By Alisha A. Renfro, Ph.D., National Wildlife Federation
Wetlands are some of the most economically valuable and ecologically productive environments in the world. Often considered “the kidneys of the landscape,” wetlands help decrease the effects of floods and droughts, cleanse polluted waters, protect shorelines, control erosion and serve as sinks for atmospheric carbon dioxide. They are also important habitat for a variety of flora and fauna.
But human activities and natural processes have greatly reduced the amount of wetlands worldwide. Since the early 20th century, the planet has lost half of its wetlands. Recent attempts have been made to restore and create wetlands, but there are still lingering questions about whether this approach returns the ecosystem’s functions to their full, pre-impact levels.
A study led by David Moreno-Mateos, Ph.D., “Structural and functional loss in restored wetland ecosystems” (PLoS Biology, Vol. 10), compiled previous studies of created, restored and natural “reference” wetlands and compared different variables to gauge the recovery of the ecological function in the restored and created wetlands.
The research found that, in general, the ecological function of restored and created wetlands was lower than in healthy wetlands, but that the recovery of ecosystem function was better in areas directly influenced by rivers and tides, and in larger restoration projects greater than 250 acres. The research will help scientists and planners design the best wetland restoration plans for different regions, such as in coastal Louisiana.
Variables measured for the study were classified as hydrologic, biological or biogeochemical. Hydrologic variables (i.e., water level, flooding and water storage) – which are often engineered into restoration projects – showed little difference between the restored, created and natural wetland sites. In contrast, the biological variables (i.e., abundance and diversity of invertebrates, macroinvertebrates and plants) and the biogeochemical variables (i.e., the storage and cycling of carbon, nitrogen and phosphorous) from the restored and created wetlands sites only recovered approximately 75% of the function of the healthy reference sites, on average.
The size of the marsh restoration or creation project, the regional climate and the hydrologic setting were also found to be important. Larger projects (greater than 250 acres), which likely have a greater connection between resources and local organisms, were found to recover their biological and biogeochemical function faster than small projects; restoration projects in warmer climates showed an accelerated return of ecological processes; and the biological and biogeochemical variables of wetlands that were linked to variations in natural water flow (rivers and tides) recovered after 20 to 30 years, on average.
Dr. Moreno-Mateos’ research covers wetlands throughout the world, but may have some important lessons for restoring wetlands and their ecosystem function in coastal Louisiana. In the 2012 Louisiana Coastal Master Plan, a considerable amount of the budget is dedicated to marsh creation projects. Implementing large marsh creation projects alongside river diversions may shorten the recovery time in restoring ecosystem function of the economically and ecologically vital Mississippi River Delta.