Solutions for Wetlands in the Face of Sea Level Rise
By Thomas Anderson
in the Department of Biological
Sciences and Director of Environmental Science
and Policy at California State University
Long Beach. Photo by Thomas Anderson.
At Seal Beach National Wildlife Refuge (SBNWR) experiments are under way. About three years ago, Dr. Whitcraft, with assistance from her Cal State Long Beach graduate students, the U. S. Navy and a coalition of land managers, began testing a process called sediment augmentation. This would raise the elevation of the marsh to withstand a moderate sea level rise. Dredge material from the SBNWR ocean inlet was “donated” and placed in test plots to raise the marsh 10 inches. Achieving the elevation was successful, but whether plant and animals would inhabit the test plots of marsh proved far more challenging. Much to the surprise of Dr. Whitcraft, only 10% of common salt marsh plants (cordgrass, pickleweed, saltwort) had returned after two years. Plants were expected to come up through the sediment augmentation but instead were recruited mostly from the edges of the test plots from runners. Without plants, the temperature of the mud is higher. Invertebrates common to the salt marsh food web—insects, amphipods, polycheates and oligochates—were not as diverse in the test plots, which meant birds and fish were not abundant either.
So many factors needed to be understood, but the main element missing was more variety in the elevations of the mudflats. The initial augmentation had been the result of an even spread of sediment. It was very difficult for the contractors to achieve uneven spreading of the sediment, and it was only in areas that were less even, around the edges and areas where channels had been created, that plants and animals were abundant. It had not been expected that the weight of the sediment would be enough to retard the regrowth of the plants. Salt marsh plants are not easy to reproduce by seed, so this fall Dr. Whitcraft and her students will plant 18,000 seedlings by hand.
Dr. Whitcraft has a second, very different project underway at the Upper Newport Bay Ecological Reserve: living shorelines that use native creatures—Olympia Oysters—in combination with assembled structures to build sediment and prevent erosion. Four experimental design plots were created in Upper Newport Bay. Mounds of ground shells that attract oysters were held in place by biodegradable materials and placed in longs rows at varying places at the tides edge. Oysters quickly colonized the structures, and eel grass, vital in sediment stabilization, increased 250% nearby. This attracted many invertebrates and fish. The only drawback appeared to be the beds that were placed too high in the tide level attracted non-native oysters.
Many laws are in place to protect wetlands, but the key is how wetlands are defined. When wetlands are defined to include as much of their upstream runoff sources as possible, preventing development that cuts off the natural replenishment of sediments, wetlands are healthier and more resilient. Under the Clean Water Act, Federal laws have defined what is considered wetlands and how much land is needed to protect them. At a time when wetlands need all the protection they can get, the current administration has rolled back wetland definitions to 1990s levels.