck population of the Mississippi Flyway. Now, more than ever, restoration and protection of coastal wetlands is critical; if wetlands continue to diminish, Louisiana will no longer be known as “sportsman’s paradise”.